Resumo em Inglês:

This work investigates the synergistic use of Theobroma cacao (Cocoa), and Elaeis guineensis (Palm oil) as corrosion inhibitors for carbon steel in 0.5 mol.L-1 hydrochloric acid solution, in the absence and presence of different mixture concentrations of the studied compounds. The efficiency of corrosion inhibitors was studied by gravimetric tests and the corrosion resistance by electrochemical tests, such as electrochemical impedance spectroscopy (EIS) and polarization curves. The chemical composition of the cocoa bark powder and palm kernel cake powder was evaluated by Fourier transform infrared spectroscopy (FTIR). The results of the gravimetric tests showed an inhibition efficiency of 79% for the cocoa bark powder and 76% for palm kernel cake powder, however, the mixture of the compounds presented an inhibition superior to 94%, showing the great synergism between the studied species. These results corroborate the values obtained from EIS.

Resumo em Inglês:

Abstract The objective of this research is to evaluate the possibility of use of tropical hardwood species (Amburana cearensis and Cedrella fissilis) for grilling plank production. Physical, chemical and organoleptic properties were evaluated and compared with properties of a well-used wood specie for grilling plank across Europe and USA, Western Red Cedar (Thuja plicata). For chemical analysis, three techniques were used: hydro distillation, soxhlet and head space. Normality test and analysis of variance (ANOVA) were used for the comparison between Thuja plicata and tropical hardwoods. The results of organoleptic, chemical and statistical analysis demonstrated the possibility of use of Amburana cearensis and Cedrella fissilis on grilling plank production, with no volatile compound present in these species being toxic, low apparent density and Nerolidol presence, chemical compound used as flavoring agent, enabling their use as grilling planks.

Resumo em Inglês:

Polycarbonate is an engineering polymer due its outstanding properties and is widely used in several different applications. In some of these applications it can be exposed to certain liquids/solvents. In many cases, this liquid exposure may cause an effect known as Environmental Stress Cracking (ESC), which may lead to crack formation on the polymer surface and consequent reduction of its mechanical resistance, with loss of lifetime. On the other hand, polycarbonate medical supplies are often exposed to gamma rays in the radio-sterilization process, at doses up to 25 kGy. This exposure causes main chain scissions. In this present work, the viscosity average molecular weight decreased about 10% at 25 kGy. Elongation at break was drastically affected by ESC phenomenon. When simultaneously exposed to the ESC agents (methanol or isopropanol) and gamma radiation, combined effects of both takes place. Moreover, the stress relaxation rate of ~1000 Pa/s (air or methanol) and ~2200 Pa/s (isopropanol) at the dose of 100 kGy, suggests strong influence of isopropanol as surfactant on PC. Results of elongation at break and stress relaxation rate were reliable data to evaluate ESC and radiolytic effects on PC.

Resumo em Inglês:

This paper evaluates the effect of adding glycerol to the electrodeposition bath on the deposition efficiency and characteristics of Ni-Mo coating in concentrations ranging from 0.07 to 0.82 mol.L-1. Evaluation of the corrosion resistance was performed by means of weight loss tests in four different periods of immersion. Electrochemical techniques, such as obtaining polarization curves, linear polarization resistance, corrosion current density, corrosion potential, and electrochemical impedance spectroscopy were applied. Corrosion measurements were obtained in 0.5 mol.L-1 NaCl acid solution and 0.5 mol.L-1 NaOH alkaline solution. The morphology and microstructures of electrodeposited were analyzed using Scanning Electron Microscopy and Spectrometry X-Ray Diffraction. The effect of glycerol on Ni-Mo hardness was evaluated by Vickers microhardness measurements. The presence of glycerol in the electrodeposition bath increased the grain size and decreased the hardness of the coating. However, it promoted the formation of a more compact and less porous coating, increasing the corrosion resistance of the coating. Moreover, the addition of 0.82 mol.L-1 glycerol increases current efficiency, thereby reducing the amount of energy consumed during electroplating.

Resumo em Inglês:

Abstract Aiming to meet current demands from the automotive industry, a third generation of advanced high strength steel (AHSS) has been developed as an alternative to previous generations. Different alloys and innovative processes have been deeply studied as, for example, quenching and partitioning (Q&P). The published papers highlight that the best heat treatment parameters for a satisfactory Q&P execution are strongly dependent on the austenite conditioning and they can be optimized if thermodynamic and kinetics calculations are performed. In this context, this work evaluated the effect of step quenching (SQ) heat treatments on the kinetics of ferrite formation and Q&P modeling for a commercial C-Mn-Si steel, predicting the microstructural evolution and the final phase fractions as a function of the heat treatment parameters. The JMAK model was optimally fitted to the ferrite fraction, as well as to the microhardness data. The kinetics characterization and the thermodynamic modeling showed that the combination of SQ and Q&P can provide a high retained austenite fraction in a multiphase microstructure. As a conclusion, it is possible to state that a well-planned SQ heat treatment followed by an optimized Q&P cycle has the potential to generate an advanced steel with a final microstructure assisted by the TRIP effect.

Resumo em Inglês:

Abstract To improve the wear resistance of cutting tools made of high-speed steel, the Diamond-Like Carbon (DLC) coating appears as a promising alternative. There are several methods to assess wear, however, it is a challenge for manufacturing engineering to work with thin films, due to the uncertainty in the boundary of the substrate and the coating. Based on this concern, this study proposed the evaluation of the tribological behavior of the DLC coating deposited on AISI M35 steel, seeking to predict its behavior in machining conditions based on characterizations, nano-indentation, micro-abrasion and ball-on-disc test. Results showed that the DLC coating produced for this study consists mainly of sp2 hybridizations. The results of the nano-indentation showed that DLC coating may have a better wear resistance when compared to high-speed steel, and the nano-hardness and Young's modulus do not necessarily obey a positive correlation. Compared to high-speed steel, DLC provided reductions of 71% and 69% without micro-abrasive wear and without friction coefficient during sliding, respectively.

Resumo em Inglês:

This research investigated the production of porous zinc oxide (ZnO) ceramics obtained by the replica method for water depollution by photocatalytic processes. Five photo-decolorization cycles were performed to analyze the reuse potential of the ceramics. Statistical analyses using R programming were conducted to investigate possible significant differences between them. The ceramics porosities were between 46.74 and 62.50% (depending on the composition). The most successful results were achieved in prepared ceramics from slurries containing 65% ZnO and 1% carboxymethylcellulose, in which the dye decolorization results reached 90.5% after 5 cycles, indicating a high reuse potential of these ceramics. Multivariate analysis proved the negative effect of increasing the heat treatment temperature on the evaluated properties. The best processing conditions to obtain porous ZnO ceramics by the replica technique were established through statistical tools, with very satisfactory results in the photo-decolorization potential of the investigated dye.

Resumo em Inglês:

The effect of Er on the structural and electrical properties of doped PZT 52/48 ceramics has been studied in this work. The ferroelectric properties (permittivity, ferro-paraelectric phase transition and hysteresis) of such materials are thus found to be strongly dependent on the degree of densification and structural phase development during sintering at high temperatures. In particular, the nature of the ferroelectric to paraelectric phase transition is in these materials that can be represented through the Curie-Weiss Law equation modified, appropriate for the characterization diffuse transitions. The substitution of Er3+ for (Zr,Ti)4+ is found to induce strong diffuse phase transition in these materials. The electrical properties reported in this work are in magnitude comparable to those exhibited by PZT52/48 materials.

Resumo em Inglês:

Abstract In order to explore the effect of different the welding heat input on microstructure and impact properties in coarse grain zone in heat affected zone (CGHAZ) of ultra-low carbon bainitic steel welded joint. In this paper, Gleeble-3500 thermal simulation testing machine was used to simulate different heat input, to study the effect of linear energy on the microstructure and impact toughness of the CGHAZ of Q420qEN steel joint. The scanning electron microscope (SEM), oscillographic impact microscope and transmission electron microscope (TEM) were used. The results show that the microstructure of CGHAZ is mainly the lath bainite and granular bainite. When the welding heat input is 30kJ•cm-1, the CGHAZ grains have obvious growth phenomenon. With the increase of the welding heat input, the grain size also grows. Meanwhile, as the welding heat input increases from 18kJ•cm-1 to 30kJ•cm-1, the impact toughness of the CGHAZ of joint increases first and then decreases at -20°C.

Resumo em Inglês:

Abstract In sheet metal forming (SMF), deformation is caused by the relative movement between the sheet and tool, which generates friction forces. However, materials behave differently during plastic deformation. In this study, a tribo-simulator was designed to investigate the effect of different contact conditions or formability tests on the tribological behavior of AISI 304 and AISI 430 stainless-steel sheets. The effects of the texture and microstructure of the sheets on the measured coefficients of friction (COFs) and changes that occurred on the tribosurfaces also were investigated. Roughness and microhardness measurements, optical and scanning electron microscopy, and X-ray diffraction were used in the analyses. The tribo-simulator was successfully manufactured, and the repeatability of the measured COFs was satisfactory (standard deviation of ~0.02). A comparative analysis of the formability tests revealed differences in the COFs. In the bending under tension test, the COF for ferritic steel was 33% higher, while in the strip-tension test, the COF for austenitic steel was 44% higher. Friction was strongly influenced by the texture and microstructural characteristics of the steel sheets. The samples exhibited galling due to severe adhesive wear.

Resumo em Inglês:

Carbon fiber reinforced polymer (CFRP) have been gaining prominence in replacing metallic alloys for infrastructure in prostheses, with the possibility of edentulous patients to acquire fixed prostheses. For this, procedures are required to connect these implants to the implant-supported fixed prosthesis, such as holes and notches that can reduce their mechanical properties. In addition, the infrastructure requires longer cantilevers, causing greater stress on the prosthetic system. Then, the objective is to analyze the stress concentration in the CFRP subjected to bending loads with holes (4 and 6 mm diameter to verify the influence of the diameter-to-width ratio) in four-point-bending test. Two composite laminates were evaluated: one with thermoplastic matrix of poly(phenylene sulphide) PPS; and another with epoxy matrix combined with carbon fibers fabric. The presence of holes in the studied dimensions did not present significant differences in the flexural modulus and maximum bending strength. Therefore, the use of CFRP showed some advantage regarding the reduced effect of stress concentration compared to metallic alloys.

Resumo em Inglês:

Abstract A novel pigment of β-LiAlSi2O6:Cr ceramic was developed by a partial proteic sol-gel process, using gelatin as a ligand. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and visible and near-infrared diffuse reflectance spectroscopy (vis-NIR DRS) were performed. XRD results confirmed that the crystal structure of the lattice corresponded to β-LiAlSi2O6 (or β‑spodumene), and the addition Cr3+ ions by doping did not interfere in the formation of this crystalline phase. EDS confirmed the homogeneous existence of Cr3+ dopant in β‑LiAlSi2O6 particles. From the vis‑NIR DRS, selective absorption of visible light wavelengths was identified in the bands of 425 nm and 600 nm, resulting in the perception of a yellowish-green color when β-LiAlSi2O6 is doped with Cr3+. CIE-XYZ colorimetric coordinates were generated to characterize the resulting colors. The obtained results demonstrated the viability of β‑LiAlSi2O6:Cr synthesis by a proteic sol‑gel route and its great potential for obtaining a yellowish-green ceramic pigment.

Resumo em Inglês:

Abstract This study aimed to improve a potentiodynamic-based methodological approach for characterising the tribocorrosion of ferritic stainless steel. Synergistic effects in tribocorrosion systems have been widely investigated and debated under potentiostatic conditions. Because potentiostatic tests can ignore essential phenomena that are typically noticeable in potentiodynamic tests (potential scanning), such as variations in the friction coefficient that are motivated by potential scanning, e.g., during active, passive, and transpassive domains, a potentiodynamic-technique-based methodology was enhanced to analyse tribocorrosion in ferritic stainless steels. The proposed method facilitates the analysis of all essential parameters for tribocorrosion phenomena based on a single figure directly associating the average friction coefficient curves from sliding tests and tribocorrosion tests. It consists of performing sliding tribological tests to evaluate mechanical wear accurately, potentiodynamic corrosion tests to determine corrosion resistance in the absence of mechanical wear, and tribocorrosion tests to associate mechanical wear and corrosion degradation caused by chemical/electrochemical effects. Validation of the methodology consisted of its application to an 11% Cr ferritic stainless steel. The results demonstrate that tribocorrosion intensifies the material loss, but only by a minimal amount. The results demonstrate that the average passivation current density in the tribocorrosive tests was significantly higher. Apparently, the corrosion products generated during the tribocorrosion tests acted as solid lubricants inducing a lower friction coefficient in the tribocorrosive tests. Finally, tribocorrosion intensifies the material loss, but only by a minimal amount.

Resumo em Inglês:

Abstract Aiming to overcome poly(lactic acid) (PLA) limitations regarding flammability and high costs, a highly refractory clay (RC) was employed to produce PLA/RC composites. The composites with clay contents of 0, 2.5, 10 and 15 wt% were produced by extrusion, conformed by injection molding, and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical analysis, scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), statistical analysis of variance (ANOVA) and flammability tests. The overall thermal stability of the materials was not affected by the incorporation of clay to the polymer matrix; improvements around 25% for Young’s modulus and slight increase in flexural and impact strength, when compared to neat PLA, were obtained; ANOVA showed the possibility of incorporating higher loads of clay, 10-15 wt%, in order to make the final material more cost effective. PLA/RC composites demonstrated self-extinguish behavior for the flame even at a lower clay content.

Resumo em Inglês:

Abstract AlCoCrFeNi alloys are widely studied due to the combination of high strength in a wide temperature range, good corrosion and wear resistance, but they typically present low ductility. Due to this limited ductility, traditional bulk fabrication processes that involve forming are difficult, and casting processes are also non-ideal due to pronounced segregation and coarse microstructure. Therefore, both the selective laser melting and the powder metallurgy are more promising routes for this alloy, both of these use powder as starting material. This work aimed to produce powder of Al20Co20Cr20Fe20Ni20 alloy by gas atomization and to perform its detailed characterization.The results show that the powder is mainly spherical, which resulted in good flowability. Most of the powder (62%) has a size smaller than 75µm, and microscopy analyses confirmed that a B2 dendritic microstructure was formed, with A2 cuboidal precipitates.

Resumo em Inglês:

Abstract Oxides (Al2O3, SiO2, TiO2, ZrO2, Y2O3, CeO2, MgO) are among the most used reinforcements for Aluminum Matrix Composites (AMC); while the combination of Al with Si, Cu and/or Mg excels among the alloying systems used as matrices. Some works in literature study the effects of the reinforcements and the alloying elements on the composites manufacturing, microstructure and mechanical properties. Nevertheless, it is necessary a recompilation of the interactions oxide reinforcement-alloyed matrix, including the reciprocal effects between them. Our search revealed that not only reactions occur at the interfacial regions, but also other phenomena depending on the reinforcement characteristics and the matrix composition, which affect mechanical properties. These phenomena include modifications in the matrix microstructure and its precipitation process, diffusion of elements through the interfaces, change in the reinforcement wettability by the liquid metal, loss of alloying elements, and deterioration of the reinforcement. This work presents the occurrence of these phenomena for Al matrices with different contents of Si, Cu and Mg reinforced with the most used oxides. Its novelty lies in exploring these combinations of conditions, which could serve as a benchmark study and help for a better understanding and selection of the matrix-reinforcement system.

Resumo em Inglês:

Abstract Micro electro-discharge machining is one of the efficient processes to create three-dimensional micro features of metallic components for various applications. Powder mixed EDM improves the machining rate and reduces the surface roughness by evenly distributing the spark. The present studydemonstrates the effect of SiC nanopowder on the machining of Inconel 718 at different Discharge Energy Regimes (DER). Significant improvement in MRR, reduction in TWR and surface roughness were observed in nanopowder mixed micro-EDM (NPMμEDM) compared with micro-EDM. The nano additive considerably improved the Material Removal Rate (MRR) by163% and reduced the Tool Wear Rate (TWR)and surface roughness by 24%, 17% respectively. Models were created to predict the Surface Roughness in NPMμEDM using two different approaches namely Support Vector Regression (SVR) and Random Forest Machine (RFM). Both SVR and RFM models were able to predict the Ra value with better accuracies.

Resumo em Inglês:

Abstract Over the years, the demand for high engine efficiency has resulted in the development of new generation superalloys with improved elevated temperature properties, especially creep resistance. This study aimed to evaluate creep and mechanical behavior of Inconel 718 superalloy. Creep tests were performed at temperature range of 650 to 700 °C and stress range of 625 to 814 MPa. Hot tensile and oxidation tests were performed and the characterization techniques used in this study were scanning electron microscopy (SEM) for microstructural and fracture surface analysis, transmission electron microscopy (TEM) for precipitates analysis; grazing X-ray diffraction for analysis of oxide formation and Vickers microhardness. The analyze of stress exponent value (n = 36.48) and activation energy (Qc = 512.97 kJ/mol), suggested that creep mechanism at 650 °C was the climb dislocation mechanism. The Inconel 718 presented ductile fracture at 650 and 700 °C and intergranular fracture to 675 °C.

Resumo em Inglês:

Abstract Previous studies have demonstrated the improved membrane properties of ceramic membranes made from thermally modified clays with cationic manioc starch and eggshell residue as additives. Based on the employment of these membranes, the relationship between thermally modified clays’ structure and cross-flow microfiltration using oil-in-water emulsion was studied (North Sea heavy crude oil). Using raw clay (M1) and thermally pretreated clay (M2), tubular ceramic membranes were prepared by the extrusion method. Critical Flux in different concentrations (250, 500, and 1000 mgL−1), fouling mechanisms, and membrane resistance were analyzed. The initial membrane resistance values for M1 and M2 membranes were 2.23 ± 0.32 × 1012 m−1 and 1.72 ± 0.293 × 1012 m−1, respectively. The membrane resistance was reduced by 22% due to the clay modification, which also decreased the contact angle, increased the pore size, and decreased the membrane roughness. Regarding the total organic carbon removal, the M2 membrane had no loss in separation efficiency despite having a slightly larger pore size. These results indicate that the clay-induced structural changes decreased the membrane resistance and improved the permeate flux but did not decrease the oil-in-water emulsion’s separation efficiency.

Resumo em Inglês:

Abstract In this paper, the relationship between Kernel average misorientation (KAM), geometrically necessary dislocation (GND) density and dislocation structures of Nb-bearing austenitic stainless steel under low cycle fatigue (LCF) was studied at 600°C at the total strain amplitude ranged from 0.3% to 1.0%. The results based on EBSD analysis show that the GND density in fatigue specimens gradually increases with the increase of strain amplitude. Under LCF loading, the dislocation structures are mainly planar slip bands (PSBs) and the cell structures. With the increase of strain amplitude, the number of PSBs increases with decrease in width, and the average diameter of cells also decreases. The PSBs originate due to the dynamic strain aging (DSA) effect, and DSA is more significant under high strain amplitude. The average diameter of cell structures has a specific relationship with GND density.

Resumo em Inglês:

Abstract In this study, magnetically separable ZnO/CuFe2O4 nanorod particles were synthesized by the green synthesis approach, using rambutan peel extract (Nephelium lappaceum L.) as a capping agent. The samples were evaluated as photocatalyst for the degradation of Rhodamine B dye driven by solar light irradiation. The XRD patterns represented the specific peaks of ZnO and CuFe2O4 in the ZnO/CuFe2O4 composite. SEM and TEM images showed the rod-like shape of the ZnO/CuFe2O4 composite synthesized using 3 mL (ZCuE3N) of rambutan peel extract. ZCuE3N sample has an increase in photocatalytic activity up to 98.8% in the degradation of Rhodamine B under solar light irradiation for 2 h. Magnetic measurement by VSM revealed that ZnO/CuFe2O4 composite was superparamagnetic. ZnO/CuFe2O4 composites remained stable in an air atmosphere and exhibited promise as a reusable photocatalyst as it can be easily separated from the solution by an external magnetic field.

Resumo em Inglês:

Abstract In this work, Zn2SnO4:Co2+ (0.1%) was obtained through a solid-state reaction at high temperature using ZnO, SnO2, and CoCO3. The sample was investigated using X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and photoluminescence spectroscopy. Rietveld refinements of the X-ray diffraction data showed two crystalline phases, Zn2SnO4 and SnO2, with proportions of 97.24% and 2.76%, respectively, while Zn and Sn atoms were observed by X-ray fluorescence. Scanning electron microscopy images showed the polycrystalline nature of the material. Photoluminescence spectroscopy showed two emission bands in the red and near-infrared regions, with the broader and more intense band having a barycenter at 694 nm. The intensity of the emission changed with the excitation wavelength, whereas the barycenter remained unchanged. The intensity, shape, and position of the bands, as well as the calculated crystal field parameters, indicate the insertion of Co2+ ions in the tetrahedral sites of the Zn2SnO4 material.

Resumo em Inglês:

Abstract In this study, the microstructure and texture evolution of hot rolled Ti80 pipe annealing at 960°C and 990°C in α+β two-phase field have been investigated. The results showed that the dissolution of α phases induced the increase of texture components of primary α phases (αP) and the αP were the main factors that determine the final texture at 960°C. At 960°C, the microtextures of secondary α phases (αS) were very close to that of αP. As the annealing temperature increased to 990 °C, the main factors affecting the microtextures of αS changed from the αP to the recrystallized β grains. The textures of β phases were greatly influenced by the annealing temperature. The β phases at high temperature were not mainly from the grow up of residual β phases. It was formed by the transformation of α phases at room temperature. Consequently, this study could provide some ideas for decreasing the texture intensities of hot rolled Ti80 pipes, such as reducing the area of α colonies before rolling, scattering the crystal orientations of αP, and controlling the size of recrystallized β grains.

Resumo em Inglês:

The introduction of biodiesel to commercial diesel is being increased every year. The need to check this addition to the engine and lubricant is important for automakers and internal combustion engine manufacturers. The oil analysis technique is a type of predictive maintenance, done by collecting oil from equipment and analyzing it later in the laboratory, or by analyzing it directly and continuously in on-line systems. In internal combustion engines, all parts have a pre-established service life, longer or shorter, according to the specific function assigned to it. By analyzing the oil, the condition of these parts can be monitored. The oils analysis reveals the first signs of wear of a component. The identification is made based on the study of the number of particles, size, shape and composition thereof, present in the lubricant samples, which provide accurate information about the conditions of the moving surfaces without the need to disassemble the assembly to which these parts belongs. In this work a lubricant contamination by biodiesels were made to simulate possible scenarios within an internal combustion engine.The lubricant recommended by an engine manufacturer was “contaminated” with commercial diesel and with different percentages and types of biodiesel. After this “contamination” they were placed in a pin on disk device under certain conditions.Through the analyzes of the lubricants extracted from the Pin on disk Equipment after the tests, some analysis were carried out in order to study the effects of using biodiesel in the internal combustion engine.These analyzes consisted of Flash point, analytical ferrography, monitoring of ferrous particles generated, viscosity, viscosity index, basicity index and X-ray spectrometry.Among the results obtained it is observed that for a 5% contamination of animal biodiesel there was an increase in the viscosity index. Conversely, the contamination of 5% of animal + vegetable biodiesel decreased the viscosity index in relation to Diesel B5. We also found that these biodiesel additions were not detrimental to the engine and lubricant at the mix ratios and test conditions used.

Resumo em Inglês:

Steel is an essential part of our life as it is used in wide applications as food equipment and heavy construction. The polymeric coating prevents the deterioration of the properties of metals due to rust and corrosion. This study investigated a reinforced polymeric coating to steel for enhancing barrier and mechanical properties. A comparison between different configurations of double-layered polymeric coatings was attained. The results showed that a maximum enhancement of 16.7%, 18.9%, 32.6%, 8.5%, and 5.7% in tensile strength, tensile strain, toughness, flexural strength, and flexural strain, respectively were achieved with a coating of epoxy filled with 1wt% Al2O3 microparticles before 1wt% Al2O3 nanoparticles on both sides as compared with pure epoxy coating. Adding micro/nanoparticles to epoxy coating enhanced the barrier properties of the coated steel against salt solution and citric acid environment as compared to pure epoxy coated steel.

Resumo em Inglês:

Abstract One-part alkali-activated binder (AAB) is a product with lower environmental impact than Portland cement, and can be a feasible commercial alternative. The main objective of this study was to propose and test a method of obtaining one-part AAB with metakaolin and an alternative powder sodium silicate from rice husk ash (RHA). To evaluate the AAB properties, mortars were produced with different SiO2/Al2O3 molar ratios (2.7, 3.1, and 3.3), and tests were conducted to characterize the binder. The results indicated that the process was efficient in generating a non-crystalline sodium silicate powdered material. With high SiO2/Al2O3 molar ratio the mortars achieved high compressive strength and it increased with age, had low permeability, and capillary water absorption. Compressive strength results varied from 6 MPa to 12 MPa at 28 days, indicating the possibility of using the proposed method for one-part AAB production. AAB produced can be applied in different building materials.

Resumo em Inglês:

For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

Resumo em Inglês:

Abstract This work evaluates microstructural changes and residual stresses on surface samples of AISI 201LN and 304L subjected to shot peening. The residual stresses were measured by X‑ray diffraction and magnetic Barkhausen noise (MBN) in different shot-peened conditions. The results showed that the 201LN steel presented more martensite than the 304L steel in the initial condition, but with lower δ‑ferrite contents. These ferromagnetic phases were present in a low amount with high tensile residual stresses due to brush cleaning and light cold‑rolling in the final stage of the fabrication process. The shot peening process promoted compressive residual stresses mainly in the δ‑ferrite. However, some “fresh” martensite exhibited tensile residual stress represented by higher and thinner peaks, which together with the low-intensity amplitude in the neighborhood, represented all formed martensite. Thus, small microstructural changes provoked high residual stresses behavior, which can be detected in ferromagnetic phases by MBN.

Resumo em Inglês:

Abstract The directional solidification technique allows the study of growth of the solid phase, as-cast structure and, finally, its mechanical characteristics as a consequence of thermal parameters. On the other hand, in the last decade, a process called equal-channel angular pressing (ECAP) has emerged as a widely-known technique in fabrication of ultrafine-grained metals and alloys. Applicability of the ECAP technique affords an excellent potential for changing, in a controlled and beneficial manner, the resulting properties of metals and alloys. For this paper, an experimental research has been conducted to study the effects of solidification parameter (cooling rate) on resulting microhardness in hypoeutectic Al-Si alloys, upon use of an ECAP procedure. The influence of cooling on the scale of the dendritic patterns is presented and discussed with recourse to equations. The resulting microhardness variation with position throughout the as-cast materials and cooling rate were characterized by experimental power laws. Results determined after the solidification experiments have revealed microhardness as a function of both cooling rate and position (P) of the as-cast materials to be dependent on alloy composition. In the ECAP process via route C with three passes, “as-solidified” microstructures have been found to be distorted and fragmented during the severe plastic deformation. This deformation imposed on the billets during the ECAP process facilitated obtaining a fine microstructure and high levels of microhardness were observed. However, even with the ECAP process, it was shown that microhardness is strongly dependent of the cooling rates.

Resumo em Inglês:

A kind of corrosion-resistant Ni-Mo-P composite coating was deposited on the surface of AZ91D magnesium alloy substrate by electroless plating method with different concentration of Ce(NO3)3 and Nd(NO3)3. The deposition mechanism of Ni-Mo-P composite coating was explored. Furthermore, the effects of Ce(NO3)3 and Nd(NO3)3 concentration on the microstructure and properties of Ni-Mo-P composite coatings were studied. Results indicated that the Ni-Mo-P composite coatings prepared by adding the optimal concentration of Ce(NO3)3 and Nd(NO3)3 had few defects. Meanwhile, the deposition rate of the composite coatings and the adhesion between the coating and the magnesium alloy substrate were improved. When the concentration of Ce(NO3)3 and Nd(NO3)3 were 0.10 and 1.00 g/L, the Ni-Mo-P composite coatings had the minimum corrosion rate of 0.826 and 0.681 g/m2·h, respectively. Herein, compared with the addition of Ce(NO3)3, the Nd(NO3)3 added Ni-Mo-P composite coating has the maximum arc radius of capacitive resistance and significant improvement corrosion resistance.

Resumo em Inglês:

Austenitic-ferritic stainless steels are alloys with controlled additions of Cr, Ni, Mo and N which, after a suitable thermomechanical treatment, results in a balanced microstructure with similar proportions of ferrite (δ) and austenite (γ). Thus, it is possible to obtain good combinations of high mechanical properties and corrosion resistance through microstructural refinement, which also leads to a relatively good Pitting Resistance Equivalent value (PRE) at both phases. However, inadequate heat treatment and/or welding processes might result in the precipitation of deleterious phases, leading to poor mechanical properties and/or corrosion resistance. In this sense, the use of non-destructive microstructural characterization techniques becomes a valuable resource to access such alterations. Therefore, this work evaluates the precipitation of deleterious phase’s in welded thermal aged joints by portable Double Loop Electrochemical Polarization Reactivation (DL-EPR) taking into account a preliminary metallographic replica characterization. The results show that the proposed portable method can detect even a small percentage of deleterious phases, in addition to having a strong potential to be a non-destructive microstructural characterization technique.

Resumo em Inglês:

Objective The aim of this study was to evaluate the electrochemical behavior of a cobalt-chromium (Co-Cr) dental alloy after immersion in denture cleansers. Method: Twenty-four specimens (Ø13x2mm) of Co-Cr were produced and divided into three groups (n=8) according to their experimental condition. The group 1 (control group) was composed only of distilled water, group 2 received a hygienic tablet (Corega Tabs™) at the moment that electrochemical test started, while the group 3 received the hygienic tablet (Corega Tabs™) 1h after immersion. The electrochemical tests recorded the open circuit potential (OCP) and current density (icorr). The surfaces of specimens were examined using a SEM. Data were statistically analyzed using analysis of variance (ANOVA) and Duncan test’ multiple comparisons post hoc analysis (α=0.05). Results: The values of OCP and icorr revealed statistically differences between the groups. The highest results were recorded for group 2 (-26.87±48.48mV; 0.29±0.22μA), which were similar to group 3 (-47.37±35.36mV; 0.26±0.10μA), and these values were difference to group 1 (-314.87±24.22mV; 0.50±0.17μA). SEM image show high corrosion with Corega Tabs™. Conclusion: The immersion in denture cleanser solution was not detrimental to the Co-Cr dental alloy and presented a lower tendency to corrosion process development than the control group.

Resumo em Inglês:

The production of hot-dip galvanized steel presents great challenges, because it is currently the main raw material in the manufacturing of automobiles, and its surface quality is fundamental for the construction of automobiles. Obtaining the best surface appearance in galvanized steels is directly related to understanding the phenomena involved in the galvanizing process. In this process, achieving thermal and chemical stability of the galvanizing pot means keeping top-dross formation under control. The top-dross is the main problem to be controlled, because it impacts the surface quality of coated steel. Some studies have been conducted to understand the formation of top-dross particles into the zinc bath, but little is known about the path of the particles formed from the melting ingots. In this study, the trajectories of these particles were simulated. It has been found that, depending on the immersion depth, dross particles may have different destinations.

Resumo em Inglês:

In this work, low-carbon steel AISI-SAE grade 1010 with copper grade CDA 101 was joined by friction stir welding (FSW) using a tapered pin profiled tool. The rotational speed of the tool is 900 rpm, a traverse rate of 30 mm/min, and an axial force of 5 kN were used to produce the joints. The microstructural analysis and mechanical properties of the weld joints have been successfully examined. The optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD) techniques were performed to examine the macropatterns and micropatterns of the welded joints. The tensile and hardness test was performed to evaluate the mechanical behaviours of the FSW joints. The fine ferrite grain features with uniform size were obtained in the microstructure of the nugget zone (stir zone). It is purely influenced by the alternating dynamic rearrangement (recrystallization) mechanism. High hardness was identified in the stir zone, even as the slightest stability was established in the heat-affected zone. The tensile investigation proposed that all the joints explored just lesser unbending nature than the parent material. The tensile strength of 181.5 MPa, the hardness of 144 VHN, and elongation of 14.03% were observed for the welded samples. The better properties for the weld joints were attained at 900 rpm spindle speed and tool traverse speed of 30 mm/min. The FSW is an attractive material joining process for both similar and dissimilar materials compared to other conventional types of joining processes, such as aerospace, marine engineering, shipbuilding, and industrial sector applications.

Resumo em Inglês:

With the growing industrialization, there is a constant increase in the world demand for steel, causing an increase on extraction of low-grade iron ores, which bear high levels of impurities. A feasible alternative is the use of residues from steel rolling processes (steelmaking mill scale) generated in the steel industry, which are composed of iron oxides consisting mainly of wustite (FeO), hematite (Fe2O3) and magnetite (Fe3O4). In line with the recycling of wastes, the application of heating by microwave energy in ironmaking processes consists in a promising new method developed in recent decades and is considered a cleaner technique. Therefore, this study aims to evaluate the self-reduction of mixtures composed of iron ore and steelmaking mill scale as iron source, together with coke fines as carbon source, heated using microwave energy. Through the rotational central composite design technique, it was possible to evaluate the best conditions for the use of steelmaking scale residue as well as the effect of the applied microwave energy power. The results indicated that the developed process has relevant utility with up to 41.48% of reduction obtained. The outcomes contribute to a better understanding of iron recovery from steelmaking residues in reduction processes using microwave energy for heating, providing significant insight for the development of new clean technologies.

Resumo em Inglês:

Abstract Dental alloys are widely used in fabrication of removable partial dentures, particularly as a dental framework. The present study aimed at studying the effect of the commercial mouthwashes on the corrosion behavior of the Co−Cr dental casting alloy. Corrosion behavior was investigated in alcohol-free and alcohol-containing mouthwashes added to artificial saliva solutions at room temperature by electrochemical tests recorded the open circuit potential (OCP) and current density, after the surface analysis of the samples was performed. During the early 250s, the OCP values showed significant changes, with the exception of one test group containing alcohol, where potential decreased continuously during the test, which also recorded the highest current density, different from the other groups. It was observed that the presence of alcohol increased the current density and the corrosion process in this alloy and the mouthwashes had more aggressive action in specimens submitted to solutions with alcohol in the composition.

Resumo em Inglês:

Abstract Microalloyed steels have a maximum of 2% in alloying elements and are used in the automotive and petrochemical industries. The microstructure and mechanical properties of these steels depend on chemical composition, processing and addition of molybdenum, niobium, titanium and vanadium. To evaluate the molybdenum effect in microstructure and mechanical properties, two microalloyed steels, with similar levels of niobium, titanium and vanadium, were prepared and forged. The steels have 0.056 and 0.160 percent by weight of molybdenum. The bars were homogenized, quenched and tempered. The specimens were machined for tensile and impact tests, hardness and microstructural analyzes by confocal and scanning electron microscopy. The ThermoCalc software was used to evaluate the carbides characteristics. The results show that steel with 0.160% Mo presents greater amount of bainite and austenite retained. It’s possible that formation of carbides by the secondary hardening mechanism increase in mechanical strength and a reduction in toughness.

Resumo em Inglês:

The depletion of conventional energy sources and the concern with the environmental impacts of the use of fossil fuels sparked interest in researching new energy sources and improving existing processes. In this context, the solar energy presents itself as one of the most promising energy sources on the planet, given its wide availability and applicability in thermal processes. However, its use still represents a great technological and economic challenge, because many systems that use this energy still have low efficiency and high cost, which makes them uncompetitive in competition with systems using other energies. With that, the search for the improvement of the processes awakens the researches in more adequate and cheaper materials, which represents a great scientific potential in the evolution of these technologies. Thus, the present work proposes to obtain and analyze a selective surface for applications in solar-thermal collectors, using CRFO (compound formed by chromium and iron oxides), varying the percentage by weight, and then mixed with aluminum oxide. For the tests, an experimental bench was built to simulate a flat plate solar-thermal collector in real operating conditions. Some characterizations were carried out, such as: techniques scanning electron microscopy (SEM), infrared analysis and UV-VIS absorptivity determination, as well as the graphs with surface temperatures and with radiation during the tests in the Sun for the composite (CRFO and aluminum oxide) and for the commercial surface (MRTiNOX). With the results obtained, it was verified in the field test that one of the produced selective surfaces obtained a result of absorptivity of 0.94 and 0.0349 of emissivity, which is close to that of the commercial surface. The results were confirmed in the characterization by UV-VIS, which showed high absorptivity values in the visible light range.

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This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al2O3). Monolithic alumina powder and Al2O3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al2O3 were processed by high energy milling, compacted and then sintered at 1600 °C - 2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values ​​between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO2 grains with average sizes of 0.6 μm well dispersed in the Al2O3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO2-tetragonal and Al2O3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m1/2. The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al2O3) to 316 MPa (20wt.% Ce,Y-TZP/Al2O3). The Ce-TZP reinforcement acts as a toughening agent of the Al2O3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.

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Abstract This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.

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The corrosion resistance of high entropy alloys was reviewed in the present work. The main focus was to explore the correlation between alloy composition, passive film stability and corrosion properties and use this information to develop a materials selection procedure based on the Ashby approach. Corrosion current densities and pitting potentials were the main design parameters used to rank different alloys, based on a careful examination of data published in the literature, considering uniform and localized corrosion, respectively. The outputs of the selection process clearly indicated a strong dependence of the corrosion resistance on passive film stability, although microstructural homogeneity and uniform distribution of alloying elements should not be disregarded. Proper combinations of elements such as Co, Al, Ti, Mo and Cr, especially, are effective at enhancing the corrosion resistance of high entropy alloys.

Resumo em Inglês:

Molybdenum trioxide (MoO3) thin films are generally deposit on metallic surfaces to increase their tribological performance. In this manuscript, MoOx coatings were for the first time deposited on plasma nitrided surfaces. Vickers microhardness tests, X-ray diffractometry, and micro abrasive wear tests characterized the samples. It was investigated the effect of temperature in hardness and tribological properties of austenitic stainless steel surfaces. When the temperature of plasma nitriding increases, the coating thickness and the nitrogen diffusion on the treated surface also increases, favoring the hardness of the coatings. After MoOx deposition, the predominant MoO3 phase with monoclinic and orthorhombic unit cells was observed. MoOx coatings after plasma nitriding demonstrated the highest wear resistance.

Resumo em Inglês:

The present work is associated with research concentrating on the innovation and use of hybrid heat treatment for eutectoid steel powder (0.8 wt%) reinforced Al-Zn-Mg (Al 7075) alloy composites. Due to high hardness, wear resistance, tensile strength and flexibility modifying heat treatment, heat treatable aluminium metal matrix composites reinforced with heat treatable hard steel particles may be the choice to explore. In this work, an attempt is made to increase hardness and tensile properties to higher levels through hybrid heat treatment, comprising simultaneous treatment to matrix and reinforcement in 3 different routes (Pearlite, Bainite and Martensite) compared to conventional age hardening treatment. SEM images and microhardness distribution witnessed the phase transformation in both matrix and reinforcement. Aging kinetics in conventional age hardening and hybrid treatments is accelerated by the increase in the quantity of reinforcement and increase in aging temperature. The improvement in hardness and tensile strength obtained by conventional age hardening path is further improved by the hybridisation path. Hybridisation route with martensite reinforcement phase shows excellent result in hardness, strength followed by bainite and pearlite path respectively in the decreasing order. In all heat treatment cycles, lower aging temperature marks greater property enhancement compared to higher temperature. Al 7075 with 6 wt% steel powder reinforced (martensite form) composite showed excellent peak age hardness, tensile strength compared to lesser quantity reinforced composites.

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Abstract Antimony doped tin oxide (ATO) thin films are deposited on corning glass substrate using the spray pyrolysis technique. The experimental parameters such as distance between the substrate and source (10-30 cm), substrate temperature (350-450°C) and atmospheres (Nitrogen and Forming gas) are varied to study their effect on the properties of ATO thin films. The ATO thin film annealed at 425°C exhibits the lowest electrical resistivity of 2.23×10-2 Ω-cm. Besides, the film annealed in the nitrogen atmosphere showed a less resistivity value of 9.06×10-3 (Ω-cm) than the forming gas atmosphere. The film doped with 3 at% of Sb revealed the highest figure of merit value of 11.45x10-2 Ω-1. The preferential orientation is observed at the (200) diffraction plane in all the cases from the structural studies. Furthermore, the intensity of the diffraction planes decreases as the temperature increases. The average transmittance of 75% is obtained for ATO thin films.

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Abstract Inverted organic photovoltaic solar cells were fabricated with the configuration of FTO/TiO2/P3HT:PC61BM/MoO3/Ag. Besides, the influence of transport layers, titanium dioxide and molybdenum trioxide, on the performance of solar cells were investigated. These compounds showed excellent optical (around 80% for molybdenum trioxide and 95% for titanium dioxide), electrical (like charge carrier density of 3.3 x1015 cm-3 and 2.5 x1014 cm-3 for titanium and molybdenum, respectively) and structural (anatase and amorphous hexagonal phase for titanium and molybdenum, respectively) properties to be used as transport layers. Also the influence of the thickness of the electron transport layer is studied, as well as the thickness, temperature and heat treatment time of the active layer. The correct selection of TiO2’s thickness (70 nm) and active layer’s thickness (250 nm) and annealing (at 100 degrees for 8 minutes) can increase the power conversion efficiency. Moreover, the cell fabricated with transport layers and the best conditions found showed a maximum efficiency of 3.3%, which indicates that the titanium dioxide and molybdenum trioxide played a determining role in the solar cell performance.

Resumo em Inglês:

Abstract Samples of fine structured Cu were fabricated by spark plasma sintering (SPS) of compacts of Cu nanopowder/micron-sized powder blend with a ratio of 3:7 by weight, and one of the SPSed samples was further processed by hot extrusion. The microstructures of the as-SPSed and the as-extruded samples and the tensile properties and fracture behavior of the as-extruded sample were studied. It was found that the microstructures of the samples consist of a concoction of ultrafine and coarse grains with high dislocation densities (~1015 m-2) as a result of microstructural evolution during material processing. Some nanograins were oxidized to form Cu2O particles residing around the coarse grains. Extrusion of the SPSed sample increases its microhardness from 70 HV to 90 HV. The electrical conductivity of the as-extruded sample reaches 87% international annealed copper standard (IACS), and its tensile properties are 200 MPa for yield strength, 218 MPa for ultimate tensile strength and 9% for elongation to fracture. The tensile test specimens from the as-extruded sample exhibit nearly ideal plastic deformation and undergo ductile fracture, suggesting that the fine-grained copper is a highly desirable material for high strength electrical conductors.

Resumo em Inglês:

Abstract The purpose of this research is to investigate the effect of heat treatment parameters on the tool life and surface roughness of dual phase steel. Optimization of machining parameters (cutting speed, feed and depth of cut) is carried out for the machinability tests on medium carbon low alloy steel. Taguchi’s method of design is used to carry out machinability tests. Analysis of variance (ANOVA) is carried out to determine the relative contribution of machining parameters on tool life and surface roughness. Microstructure analysis is carried out to ascertain the machining behavior of the steel. Results have shown that, depth of cut and cutting speed are the most significant factors contributing on the variation of the tool life and surface roughness. Optimized machining parameters are calculated in order to obtain higher tool life and lower surface roughness value.

Resumo em Inglês:

Abstract In this paper, Fe-15at.%Nb alloys were produced from high purity Fe (min. 99.8%) and Nb (min. 99.8%) powders via a mechanical alloying process. The effects of different Process Control Agents (i.e., methanol, hexane, and stearic acid) were investigated with powder morphologies, particle size distribution, and phase formation, and were sampled after up to 80 milling hours at 350 rpm. The powder morphologies and particle sizes were evaluated using scanning electron microscopy and laser diffraction analysis, respectively, and phases were identified via X-ray powder diffractometry. The results demonstrate for all conditions that, in the early stages, there was significant particle agglomeration due to the ductile-ductile feature of Fe and Nb powders, and latter an amorphization trend up to 80 milling hours. Methanol was the most efficient Process Control Agent in terms of avoiding cold welding, reducing of agglomeration, particle size distribution, reducing contamination and crystallinity reduction rate.

Resumo em Inglês:

The inhibition effect of the cocoa bean shell powder (CBSP) on SAE 1008 carbon steel was studied in acidic medium (HCl 0.5 mol L-1) by electrochemical techniques and gravimetric measurements. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to the chemical and morphological characterization. The gravimetric and EIS results showed that the corrosion rate decreases with increasing inhibitor concentration, reaching the maximum value of 97.92% in 1.77 g L-1 inhibitor (highest concentration studied). Even at the lowest concentration (0.44 g L-1) good corrosion inhibition efficiency (96.03%) was observed. The polarization curves indicated that the CBSP acts as a mixed type inhibitor. The inhibitory molecules adsorption followed the Langmuir isotherm model. The inhibitor economic evaluation showed that the use of CBSP is 48-616 times cheaper than traditional inhibitors. The results showed that CBSP is an efficient corrosion inhibitor for carbon steel and its production is financially attractive.

Resumo em Inglês:

Inorganic ternary type materials are induced compound is worked as fundamental applications in transformation of the solar light energy into electrical energy. Copper zinc selenide thin films have been synthesized by chemical bath deposition method on to stainless steel plate. The configuration of fabricated cell is p-Cu0.5Zn0.5Se| NaOH(1M) + S(1M) + Na2S(1M) |C(graphite). The Photovoltaic cell characterization of the films is carried out by studying current–voltage characteristics in dark, capacitance–voltage in dark, barrier height measurements, power output, photoresponse and spectral response. The study shows that Cu0.5Zn0.5Se thin films are p-type conductivity. The junction ideality factor was found to be 2.93. The flat band potential was found to be -0.708V. The barrier height value was found to be 0.186 eV. The study of power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency were found to be 150 mV, 21 μA, 42.13%, and 0.63%, respectively. Photoresponse shows lighted ideality factor is 2.89. Spectral response shows the maximum current observed at 580 nm.

Resumo em Inglês:

The mechanical and thermal behavior of ultra-high molecular weight polyethylene (UHMWPE)/metallic quasicrystal powder (MQP) composites are evaluated at filler volume fractions (∅f) of 0.01, 0.02, 0.06 and 0.15. MQP is based on an aluminum alloy, synthesized and characterized to act as a filler for UHMWPE. The preparation of the composites was conducted by compression molding. Morphological analysis reveals larger and smaller MPQ particles, being well distributed, and mechanically anchored in the matrix. The melting temperature was maintained after adding filler, while the crystallinity values decreased. When adding MQP, an improvement in thermal stability is observed by increases in both the initial and maximum weight loss rate temperatures (Tmax). However, when the temperature is about 700°C all composites present oxidation due to the MQP presence. The Pukansky model shows that the 0.06 MQP composites have better interfacial adhesion. This is confirmed by the Nicolais-Narkis equation. This contributes to an increase in the modulus of elasticity of the 0.06 MQP composite in respect to the others. The elongation at break was reduced for the 0.15 MQP composite. However, the higher volume fraction of MQP increased the stiffness of the UHMWPE, reflecting its potential for use as a reinforcement.

Resumo em Inglês:

Abstract The main production route for cast iron and steel is through the blast furnace. The silicon content in cast iron is an important indicator of the thermal condition of a blast furnace. High silicon contents indicate an increase in the furnace's thermal input and, in some cases, may indicate an excess of coke in the reactor. As coke costs predominate in the production of cast iron, tighter control of the silicon content therefore has economic advantages. The main objective of this article was to design an artificial neural network to predict the silicon content in hot metal, varying the number of neurons in the hidden layer by 10, 20, 25, 30, 40, 50, 75, 100, 125 , 150, 170 and 200 neurons. In general, all neural networks showed excellent results, with the network with 30 neurons showing the best results among the 12 modeled networks. The validation of the models was confirmed using the Mean Square Error (MSE) and Pearson's correlation coefficient. The cross-validation technique was used to re-evaluate the performance of neural networks. In short, neural networks can be used in practical operations due to the excellent correlations between the real values ​​and those calculated by the neural network.

Resumo em Inglês:

Abstract The influence of Al2O3 content in refining slag on the cleanliness and fatigue property of ultra-low-carbon (ULC) automotive steel were investigated based on the industrial experiments. The inclusion-adsorption capacity of the refining slag was calculated and the total [O] (T.O) content of ULC automotive steel was measured. The number density, size distribution and morphology of inclusions were analyzed and their effects on the cleanliness and fatigue property of ultra-low-carbon (ULC) automotive steel were investigated. The results showed that as the Al2O3 content in refining slag increased from 19.92% to 39.73%, the inclusion-adsorption capacity of ULC automotive steel decreased from 210.30 down to 57.12, and the fatigue life from 1.4x104 down to 0.9x104 cycles, while the T.O content of steel increased from 12 up to18 ppm and the inclusion number density from 4 up to 9 per mm2.

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Abstract Structural rejuvenation is one of the key topics in the field of metallic glasses (MGs). In this work, we evaluated the combined effects of annealing treatment and elastic cyclic loading to discover pathways for promoting structural rejuvenation and improving the mechanical properties in the MGs. Using molecular dynamics (MD) simulations, it was revealed that the sole cyclic loading led to the increase of rejuvenation degree; however, a saturated state was observed upon the 40th cycle. On the other side, the sample exposed to the combined treatment exhibited a slight relaxation at the first step of cycling process and then a sharp rejuvenation degree was detected in the material. The thorough analyses indicated that the change in the fraction of coordination polyhedrons at the relaxation stage was the main reason for the extra rejuvenation in the sample exposed to the combined treatments. The results also suggest that the combination of rejuvenation treatments improves the magnitude of rejuvenation in the amorphous alloys. It should be noted that the increase of rejuvenation in the alloying systems accompanied with a reduction in the tensile strength and an enhancement in the homogenous plastic deformation.

Resumo em Inglês:

Abstract This research aims to investigate the influence of water soaking and re-drying on the mechanical and wear properties of nanoclay-polyester nanocomposites (NPNCs). The nanoclay addition significantly enhances the mechanical properties of NPNCs in as-made, water-soaked and re-dried conditions. Also, the addition of nanoclay decreased the percentage of reduction in mechanical properties under water-soaking condition. Re-drying recovers more than 90% in values of mechanical properties compared to original values. In contrast, the addition of nanoclay reduces the mass loss (wear test) of specimens in all three conditions. Re-dried specimens have lesser mass loss than water-soaked specimens and greater mass loss than as-made specimens. SEM images illustrate that the absorbed water can alter the fracture and worn-out surface by swelling and plasticization. Also, SEM images reveal that re-drying can reverse the effect of swelling and plasticization of the specimens.

Resumo em Inglês:

Abstract This work investigates the effect of eco-friendly chemical treatments on the mechanical and physical properties of composite laminates based on sisal fibres. A 2231 full-factorial design is conducted to test the influence of chemical solution types, fibre treatment time, and polymer matrix type on the mechanical and morphological characterisation of the composites. Chemical treatments remove impurities from fibre surfaces, and enhance fibre-matrix adhesion. The treatments, especially with sodium carbonate (Na2CO3), also progressively reduce the hemicellulose fibre content. Polyester composites made with sisal fibres treated with Na2CO3 for 96h achieve enhanced strength and stiffness under tensile, compressive and impact loads. The results evidence the feasibility and efficiency of the proposed eco-friendly treatments for natural fibres and the application of renewable fibre laminates in secondary structural applications.

Resumo em Inglês:

Abstract The present investigation aims to coat the layer with Nickel (Ni) and Copper (Cu)over the surface of strenx 900 steel using semi sintered Cu-10Ni-Crx electrodes(x = 2, 4 & 6 wt. %). Three different proportions of semi sintered electrodes such as, Cu-10Ni-2 weight percentage of Chromium (Cr), Cu-10Ni-4 wt. % Cr,and Cu-10Ni-6 wt. % Cr were prepared by powder metallurgy route. Electric discharge alloying was completed based on L9 orthogonal array and alloyed parameters were optimized using Taguchi method. The alloyed surfaces were characterized using scanning electron microscope and atomic force microscopy. The deposition of formation of intermetallic was studied using X- ray diffractometer. Higher Material Transfer Rate (MTR) was obtained at 9A, 350A and 6% chromium using Cu-10 Ni-Cu electrode. The chromium percentage was the foremost factor on Surface Roughness (SR) (73.71%) and MTR(96.56%). From Taguchi approach, the minimum SR was attained at percentage of chromium of 2%, compaction pressure of 250 Megapascal (MPa) and peak current of 9A. The maximum MTR was achieved at 6 percentage of Cr, compaction pressure of 350 MPa and peak current of 3A. Wear loss for Cu-10 Ni-Cr increases linearly with increase in sliding speed from 2m/s to 4m/s respectively.

Resumo em Inglês:

Abstract With the growing industrialization, there is a constant increase in the world demand for iron ore, thus implying an increase in the volume of mining, resulting in the extraction of ores with higher levels of silicon, phosphorus and sulfur impurities. Therefore, it is highly relevant to use beneficiation techniques that allow the use of iron ores with high levels of impurities, and it is known that a widely used alternative is to perform a pre-treatment of iron ore particles in order to reach the limit of acceptable phosphorus before application in steel production. Therefore, this study aims to evaluate the pre-treatment process of iron ore particles aiming at reducing the phosphorus content using the bacterial strain burkolderia caribensis in contaminated iron ore samples. Through the rotatable central composite design technique, it was possible to evaluate the best conditions for the use of the bacterial strain to reduce the phosphorus content in the particles. The results indicated that the developed process has relevant applicability. The results contribute to a better understanding of the use of the bacterial strain as a pretreatment process to reduce the phosphorus content of iron ore particles and also to the development of new cleaner technologies.

Resumo em Inglês:

Abstract Aluminium casting alloy LM4 (EN 1706 AC-45200) composites with TiB2 (1, 2, and 3 wt.%) as reinforcements were produced using the two-stage stir casting method. OM and SEM study shows uniform and homogeneous reinforcement distribution in LM4 + TiB2 composites. As-cast composites were subjected to single-stage solution treatment at 520°C for 2 h and multistage solution treatment at 495 and 520°C for 2 and 4 h, followed by hot water quenching at 60°C and aging at 100 and 200°C for different time intervals. The hardness of as-cast and artificially aged composites were compared in both conditions. Compared to as-cast LM4 alloy, 20-45% improvement in hardness was observed for LM4 + TiB2 as-cast composites. 60-150% improvement in hardness was observed in artificially aged LM4 + 3 wt.% TiB2 composites when aged at 100 and 200°C during peak aged conditions. TEM images confirmed the presence of primary strengthening solute-rich phases after age hardening treatment such as θ’-Al2Cu and θ”-Al3Cu, which are responsible for hardness increment. An artificial neural network (ANN) model was created to predict the hardness trend of these composite samples using MATLAB R2021b, and results proved that the ANN model developed can be utilized as an effective tool to predict the hardness of treated composite samples.

Resumo em Inglês:

Abstract Residual stresses (RS) in pipes welded by a fully automated friction welding process, called FRIEX, are investigated using the contour method (CM) and the X-ray diffraction method (XRD). Samples were produced using a self-developed equipment, which is based on the interaction between a consumable intermediate rotary ring and two stationary pipe sections, by varying the loading rate applied during the welding of API 5L B pipes with an API X65 ring. Mechanical and metallurgical properties were locally analyzed through metallography and microflat tensile tests. RS measured by XRD and CM showed comparable values; tensile zones were found in the pipe HAZ and compressive stresses were found in its adjacent areas. Tensile RS of approximately half the local yield strength of the components were also found, mostly on the internal surface, and their values decrease with increasing welding loads. Microflat tensile tests showed an increase in yield strength of pipe TMAZ and HAZ, with a clear influence of loading rates.

Resumo em Inglês:

Abstract The mechanical behavior of metallic materials depends on several variables, such as the material structural characteristics, the process parameters, the temperature, the strain rate and the anisotropy features due to strain paths in different metal forming operations. Considering the last one, the effect of shear direction loading on the work-hardening after the rolling/shearing loading of a ferritic stainless steel, AISI 409, was investigated in this work. The annealed AISI 409 sheets were predeformed by cold rolling up 0.19 effective strain and then sheared at three different directions: at 0°, 45° and 90° from the original rolling direction. The samples were characterized through tensile, shear and Vickers microhardness tests while the study of crystallographic texture was performed using the electron backscatter diffraction (EBSD) technique. The work-hardening behaviour of the material was analyzed considering the work-hardening rate and the Hollomon work-hardening exponent after each strain path change applied to the AISI 409 steel. The results indicated the presence of preferential crystallographic orientation and the occurrence of transients on the work-hardening rate mainly for the sample sheared at 45° from the original rolling direction due to structural arrangements assumed by the AISI 409 steel after the strain path changes.

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Abstract A previous constitutive modeling for single-phase steels is extended using the mixing law to predict the behavior of hot deformation in the dual phase ferritic-austenitic intercritical zone of Fe-C-Mn-Si alloys. Mixing law considers two phases instead one, so one phase formula was modified. The constant’s values used represents average values to the same conditions in austenitic and ferritic model. The amount of each phase is determined as function of temperature and chemical composition. The developed constitutive modeling is validated by comparing the theoretical stress-strain curves with experimental isothermal uniaxial compression tests of 1008 and 1035 carbon steels at different temperatures and strain rates. The compression tests were carried out in a dilatometer with the compression load at strain rate of 10-3, 10-2 and 10-1 s-1. A good agreement was obtained between the calculated and experimental results over different stages of deformation and hardening. Microstructural analysis was also carried out to relate the deformation results to the microstructure of the steels. Finally, a general constitutive equation has been proposed for hot deformation of steels in the intercritical zone.

Resumo em Inglês:

Abstract This research aimed to investigate the structural and magnetic properties of Yttrium Iron Garnet by Ni-doped using self-combustion method. Ni-doped directly changed the structure into Y3Fe5-XNixO12 (x=0.00, 0.02, 0.04, 0.06, 0.08). Self-combustion method was obtained by stirring raw materials at room temperature (27°–28°C) and heated at 150°C until combustion occurred. The samples were sintered at 900°C with 120 minutes holding time. The phase identification revealed the cubic structure of garnet phase with the crystallite size from 62.73–62.87 nm. The molecular bonding from molecular bonding displayed Ni-O and Fe-O bonds, while the magnetic properties shown the highest saturation magnetization of 27.04 emu/g in the sample with additional Ni x=0.02, the highest magnetic remenance of 16.09 in the sample Ni x=0.02, and the highest coercivity of 0.029 in the sample with Ni x=0.08. This research, by adding nickel element, shows that the coercivity of Y3Fe5-XNixO12 decreased when the particle size is increased. The increase in Ni concentration as doping material cause the double exchange interaction and affected the lattice parameter, molecular bond, and magnetic properties.

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Abstract The microstructure and properties of shielded metal arc welding (SMAW) joint of P91 heat-resistant steel annealed at different holding time were observed and analyzed. The results show that the martensite and residual austenite structures in the weld zone and coarse grain heat affected zone (CGHAZ) were transformed with the extension of holding time. After 760°C+4h annealing, a large number of white rod-shaped precipitates appeared in the weld zone. The main components of precipitates were Fe, Cr, Mn, V, Si, and a small amount of oxides appeared. After 760°C+5h annealing treatment, relatively fine white granular precipitation appeared in the weld zone, and a large number of oxides and some precipitates have been dissolved. After 760°C+6h annealing treatment, the precipitated phases were composed of Fe-Cr, Fe3Si, Ni-Cr-Fe, Fe2MnAl. Compared with the annealing treatment for 5h, the microstructure of the precipitated phase is fine and uniform, dispersion distribution of second phase particles, and the material mechanics is relatively stable.

Resumo em Inglês:

Abstract ASTM A 182 F22 steel, used in components subsea for oil extraction, are previously buttered with ductile metal such as Inconel 625, before being welded to steel pipes similar to ASTM A36 steels. The thermal buttering weld cycle provides the formation of high hardness micro-phases and carbides at the interface between F22 steel and the buttering with Inconel, which when in contact with hydrogen, originating from the cathodic protection applied to these equipment, can lead to the embrittlement of this region, causing fragile fractures. In this work, ASTM A 182 F22 steel, buttered with Inconel 625 and welded to A36 steel, submitted to post-weld heat treatment without hydrogenation and subjected to cathodic protection for hydrogen permeation were submitted to fracture toughness test. The welds and buttering were done using GMAW process with AWS ERNiCrMo-3 wire as filler and buttering metal and a mixture of Ar and He as shield gas. The results indicated a 56% of area reduction, and 15% in the elongation values in the tensile tests, in addition to a 13.3% reduction in the CTOD value, for welded joints subjected to hydrogen permeation, which showed a quasi-cleavage fracture mechanism.

Resumo em Inglês:

Abstract The objective of this work was to investigate effects of magnetically treated tap water quenchant on hardenability and quenching crack resistance of S45C steel. The magnetically treated water quenchant was prepared by circulating regular tap water though a 130 mT magnetic field. The S45C steel was austenized at 860°C for 30 minutes. The hardenability in transverse section measurement of S45C steel quenched in magnetically treated tap water did not differ from that prepared with regular tap water quenchant. In measurements of the quenched end, the hardenability of S45C Steel quenched in magnetically treated water was below that with tap water quenchant. On the other hand, quenching crack resistance of S45C steel quenched in magnetically treated tap water was higher than that prepared with regular tap water. Moreover, microstructures of specimens quenched in magnetically treated tap water quenchant were different from that with regular tap water quenchant. Fine martensite structure formed in specimen quenched in regular tap water quenchant, while coarse lath martensite formed in specimens quenched in magnetically treated tap water quenchant.

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Abstract A novel method to classify the aggressiveness of soil considering its physicochemical content and the development of new synthetic solutions for lab uses is proposed. The results showed that the main criteria existing in the literature for soil corrosivity classification might cause misunderstandings about the real aggressiveness. The synthetic solutions proposed aim to cover a wide range of soil found worldwide in order to refine the assessment of their characteristics hence their corrosivity. For the lab experiments, an API 5L X65 pipeline carbon steel was used. The solutions presented great reliability, and they seemed to be adequate to simulate soils with the presence of sulfate-reducing bacteria (SRB), chloride, and high pH.

Resumo em Inglês:

Abstract Effect of two distinctive tool designs along with other tool related parameters including speed of traverse of tool and offset distance of tool pin during friction stir welding of dissimilar AZ91C and AZ31B alloys of Mg were investigated. Experimental recordings revealed that all the joints fabricated during 1st set of investigations employing cylindrically tapered pin geometry and their offset distances being 0.5 mm or 1mm towards any one of the parent metals possessed flaws. Joint No: II-3 fabricated in 2nd set of investigations by employing 15mm diameter inner shoulder tool with threaded cylindrical tapered pin geometry at a tool offset distance of 0 mm was found be free from flaws. This joint exhibited a tensile strength of 186 MPa which was 78.81% of AZ91C and 70.72% of another parent metal AZ31B. Existence of intermetallic phased constituents, namely, Mg17Al12 in several regions of fractured surfaces have contributed to the supplementary brittleness in the zone of nugget, and have reduced the tensile strength of the joint.

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Abstract The high temperature oxidation of Cu-32.02% Zn-2.30%Pb brass was carried in N2-5wt.% O2 and N2-12 wt.% O2 atmospheres. The amounts of oxygen in the oxidizing atmospheres and the time of the oxidation affected the oxide morphologies and kinetics of the oxide growth. In the first hour of the oxidation at 650 °C, oxide nanowires were noted. The average diameter, length and distance between the observed nanowires were 27 ± 0.01 nm, 0.20 ± 0.04 µm and 0.20 ± 0.04 µm respectively for the samples oxidized in N2-5wt.% O2 atmosphere and 102 ± 23 nm, 0.36 ± 0.24 μm and 0.24 ± 0.08 μm respectively for the samples oxidized in N2-12wt.% O2 atmosphere. The EDX and XRD analyses of the nanowires and the oxide granules confirmed ZnO nanowires and a continuous oxide layer of ZnO. The x-ray diffraction confirmed minor presence of PbO. The oxide growth kinetics followed the linear oxide growth model, for the alloy samples that were thermally oxidized in N2-5 wt.% O2 atmposphere and parabolic growth model for those thermally oxidized in N2-12 wt.% O2 atmospheres respectively. The values of 6.8 µm/hour and 23.03 µm/(hour)1/2were determined for growth constant (k), based on the two models respectively.

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Abstract The cellulose from Komagataeibacter hansenii is synthesized as a thin film at the surface of glucose based media. Strong acid hydrolysis release sections of crystalline cellulose chains in nanometric scale that leads to persistent suspensions in water. The cellulose anhydro-glucose hydroxyls are suitable to receive functional groups as enzymes, and lipases have great economic value being a valuable model for protein immobilization. In this work both, the membrane of bacterial cellulose as well the nanocellulose produced trough acid hydrolysis, was functionalized with a lipase. The bacterial cellulose membranes were produced by Hestrin-Schramm medium, and nanocelluloses produced from the pristine material was characterized using techniques as 13C solid state NMR and transmission electron microscopy (TEM). The pristine membranes and nanocellulose were functionalized with succinic acid as linker, then lipase was conjugated using EDC (N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride), and NHS (N-Hydroxysuccinimide). The effectiveness of the chemical process was characterized, and the lipase activity were measured. The presence of the succinic acid and amide linkage, as well physical-chemical changes on the functionalized polysaccharide. Hence, we inferred that after immobilization the enzyme maintained its activity in both cellulose and the cellulose membrane.

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Abstract A metallurgical process using a very high temperature Mo-Ru brazing filler alloy to join a controlled porous tungsten cathode button and a single-crystalline molybdenum cathode body for microwave tubes manufacture was developed†. The Mo-Ru brazing alloy was obtained by mixing and milling powders in the eutectic composition with a binder, and a braze paste was applied on the surface cathode parts. Brazing was performed in two temperatures by using a resistive dry hydrogen cold wall furnace for 10 minutes: at 1890 °C and 1967 °C. It was observed a fillability by the Mo-Ru system only in the tests performed in temperatures above 1967°C. The brazed samples were analyzed by Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy. It was observed absence of microstructural defects in the interface between the tungsten porous and dense molybdenum joint. Stress-strain tests, followed by SEM analysis were performed to determine the mechanical behavior of the brazing joining. The results indicate the origin region of the cracking and show an intergranular propagation; some evidence as grain cleavage indicates a brittle failure behavior.

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Abstract Thin film solar cell materials such as 3D metal halide perovskites are cheaper alternatives to silicon. Presently, the conversion efficiency of 3D lead halide perovskites is 25.5% (2021), which represents an increase of more than 550% since their discovery in 2009 (3.8%). Despite this remarkable progress, concerns about the toxicity of lead have sparked the quest for possible substitutes, in particular, 3D tin halide perovskites. This review covers the general properties of tin halide perovskites, synthesis and stability. It also identifies possible gaps and application beyond solar cells.

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Abstract Solar thermal energy is one of the ways of using solar radiation that can be applied to meet the energy needs for heating. To achieve efficient photothermal conversion, selective surfaces are applied to solar collectors to absorb more radiation and minimize heat loss. The present work produced absorber surfaces from black chromium electrodeposition on stainless steel substrate, the main parameter evaluated was the deposition time and its effect on optical and morphological properties. In this sense, the techniques of characterization UV-Vis-NIR Spectroscopy, Infrared Spectroscopy, X-Ray Diffraction, Optical Profilometry and Thermogravimetric analysis were used. It was observed a great influence of the electrodeposition time in the absorptance of the films, where films with deposition times of 2 to 10 minutes obtained absorptances greater than 92%. The metallic Cr phase was identified in the films, and it is estimated that chromium oxides may have been formed in the amorphous form. With increasing time, the roughness oscillated due to the constant nucleation of chromium throughout the process. Furthermore, a 5% mass loss indicates good thermal stability of the film up to 400 °C.

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Abstract One of the most important thin film deposition techniques on a silicon, quartz or sapphire substrate in the world is the spin coating method. Hematocrit centrifuge was used to elaborately manufacture the spin coating machine from affordable materials without vibrations. The vacuum holder substrate in this system is used for substrate adhesion. This method provides a dimensionally free substrate with appropriate adhesion for sedimentation upon high-speed spinning. A platinum thin film was deposited on a fluorine-doped tin oxide glass (FTO) substrate with a specific concentration of hexa-chloro-platinic acid. Platinum thin films were investigated by Field Emission Scanning Electron Microscope (FESEM) and UV-Vis spectroscopy. FESEM displays successfully produced platinum thin films. The results showed a platinum film transmittance decrement with increasing of hexachloro-platinic acid content. Therefore, the suggested spin coater in this work can deposit platinum thin films with high transmittance up to (98 a.u.).

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Abstract Shifting the Curie temperature in dependence on both uniaxial pressure and electric field in BaTiO3 crystals was studied based on literature data. It was shown that both these dependences perfectly coincide when adjusting the scale. Based on coincidence of these dependencies a relationship between both an uniaxial pressure and an electric field when shifting the Curie temperature was established. The specific heat is calculated using this relationship.

Resumo em Inglês:

Abstract The aim of this work was to use the Washburn capillary rise method to evaluate changes in surface energy promoted by the insertion of CuO in a 58S glass and its implication in bioactivity. The presence of CuO decreased the surface wettability by decreasing the Lewis acid-base component γSAB and increasing the Lifshitz-van der Waals component γSLW. The insertion of CuO also diminished the value of the electron donor parameter γS-; i.e., the number of negative groups. This was accompanied by a nonuniform apatite formation on the surface, likely because the presence of CuO-rich regions with lower electron donor values impaired the adsorption of Ca2+, preventing uniform apatite precipitation. Therefore, surface energy was extremely sensitive to small physical and chemical changes in the glass structure and the behavior of the electron donor parameter could be used as an adequate probe to predict glass bioactivity.

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Microwave heating potentially reinforces the muddy intercalation to eliminate slope failure. Montmorillonite has the worst water resistance among the muddy intercalation components, which is a primary facet of inducing muddy intercalation failure. This study investigates the mechanism of shear strength and water stability enhancement of montmorillonite heated by the microwave oven and muffle furnace from room temperature to 800 °C. Results show that montmorillonite mineralogical evolution can be divided into three stages: room temperature-300 °C, 300-600 °C, and 600-800 °C. Microwave heating is more efficient in montmorillonite heat treatment than muffle furnace heating and makes the montmorillonite dehydroxylated earlier. It is worth noting that hot spots formed inside the montmorillonite specimens during the microwave heat treatment. Microwave significantly promotes the shear resistance of montmorillonite, where the maximum increases are 39.94% of cohesion at 600 °C and 20.54% of internal friction angle at 700 °C. This enhancement is due to the rough surfaces and large particles produced by dehydroxylation and Mg-Al spinel synthesis, and the significant degree of disorder state of MMT after dehydroxylation also plays a vital role. The microwave-heated montmorillonite over 500 °C presents good integrity in the water immersion test over 24 h. Considering the shear behavior and water stability, we believe the most reasonable heating interval for microwaves is 500-600°C.

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Abstract The corrosion evaluation of steels in the oil and gas industry environments is a crucial issue because corrosion can cause economic and human losses. It is well known that H2S can be originated from different processes in the oil and gas industry, accelerating the corrosion process. The objective of this work was to evaluate the H2S corrosion resistance of an API 5L X80 steel and its welded joint obtained by submerged arc welding process (SAW). All tests were performed in an aerated 5% wt NaCl and thiosulphate aqueous solution. The H2S concentration, pH, weight loss, electrochemical tests, and microstructure were considered. The results obtained showed an increase of the corrosion rate values, with decreasing pH and increasing concentration of H2S generated by the thiosulphate. For the lowest H2S concentrations, the corrosion process was inhibited, due to the formation of a partially protective film on the samples’ surfaces. The heat affected zone (HAZ) showed severe localized corrosion attack which was attributed to the microstructural characteristics of this region.

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In this work, the crystalline structure, chemical composition, size, and morphology of core@shell nanoparticles based on Zn-Mn ferrite nanocrystals were investigated. These materials have been proposed as promising candidates for multifunctional applications in biomedicine, catalysis, environmental remediation, among others. Those properties were probed by using several experimental techniques such as Synchrotron X-Ray Diffraction, Energy-Dispersive X-ray Spectroscopy, Transmission Electron Microscopy and Selected Area Electron Diffraction. Results show that all synthesized nanoparticles present a single crystalline spinel phase without the appearance of undesirable byproducts. The nanoparticles present a non-stoichiometric Zn-Mn ferrite core, due to a Fe enrichment and a Zn loss with respect to the synthesis medium. The surface treatment of the nanoparticles induces a greater iron enrichment, which occurs at the nanoparticles surface without changing the crystalline structure. Finally, modifications in lattice parameters and strain suggest a contribution of the Mn2+ cations, mainly related to their easy oxidation in the synthesis route, which increases the structural vacancies of Mn-richer ferrites.

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The purpose of this research is to analyze the mechanical properties and corrosion resistance of spot welding of stainless steels AISI 316L using the process of resistance spot welding varying welding parameters with three level for each of welding parameter; welding current (A.), electrode Pressure (bar), squeeze time (s.), and welding time (s.). The welding current was (4500, 5500 and 6500) A, the electrode Pressure was (20, 30 and 40) bar, the squeeze time was (0.6, 0.8 and 1) Sec., and the welding time was (0.3, 0.6 and 0.9) Sec. The specimens were inspected by a tensile-shear test, corrosion test and the inspection of scanning electron microscope (SEM). The technique of design of the experiments (DOE) was utilized to examine the influence of the welding process parameters on the joint tensile-shear force. The results were analyzed by the DOE method to determine the optimum tensile-shear force, where can be obtained by utilizing the welding parameters by welding current 5500A, electrode pressure of 30 bar, squeeze time 0.8s., and welding time of 0.3s. The examination of SEM indicated that the increment of welding current and electrode pressure leads to increment pitting and corrosion rate.

Resumo em Inglês:

Abstract The development of low-cost high quality surface finishing methods for silicon carbide (SiC) is an arduous task. Nowadays, the SiC mirrors manufacture involves extensive, complex, and costly finishing processes carried out on highly expensive ultra-precise machines. In this work, a cost-effective surface finishing method has been successfully developed, using conventional machines for the optical finishing of SiC. The results showed that the combination of ductile grinding and polishing in conventional low-cost machines allowed to obtain high-quality surface finish on SiC substrates with low roughness (4 - 10 nm Ra ) and optical figure in the range λ / 4 - λ / 8, at a reduced 32 hours total processing time.

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Abstract ADI are the result of graphite nodules and ausferrite microstructure (acicular ferrite + retained austenite). Over the past few years, ADI has become an important material for engineering due to its excellent mechanical properties (outstanding ductility, high mechanical strength and good toughness) and low cost. It is known the discussion of process variables such as austempering time and temperature are extremely important for the microstructural and hardness study of these materials. Thus, in the present work, ADI cast iron was investigated under twelve different austenitic conditions, aiming to characterize the influence of the amount of austenite on the ferritic matrix on the mechanical property of hardness. The heat treatment parameters vary from three different times (40 min, 90 min and 180 min) under four temperatures (280ºC, 300 ºC, 320 ºC and 370ºC). Results show there is a decreasing of hardness linked to the increasing of retained austenite % volume. The greater amount of retained austenite % volume in the matrix was presented by sample A14, treated during 40 minutes under 370ºC and presenting 32.30% of this microconstituint. The amounts of each phase present in the studied materials were raised by quantitative metallography through the software Fiji-ImageJ, allowing a comparison of the results obtained by these two methods. Time differences on the austempering heating treatment did not show several implications on ADI microstructure. In addition, analyzes of the graphite nodules were performed.

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Abstract Close-Coupled Gas Atomization (CCGA) is often used to produce spherical metal powders with a wider Particle Size Distribution (PSD) (10 – 500 µm) compared to that required by the main Additive Manufacturing processes (10 – 105 µm). This work presents an accuracy evaluation of a mathematical model based on the Lubanska equation to predict the d50 for CCGA. Atomization experiments of 316L steel were conducted to evaluate the tip diameter and atomization gas pressure effects on PSD and, the d50 experimental results were used as the reference to the mathematical model evaluation. The mathematical model accuracy could be improved by: (i) considering the backpressure phenomenon for the metal flow rate calculation, since it was an important inaccuracy source; (ii) reviewing the tip diameter effect, which had a lower impact on d50 than that predicted by the Lubanska equation. The atomization gas pressure was the most influential parameter on d50 and d90 and the increase of the gas pressure led to a significant reduction in PSD and, consequently, increased yield.

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Abstract Degradation kinetics is an important tool in order to understand and improve energy conversion and the final application of a material. Cellulose cryogels (CC) are a new class of materials that can be reinforced by several types of particle, including biochar. Apart from it, degradation kinetics and lifetime prediction of biomass cellulose cryogels reinforced by cellulose pyrolysis waste (BC) has been investigated using TG techniques and iso-conversional model free methods. Additionally, the same study was applied to cellulose cryogels reinforced by graphene nanoplatelets (NPG) to compare the behavior of a filler from waste (BC) and a noble filler (NPG). Furthermore, the influence of the addition of the fillers into the cellulose biomass were evaluated in terms of thermal stability and crystallinity. BC and GNP led to higher values of activation energies (Ea) calculated from model-free isoconversional methods and all samples degraded in two-steps. Finally, lifetime prediction was successfully applied and the CC cryogel became more stable over time, maintaining almost 80% of the mass for 1 year exposed at 180 °C. The results of this study shown that only cellulose biomass cryogels are more suitable to produce thermal insulators due to it higher thermal stability.

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Nanocoatings thin films are layers deposited to improve required properties and corrosion resistance as a major objective for materials that are used for various biomedical applications such as biosensors. In this study, Gold (Au) thin films with 50 nm and 100 nm have been synthesized on Ni-Cr-Mo alloys by magnetron sputtering deposition technique. X-Ray diffraction (XRD), Atomic Force Microscopy (AFM), and Energy-dispersive X-Ray spectroscopy /Scanning Electron Microscopy (EDS/SEM ) have been used to distinguish the surfaces morphology. The results showed that there is no defects or micro-cracks with a uniform and homogenous film. It has spherical nanoparticles diameter morphology with 200-400 nm shaped to fine aggregation. The roughness average (Ra) decreased from 3.91 nm for 50 nm films to 3.70 nm for 100nm films with FCC crystal structure (111) for gold thin films. In vivo, after 50 nm and 100 nm nanocoated thin film by gold, a significant improvement in the localized corrosion resistance has been obtained in artificial saliva corrosive media at 37 °C compared with the uncoated surface.

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Despite of their excellent combination of high mechanical strength, toughness and corrosion resistance, duplex stainless steels (DSS) are susceptible to sigma phase formation, negatively affecting their superior properties. Sigma formation continuous cooling transformation (CCT) diagrams can be a useful tool to avoid sigma formation during cooling from solution treatment temperatures; however, non-isothermal information about sigma formation in DSS are scarce in literature. This work presents a methodology to simulate CCT diagrams in DICTRA® software, showing excellent adherence to literature data. The methodology here presented was also able to describe sigma phase formation behaviour for different DSS compositions.

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This work aimed to clarity the influence of filler alloy on microstructures and properties of induction brazed Al/Cu joints. It was found that the alloying elements in the filler alloy changed the morphology and phase type of interfacial layer in the joint. Mg converted the native Al2O3 film into MgO and stopped the re-oxidation of aluminum. However, excessive Mg caused planar inter-metallic compounds (IMCs) to become wavy, which decrease the ductility of the joint. A suitable amount of Cu and Si removed residual oxide film and resulted in a thin planar IMCs layer, which is beneficial to Al/Cu joint. Al-8Si-4Cu-2Mg-1Ga-0.05Ce filler foil produced an excellent joint consisting of a 2μm Cu9Al4/CuAl2 planar layer and free from oxide film. The tensile strength of the joint is higher than that of aluminum. The bend angle is higher 130°. The electrical resistivity of the joint is lower than the theoretical value.

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The hydrogen storage properties of pure magnesium and magnesium ZK60 alloy containing 2.5 wt% of mischmetal (Mm) processed by Cold Rolling (CR) and Low Temperature Rolling (LTR) were investigated. Before CR and LTR processing, Equal Channel Angular Pressing (ECAP) was employed in the alloys as an initial processing step to refine their microstructures. Microstructure findings showed that the ECAP+LTR route is more effective than the others to generate grain refinement - a desirable aspect in hydrogen storage materials. SEM and TEM results in combination with XPS analysis revealed that the ZK60 + 2.5 wt. % Mm alloy after being processed by ECAP + LTR had more refined grains (with sizes < 1μm) and exhibited superior resistance to the formation of oxides and/or hydroxides when compared with the pure magnesium alloy. The refined microstructures of the ECAP+LTR samples combined with the presence of highly oriented grains along to the (002) plane and large amount of defects – which are features associated to the LTR route - such as cracks and voids, resulted in a fast activation kinetics than for the samples processed by ECAP + CR route.

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Abstract The main problem in metal oxidation is the spalling and de-cohesion of the oxide layer, which results in delamination due to strong compressive stress gradient through the layer. Present paper proposes the use of a modified process named Asymmetric Bipolar Pulsed Plasma (ABiPPS) for plasma-oxidation treatment of low carbon steel AISI-1006 samples. Results show that the ABiPPS process ensures high plasma stability and enables the growth of uniform oxide layers (with thickness up to 6 µm) on metal surfaces. Plasma generated through bipolar asymmetric voltage pulses provides better control on surface bombardment through interspersed jets of ions and electrons, during the oxidation process. The control of intermittent ions and electrons bombardment (through voltage peaks up to 1.5 kV and period about 1µs), during plasma oxidation, make it possible to improve the adhesion between the oxide layer and the substrate, moreover the control of crystalline phases, such as hematite and magnetite.

Resumo em Inglês:

Abstract The effect of temperature was investigated on the consolidation of blended elemental powders of aluminum and copper by equal channel angular pressing (ECAP). Aluminum and Copper powders (1:1% vol.) were blended and consolidated in a 90° ECAP die at room (RT) and cryogenic temperatures (CT - ~77 K). ECAP samples were pressed until 4 passes at room temperature in route Bc. As a reference, a sample was obtained by conventional uniaxial pressing. The obtained results indicated a much denser (>99.5%) and harder structure by cryogenic ECAP. The hardness after one pass at CT was comparable with 4 passes at room temperature. Tensile tests performed at CT for materials with similar chemical composition showed a simultaneous increase in strength and ductility at CT, corroborating the results obtained by ECAP. The partial suppression of dynamic recovery and the activation and the transition between deformation mechanisms at CT, as well as stacking fault energies (SFE) of such metals, played an important role in these results. Copper presented a much higher capability of strain hardening than aluminum, due to its lower SFE and much lower homologous temperature. X-ray diffraction indicated a strong correlation between the variation of average microstrain and the variation of hardness on both metals. The results of this study demonstrated the great potential of the application of very low temperatures for the obtaining of deformation metal-metal composites.

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Abstract In this work, an evaluation of corrosion resistance of boride layers formed on carbon steel C35 in different solutions of H2SO4, HCl, HNO3, NaCl and NaOH was carried out. Boriding treatment was applied on C35 carbon steel using Ekabor powder at 950 °C for 4 h. The corrosion behaviour was analyzed by the weight loss method after total immersion tests in different solutions at variable times from 24 hours to 6 months. The corrosion rate has been determined by electrochemical method using the polarization curves. Results obtained show that boriding treatment improved significantly the corrosion resistance of C35 steel in some acidic environments. The corrosion resistance of boride C35 steel is higher compared with that of untreated C35 steel, and the corrosion potentials Ecor of boride C35 steel are more electropositive than those of untreated C35 steel in some solutions.

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This paper makes an investigation on the synthesis of tantalum carbide (TaCx) based chromel composites and their tribological behaviour using pin on disc under various load conditions. The reinforced chromel alloy with TaCx was prepared at the rate of 0, 3 and 6 wt.% of TaC using stir casting route. The wear resistance of composites was found to improve with the increase in weight percentage of TaC. The wear properties of Chromel-TaCx composite were enhanced due to the presence of 6% TaC. The wear worn out surface of chromel composite was studied through microstructures. The optimal process factors and their effect on responses have been analyzed through Response Surface Methodology (RSM) and Analysis of Variance (ANOVA).

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Abstract This article evaluates the effect of recrystallization annealing soaking time on the tribological behavior of cold upsetted low carbon steel. The 40% cold formed steel was subjected to annealing at 900 °C, for 10, 20, 30, 40, 50 and 60 minutes. The mechanical properties of hardness, tensile strength, yield strength and ductility, measured through specific deformation, as well as the precipitation of carbides through microstructural analysis were examined. In order to analyze the volume of removed material, the wear test was performed using a pin-on-disk tribometer according to ASTM G99. The results showed that the combination of lamellar perlite precipitation and pearlitic interlayer spacing reduction increases the mechanical strength of 1020 steel, reduces ductility, increases friction coefficient and increases wear observed by the volume of removed material increase.

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A single-pulse spot welding test was performed on 0.13C-6.98Mn medium manganese TRIP steel. The test results showed that the joint performance increases with a rise in welding heat input before splashing occurs. Owing to the fusion zone (FZ) being closest to the heat source, its austenite content was completely transformed and its performance was worse than that of the heat affected zone comprising austenite. The segregation bands of C and Mn observed in the FZ were considered to be the main reason for the deterioration of grain boundary strength. These characteristics of the weld zone led to evident intergranular cracking and transgranular fracture in the tensile test, and all samples in this test showed partial or complete interfacial fractures.

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Abstract Q420 structural steel, which is widely used in transmission towers and offshore platform structures, has been studied less than other steels. However, fatigue failure of offshore platform structures can occur under repeated wave loads. The fatigue strength applied stress–number of cycles (S-N) curves of Q420C structural steel were obtained by performing static tensile tests and high-cycle fatigue tests, and the fatigue crack formation and development were investigated based on the fracture morphology. The steel fatigue lifetimes were compared with standard curves and those of steels with various strengths reported previously. The results showed that the fatigue failure of the specimen was typical, and the fracture surface could be divided into a crack initiation region, a propagation region, and a transient fracture region. The Q420C curve was above the BS7608:2014, GB50017-2017, and ANSI/AISC360-10 standard curves. The S-N curve specified in the standard is conservative for Q420C steel. The strength of the steel directly affected its fatigue properties, and the thickness of the steel plate had a significant effect on the fatigue properties.

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Rolled mill scale is one of the most valuable industrial waste. The produced mill-scale briquettes are reduced by hydrogen at varying temperatures. The reduction is carried out at 800°C, 900°C, and 1000 °C and lasts for 120 minutes. The reduced samples are studied by X-ray diffraction and scanning electron microscopy. The reduction of mill scale allows the new use and development of this material to obtain sponge iron that can be reused to produce iron-based powder metallurgy components. From the SEM, EDS, and XRD analysis, it is clear that as the reduction temperature increases from 800°C to 1000°C, the amount of produced iron powder also increases at constant holding time, where the amount of iron powder produced at 800oC is 94.55%, but it is 98.22% at the reduction temperature of 1000°C. The proposed reduction process allows obtaining a sponge iron powder of an irregular morphology with different crystallite sizes as measured by the Scherrer equation, where the crystallite size increased with the reduction temperature. The minimum crystallite size value is 44.45nm at the reduction temperature of 800°C, but it equals 60.1nm at 1000°C.

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The main objective of this work was to study the use of kaolin processing wastes in the production of steatite ceramics, emphasizing mechanical strength and dielectric properties. Steatite ceramics were prepared using mixtures of talc with fine and coarse particle kaolin wastes (7.5, 10 and 12.5 wt.%) sintered at different temperatures (1200, 1250 and 1300°C). After sintering, the specimens were submitted to mineralogical and microstructural characterization. Linear shrinkage, apparent porosity, flexural strength and dielectric properties were also evaluated. Results showed the formation of the crystalline phases protoenstatite and quartz for all produced ceramics. The results verified for porosity, mechanical strength and dielectric properties proved to be suitable for the application of this material in electrical insulation.

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The effect of different electrodeposition variables of chitosan coatings on Ti-6Al-4V substrates is studied. Electrolytic solutions containing chitosan at 0.1, 0.5, and 1.0 wt/v% was used to coat Ti-6Al-4V grit-blasted samples through electrodeposition, at 1.5 and 3.0 V, for 2.5, 20 and 30 min. Coating surface morphology was analyzed by scanning electron microscopy. Adhesion behavior was characterized by scratch testing, and coating stability under physiological conditions was assessed by swelling test. Electrodeposited coatings with longer times and high chitosan concentrations produced porous coatings, with a hydrogel-like structure, with better surface adhesion than those at lower concentrations and times. Swelling tests displayed a high initial swelling with posterior rapid degradation and stabilization at 3h, indicating the potential need for a crosslinking agent. These results suggest that chitosan electrodeposition has great potential for coating applications of metallic implants, and further in vitro cell assays are proposed for future studies.

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Abstract Previous studies have investigated the preparation of heterogeneous biocatalysts based on the immobilization of lipases on distinct types of supports. However, few works have investigated the influence of the textural properties of these supports on the immobilization parameters. Thus, the present article reports the preparation of copolymers based on divinylbenzene by aqueous suspension polymerizations, using different amounts of porogenic agents to prepare particles with distinct textural properties. The particles were used for immobilization of lipase from Candida antarctica fraction B and the performance of the biocatalysts was evaluated in hydrolysis reactions, using p-nitrophenyl laurate as substrate. The use of Sty/DVB particles resulted in higher immobilization yields (89.5% and 99.2%) and higher hydrolytic activities, when compared to the Sty/VBC/DVB particles. Particularly, the increase of the pore diameters of the particles resulted in higher immobilization yields. Also, the hydrolytic activities depended simultaneously on the average pore diameter, porosity, and specific area (the most influential variable) of the supports. Thus, it was observed that the distinct morphological features of the polymer support can exert significant and conflicting effects on the final biocatalyst performance, since the specific surface area is normally expected to decrease with the increase of the average pore size.

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Abstract This work reports an experimental investigation on the thermodynamic and kinetic view-point of the nitrided layer growth behavior, carried out separately at ferrite and austenite phase grains, for the UNS S32750 super duplex stainless steel (SDSS). For this purpose, and motivated by the DSSs distinct behavior showing formation of two- or single-phase nitrided layers, which apparently depend on the steel substrate chemical composition, two series of treatment were studied here, one varying the nitriding temperature on the 300-450 °C range for 4 h time, and other one varying the time on the 2-8 h range at 350 °C. Microstructural characterization of studied layers by means of SEM and EDS analysis, XRD and microhardness measurements showed precipitation-free nitrogen-expanded austenite layer formation on both steel phases for all samples treated up to 400 °C. The nitriding kinetics study showed that the layer thickness on both steel phases is proportional to the square root of the treatment time and follows an Arrhenius law for the studied treatment temperatures. The nitrogen diffusion activation energy, separately determined from the layer growth on each steel phase, was 115±3.2 and 120±5.4 kJmol-1, for austenite and ferrite grains, respectively.

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The objective of this work was to evaluate the effects of different pressing temperatures on the physical and mechanical properties of Medium Density Particleboard (MDP) manufactured with sugarcane bagasse and waste plastic bags.The temperatures of 160, 180, 200 and 220ºC were evaluated for the panels pressing. The panels were produced with a nominal density of 0.70 g/cm3, a face/core ratio of 40:60, 12% urea-formaldehyde adhesive for the faces and 8% for the core. The panels were evaluated for properties of density, compaction ratio, humidity, water absorption after two and twenty-four hours (WA2h and WA24h), thickness swelling after 2 and 24 hours of immersion in water (TS2h and TS24h), module of rupture (MOR) and module of elasticity (MOE) in static bending, internal bonding, janka hardness and screw pulling. There was no significant effect of pressing temperature on density, MOR, MOE, internal bonding and janka hardness of the panels.The pressing temperature significantly influenced the properties of WA, TS and screw pullout, promoting a decrease in the mean values of WA2h, WA24h, TS2h and TS, and an increase in screw pullout resistance. The temperature of 220°C resulted in MDP panels with sugarcane bagasse and residual plastic bags of better quality.

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This paper presents an experimental study of the propagation of ultrasonic Rayleigh waves in the walls of a pressure vessel in order to estimate mechanical stresses. The ability to assess stresses using ultrasonic methods is based on the acoustoelastic effect, ie. the change of velocity of propagation of the ultrasonic Rayleigh waves (URW) in stressed media. The experiments were carried out using a hydraulic test conducted in a pressure vessel. Measurements of the travel time of the URW over the walls of the vessel in the axial and circumferential direction were carried out with a pressure change of up to 7 MPa at a constant temperature. Relations between the relative changes in the travel time of waves and the change in pressure were found. The influence of temperature and thermal stresses on the velocities of ultrasonic waves was not taken account. The conducted experiments confirmed the finding that the difference in the relative changes in the travel time of URW in circumferential and axial directions changes linearly with the change in the pressure in the vessel.

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Abstract In this study, it is investigated the anti-adhesive effectiveness of ZrN/Ti and TiN/Ti, deposited by magnetron sputtering, as coating materials of electrosurgical electrodes of steel in protein adhesion tests. Stoichiometry and the thickness of the systems were assessed with Rutherford backscattering spectrometry measurements. Vertical surface deviations were evaluated with the five-point mean height and the arithmetic average height and correlations between the amount of adhered protein in the electrosurgical electrodes and measurements of wettability and electrical resistivity were investigated. The quality of both coatings was put to the test through protein adhesion tests at high temperatures. Cuts with electrosurgical electrodes were performed in an abdominal flap for different electric power and cutting times. The results indicate less adhesion of protein on both proposed coatings, compared to the traditional electrodes of stainless steel, proving to be cheaper alternatives for the surgical industry than other massive anti-adherent electrodes as Au and Ti.

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Interest in developing novel wound dressings with antibacterial properties elaborated from natural sources continues to grow. In this study, a Tween-80 (T80)-stabilized carvacrol (CAR) emulsion was incorporated into pectin (PEC) membranes at 0 (control), 0.25, 0.50, and 1.00% (v/v). Membranes were obtained by the dry-casting method, characterized by scanning electron microscopy, infrared spectroscopy, and CAR retention (HPLC), and tested for antibacterial activity. The retention percentage of CAR in the membranes ranged from 9.1-13.9%. Infrared spectra analysis indicated changes in the hydrogen bonds of the membranes that suggest an interaction between the polymer matrix and the CAR:T80 emulsion. Microstructural analysis of the membranes showed the presence of hole-like features on the surface (≈ 4-6 µm diameter) that indicate entrapment of the micelles in the matrix (microcapsules). The PEC-CAR membranes exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus, two pathogens commonly associated with wounds and intra-hospital infections.

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This work developed ternary films based on Poly(Lactic Acid) (PLA), Cloisite 30B (C30B) and Oregano Essential Oil (OEO) as proposal to be applied in food packaging. The films thus manufactured were unscathed, with reduced surface defects. Their thickness and moisture content varied according to the composition and content of each component in the formulation. Optical micrographs indicated a homogeneous morphology, with good distribution of clay in the matrix. FTIR data confirms the incorporation of OEO into the films. TGA analysis indicated that the thermal stability of the films was not significantly affected by the incorporation of C30B and OEO. OEO incorporation did not promote an efficient antimicrobial action which is probably due to its retention by the clay. Further studies are needed to confirm this hypothesis. The combination between C30B and OEO in the PLA polymeric matrix is a promising proposal.

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Abstract This work focuses on characterizing the role of different triblock copolymers on the dispersion of nanoparticles in an epoxy matrix and in the thermal and mechanical properties of the resulting nanocomposites, using Poly (ethylene glycol) - block-poly (propylene glycol) - block-poly (ethylene glycol) (PEG-b-PPG- b-PEG) with 30% PEG, and poly (propylene glycol) - block-poly (ethylene glycol) - block-poly (propylene glycol) (PPG-b-PEG-b-PPG) with 50% PEG. The nanoparticles employed have different geometries: carbon nanotubes, graphene nanoplatelets and carbon black (spherical). Both copolymers were miscible in epoxy. The results suggest that the copolymers viscosity may be interfering with the dispersion of the nanoparticles in the matrix: the PPG-b- PEG-b-PPG50% copolymer has a higher viscosity than the PEG b-PPG-b-PEG30%, which facilitates their dispersion and an increase in mechanical properties. The PEG fraction was an important factor in the dispersion of nanoparticles in the epoxy matrix. The higher the PEG content in the copolymer block, the greater the synergy shown in the mechanical properties, since the nanoparticles inhibited the plasticizing effect of the block copolymer.

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Ti-34Nb-6Sn alloy were prepare by powder metallurgy milled in two different times (40 and 60 min) using Ti and Nb hydrides with or without Mg, as spacer then sintered at 700ºC and 800ºC. Characterizations were made by scanning electron microscope (SEM), X-ray diffractometer (XRD) and by Archimedes. Microhardness was measured by Vickers microhardness. Mesenchymal stem cells derived from equine bone marrow (BMMSCs) were used to evaluate the sample cytotoxicity. Hydration and dehydration process was confirmed, also the formation of brittle particles during the milling. Materials were structured under α and β phase, and the samples that received Mg as a spacer had slightly lower β phase content compared to samples without Mg, suggesting difficult α→β transformation due to the presence of barriers formed by pores. Mg provided greater porosity, and prepared milled in a shorter time promoted an increase in the macropores. Microhardness was similar to that of commercial materials (i.e., CP-Ti and also to other alloys with similar nominal composition. Cells treated with conditioned medium with the samples showed viability comparable to the control group, and after 48 h of culture on the samples, there was significant growth and more circular morphology, when adhered on materials that received Mg.

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Two processing methods for preparation of microbial biomass-silica biosorbent to remove cadmium ions from aqueous solution were developed. The first method involved a slow addition of sulphuric acid into previously prepared dispersion of viable Saccharomyces cerevisiae or Leuconostoc mesenteroides biomass in sodium silicate solution. The obtained material was mesoporous with irregular shape and size between 1 and 10 μm. The second method for the immobilization of microbial biomass by silica gel entrapment was developed in order to restrict desorption of microbial cells and to obtain larger particles with uniform size. The obtained particles were spherical with average particle size of 1.5 mm. Both materials with viable L. mesenteroides cells displayed higher removal efficiency compared the efficiency of materials that containing viable S. cerevisiae cells. Infrared spectra revealed an intensive secretion of dextran by Leuconostoc mesenteoides cells in the presence of cadmium ions. EDS maps clearly showed the dispersion of cadmium in the cross-section of microbial biomass-silica biosorbent. The maximum theoretical binding adsorption capacity for the silica-alginate-S. cerevisiae composite was 54 mg/g. The adsorption capacity for the silica-alginate-L. mesenteroides composite obtained after 24 cycles was about 93 mg/g. The extracellular secretion of dextran by L. mesenteroides cells immobilized in silica-alginate composite enabled efficient removal of cadmium ions. The efficiency of Cd(II) removal by microbial composite was not affected by the presence of co-existing ions at initial cadmium concentration of 1 and 4 mmol/L.

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In this study, the influence of gadolinium dopant composition on the microwave response performance of yttrium iron garnet was investigated. A hydraulic pressing was used to create the ferrite garnet sample. As the test material, pure oxide powder with an average grain size of 1 micron was employed. A pressure force of 700 MPa was used to compact the sample pellets. The sintering process was carried out in a high-temperature tube furnace at 1450 oC for five hours. This research shows that the calculated findings match the experimental data, demonstrating that the addition of gadolinium reduces the total magnetic moment and insertion loss of yttrium iron garnet. Adding 14 to 25% mol of gadolinium to one mol of iron oxide resulted in an insertion loss value near to zero, according to the calculations. To validate this calculation value, the microwave response of a sample of yttrium iron garnet with 15% mol of gadolinium doping was measured at frequency 4 GHz, yielding an insertion loss parameter value of 0.25 dB, which has a crucial function in lowering the insertion loss value of yttrium iron garnet.

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Herein, the structural, morphological, optical and electrical properties of CdO stacked layers comprising Si slabs of thickness of 100 nm are investigated. The performance of the stacked layers, which are prepared by the thermal evaporation technique under vacuum pressure of 10-5 mbar, is remarkably enhanced via insertion of Si thin slabs. The presence of Si slabs between the layers of CdO improves the crystallinity and surface morphology, increases the light absorbability in the ultraviolet and visible ranges of light and also increases the dielectric constant, the quality factor, and optical conductivity values. The optical conductivity parameters, which are analyzed in accordance with Drude-Lorentz approach, have shown that the insertion of the Si layers rises the values of the drift mobility of holes in CdO and lowers the free holes concentration. The energy band gap of CdO films is narrowed from 2.20 to 1.27 eV upon insertion of Si slabs. The applicability of the plasmonic CdO/Si/CdO devices as low pass filers in the frequency domain of 0.01-1.80 GHz is verified through impedance spectroscopy measurements.

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Abstract LaFeO3 is one of the multiferroic perovskite that is widely used for gas sensor applications. In this study, an analysis of the electronic properties of the band gap energy data was conducted using density functional theory with Generalized Gradient Approximation-Perdew-Burke-Ernzerhof (GGA-PBE) method on LaFeO3 for ethanol gas sensor. Changes in the value of the band gap energy resulting from the adsorption-oxidation-desorption mechanism, were discussed in this paper. The results showed that the band gap energy for LaFeO3 before, during and after being exposed to ethanol gas molecules were ±1.4 eV, ±0.4 eV, and ±0.9 eV, respectively. Changes in the value of the band gap energy indicate that there has been an adsorption-oxidation-desorption mechanism in the system, which is the basic mechanism for a gas sensor to work. Therefore, this mechanism is used as an indication for gas sensors. Hence, LaFeO3 can be a candidate for gas sensor applications, especially ethanol gas.

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Abstract The ever increasing fuel price created urgency for weight reduction of products in automotive and aerospace industries. Requirement of better mechanical properties, quality, improved wear resistance, lower coefficient of thermal expansion leads to the development of aluminum composites of lighter weight. The properties of the aluminium metal matrix composites are greatly influenced by the process parameters of the production methods. In this paper, aluminium metal matrix composite with reinforcement of 10% by weight proportion of silicon carbide is prepared by powder metallurgy process. The process parameters such as compaction pressure (100-130 MPa), sintering temperature (300-600°C) and sintering time (120-300 min) are considered. Properties such as compression strength, sliding wear resistance, micro abrasive wear and coefficient of thermal expansion of aluminum metal matrix composite are measured. Taguchi’s experimental design is adopted for laying out the experimental conditions and Principal component analysis approach is used to identify the optimum and significant parameters which provide the preferable properties of the composite. It is found that sintering temperature (300-600°C) is significant parameter influencing the measured properties of aluminium metal matrix composites.

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Abstract The paper shows that the strengthening mechanisms at the duplex stainless steels' heat-affected zone (HAZ) are sensitive to the volume fractions of the different austenite morphologies and the orientation relationships of these austenite morphologies with ferrite. Also, the nitrogen content in these phases and the ferrite grain size significantly influence the strengthening mechanisms at the HAZs for the tested cooling times. Considering their morphologies and geometrical distributions, the different austenite volume fractions were calculated for each cooling time at the HAZ corresponding to two duplex stainless steels (UNS S31803 and UNS S32304). Predictions of the main macroscopic mechanical properties, as the yield and ultimate tensile strengths, were developed by knowing the features of the local phases. This approach clarifies the contribution of the different strengthening mechanisms during the strain at the simulated HAZs of the studied duplex stainless steels.

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Abstract The vast majority of advanced industrialized products are formed from the joining of individual components. However, when the joining must be permanent, welding is one of the most used processes. Among the welding processes, the Friction Stir Welding (FSW) process stands out in this category specially for producing joints with extremely high mechanical resistance and low distortions leading to modern automotive and aerospace applications. This study aimed to evaluate the mechanical and corrosion properties of FSW welded profiles of Aluminum AA6005 alloy as a function of the welding parameters. For this purpose, tensile and microhardness tests were performed, followed by a detailed microstructural analysis. The results showed that the high rotational speed provided tunnel-type defects which impair the mechanical properties, leading to a loss of efficiency. The corrosion properties results showed that the different welding conditions do not significantly affect corrosion characteristics but the changes observed are related to the dispersion of the precipitates in the Al matrix.

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Abstract PdSb catalyst prepared in different compositions were applied as an anode in a polymeric electrolyte reactor - fuel cell type (PER-FC) to convert methane into oxygenated products and energy in mild conditions. The PER-FC polarization curves for Pd90Sb10/C presented maximum current density about 0.92 mW cm-2 about 15% higher than PdSb materials. However, the material Pd50Sb50/C showed higher reaction rate for methanol generation than the other materials occurring close to the OCV (r ~ 7 mol L-1 h-1). The qualitative analyses of PER-FC effluent by FT-IR identified products as methanol, carbonate and formate ions from the partial oxidation of methane for all materials.

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Abstract Considering the BSSF steelmaking slag generated in a Brazilian steelwork, it would be worth to separate iron and calcium from it, with the objective of increasing its iron content, or producing Fe2O3 and CaO by selective precipitation from cations in aqueous solution. In this way, materials could be produced and used in-house, e.g., sintering plant. This possibility was explored through acid leaching for an industrial sample. A possibility to increase concentration of iron of the slag is to leach it with a 2 mol.L-1 HCl solution; in this condition, 63.6% of the CaO is extracted from the slag to the aqueous solution, and Fe content of the slag increases from 27.4 to 37.1 wt%. Another possibility is to use HCl 5 mol.L-1; in this condition, 86.8% of the Fe and 90.7% of the CaO are transferred to the liquid solution. Then separation of iron and calcium can be achieved by selective precipitation: firstly, adding ammonia to precipitate Fe(OH)3, and then calcinating it to produce Fe2O3 (~ 200 °C); in the following, adding sodium carbonate to precipitate CaCO3, which in turn can be calcinated to produce CaO (~ 900 °C). In this way, Fe2O3 and CaO could be produced.

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Abstract Crosslinking of chitosan (CS) woven meshes is reported in this study. CS filaments were obtained by wet spinning and hand-waved. The weft was coated with CS solutions (3 and 4% w/v) and crosslinked with sodium tripolyphosphate or genipin. CS filaments were free from superficial pores, and their mechanical properties were suitable for the weaving process. CS concentration in the coating, type, and the crosslinking time affected the mesh morphology obtained. Crosslinking by both agents was confirmed by spectroscopy, corroborating the reduction of the hydrophilicity of the crosslinked samples in the swelling and contact angle tests. Crosslinking conditions were effective in reducing the mechanical properties variation in the wet state, as well as regulating the degradation rate of the samples. Furthermore, it was observed that crosslinking did not significantly affect the cell viability of CS woven meshes, making them promising materials for application as stress material in a physiological environment.

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Abstract Niobium pentoxide (Nb2O5) has gained prominence as an anti-corrosive pigment. The performance of anti-corrosive coatings based on Nb2O5 was tested in an environment with an acid atmosphere and at high temperatures. For comparison, SAE 1020 carbon steel samples were coated with two anti-corrosive coatings based on Nb2O5: applied by thermal spray and epoxy paint. The samples were partially immersed in the laboratory for 720 h and 1440 h in a 40% (v/v) H2SO4 at 25°C, 60°C, and 80°C. An in-situ evaluation was carried out of chemical industry installations over 4383 h in microclimates with the presence of corrosive agents at temperatures up to 70°C. The results obtained showed that the Nb2O5 coatings applied by thermal spray offer better anti-corrosive performance under immersive conditions. In contrast, under conditions submitted to steam, both the Nb2O5 coatings applied by thermal spraying and epoxy-Nb2O5 paint show excellent anti-corrosive behavior.

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Abstract This study investigated the corrosion inhibition of polyeugenol on API P110 in 1 M HCl. Its monomer – eugenol – is obtained from clove and cinnamon, making the oligomer environmentally friendly. The influence of molecular weight and polymerization degree was evaluated by increasing the polymerization initiator/monomer ratio. This enabled the polymerization of three different oligomers (P10, P20 and P30), which were characterized by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), thermogravimetric analysis (TGA/DTG), and size exclusion chromatography techniques. The inhibition performance of polyeugenol was determined by weight loss (WL) and electrochemical tests to assess the influence of structural differences. WL indicated that the oligomer with the lowest polymerization degree (P10) exhibited greater efficiency (82-84%) due to more uniform surface coverage. Electrochemical tests confirmed polyeugenol as a mixed inhibitor. Energy-dispersive X-ray spectroscopy (EDX) calculations indicated the presence of an organic layer covering the steel surface.

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ABSTRACT This work reports the mechanical properties of ab and a(b)c-plane of melt textured Y1-xPrxBa2Cu3O7-δ (x = 0.00 and 0.05) superconductor. Y1-xPrxBa2Cu3O7-δ have been prepared by top seeding technique. Hardness and elastic modulus were obtained by instrumented indentation. Independent of the plane, the hardness values were around 5.0-7.5 GPa. Young’s modulus was approximately the same for both samples for ab-plane, around 132 GPa at the deepest tip penetration. However, for a(b)c-plane, the value of Young’s modulus for x = 0.05 is higher than observed for x = 0.00 sample.

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Abstract Automotive windshield represents a large volume of solid waste due to limited recycling. Glass-ceramics were produced from discarded windshields with Nb2O5 as a nucleating agent at concentrations of 0, 5, 10, and 15 wt% at 700 and 800 °C sintering temperatures. Mechanical and electrical characterizations of glass-ceramics were performed. Equibiaxial flexural strength was performed and related to porosity. At 700 °C, Nb2O5 favors the monoclinic NaNbO3 phase with perovskite structure. At 800 °C, high Nb2O5 content formed crystalline phases of perovskite and quartz. Dielectric constant and electrical conductivity increased with the addition of Nb2O5, reaching 64 and 4.3 μS/m for 15 wt% Nb2O5 at 700oC. At 800oC, niobium pentoxide reduces the biaxial flexural strength from 28.7 to 14.4 MPa; while increasing the electrical conductivity from 0.10 to 0.33 µS/m for samples with 0 and 15 wt%.

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Abstract To study the effect of the incorporation of silver nanoparticles into polyvinyl alcohol (PVA) films on their optical and conducting properties, silver nanostructures with different sizes covering from spherical to polyhedral shapes were synthesized and embedded into the polymer. The sizes of the obtained silver nanostructures were analyzed by Dynamic Light Scattering (DLS), which exhibited high stability, attributed to their surface potential. Multimodal distributions suggest changes in shape ranging from spheres (~40 nm) to prisms (~100 nm), which was confirmed by Scanning Electron Microscopy (STEM/SEM) analysis. By embedding these nanostructures in polyvinyl alcohol (PVA), AgNPs loaded PVA polymer films were prepared, exhibiting a hypsochromic shift in the surface plasmon resonance band of the nanostructures. For conductivity determination of AgNPs loaded PVA polymer films, Electrochemical Impedance Spectroscopy (EIS) was used. The results indicated that the conductivity of the samples is highly dependent on the size and shape of the AgNPs embedded into the polymer, resulting in higher conductivity for smaller silver nanostructures.

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Abstract New multi-component alloys have been recently developed for applications in coatings deposited by welding. These microstructures consist on the precipitates of ultra-hard carbo-borides in a matrix with high hardness. Post-weld heat treatment is a relevant aspect to adjusting the final propierties of the deposit. In the present work, the microstructural evolution, phase properties and resistance to abrasive wear of a Fe-Cr-Nb-B-C-Si-Mn alloy deposited on a low carbon steel by semi-automatic welding process were studied. The samples were heat treated for 3 hours at temperatures between 500 and 900 °C. They were compared with respect to the samples “as welded”. The microstructure was analized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. A microstructure formed by tetragonal carboborides M2B and niobium carbides, with a microhardness of 1800 HV and 2440 HV, respectively, in a matrix formed by high hardness martensite (870 HV) was observed. The post-weld heat treatment produced the tempering of the martensite and the precipitation of secondary carbides from 500 to 800 °C, producing a decrease in hardness with increasing temperature. In the specimen heat-treated at 900 °C, the hardness increased at 1130 HV, reaching higher values than those obtained in the “welded” condition (940 HV), due to the formation of martensite and M23X6 carbides. A linear relationship was found between hardness and abrasive wear rate.

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Abstract UNS S39274 is a W-alloyed superduplex stainless steel used in critical services in the oil and gas production. This material was selected for tubullars used in oil country tubular goods, below the Christmas tree. In order to achieve high mechanical strength the seamless tubes are cold drawn in a costly operation. In this work the mechanical properties of a cold drawn seamless were characterized and compared to three solution treated materials. Tensile curves were obtained and modelled by Hollomon’s, Ludwik’s and Voce’s models, where the last one presented the higher correlation coefficients in all cases. The hardness and impact toughness at -46oC were measured and discussed. The results were analyzed taking into aconunt the microstructural changes produced by cold drawning and annealing.

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Abstract In the present work the influence of the two organic inhibitors, namely : phenyl (2- (3,4,5 trimethoxyphenyl) -1H-benzo [d] imidazol-1-yl) methanone (P3) and ( 2- (4 -methoxyphenyl) -1H-benzo [d] imidazol-1-yl) (phenyl) methanone (P4) on the ordinary steel corrosion in 5.0 M HCl solution was investigated by using electrochemical measurements, scanning electron spectroscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDX), UV-visible spectroscopy and theoretical study. The obtained results showed that these compounds act as mixed inhibitors. It is obtained that the inhibition efficiency increases with their concentrations and reaches 97.0% and 91.3% at 10−3 M of P3 and P4, respectively. These findings were confirmed by the electrochemical impedance spectroscopy measurements, where the transfer resistance values increase with the concentrations. In addition, the effect of temperature range from 298 K to 328 K was investigated and indicated that P3 and P4 keep their performance at height temperature. Moreover, density functional theory explained the relationship between the molecular structure of imidazole derivatives and inhibition performance obtained experimentally. Additionally, the morphological surface and EDX analyses indicated that these compounds act by the formation of a protective layer on the ordinary steel surface. In order to confirm the possibility of the formation of P3-Fe and P4-Fe complexes, the UV–Visible absorption spectra was used. The obtained results indicated the formation of a complex between Fe2+ and molecules inhibitors.

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Our work presents a comparative study of morphological characteristics and the osteogenic potential of MC3T3-E1 cells on different modified surfaces of titanium: nanostructured TiO2 with 20 and 100 nm nanotube diameter, and sandblasting and acid etching, commercially known as SLA. Nanostructured TiO2surface was prepared by anodizing of titanium plates, while SLA surface was provided by commercial supplier. Surfaces were characterized by SEM, EDS, AFM, and water contact angle measurements. In order to evaluate cell response,in vitrotests of MTT, alkaline phosphatase and staining with alizarin red were performed. From the results ofin vitro tests, 100 nm nanotubular surface showed lower levels of cell mineralization, differentiation and adhesion. In general, 20 nm TiO2nanotubular and SLA surfaces promoted similar response from osteoblasts. As a result, 20 nm nanotubular surface proved to be a possible alternative to SLA surface with potential for use in oral implantology market.

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The microstructure of a melt-spun Zr28Ni44Cu28 (at. %) alloy was characterized in order to determine the structures and compositions of the crystalline phases that compete with glass formation during rapid solidification. Two crystalline phases were identified, namely, a face centered cubic (FCC) zirconium oxide phase and a primitive cubic version of the big-cube oxide phase, using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. Our results indicate that the Zr-O atomic pair interaction is preferential compared to the other atomic pair possibilities, supporting the formation of Zr-based oxides over the equilibrium phases in the ternary Zr-Ni-Cu system. Further, the results provide insight into the mechanisms of oxygen-induced crystallization in Zr-based BMGs and the corresponding decrease in glass forming ability (GFA) with increasing oxygen concentrations.

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Natural rubber (NR) and halloysite nanotube (HNT) composites are known to perform poorly due to polarity differences between the two components. As such, many extant studies have attempted to increase their compatibility. Therefore, this study introduced epoxidized natural rubber (ENR) together with silane coupling agents into the composite to ensure rubber-filler interactions. Four different silanes namely bis-[(triethoxysilyl)propyl] disulphide (TESPD), bis[(triethoxysilyl)propyl] tetrasulfide (TESPT), triethoxyvinylsilane (VTEO), and 3-mercaptopropyl-di(tridecan-1-oxy-13-penta(ethyleneoxide)) ethoxysilane (VPSi-363) were used. Fourier-transform infrared (FTIR) spectroscopy of the composite confirmed the formation of hydrogen bonds between the silane as the peak of Si-O shifted to higher wavenumbers; i.e., 1080 cm-1 to 1042 cm-1. Silane was also found to improve the tensile strength, modulus and tear strength regardless of functionality. This was further supported by the findings of the Payne effect. As for strain-induced crystallisation (SIC), the stress-strain curves agreed well with the development of crystallinity observed during synchrotron wide-angle X-ray scattering analysis.

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Abstract This work investigates the effect of the addition of glycerol on the microstructure, corrosion resistance, and efficiency of the electrodeposition process of Cu coating in an acid sulphate solution. The morphology and microstructures of electrodeposits were analyzed using Scanning Electron Microscopy (SEM), Spectrometry X-Ray Diffraction (XRD) and laser scanning confocal microscopy (LSCM). Evaluation of the corrosion resistance was performed in 2.0 mol⋅L−1 NaCl by means of weight loss tests and electrochemical techniques. The addition of glycerol resulted in a decrease in grain and crystallite sizes, a decrease in roughness and an increase in the tensile strain of the coating. The deposition efficiency and the corrosion resistance increased with the addition of glycerol exhibiting a maximum value at the concentration of 0.42 mol⋅L−1, increasing the efficiency of electrodeposition by approximately 96%. This is related to the roughness of the coating, which is minimal at this concentration.

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Abstract Controlling the recrystallization is an important way to reach grain size refinement and outstanding strength and toughness on alloy metals. This study sets out the application and investigation of mathematical microstructure modeling of a newly designed bainitic steel for hot forging industrial applications. The macro-scale model was used to observe and predict the austenitic grain size behavior during the controlled forging of a gear. Arrhenius grain growth kinetic and recrystallization model for a new class of bainitic steel was established for the given strain rate ranges and temperatures. This model was calibrated through microscopic analysis and used to simulate the unpublished constants of low alloyed bainitic forging steel DIN 18MnCrSiMo6-4 microstructure module using DEFORM® commercial finite element code. The increased temperature due to the adiabatic effect was investigated by numerical analysis, demonstrating its influence on grain coarsening. Local tensile test and Charpy-V notch were compared at different industrial hot forging temperatures and local plastic strain. Changes in yield strength and ductility have demonstrated the grain size influence on the processing parameters. The employed numerical model was an efficient tool to predict and present an alternative path to develop robust industrial forging using semi-empirical models.

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Reinforced concrete beam (RCB) elements show low mechanical performance when interfacial bonding strength (IBS) is not well controlled. New tailorable material-structure arrangements - Metamaterials - offer solutions to the IBS problem. This paper analyzes the mechanical characteristics of IBS on RCBs for reinforced cement mortar containing Metamaterial bars (MMB) that were machined from SAE 1020 Carbon steel. Each MMB has a stepped geometrical shape, with a cylindrical bar divided into equal-length segments, along with a ’rise height’ (p) change. Four geometries were defined, i.e., R0− Smooth bar, R1− p = 0.1mm, R2− p =0.3mm and R3− p=0.5mm. Three-point flexural strength tests were performed on the RCBs to determine the maximum bond strength (ML) between the MMB and cement mortar. Images of interfacial regions were obtained using SEM and 3D Roughness Reconstruction software to calculate the average roughness (Ra) and the roughness height (Rz). The reinforcement MMB geometry had a significant impact on the ML results, particularly on the first crack strength and the failure mode. The R3 geometry ML values were higher than the other tested geometries (44.5%). The results of the scale models are encouraging and offer a novel and prospective direction for further experimental and even numerical Metamaterial research to improve interfacial bond strength.

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Abstract The pigeon pea (PP) stalk is a sustainable lignocellulosic material left by the farmers after harvesting its pulses. The use of agricultural residue in the development of polymer composites is a step towards sustainability. This study focuses on developing and characterizing the mechanical properties (the tensile, flexural, interlaminar shear, compression, impact, and hardness) of less utilized agro-based PP stalk particle reinforced epoxy composites and their hybrid composites. In addition, the density, dynamic mechanical analysis, water absorption, and morphology were also investigated for a better understanding of these composites. In comparison to other agro-residue reinforced composites, PP stalk particles (up to 20 wt.%) reinforced epoxy composites have demonstrated comparable mechanical, viscoelastic, and water absorption characteristics. Jute/PP/epoxy and glass/PP/epoxy hybrid composites outperformed PP/epoxy composites in mechanical, dynamic, and water absorption characteristics. The ranking of the composites based on the characterization was done using the TOPSIS method, and glass/PP/epoxy composite with a 20 wt.% was identified as the best performer among all the composites. The results demonstrated that PP stalk particle reinforced composites are a viable alternative to wood and other natural fiber-based composites and could be used in lightweight structural applications such as automotive interiors, furniture, packaging containers, and cascading applications.

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Abstract Output couplers for TEA CO2 lasers were made from Ge substrate coated with dielectric layers of ZnS, Ge and Y2O3 using physical evaporation technique (PVD). The laser-induced damage thresholds (LIDTs) of manufactured mirrors have been investigated using an experimental setup, based on TEA CO2 laser. The effect of preparation conditions, such as grinding, polishing and cleaning, is shown. The maximum value of LIDT about 8 J/cm2 was achieved using a fine grinding with loose abrasive grade 3 µm, then polishing with alumina powder grade 0.3 µm and finally hot cleaning with ultrasonic waves.

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The characterization studies of tailings from mining are crucial for the development of its reuse processes and the reduction of impacts caused by its conditioning on the earth’s surface. This study characterizes the magnetic tailings from phosphate-rock processing using X-ray diffraction, X-ray fluorescence spectrometry and quantitative electron microscopy techniques. Samples were obtained from the magnetic tailings deposit of a mining company in the Alto Paranaíba region, Minas Gerais. The tailings are mainly composed of hematite/magnetite (74.92%), ilmenite (8.91%), fluorapatite (8.8%), anatase (3.07%), calcite (1.67%), goethite (1.62%), and quartz (1.02%). The particle size of the tailings is smaller than that specified for the production of sinter feed. The hematite/magnetite phase is strongly associated with ilmenite and fluorapatite. New stages of comminution and separation are needed due to the low degree of liberation of these minerals for a possible reuse of the components.

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Abstract Currently, the industry requires the use of new materials that have better technical characteristics and that have a minimal environmental impact. A viable option to meet these requirements are biocomposite materials reinforced with natural fibers. Recent research in this field of composite materials has sought to develop better properties in the materials, giving rise to hybrid composites, which are composed of more than one fiber as reinforcement together with the matrix; however, these studies are mainly focused on synthetic fibers, leaving a large area of research regarding natural fibers. This article describes the manufacture, mechanical, and morphological characterization of new natural hybrid biocomposite materials of fique - mulberry. Five biocomposites were elaborated under the hand lay up manufacturing technique using various layers of fique and mulberry and using polyester resin as a matrix. The mechanical characterization was carried out by means of the tensile and bending test, obtaining the best mechanical properties in the composite with the greatest amount of natural fiber, which presented a tensile stress of 30.27 MPa and a bending stress of 18.97 MPa. The morphological characterization was carried out using scanning electron microscopy, where a medium resin-fiber adhesion and a decomposition of the matrix were observed.

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Abstract Determining the flow stress curves of metals and alloys in hot working conditions is essential for designers of metals forming processes. In this research, samples of a super duplex stainless steel with a ferrite matrix and dispersed austenite particles were deformed by torsion tests at temperatures ranging from 900 °C to 1200 °C and strain rates from 0.01 s-1 to 10 s-1. The level and shape of the plastic flow stress curves depend on the temperature and the strain rate and varies with the austenite volume fraction. When the two phases are deformed together, the marked difference in the softening behavior of austenite and ferrite leads to the uneven strain partitioning between these phases. As a consequence, the plastic behavior of this biphasic material is more complex than that of a single-phase material. A four columns spreadsheet was built using the experimental data obtained from the hot deformation testing. The first three columns contain the input data attributes (temperature, strain rate and strain) and the fourth the strength (stress) resulting from the material during deformation. These data were submitted to machine learning algorithms; initially in an artificial neural network with one hidden layer (ANN) and subsequently to a neural network with a specialist system (ANFIS). After the machine learning processes, the plastic flow curves were rebuilt and compared with those obtained experimentally. The ability of both algorithms to rebuilt the plastic flow curves of the super duplex stainless steel were associated with changes in the shapes of the flow curves and microstructure evolution.

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Abstract Aluminum alloys have been widely used in multiple applications, such as in civil construction and engine pistons. They are subjected to loads that may impair their mechanical properties. Thereby, this research aims to study the influence of anodization on the mechanical properties of alloy samples and evaluate the behavior of oxide films when subjected to tensile testing. The mechanical properties of specimens have been evaluated based on tensile and Knoop hardness tests, and strain, tensile strength, and modulus of elasticity of specimens have been determined based on the stress-strain curve. The morphology of oxide films was analyzed by scanning electron microscopy (SEM) and optical microscopy (OM). Results of anodized Al-Si alloys in both modes, i.e. pulsed and direct currents, were compared, and it was found that pulsed current was more efficient than direct current with respect to uniformity of the formed film, and that the anodization process can affect a few mechanical properties of samples. The tension testing results also revealed that the oxide film has been fractured perpendicularly towards traction. However, the oxide film hardness was not affected by the anodization mode (pulsed or direct currents). In addition, a heat treatment was efficient at improving the uniformity of anodic films.

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This work investigated the effect of adding ceria-stabilized tetragonal zirconia (Ce-TZP) on the fatigue behavior of alumina-based ceramic composites. Alumina powder (control group) and mixtures containing 5 wt.% (group A) and 20 wt.% (group B) of a commercial m-ZrO2/Al2O3/CeO2 powder mixture were milled/homogenized, compacted, sintered at 1600°C-2h, and submitted to hydrothermal degradation. The samples were characterized by relative density, microstructure, crystalline phases, and static mechanical properties. The cyclic fatigue strength was determined using the modified staircase method in 4-point bending tests. The results indicate that adding the m-ZrO2/Al2O3/CeO2 powder mixture to the Al2O3-matrix increases the tetragonal-ZrO2 grains (Ce-TZP) content, presenting 2.9 wt.% of Ce-TZP and 11.9 wt.% of Ce-TZP for group A and group B, respectively. Furthermore, the addition of Ce-TZP improves densification (98.5% → 99.1%) with a slight reduction in hardness and modulus of elasticity and a significant KIC increase of the composite (KIC = 6.7 MPa.m1/2, group B) when compared to monolithic alumina (KIC=2.4 MPa.m1/2). The fatigue strength limit of the control group was around 100 MPa, while the composites (groups A and B) presented the values ​​of 279 MPa and 239 MPa, respectively. The results indicated that the incorporation of Ce-TZP significantly improves the fracture toughness of alumina-based ceramics. On the other hand, regarding the fatigue behavior, there was an increase in fatigue resistance in group A, resulting from the benefits of the t→m Ce-TZP grains transformation, which occurs during cyclic loading, producing a zone shielding that involves the tip of the crack, slowing its growth. The increase in the amount of Ce-TZP (group B) leads to an increase in the internal residual stresses between the phases due to anisotropy and difference in the thermal expansion coefficients, which accelerates the phase transformation and formation of microcracks at grain boundaries, reducing the fatigue strength of composites of group B.

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Abstract Mn1-xZnxFe2O4 (0 ≤ x ≤ 0.65) nanoferrite particles were used as filler in a silicone polymer matrix in order to obtain a composite material with the purpose of absorbing electromagnetic radiation. The composite was characterized by X-ray diffraction, transmission electron microscopy and force modulation microscopy (FMM) and the electromagnetic properties by means of network and impedance analyzers. It was observed that the composite with higher concentrations of Znx (x = 0.5 and 0.65) presented the lowest dispersion, due to the size of the zinc particles. This paper provides a framework for the practical application of absorbent composite materials of MnZn nanoferrite particles combined with silicone rubber to be used in 1-10 GHz frequency bands, with reflectivity values of -24 dB in the 6 GHz frequency range.

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Present research work is focused on investigation of material removal rate in Wire-ED Machining (EDM) of artificially aged Al-6061/ B4C reinforced composites with 2-6 wt.% in peak aged condition. Combined effect of B4C and artificial aging at 100°C improved the hardness by 20 - 170% under as cast and artificially aged condition. Initially the wire EDM experiments are conducted on Al6061 alloy and then the process parameters such as current, pulse-on time (ton) and pulse-off time (toff) are optimized to obtain the high material removal rate (MRR). At optimized conditions test samples with various % of B4C are machined to study their influence on MRR. The study revealed that current and toff had a significant influence. MRR increased as current is increased and it decreased as toff is increased. Maximum MRR at optimum settings, current : 5.53 A, Toff: 10 µs and Ton: 36.46 µs is 2.45 mg/min. Considering the limitation of the experimental set up the modified optimum settings (Toff: 10 µs, Ton: 30 µs and current : 5 A) resulted in average MRR of 2.39 mg/min with deviation of 0.20 mg/min. The study showed that there is no significant difference in MRR and the morphology of the machined surface with respect to test samples of different % of B4C particles as reinforcement in Al6061 composite.

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Abstract The effects of homogenization, cold working, and subsequent annealing treatment were studied on the microstructural evolution, mechanical properties, and passive properties of duplex stainless steel (DSS). A hot-rolled 2205 DSS was subjected to two processing routes. In one, the DSS goes through an extra homogenization step at 1100 °C for 1800 s before cold rolling. After cold deformation (~75%) the specimens were isothermally annealed at 900, 1000, and 1100 °C for 180 s. The microstructure evolution was studied by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XDR). Mechanical properties were evaluated by microhardness and tensile tests. The electrochemical behaviors were investigated by potentiodynamic measurements, electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis (MS). Chemical composition of the lowest corrosion resistant passive film was assessed by X-ray photoelectron spectroscopy (XPS). Homogenization before cold rolling lowered strain hardening, slowing the microstructural transformation process. The thermomechanical process did not change the semiconductor type of the passive films. However, grain refinement after annealing improved the corrosion resistance in borate buffer solution. Cold rolling significantly decreased the corrosion resistance. The passive film of the specimen homogenized before cold rolling had the lowest corrosion resistance and high amounts of Cr(OH)3 and FeO.

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Abstract There is anisotropy in 30SiMn2MoVA steel gun barrel processed by radial forging which results in the low service life of the gun barrel. While the texture is the main reason for the anisotropy. The crystal plasticity finite element (CPFE) method is usually used to simulate the microstructure and the texture of the metal. In the present work, a two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline 30SiMn2MoVA steel. The displacement of nodes in the macro radial forging process finite element model is used as the cross-scale boundary condition in the CPFE model which realizes cross-scale simulation. The texture evolution and inhomogeneous deformation of 30SiMn2MoVA steel in the radial forging processing under three different forging ratios were simulated. The simulated texture results are consistent with the experimental results. The inhomogeneous deformation of grains is obvious and will intensify with the increase of the forging ratio. The distributions of stress and equivalent plastic strain in polycrystals are statistically Gaussian. With the increase of deformation, the further refinement of grains is due to the large shear strain in large grains.

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The primary goal of this study is to see how multi-walled carbon nano tubes (MWCNTs) and nano silicon carbide particles (SiC) affect basalt reinforced epoxy composites made using pressure mould. The aluminium 8090 metal plate was used to strengthen the laminate's core. Tensile, bending, and low velocity impact tests, as well as aesthetics, were investigated and presented for the debate. The physical and low velocity impact characteristics of the produced laminates are considerably improved by including MWCNT/SiC into the epoxy matrix and basalt mixture. The 9 wt. % and 12 wt. % of SiC filled combinations show higher tensile and flexural performances up to 40% than neat composites among the investigated combinations. Drop weight impact tests show a progressive improved energy absorbing response of up to 60% as SiC reinforcement increases. SEM morphology of pure, SiC/MWCNT filled specimens, as well as fragmented surface analyses, were also presented. It was observed from morphological studies that there is a reasonable wettability between matrix/filler/reinforcements. This research work will lay a path for using Basalt/Epoxy/MWCNT/SiC Reinforced Hybrid Fiber Metal Laminates for aerospace and structural applications.

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Although micro-arc oxidation (MAO) coatings are widely used for anti-wear protection of metals, they usually contain lots of pores and exhibit high coefficient of friction. In this work, porous MAO coatings consisting of Al2TiO5 were fabricated on the titanium substrate, and then Ni-P and Ni-P-polytetrafluoroethylene (PTFE) were deposited via electroless plating to fill MAO pores and improve the tribological performance. Electroless deposited Ni-P has high wear resistance and the incorporated PTFE particles have self-lubricating property. Results show that the micro-pores of the MAO coating were completely filled by deposited Ni-P and Ni-P-PTFE, and the self-lubricating PTFE particles distributed uniformly in the coating. For the MAO-Ni-P-PTFE coating, the MAO and Ni-P components mechanically interlocked and played a load-carrying role during the tribological test, and the dispersed PTFE particles produced low friction. Compared with the MAO and MAO-Ni-P coatings, the MAO-Ni-P-PTFE coating exhibited much lower coefficient of friction and wear rate.

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Abstract Pure titanium and various alloys, such as Ti-6Al-4V, are widely used as biomaterials. In this application, surface finish conditions, topography, and surface reactivity determine excellent cellular adhesion and osseointegration characteristics. The study evaluated the influence of four surface finishing treatments (sanding #120, 600, 1200, and polished with 3 µm alumina paste) and three shapes (concave, convex, and flat) on the corrosion resistance of Ti-6Al-4V at 37 °C in simulated body fluid (SBF) through potentiodynamic polarization and electrochemical impedance spectroscopy. The SBF's ionic composition allowed the formation of a stable passive layer with a low presence of pores on the surface. In addition, the combination of polished surface and convex shape showed the best electrochemical passive behavior.

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In this study, foaming-agent free novel polyvinyl acetate (PVAc) foams reinforced with bio polymers were manufactured through freeze-drying technique. The physical, morphological and antibacterial properties of foams which were reinforced with different ratio of zinc borate and water-soluble chitosan were investigated according to relevant standards. The PVAc foams showed low densities (0.12 g/cm3 – 0.21 g/cm3) and high porosity rates (87.50% - 79.05%). The results showed that although the foams have no antibacterial character against Escherichia Coli, they have antibacterial character against Staphylococcus Aureus bacteria. This study mainly focusses on physical and morphological properties of the foams. However, researchers also performed accelerated weathering tests to determine its usability in different industries. The effects of accelerated weathering on the surface of foams were investigated by measuring surface color. The highest color difference was determined 8.09. This foam can be used as a low-density packaging material and/or medical box with its promising physical and morphological properties with hazardous-chemical free structure.

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The present investigation deals with wear and machining behaviors of manufacture nitinol composite through Vacuum Induction Melting (VIM). The major composition of nickel and titanium was reinforced with tungsten carbide (WC). Scanning Electron Microscopy (SEM) was employed to investigate the morphology of the synthesized nitinol composite. For investigating the topography of the surface of the nitinol composite was analyzed by scanning force microscopy or atomic force microscopy. Spark erosion machining has been applied to explore the machining behavior of the nitinol composite. Abrasive Wear Rate (AWR) is evaluated by using abrasion tester. Machining and wear parameters are optimized by applying taguchi approach. The contribution and the effect of input constraints on the responses are investigated by analysis of variance.Optimal abrasive wear rate was attained at 900 rpm of disc speed, 12 gm/min of abrasive flow rate and 400m of sliding distance. Disc speed was a dominant factor and it has developed 43.86% effect on abrasive wear rate. Optimal rate of metal removal was achieved at 45A of current, 200µs of pulse on time and 35V of Volts. The current was the leadingfactor and it has produced 86.38% effect on the rate of metal removal.

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Abstratc This work reports the production of low-tin Cu-Sn alloy coatings on carbon steel substrates using a bath containing CuCl2, SnCl2, and sodium citrate. In the first part of this study, the coatings were electrodeposited by direct and simple pulse current processes (DC and SPC, respectively). Different current density values were used, while the pulse frequency and duty cycle remained constant. Independent of the current mode used, low-tin Cu-Sn coatings, showing globular surface morphology and Cu6Sn5 as the main compositional phase, were produced. Both the current mode and the applied current density affected the anticorrosive properties of the coatings. The most protective DC and SPC coatings, showing Sn content < 3 wt.% and compact morphology, were prepared using j = 80 A m-2 and jc = 167 A m-2, respectively. High charge transfer resistance values were verified even after immersion for 24 h in 0.5 mol L-1 NaCl solution.

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Abstract Thin-walled tubular structures are widely used in industries such as automotive, aerospace and military because of their lightweight and excellent performance under different loading conditions. This study aimed to investigate the lateral crushing performance of square aluminium tubes filled with different cores (honeycomb, polyurethane foam and mixed of these two fillers). Different failure modes of tested structures have been observed and they are progressive failure with plastic hinges formed in the middle of the tube wall, cracks at the corners of some tested tubes and fractures in the mixed foam and honeycomb core. Results show that the lateral crushing performance of aluminium tubes was significantly improved when using mixed filler (honeycomb and foam). The average load, energy dissipation and specific energy absorption of mixed core filled tubes increased up to 638%, 451% and 177% respectively when compared to those for hollow tubes.

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Bio-based linear low-density polyethylene (green LLDPE) composites are used as electrical jackets/insulator for cables. Assessments of gamma-irradiation (Co-60) effects on these materials are of interest as they might be used in nuclear power plants (NPPs). Brazilian sugarcane juice-based green LLDPE composite electrical jackets were irradiated until 1000 kGy and analyzed for thermal stability and mechanical characteristics. Thermogravimetry analysis (TGA) showed increasing of pyrolysis activation energy (Ea) (under N2) from 42.7 ± 4.2 kJ/mol in unirradiated samples to 72.8 ± 4.6 kJ/mol after 60 kGy dose, as resulted of radiation-induced effects. FTIR spectra evidenced radiation-induced formation of conjugated C=C bonds after 250 kGy dose. Tensile stress and Young modulus did not change significantly until 150 kGy dose, whereas elongation at break decreased and reached 50% at 91 kGy dose. These results suggest that green LLDPE might withstand radiation damage through a NPP operating life (~ 40 years).

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This study investigates the wear performance of Hybrid composite of Aluminium Al 7075 (SiC/Al2O3). The Reinforcements used for the Hybrid composite preparation are Silicon Carbide (SiC) and Aluminium Oxide (Al2O3). Reinforcements are added in 5%, 10% and 15% in volume percentage in to aluminium alloy for composite preparation. The wear performance of the developed composites was analysed using dry sliding test apparatus. The effect of wear study parameters such as load, sliding distance, sliding velocity on the response of wear rate were predicted. This study revealed that Wear rate was influenced by the load significantly. The addition of reinforcement in hybrid composite increases the wear rate up to 10% of addition and reduces the wear rate at 15% of addition. Scanning Electron Microscope (SEM) study displays the wear mechanism clearly. This study concludes that the introduction of reinforcements into the aluminium enhances the wear confrontation of the composites considerably. The developed composite may be used in high wear prone zones effectively.

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Abstract Aluminum alloys of 7xxx series have excellent characteristics and mechanical properties, being widely used in primary aircraft structures. However, the welding of these alloys by conventional arc welding processes results in an excessive mechanical resistance degradation and increasing in residual stress level. In this context, Friction Stir Welding (FSW) process has received attention in recent years mainly because it does not reach the materials melting point during the process. This work aims to evaluate the influence of the tool rotation and welding speed on microstructure and mechanical properties of AA 7075-T651 aluminum alloy welded joints by FSW process. Therefore, four welded joints obtained with different welding and tool rotation speed were subjected to tensile and microhardness tests. The microstructures of the welded joints were evaluated through analysis by optical microscopy and Scanning Electron Microscopy (SEM). The retreating side of the welded joints showed a higher occurrence of microstructural welding defects. Welded joints with yield strength (YS) 50% higher than those of base metal and with ultimate tensile strength up to 380 MPa were achieved.

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Abstract Zinc-ferrite ZnFe2O4 and CoxZn1-xFe2O4 (x= 0.2, 0.5 and 0.8) were prepared by two different techniques. The first was the solid state reaction based on utilizing electric arc furnace dust (waste material), and the second was the microwave treatment (pure materials). The structure and characterization of the prepared samples were studied by using XRD and SEM which ensured the formation of cubic spinel structure with some hematite phases. The physical properties as the density and porosity were measured where the microwave samples showed lower porosity and higher density than the solid state samples. Semiconducting properties has been observed for the prepared samples. The electrocatalytic activity of the hydrogen evolution reaction (HER) has been studied for all the samples in 1.0 M KOH (25 °C) by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance techniques. The results showed that the catalytic activity increased with increase of Co content as the surface area and the total pore volume increases in the ferrite prepared by solid state method while Co0.2Zn0.8Fe2O4 prepared by microwave method showed the highest surface area and optimum improvement in the apparent HER catalytic activity. Lower resistance and faster charge transfer were shown for CoxZn1-xFe2O4 than the pure phase.

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Abstract Nanostructured niobium nitride was synthesized through a solid-gas reaction in an atmosphere of nitrogen and hydrogen using an oxalic niobium precursor. Crystal phases evolution throughout the reactive processes were evaluated using X-Ray Diffraction, reaction parameters modifications were performed in isotherm time, gas flow, and precursors’ mass. It was verified the synthesis of a stable NbN material with a hexagonal structure under the following conditions: 1g of precursor, 300 min of isotherm at 1100 °C and, the gas flow of N2 = 40% (v/v), and H2 = 60% (v/v). The increase in gas phase flow and the decrease of solid load favored the process, and a pure and single-phase powder was obtained. This set indicates the importance of physical resistance in the fluid-particle interaction process. Under these conditions, the solid obtained had a crystallite size of 30 - 50 nm.

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Abstract This work aims at investigating the charge transfer resistance (RCT) of the two membranes derived from vegetable oils which are intended to protect materials against corrosion. The membranes were characterized by thickness measurement (328±1 μm and 491± 1 μm), atomic force microscopy (AFM) to estimate of roughness (<0.5 μm), Raman spectroscopy while the RCT values were evaluated by electrochemical impedance spectroscopy (EIS) in 0.1 mol/L KCl solution. EIS was used to measure the impedance at low frequency (Z0.01Hz ≅ 109 Ω cm2), RCT ≅ 109 Ω cm2 and exchange current density (i0 ≅ 10-11 Ω cm2), employing simple instrumentation. The thickness of the membrane must be considered for coherent interpretation of the impedance results. The study of electrolytes permeation in membranes is important to previously estimate the lifetime offered to a substrate over the time of immersion even before being applied to the metallic surface. The impedance measurements demonstrated that the most resistant membrane to permeation presented a RCT around 2 GΩ cm2. This EIS measurements approach enables the optimization of membrane fabrication by conveniently identifying the best formulation.

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Austenitic stainless steels processed by rolling are widespread in technological applications, since they have excellent mechanical and corrosion properties. This study investigated the effect of the cooling rate, microstructure and properties of 316L austenitic stainless steel under cold rolled conditions and by rapid solidification. The microstructure of the cold rolling processing steel was composed of austenite and a low percentage of delta ferrite. For the rapid solidification condition, the microstructure evolved from columnar and acicular dendrites to equiaxed dendrites with decreasing cooling rates, without the presence of delta ferrite due to the high cooling rate. Furthermore, thermal analyses in both routes revealed that oxidation kinetics was slower after rapid solidification in synthetic air. The microhardness in the cold rolling condition was lower than in the rapid solidification condition since the microstructure under the solidification condition is more refined. The sample in the rapid solidification condition region RS1 presented the highest corrosion resistance considering the pit potential. The passivation current density in the cold rolled condition was 5.72x10-5A/cm2, while under the rapid solidification condition, regions RS1 and RS2 were 2.24x10-5 A/cm2 and 3.72x10-6 A/cm2, respectively, and region RS3, did not present a passivation region in a broad range of potentials.

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Abstract The present investigation is used to analyze the effect of crater wear modeling in the machining of aluminium composite. Response surface methodology (RSM) is one of the best optimization technique used to bring out the optimal values of speed, feed and depth of cut for attain minimum surface roughness, cutting tool temperature and tool wear. AA7075 alloy with 15wt% of silicon carbide has been investigated in the dry machining condition. The double layered TiCN/Al2O3 coated tool was preferred. The worn surface analysis in coated tool was concentrated. The outcomes of the machining conditions were expected to improve surface finish. Novel approach of this investigation is to analyze the surface morphology to visualize the surface peak and valley profile of the coated tool and analyzed with various surface parameters that decide the surface roughness of the profile.

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Ionomeric Polymer-Metal Composites (IPMCs) are sandwich-like materials based in a polymeric membrane covered on both sides by metallic electrodes. Its operation mechanism consists of hydrated ions migration in response to an external electrical field generated between the electrodes, leading to a spatially nonuniform mass accumulation which causes the device to bend. Its performance as an actuator depends mainly on the environment's relative humidity and electrical stimuli. Consequently, IPMCs present variations in the electromechanical properties exhibiting nonlinearities and time-varying behaviors, limiting the major applications. For this reason, this paper investigated a PI controller performance to overcome these drawbacks and effectively control a Nafion-based IPMC-Li+ exposed to different relative humidities and electrical stimulis. The PI control system uses a camera with a machine vision application as a feedback sensor. Support instrumentation was developed to control the relative humidity, apply an electrical stimulus, and measure the electromechanical response. The pattern recognition algorithm implemented in the controller is efficient, with accuracy above 95%, making the feedback sensor reliable. Therefore, the PI controller was effective, stable, and capable of controlling and characterizing IPMC devices when relative humidity was above 60% at a low-frequency displacement and avoided the undesired back-relaxation phenomenon.

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Abstract High chromium cast iron (HCCI) with levels around 26% Cr - 2.9% C according to ASTM A 532 IIIA is widely used in systems where high abrasive wear resistance is required. To evaluate the niobium influence, HCCI with 0.5% Nb and 1% Nb additions were melted, besides one without niobium addition of for comparison. For characterization, X-ray diffractometry, scanning electron microscopy (SEM), Vickers microhardness tests, Rockwell C hardness, carbide quantifications, quantification of the retained austenite by Mössbauer spectroscopy, and rubber wheel abrasion test according to procedure A of ASTM G-65 were performed. The results indicated a reduction in the average size, average perimeter, and carbides volumetric fraction (CVF) due to the addition of niobium, also changing the microstructure of the HCCI from eutectic to hypoeutectic. In some regions, NbC0.75 carbides formed a coating around M7C3 carbides. The 0.5% Nb alloy showed the best performance in the rubber wheel abrasive wear test, with a 37% average volume loss reduction as compared to the sample without niobium addition with a 130N load and 34% with a 45N load. The 0.5% Nb alloy also had the highest content of retained austenite among the investigated alloys.

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Abstract Percolation threshold is an important phenomenon to be addressed when producing nanocomposites, especially because the literature suggests a depression of properties near this region. In this study, epoxy matrix nanocomposites were produced with different volume fractions of multi-walled carbon nanotubes and were characterized according to their electrical, thermal, and mechanical properties. In addition, digital image correlation (DIC) was used to measure the strain of nanocomposites and to show how it behaves in different percolation states. Electrical conductivity indicated a percolation threshold near 0.22% v/v of nanoparticles. Differential scanning calorimetry analysis showed a depression followed by an increase in glass transition temperature near the percolation threshold. Tensile strength tests presented a depression followed by an increasing near percolation threshold. DIC images showed that nanocomposites present a different behavior when near the percolation threshold, with a more distributed strain over the surface of the sample under stress and fracture toughness decreased near the percolation threshold.

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Abstract The development of new environmentally-friendly cutting fluids is an important technological advancement. The aim of this study was to assess the tribological behavior of microemulsions (W/O) developed with epoxidized soybean oil and nonionic surfactants with different degrees of ethoxylation (NP4EO, NP6EO and NP9.5EO). The tribological performance of the microemulsion systems was assessed in a High Frequency Reciprocating Rig (HFRR) tribometer. Microemulsions showed Newtonian fluid behavior, with viscosities compatible with conventional cutting fluids. In addition, contact angle values above 90º indicate spherical-shaped drops on the surface on which they are deposited, due to their hydrophobic nature. The microemulsions formulated using surfactants with lower ethoxylation numbers and 20% concentration exhibited greater stability, lower viscosity and better friction reduction during tribological contact between surfaces, given that the average wear scar diameter was 118 µm with smooth surfaces exhibiting slight slippage wear caused by abrasion, as identified by SEM/EDS analyses.

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Based on the face-centered cubic structure, several different types of cubic lattice structures are designed in this paper, the quasi-static compression behavior of the lattice structure is thoroughly investigated by finite element simulation and experimental testing, in which mechanical properties and energy absorption capacities are summarized. The experimental specimens made from thermoplastic polyurethane TPU are additively manufactured using the fused deposition technology. Effects of strut style, strut distance, arrangement form, curvature, and several honeycomb lattice structures are considered. The results show that: under the condition of the same relative density, the selection of sinusoidal struts with larger curvature, the arrangement of 45°/135°, and the inward gradient of the strut distance can all improve the energy absorption characteristics of the structure. Compared with the traditional face-centered cubic structure (specimen L-1), the SEA of the structure with the strut curvature of 0.25, the 45°/135° arrangement of the sinusoidal struts, and the inward gradient of the strut distance is improved by 64% , 190%, and 107%; the introduction of a honeycomb structure with a high relative density can effectively resist the buckling deformation of the structure, and the SEA of the triangular, re-entrant and hexagonal honeycomb structures are 354%, 603% and 548% higher than that of the basic structure, respectively. In addition, reducing the lattice height also resists destabilization.

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The present work investigated the influence of heat input and aging time on the microstructural characteristics and the mechanical properties of dissimilar AISI 317L austenitic stainless steel welded joints. The AWS ER2209 wire-electrode was used as filler metal, and two different heat input levels were applied (4 and 8 kJ/cm), aiming to verify the influence of this parameter on the deleterious phases precipitation. An aging heat treatment (AHT) was carried out at 700 °C for two different exposure times: 50 and 100 hours. It was observed that aging promoted a refinement of the base metal region, and all delta ferrite was transformed into the sigma phase. The microstructure of the fusion zone (without AHT) presented a significant amount of austenite that precipitated in three different morphologies: allotriomorphific of grain boundary, Widmanstätten, and intragranular. For all the thermally treated samples, it was possible to identify the presence of the σ and χ phases. Additionally, the highest concentration of the χ phase was identified in the samples submitted to 50 hours of AHT. The welding condition and AHT that presented joints with higher mechanical resistance and remarkable toughness were those welded with 4 kJ/cm heat input and with 100 hours of AHT. All welded joints showed an increase in the hardness profile after AHT. The microhardness values showed a good correlation with the microstructure and the mechanical tests so that the highest values of microhardness were observed in welded joints with heat input of 4 kJ/cm and 100 hours of AHT

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Abstract Naturally sourced materials have an important place in bone tissue engineering due to their biocompatibility and biodegradability. Non-diatom, diatom-doped chitosan/hydroxyapatite (CS/HAp) and collagen/chitosan/hydroxyapatite (Col/CS/HAp) as three-dimensional tissue scaffolds were produced by freeze drying technique. It was determined by SEM analysis that CS/HAp, CS/HAp/Di, Col/CS/HAp, Col/CS/HAp/Di scaffolds have 160 μm, 130 μm, 390 μm and 340 μm pores, respectively. The diatoms in the structure have approximately 9-16 μm in length, 8-20 μm in diameter and nanopore sizes of 260-330 nm. Cell culture studies were performed using the 3T3 cell line to study the non-toxic nature of biocomposite scaffolds that support cell attachment and proliferation. The cells in the scaffolds without diatom proliferate in a reticulated manner, whereas in the scaffolds containing diatom the cells were wrapped around the scaffold like a cover. The suggested scaffolds have the potential to meet the basic requirements in biocompatibility, cytocompatibility and interconnected pore structure.

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Abstract Cryo-milling was used to make calcia stabilized zirconia (CSZ) powders with 9 mol%, 12 mol%, and 15 mol% of calcia. Powder X-ray diffraction was done to examine the phase growth in prepared powders over the course of 80h of mechanical alloying (MA) in cryogenic environment at 300rpm. The calcined powders were hydraulically pressed into cylindrical shaped sensor elements in a uniaxial press and then sintered for 4h at 1400°C. The microstructure of sintered pellets were studied using Scanning Electron Microscope (SEM). Electrical Conductivity measurements of the prepared stabilized zirconia at various temperatures over a temperature range of 200°C to 500°C using a dual-probe impedance analyzer is carried out and the effects of composition and temperature on the grain boundary impedance of CSZ were analyzed. Conductivity is discussed in terms of ionic vacancies in the bulk due to calcium ion substitution and available grain boundary paths. Ionic Conductivity of prepared CSZ is compared for suitability in oxygen sensing applications.

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Abstract A low-temperature sintering process was used to produce pellets at different temperatures using TiO2 anatase (Vetec) and P25 (Evonik) commercial powders. The initial powder was mixed with 75% acetic acid aqueous solution and pressed under 375 MPa. The temperature was applied after the pelletization in a conventional furnace for 4 hours. The best sintering temperature for anatase was 800°C, which is higher than typical cold sintering temperatures but below conventional ones. However, the optimal temperature was 450 °C for P25 due to its density and SEM results. The sintered pellets' maximum densities were 70% (anatase, 800oC) and 66% (P25, 450oC). It was not possible to measure the anatase pellets treated under 800oC because they disintegrated in water. This work studied the effects of the applied pressure, solvent concentration, particle size, and sintering temperature on the properties of sintered pellets, such as integrity, density, and presence of porous. It also evaluated the electrochemical activity measured by cyclic voltammetry (CV), which indicated that the sintered TiO2 pellets are porous with a partial capacitive response.

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Researchers are constantly developing processes aiming to improve the properties of metal surfaces, especially related to the wear resistance of components, as in the case of the nitrided layer obtained by die-sinking electrical discharge machining (EDM). Following this line of research, this work investigated the effects of sodium octaborate (Na2B8O13.4H2O), mixed into deionized water as a dielectric fluid on AISI 4140 steel surfaces machined by die-sinking EDM. An adapted EDM machine was employed in the process using electrolytic copper as tool. The effects on AISI 4140 steel-machined surfaces were evaluated by optical microscopy, Vickers microhardness, X-ray diffraction, and energy dispersion X-ray spectroscopy (EDS) analyses. The results showed a hardness gain of approximately 146.8% in the modified layer when compared to the AISI 4140 steel (base material). This suggests the formation of a borided layer, such as the Fe2B phases identified on sample surfaces, which can be explained by the boron element decomposed from the dielectric solution.

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The present research of the article is used to describe the microwave sintering of nitinol composite and its surface topography analysis by atomic microscopy (AFM). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) technique is used to analyze the characterization and alloying composition of the composite. Silicon carbide is the reinforcing particle between nickel and titanium. Wear test is conducted to investigate the worn surface morphology of the sintered specimen. The synthesized composite has exceptional material properties such as ultimate tensile strength of 1020MPa, 16% of elongation to fracture, 7.51 g/cc of density and hardness of 310 HV. Low wear rate of 0.01 mg/m is perceived at minimum load and minimum sintering time. Surface roughness is varied from 22.87 to 54.05nm at different sintering time. Maximum roughness height of 327.6 nm is observed in the surface profile of the composite.

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High-carbon steels have been used to high-strength steel wire and strands for prestressing concrete. The necessity of high-strength levels at increasingly larger diameters of wire rods is a technological challenge. Two steels with and without Nb were obtained in a steel mill, submitted to detailed microstructural (previous austenitic grain size, pearlite interlamellar spacing and colony size) and mechanical characterization through tensile tests and hardness. Hot torsion and dilatometry tests were performed to simulate steels processing and to verify the influence of Nb on phase transformation. Adding Nb to steel resulted in a refinement in austenitic grain size and pearlite colonies but had no effect on pearlitic interlamellar spacing. There was a decrease at the start transformation temperature austenite/pearlite and therefore an increase in the hardenability of the Nb-added steel. Finally, Nb addition proved to be a technical and economical way to increase tensile strength and to reduce the variability of the mechanical properties.

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Abstract Bismuth (III) sulfide thin films are prepared on glass substrates by physical vapor deposition technique. Then, the films are annealed at different temperatures from 150 to 350°C with nitrogen and nitrogen-sulfur atmospheres, respectively. The effect of annealing temperature on the optoelectronic properties is investigated. The layers were characterized using ultraviolet-visible spectroscopy, XRD, Raman spectroscopy, EDS analysis and Hall effect. The film annealed at 250°C in a nitrogen-sulfur atmosphere exhibited the best condition with an initial thickness of 106 nm and band gap of 1.37 eV. Also, Bismuthinite phase was obtained, close to the stoichiometry with 59.95 and 40.05 at % for bismuth and sulfur, respectively. The charge carrier concentration of 6.9x1019 cm-3 with a n-type conductivity, the resistivity of 0.19 Ω-cm, and mobility of 0.44 cm2V-1s-1 are obtained.

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Abstract Herein, the design and characterization of Ag/SeO2/C avalanche type resonant tunneling devices are reported. Thin pellets of SeO2 nano-powders pressed under hydraulic pressure of 1.0 MPa which is used as the active material are characterized. They showed tetragonal structure refereeing to space group of P42mbc and lattice parameters of a=b= 7.866 Å and c=5.336 Å. The current-voltage characteristic curves have shown that SeO2 can perform as active media to produce resonant tunneling diodes when forward biased and as avalanche type diode when reverse biased. The peak to valley current ratios of these diodes reached 18.3. In addition, the impedance spectroscopy measurements have shown that the device works in the low impedance mode when operated in the microwave range of frequency near 1.50 GHz. Negative conductance effect is observed in that frequency domain. The features of the Ag/SeO2/C nominate them for use as signal amplifiers and microwave oscillators.

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Titanium dioxide was extensively used in solar cell industry and currently has been studied to produce passivated contacts in PERC/PERT and TOPCon solar cells. The aim of this paper was to analyze the impact of the thickness of TiO2 thin films deposited by electro-beam evaporation on the weighted reflectance and the surface passivation on silicon solar cells. Thin films with different thicknesses were deposited to produce PERT solar cells, varying from 50 to 90 nm. The surface passivation was enhanced as the thickness was increased. For instance, at 400 nm, the internal quantum efficiency increased from 71% to 76% when the thickness of the TiO2 was augmented from 50 nm to 90 nm. The lowest weighted reflectance was obtained in samples with 80 nm thick TiO2 films. Considering the compromise between antireflection properties and surface passivation, the highest efficiency solar cells were produced with 80 nm thick TiO2.

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In this work, various proportionate (0%, 1%, 3% 5% & 7%) of titanium di-oxide nano-filler was utilized as particulate matter along with the sisal/jute fiber reinforcement, in the view to increase the physical properties of the composite materials. Beside, as matrix material the mixture of Epoxy (E) and Polyurethane (PE) was chosen with the proportionate of 70 and 30 wt.% respectively, in order to extract the specific qualities of both the matrices to achieve the interpenetrating polymer networks (IPNs). Moreover, to exactly find out the thermo-mechanical characteristics of the sisal/jute fiber reinforced IPN composites, tests like thermo-gravimetric analysis (TGA), tensile, flexural, Impact, short beam strength and water absorption tests were carried out as per standards. It was found that, incorporation of 5% of TiO2, increases the mechanical properties such as tensile, flexural, impact and short beam strength. Similarly, incorporation of TiO2 into IPN matrix enhances the thermal stability and water absorption resistance. All the obtained values of various filler weight % of TiO2 were compared with each other against with and without particulate incorporated IPN laminate in the purpose of using the same in construction industries.

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In this study, quantum-mechanical calculations in the framework of the Density Functional Theory (DFT) were performed to investigate the role of exchange-correlation functional in describing structural, electronic, and magnetic properties of ZnFe2O4. Herein B3LYP, PBE0, B1WC, and WC1LYP functionals implemented in the CRYSTAL17 code were considered due to the different amounts of the exact Hartree-Fock exchange fraction. In particular, the role of HF fraction on ZnFe2O4 properties was addressed for the first time. Indeed, structural, electronic, and magnetic properties indicate the dependence upon the exchange fraction, where WC1LYP with a 16% exact HF exchange exhibits the best performance compared to the other hybrid functionals. The obtained results reveal an excellent agreement for bandgap, local magnetic moment, long-range magnetic ordering, and unit-cell lattice parameters, overcoming previous theoretical studies based on local/semilocal exchange-correlation treatments. These results confirm the importance of hybrid HF/DFT with controlled HF term contribution to describe the essential features of strongly correlated materials.

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Abstract The surface of Fe3O4 nanoparticles is very reactive and can oxidize to γ-Fe2O3 (maghemite) and α-Fe2O3 (hematite) structures. Based on this, the oxidation process of Fe3O4 nanoparticles must be prevented, and one of the strategies is surface functionalization with organic or inorganic molecules. Thus, this study analyzed the thermal behavior of Fe3O4 and Fe3O4-EDTA nanoparticles using X-ray diffraction (XRD), simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC). Results showed that γ- Fe2O3 was obtained as an intermediate in Fe3O4 and Fe3O4-EDTA decomposition, as confirmed by TG-DTA and DSC curves. Moreover, Fe3O4-EDTA exhibited a temperature peak (Tp = 573.5°C) of phase transformation (γ-Fe2O3 → α-Fe2O3) higher than that of Fe3O4 (Tp = 533.0°C), confirming that EDTA molecules stabilized the nanoparticles efficiently. The kinetic behavior of samples changed, and the activation energy for functionalized samples decreased.

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Abstract This paper presents an integrated approach for an ultimate high-performance safety toe cap with significant milestones in slim design and weight saving. The study of crashworthiness properties was performed through impact-crash test conditions exploring the potential of applicant solutions by the combination of an advanced high-strength steel and enhanced geometric stiffening models. The structural response for a significant thickness reduction was assessed and it provides an evolved discussion for improvements in energy absorption capacity. The present case study focuses on two geometric models from the S3 slim toe cap development by prototypes made of a martensitic 1200 steel alloy. The comparison of results is complemented using numerical simulation models with mathematical description of the dynamic plasticity behaviour by applying a constitutive Cowper-Symonds equation with fundamental parameters for material strain-rate dependence.

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Abstract Over the past years, Al-Mg-Si alloys have been largely applied in automotive industry, which has required a deep knowledge of their mechanical properties and the influence of precipitates distribution on their mechanical behavior. This work evaluated the main mechanical properties of AA6005, AA6063, and AA6351 alloys by means of tensile and low cycle fatigue tests with 0.005 seg-1 deformation rate and 0.3% < εat <1.2% strain amplitudes. Besides, the hysteresis loop and internal stress analysis were investigated to analyze hardening and softening phenomena and to evaluate the friction and back stresses, respectively. Macro and microstructural were performed focusing in intermetallic distribution. Concerning the low cycle fatigue behavior, AA6351 presented shorter lives for strain amplitudes higher than 0.5%, and AA6005 showed the highest fatigue strength and fatigue ductility. AA6063 showed the lowest fatigue strength due to the presence of coarse particles (Fe,Mn)SiAl. During internal stress analysis, the highest value of friction stress for AA6351 indicates the effect of hardener precipitates are the most relevant role for cyclic loadings and the lowest back-to-friction stress ratio indicating that deformation is controlled by particles. In the other hand, AA6063 showed the lowest friction stress due to low amount of fine precipitates.

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Utilizing biomaterials for every conceivable purpose area, such as automobiles, sporting goods, medical, civil, and textile industries, is the aim of the research field. Applications of Natural Fiber (NF) reinforced polymer composites in structural and tribological engineering are rapidly expanding. For the first time in this work, Prosopis juliflora bark and two different types of NF (jute and kenaf) were reinforced with polyester matrix by the hand layup method. The objective of the work is to determine the wear performance and viscoelastic properties of the new hybrid bio-composite. Under dry contact conditions, the tribological performance of the proposed hybrid composite material was evaluated using a range of process parameters, including sliding distance (1000-2000 m), applied load (10-50 N), and sliding velocity (1-5 m/s). The wear behaviour of the fabricated NF composite was greatly enhanced (17.5 x10-8 mm3 /N-mm) by the higher composition of kenaf fibers has been observed. The dynamic mechanical analysis (DMA) showed that the manufactured composites had high storage modulus (4.1 GPa) and loss modulus (3.8 GPA). SEM was used to investigate and propose a potential wear mechanism for the developed composites by evaluating the exterior geomorphology of samples after wear tests. AFM provided details on the fiber surface properties of hybrid composites.

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The packaging industry is the industrial segment that, historically, is one of the largest consumers of polymers, highlighting the great use of polypropylene. Seeking to reduce the consumption of non-renewable raw materials in packaging, this work aimed to study the use of bamboo fiber in polypropylene composites with 15wt% and 25wt% of fiber. Also, the mechanical and thermal properties were evaluated. The density and fluidity of the composites were compared with the virgin polymer. Regarding the density of the composites, it was observed that this was not significantly affected by the addition of fibers. In the melt flow index of the composites, it was observed that the fluidity of the composite with 25wt% bamboo fiber was reduced by more than 50%. The fluidity of the composite with 15wt% fiber has not undergone considerable change compared with the data of the virgin polymer. In tensile analysis, the only property that increased with adding fibers to the polymer was the modulus of elasticity. The impact resistance analysis showed that the composites significantly increased impact resistance and energy absorption. It was concluded that the composites of PP with bamboo fiber showed potential application in the packaging industry.

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Abstract This study investigated the pitting and crevice corrosion behavior of the gas tungsten arc welding (GTAW) process in the UNS S32205 according to industrial parameters. Results revealed that the welding process presented a weld metal chemical composition similar to the base metal and an adequate balance of the austenite and ferrite phases. No relevant variation in the hardness was observed and XRD spectra did not identify the presence of deleterious phases in the weld bead. Cyclic polarization tests revealed similarities between welded and base metal samples (20±2°C, NaCl 3.5% wt.). When comparing the behavior obtained in the crevice, and pitting tests, a decrease in the corrosion resistance was observed in the presence of a crevice former. The SEM-EDS proved that the attack occurred mainly in secondary austenites. Profilometry measurements revealed that the crevice corrosion in the weld region was deeper than in the base metal. However, considering the welded samples as a unit, making no difference between regions: weld metal, HAZ, and base metal, the average crevice corrosion depth was comparable to that of the base metal samples. Finally, it was concluded that the welding process used for the UNS S32205 steel did not harm its corrosion resistance.

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Abstract Whilst the optical and structural properties of the glasses containing tantalum oxide have been considerably investigated, research into their mechanical properties is not substantially established. This work reports on the mechanical characterization of transparent germanate glass samples, obtained via the melt-quenching technique, with a molar content of Ta2O5 ranging from 0% to 20%. The introduction of Ta2O5 in the samples is related to significant improvements in the mechanical properties. The transition from glass to transparent glass-ceramic via the controlled crystallization of Ta2O5 proved to be a tool to increase both the elastic modulus and the hardness while keeping the transparency of the material. The average elastic modulus of the studied compositions ranged from 69.2 GPa to 99.1 GPa, while the average hardness of the same samples varied from 5.10 GPa to 7.34 GPa.

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The growing process of a spinel-like oxide film can be obtained through different atmospheres; in this sense Air, O2, steam, and nitrogen atmospheres were used in different steps during the aging heat treatment at 490ºC of maraging 300 and 350 alloys. The oxidation layer produced under different atmospheres was chemically, microstructurally and mechanically characterized by means of advanced techniques. The results showed (in both alloys) a non-homogeneous mix oxide formed by magnetite, nickel and cobalt ferrites and MoO3 heterogeneously distributed along the oxide thickness. It was also founded TiO2 in the innermost areas and a particularly important quantify of hematite on the external surface. A nickel-rich austenite phase was produced at the interphase due to the combination of nickel stability and the preference of cobalt, molybdenum, and iron diffuses through the film as ions. The highest thickness values were found in the oxides produced in maraging 300 steels which could indicate greater susceptibility to oxidation comparing with grade 350 maraging steel. The oxide films produced in both maraging alloys using air atmosphere presents excellent adherence, and the results show the capability for being used for tribological applications under sliding contact tests.

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Abstract Friction stir welding (FSW), a new solid-phase connection method, is considered an excellent welding method for aluminium alloys. Grain orientation, grain boundary structure, and texture types in different regions were characterized by a high-resolution electron backscattered diffraction technology. The results revealed that during the welding process, the coarse grains of the base metal are refined, grains in region 1 (600 μm away from the edge of the keyhole) are arranged in a long strip, and the long axis is approximately parallel to the shear direction. The thermal cycle of the welding process causes some grains to recrystallize, further forming a recrystallization (100) [011] rotating-cube texture. The metal in region 2 (100 μm away from the edge of the keyhole) was severely squeezed by the pin, resulting in an increase in the degree of grain breakage in this region, which were mainly equiaxed grains. Due to the eccentric movement of the pin, the (100) [001]-oriented and (110) [001]-oriented grains alternate on the middle layer, forming a banded structure. Plastic deformation and recrystallization occurred in the base metal, within 383 μm in front of the pin, forming a (110) [001] Goss texture and (100) [001] recrystallized cubic texture.

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The thermomechanical stability of majority precipitates formed by conventional alloying elements in magnesium alloys is generally poor. Hence the morphology and structure of these precipitates are highly susceptible to the welding thermal cycle, which results in the softening of the heat-affected zone (HAZ). Rare-earth (RE) precipitates are generally thermodynamically stable. Therefore, it is necessary to conduct an in-depth discussion on whether RE precipitates reduce the softening of the HAZ. In this paper, Ce-containing magnesium alloy was successfully welded by fiber laser welding. Scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and micro-hardness tester were employed to analyze the welded joints. Consequently, the distribution characteristics of RE precipitates in both fusion zone (FZ) and HAZ were revealed. Moreover, based on the solution experiments of the welded joints, the evolution mechanism of the precipitates in welded joints during the thermal cycle was deduced, and the softening mechanism of the HAZ was clarified. Thereafter, the relative intrinsic mechanism of RE precipitates in reducing the softening of the HAZ and improving the mechanical properties of FZ was explored. The results showed that the HAZ was narrow, with a width of only 100-200 μm. The morphology and distribution of the less thermally stable Mg17Al12 precipitated in HAZ changed significantly after the thermal cycle. In contrast, RE precipitates remained stable, which is extremely important for reducing the softening of the HAZ. In addition, the precipitates in FZ were transformed into micron-sized particles and precipitated at the edge of dendrites, resulting in a hardness improvement of the FZ.

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Abstract The market for electric vehicles is growing, seen as the best alternative to replace internal combustion-powered vehicles. Recent developments in electric vehicles have allowed them to reach a level of performance, comfort, and safety that enables them to compete with traditional vehicles. However, several studies are directed towards increasing the autonomy of these vehicles, aiming at weight reduction of structural components. Aluminum alloys are increasingly being chosen to produce structural elements, due to their low density and suitable properties. The 6000 Al alloys are often used in chassis and bodywork. In view of this, this work proposes a comparison of 6000 series alloys, by means of thermodynamic (using Thermo-Calc®) and property computations (Ansys® Granta EduPack and Selector) to select the best alloys considering application properties, processability, and environmental impact. It was observed that the T6 heat-treated alloys presented better mechanical properties, but, on the other hand, they have more impact on the environment. As such, the 6010-T6 alloy was classified as the best alloy regarding performance, the 6061-T4 alloy the best in terms of processability, and the 6009-T4 alloy presented the lowest environmental impact. The 6111-T4 alloy was highlighted as the alloy showing the best balance between the examined properties.

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Al-Fe alloys are usually used as packaging and structural materials, but in the recent years, there have been considered for possible applications in aerospace field. The solidification sequence in pure aluminum containing 1 wt.% Fe is described in term of the formation of macrostructure, microstructure, microsegregation, porosity and mechanical properties. This material was studied in the upward unidirectional solidification system under transient heat flow conditions. Differences in microstructure, microsegregation, porosity and mechanical properties such as ultimate tensile strength, elongation and microhardness, due to the thermal parameter effects were observed and discussed. Experimental growth laws relating cellular spacing to the cooling rate and solidification speed have been determined, indicating that the increase in thermal parameter have induced a refinement effect on cell morphology. Microsegregation profiles of Fe solute were experimentally determined from the central region of the cell to the intercellular region under different solidification speeds. The Fe microsegregation determined from central region of the cell (FS = 0) to the intercellular region (FS = 1) show a growing profile, in any case considered. However, the profiles move upward with the increase in solidification speed, which indicates that Fe solubility in solid, increases with the increase in solidification speed. The effect of the solidification thermal parameters and cellular spacing on the porosity content were experimentally investigated. The value of porosity content increased along the casting. These results have pointed out that porosity content is affected by solidification parameters and cellular patterns. Further, measurable effects of the thermal parameters, cellular spacing and porosity content on the mechanical properties were experimentally determined. It stands out among experimental results the influence of porosity on the mechanical properties of as-cast material. In any case analyzed, mechanical properties increase with decreasing porosity content.

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Plasma Electrolytic Oxidation (PEO) was employed for the generation of porous niobium-containing surfaces with enhanced photocatalytic activity. Pulses of 500 and 600 V, with a repetition rate of 60 Hz, were applied to titanium disks immersed in niobium-containing electrolytic solutions. The treatment time ranged from 180 to 600 s, and the surface morphology was analyzed by scanning electron microscopy, while X-ray diffraction was employed in the evaluation of crystallographic structure. The optical gap of the samples was determined from UV-Vis reflection spectra, and an automated goniometer was used for contact angle and surface energy measurements. More than 35% of Nb has been incorporated into the samples. Under certain conditions, the treatments resulted in a reduction of the optical gap from 3.18 to 2.63 eV as compared to as-received samples. Photocatalytic degradation rates of methylene blue as high as 70% have been reached after 120 minutes under irradiation with UV-Vis light.

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This study investigates the effects of Gamma-irradiation on the structural, morphological and optical properties of 3,16-bis(tri isopropyl silylethynyl)pentacene (TIPS Pentacene) organic semiconductor films. The TIPS Pentacene thin films were irradiated at 10 to 300 kGy at a dose rate of 1.58 kGy/hr. The films were characterized using X-Ray Diffractometer (XRD), Atomic Force Microscopy (AFM) and Ultraviolet-Visible Spectroscopy (UV-Vis). The XRD analysis showed that the pre-irradiated thin films were of crystalline structure, indicating a broad wave diagram. The XRD and AFM results show that these variations can be attributed to the radiation-induced local heating and microscopic atomic mobility. Based on the UV-Vis results, the thin films exhibit approximately 70% optical transmittance in the visible region at pre-irradiation. At post-irradiation, optical transmittance decreased to 55% at the maximum absorbed dose. The corresponding optical bandgap decreased from 1.87 to 1.50 eV after a total ionizing dose of 300 kGy. The findings showed that TIPS Pentacene thin film has good mitigation towards gamma irradiation and can withstand harsh radiation while retaining its semiconductor properties. It is a potential candidate for flexible electronics for space applications.

Resumo em Inglês:

The use of computer simulation to predict the behavior of devices and materials allows for the acceleration of system operation and reduces costs, as it eliminates the need to build prototypes for testing. This work proposes the construction of 3 models with different complexities to simulate the electrical behavior of a solid electrolyte fuel cell. Experimental data were compared with simulation data. The experimental data were obtained from the production of a solid YSZ by tape casting, sintered at 1550 °C. The material was characterized using impedance spectroscopy in atmospheric air. From the experimental data, a computer simulation was conducted by using commercial code (COMSOL Multiphysics v.5.4). The construction of the model was developed to 1D, 2D axisymmetric and 3D dimensions to simulate an electrolyte to use in cylindrical planar SOFC. Nyquist Impedance graphics were plotted for the three geometries in comparison with the experimental value. No variation was observed between the curves obtained by the different geometries for the same interface. In other words, the interface complexity did not interfere in the result obtained for the same experimental data. We concluded that the 1D model is ideal to predict the influence of operational parameters because it is simpler and saves analysis time, maintaining the reliability and accuracy of the results.

Resumo em Inglês:

Two artificial neural networks (ANNs) were developed for producing an austempered ductile iron (ADI) with low-cost chemical composition and mechanical properties as per ASTMA897/897M-16-grade-1050/750/07 standard. Thus, the first ANN predicted the chemical composition range within the lowest cost and required mechanical properties. Next, in the second ANN, the resulting values from the first ANN were refined considering the target chemical composition suggested in the standard. Moreover, mechanical properties and microstructural analyses were undertaken in the ADI produced to support the ANNs’ findings. Hence, ANNs can be used to make a standard-compliant ADI and achieve cost savings.

Resumo em Inglês:

Stainless steels have been evaluated in the form of coatings or thin films deposited using magnetron sputtering in various investigations. In most of these investigations, mainly the microstructural evaluation of this type of coating has been reported, while the evaluation of wear resistance has not been widely studied. In the present investigation, ferritic-austenitic stainless steel coatings with different percentages of silver were deposited by means of unbalanced DC magnetron sputtering. A stainless steel target doped with different numbers of silver inserts (0, 1, 2, 3, and 4 inserts) was used, obtaining coatings with silver percentages of up to 7.7 at. %, in order to evaluate their tribological properties. During the synthesis, the first layer of the bilayer was deposited with argon and the other in an atmosphere of argon and nitrogen. The structure of the coatings was evaluated by use of X-ray diffraction (XRD), and the morphology and the chemical composition were studied by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The hardness was tested through nanoindentation, and the wear test was carried out using the pin-on-disc technique. The wear tracks were evaluated via profilometry, SEM, and EDS. In general, the deposited films exhibited BCC and FCC phases and a compact morphology, as well as good adherence to the substrate. The results of the evaluation of the mechanical properties revealed an increase in the hardness of the coatings when the silver content was augmented, obtaining values of 9.8 GPa and 12.1 GPa for coatings with 0 and 4 silver inserts, respectively. Likewise, it was found that the wear resistance of coatings was higher, up to two orders of magnitude compared to the 316L stainless steel substrate. Finally, the wear rate of the multilayers decreased slightly with an increase in the percentage of silver in the films produced, up to an order of magnitude for the coating with 4 silver inserts relative to the coating with 0 silver inserts.

Resumo em Inglês:

Abstract Numerous research incorporating precipitation hardening and/or strain hardening on Al-Mg-Si alloys has demonstrated improved mechanical properties in the alloys. However, there is a lack of research on how these processes can be combined efficiently to provide better strength and hardness for the alloys. The present study describes the effects of low temperature thermomechanical treatment (LTMT - combination of conventional age hardening and strain/work hardening) carried at two isothermal aging temperatures on the hardness and strength of the aluminium alloy 6061 (AA6061). Further, an innovative LTMT process is also proposed, which aims at further enhancing the mechanical properties of the alloy. The study revealed the increase in degree of deformation improved the strength and hardness of the alloy with reduced aging time. The effect of the degree of deformation, pre-deformation, and alternate deformation and aging cycles on the hardness and strength of the alloy was studied with the help of fracture surface analysis.

Resumo em Inglês:

Abstract Recently, there has been increasing importance on scaffold materials that could be used in biomaterials. In the present study, equimolar TiNbZr medium entropy alloys (MEAs) and porous TiNbZr alloy scaffolds were produced by mechanical alloying (MA) that is a powder metallurgy processing technique. The MA process was carried out using high energy planetary ball mill. Ammonium bicarbonate (NH4HCO3) at different percentage ratio was used as space holder to fabricate the porous TiNbZr scaffolds with using space-holder sintering method. Cold Isostatic Pressing (CIP) was performed for consolidation of mechanically alloyed powders. Finally, the green compact samples were sintered in tube furnace under vacuum atmosphere. The microstructural analyses, phase composition, porosity and density measurement, compression and microhardness tests and wear resistance of bulk alloys were examined. The X-Ray Diffraction (XRD) patterns of all samples indicated the dominant β-Ti phases and small amount of α-Ti phase. SEM (scanning electron microscope) images for porous TiNbZr alloy scaffolds demonstrated that porosity increased with increase of space holders amount. With the increasing porosity content, density, hardness, compressive strength and the elastic modulus of samples decreased while wear rate increased.