Resumo em Inglês:

High chromium cast irons (HCCIs) are widely applied in the mining industry as components of equipment for iron ore transportation, in which their surfaces are subjected to abrasive and erosive wear. The present work evaluated the erosion-abrasion behavior of a HCCI possessing different amounts of austenite and martensite, using a laboratory impeller-tumbler wear test apparatus and iron ore pellets as abrasive material. The results showed that the wear dominant mechanism on the worn surface of the as-cast material depends upon the material microstructure. For HCCI destabilized at 930 and 990 °C, the matrix has high martensite/austenite ratio and finely dispersed secondary carbides, offering high abrasion-erosion wear resistance. The absence of fractured eutectic carbides indicates that such matrix has hardness and load bearing capacity, enough for mitigating a significant plastic deformation during the impact pellets. For HCCI destabilized at 1050 °C, the matrix has a low martensite/austenite ratio and coalesced secondary carbides, leading to high wear rates during erosion-abrasion tests.

Resumo em Inglês:

In the present work, synthetic slags (FeO-SiO2-CaO-P2O5-Al2O3-TiO2-V2O5 system) mimicking the composition of the slag inclusions of Ipanema were solidified at different cooling rates. FactSage software was used to calculate the slag’s phase equilibria from 500ºC to 1600°C to guide the microstructural characterisation. The samples solidified with slower cooling rates featured wüstite dendrites and a eutectic-like matrix, with intradendritic (Al,V,Ti)-containing iron spinel precipitates in the wüstite. The rapidly solidified slag showed refined wüstite dendrites surrounded by a Fe-O-Si-Ca-containing amorphous single-phase matrix without intradendritic (Al,V,Ti)-containing iron spinel precipitation. The comparison of the calculated phase diagram with the as-cast microstructures showed a few discrepancies. For instance, the FactSage’s database must be updated to consider the simultaneous solubility of Al, V and Ti in the thermodynamic description of the spinel phases, such as FToxid-SP-V, FToxid-SPINA, FToxid-TiSp and (FeO)2(TiO2)(s). Finally, the intradendritic precipitation of (Al,V,Ti)-containing iron spinel phases in the wüstite of the slag inclusions indicated that an Ipanema’s iron artefact was exposed to high service temperatures between 750 and 1050ºC.

Resumo em Inglês:

Double-layer Ni-P coatings with low phosphorus content in the inner layer and high phosphorus content in the outer layer and Ni-Mo-P composite coatings are successfully prepared on the surface of AZ91D magnesium alloy by chemical plating process. The microstructures, friction and corrosion resistance of double-layer Ni-P and Ni-Mo-P coatings are studied in comparison. Meanwhile, the deposition and corrosion resistance mechanism for the coatings are investigated. Results convey that both Ni-P and Ni-Mo-P coatings showcase an amorphous structure. The coating possesses denser and more homogeneous structure with the co-doping of Mo. The micro-indentation hardness (859.7 HV) and friction coefficient (0.58) of Ni-Mo-P coatings show that the ternary alloy coating is firmly bonded to the magnesium alloy substrate. Besides, the Ni-Mo-P coatings demonstrate exceptional wear resistance attributed to Mo co-deposition, fostering grain refinement and facilitating the growth of passivation films.

Resumo em Inglês:

Ferroelectric thin films of 0.2BaTiO3 – 0.8BaZr0.5Ti0.5O3 (BT-BZT) are dielectric materials applied in various sensors, particularly in capacitor manufacturing, due to their excellent electrical properties. This ferroelectric material also has a high dielectric constant value, such that it is suitable for use in Ferroelectric Random Access Memory (FeRAM) and microwaves. Therefore, this study aimed to synthesize thin BT-BZT films with annealing temperature variations of 700 °C, 750 °C, and 800 °C. To achieve this, the sol-gel method was applied to Fluorine Doped Tin Oxide (FTO) substrate, a selected technique for its simplicity and cost-effectiveness. The electrochemical properties were characterized using electrochemical impedance spectroscopy (EIS). The research results show that at a frequency of 100 Hz, the highest dielectric constant obtained was 58975.43 at a temperature of 800 °C. This temperature has the highest resistance compared to other samples. The highest capacitance value is 2.9 µF at a temperature of 700 oC. Therefore, it was concluded that the annealing temperature influenced the dielectric constant and the capacitance values of the capacitor.

Resumo em Inglês:

Membrane technology offers solutions for separation of complex gas mixtures. Therefore, new efficient and durable membranes are required to produce gas permeation modules with high area/volume for CO2 removal from natural gas. This study aims to develop cost-effective zeolite DD3R alumina composite hollow fibers to achieve these process requirements. A porous hollow fiber support from low-cost alumina was prepared via phase inversion followed by thermal treatment. DD3R zeolite seeds were then implanted over the surface of the microporous hollow fibers to form a selective layer by hydrothermal synthesis. The thickness of the selective layer was controlled by the seed concentration, which also affected the crystal intergrowth and competing zeolite phase formation, Sigma-2, which influenced the membrane performance. A reduced-diameter composite DD3R-alumina hollow fiber was obtained with a selectivity of 203 and a CO2 permeance of 5.4 x 10-8 mol m−2 s−1 Pa−1 at a pressure of 2 bar.

Resumo em Inglês:

The integration of Inconel 718 (IN718) and Cold Metal Transfer (CMT) based wire + arc additive manufacturing (WAAM) for wall fabrication with a near-net shape and low buy-to-fly ratio presents a novel and promising approach with potential applications in various industrial sectors, including aerospace and automotive industries. This research aims to investigate the microstructure and mechanical anisotropy of thin-walled IN718 components that were produced using CMT based WAAM, and to compare the properties of as-deposited and heat-treated samples that underwent aerospace (AMS5663) procedures. To characterize the microstructure of the specimens, we employed optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and an element probe microanalyzer (EPMA). Tensile and hardness tests were conducted to evaluate the mechanical properties of the specimens. Our results revealed that the as-deposited samples exhibited a dendritic microstructure with a high degree of segregation, leading to lower mechanical strength than that of the heat-treated specimens. Precipitated heat treatment promoted the precipitation of strengthening phases, such as gamma prime and carbides, improving the mechanical properties. In contrast, the precipitated heat-treated specimens exhibited a more refined microstructure with equiaxed grains and a significantly enhanced mechanical strength. This study provides critical insights into optimizing the material for different applications, leading to the development of more efficient and effective parts.

Resumo em Inglês:

In this work, electrochemical tests were performed to measure hydrogen permeation during free dissolution of carbon steel in the presence of the ionic liquids (ILs) 1-ethyl-3-methylimidazolium acetate [(EMIM)+(Ac)-], 1-ethyl-3-methylimidazolium bromide [(EMIM)+(Br)-], and 1-butyl-3-methylimidazolium tetrafluoroborate [(BMIM)+(BF4)-] in 5.4 mol L-1 HCl aqueous solution. The permeation inhibition efficiencies (IEp (%)) of 5-hydroxy-2-nitromethylene-hexahydropyrimidine (HPY) and a commercial corrosion inhibitor (CCI) were also evaluated. Among the ILs, the (BMIM)+(BF4)- compound presented the highest corrosion and hydrogen permeation inhibition efficiencies, with values of 23% and 30%, respectively. The (EMIM)+(Br)- and (EMIM)+(Ac)- compounds were not effective against corrosion, but they presented IEp of 15.8% and 23%, respectively. The HPY compound demonstrated 61% effectiveness in preventing corrosion, while in silico evaluation indicated no toxicity. However, neither the HPY compound nor the CCI compound inhibited the entry of hydrogen into the carbon steel during the pickling process.

Resumo em Inglês:

The novelty of the present study lies in synthesized ZnO film in a single step by chemical bath deposition. The typical conversion of zinc hydroxide (Zn(OH)2) into ZnO material through thermal annealing is not required. A direct synthesis has achieved using four different zinc salt sources, yielding equivalent results. All the synthesized ZnO films were non-specular and adhered well to the glass slide substrates. We present the results of the structural, optical, and morphological characterization techniques. These revealed a hexagonal structure, a band-gap energy of around 3.2 eV, and a hexagonal nanorod shape for all the synthesized ZnO films.

Resumo em Inglês:

A highly efficient NiFe2O4/TiO2 nanofibrous photocatalyst was prepared by a simultaneous solution blow spinning method. The hybrid fibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and magnetometry. The photocatalytic properties were evaluated using Crystal violet (CV) and Congo red (CR) dyes under visible light irradiation. Fibers calcined at 600 ºC and 700 ºC showed the highest CV decolorization (77%). On the other hand, for CR, the best performance was encountered with the photocatalysts heat-treated at 500 ºC, which exhibited photocatalytic degradation of 87% after only 30 min of visible light irradiation. The high reaction rates (0.018 to 0.067 min-1) explain the fast decolorization yielded by the combined effect of adsorption and photocatalytic processes. Moreover, recyclability assays showed stable CR dye efficiency after five recycling cycles. Therefore, the NiFe2O4/TiO2 nanofibers present a high potential for application in the decolorization treatment of wastewater from the textile industry.

Resumo em Inglês:

In most situations, predicting wear requires a variety of microstructural characterizations and experiments with contact surfaces. Based on physical principles, mathematical models might be of great assistance in understanding and thereby predicting this event. Considering the significance of heat generation in war, it appears that the parameters of thermodynamics are appropriate measurements for wear modelling. Entropy is among these parameters of thermodynamics. The Miedema model is a good method to predict the Gibbs free energy and entropy of solid solutions of binary and ternary systems. In this study, the wear behaviour of iron-based alloys according to their estimating values of Gibbs free energies and entropy was studied under lubricated conditions. The wear test was performed in accordance with ASTM-G99, utilizing the vertical universal friction testing machine MMW-1A and the pin-on-disk test methodology. Results show that the lowest negative value of Gibbs free energy was noted in the Fe-Al-Sn ternary system (-14.37 KJ/mol), while the highest negative value was found in the Fe-Al-V (-25.16 KJ/mol) binary system. It was also concluded that the wear rate decreased when the entropy estimate increased. The higher value of the wear rate was (6.935 mm3\N.m x107) for Fe-Al binary alloy with an entropy value (1.717 J\k Mole). The lowest value of wear rate was (3.581 mm3\N.m *107) for Fe-Al-Sn ternary alloy with an entropy of (2.71 J\k Mole). This is due to the micro-distortion that was mechanically indicated with the ternary alloys Fe-Al with V, Mn, Ga.B, and Sn additives that affected the wear mechanism and caused high values of wear.

Resumo em Inglês:

This study assessed the morphology and thermal, mechanical, and chemical properties of electrospun membranes made of acrylonitrile-methacrylic acid copolymers (PANCMAA). Copolymers were synthesized using the aqueous suspension method with varying comonomer contents (homopolymer,PAN, lower acid, PANCMAA1, and higher acid, PANCMAA2) and characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). Electrospun fibers were produced by adjusting the polymer concentration in the DMF solution, and the optimal conditions yielded nanofibrous membranes. PAN and PANCMAA membrane properties were evaluated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), stress-strain tests, and swelling behavior in a phosphate buffer solution. The comonomer content influenced the crystallinity of the electrospun nanofibers, reducing the 16.8° XRD peak intensity from PAN to PANCMAA2. DSC indicated an increased Tg (from 113°C in PAN to 127°C in PANCMAA2) and a decreased exothermic cyclization enthalpy (311 J.mg-1 in PAN to 271 J.mg-1 in PANCMAA2). PANCMAA1 exhibited higher stiffness than PANCMAA2 and PAN, with a storage modulus of 0.16 GPa, a Young’s modulus of 135.7 MPa, and a lower elongation at break (3.98%). The presence of the acid comonomer significantly enhanced the swelling behavior of the electrospun membranes in phosphate buffer solution.

Resumo em Inglês:

It is particularly important to investigate the mechanical performance of carbon fiber (CF) reinforced polyamide 6 (PA6) composites used for automotive and aerospace applications, where diffused moisture of the environment may potentially weaken the material over time. In this work, CF/PA6 composites were subjected to two different types of conditioning: distilled water at a temperature of 80 ºC and saline solution for 12 weeks. The volumetric fraction of CF, PA6 matrix, and the voids of the CF/PA6 composites were determined by acid digestion analysis. At the end of the environmental conditionings, the moisture absorption content and the diffusion coefficient (D) were determined. The mechanical performance of CF/PA6 composites unconditioned and conditioned was evaluated through tensile and interlaminar shear strength (ILSS) tests, and morphological characteristics of the fracture surface after the mechanical tensile test. CF/PA6 composites conditioned in saline solution showed a decrease of 53% (tensile sample) and 72% (ILSS sample) in the diffusion coefficient (D) and insignificant losses of mechanical properties when compared to CF/PA6 composites conditioned in distilled water at 80 ºC. This behavior is attributed to the salt molecules blocking the pores and consequently reducing the migration of water into the samples, maintaining the internal integrity of the specimens.

Resumo em Inglês:

Ni0.5Co0.5Fe2O4 nanoparticulate powders were synthesized using coprecipitation and sol-gel methods. The crystalline structure of the nanocompounds was determined through X-ray diffraction analysis. The chemical composition of the synthesized nanopowders was analyzed using infrared spectroscopy measurements. The size, morphology, and aggregation of the nanoparticles were determined from electron microscopy images. The magnetic properties of the nanocompounds were studied through magnetization measurements as a function of temperature and applied magnetic field. The synthesized powders consist of aggregates of nanoparticles with mean particle sizes of 24 nm and 43 nm, with those synthesized using the coprecipitation method being smaller. The compounds exhibited a single crystalline phase corresponding to the cubic spinel structure, with a unit cell parameter of approximately 8.35 Å and an inversion parameter with values of 0.94 and 0.95. The synthesized Ni-Co mixed ferrites presented an ordered magnetic behavior below 320 K, with the nanoparticles being in the blocked magnetic regime.

Resumo em Inglês:

Reports on freeze-cast ceramic materials frequently focus on the study of the organized macroporosity and the properties of the materials. This study aims to describe the microstructure evolution of freeze-cast alumina during the sintering process, analyzing grain growth, densification, pore elimination and crystal structure at different sintering temperatures (1300-1500 °C). Aqueous suspensions with 20 vol% alumina were freeze-cast in liquid N2 and sintered. The microstructure was analyzed by stereological analysis, N2 adsorption and X-ray diffraction. Grain sizes varied within 237-500 nm, and the intergranular porosity decreased from 8.8% at 1300 °C to 1.4% at 1500 °C. N2 isotherm analysis revealed pore shrinking from the region of macro and mesopores (20-80 nm), to smaller residual mesopores (3.7-15 nm) at temperatures above 1400 °C. Rietveld refinement of the XRD diffractograms confirmed increased crystallite size and decreased lattice strain at higher sintering temperatures. This comprehensive description of microstructural evolution of the freeze-cast alumina contributes to understanding the sintering of highly porous ceramics produced via freeze-casting.

Resumo em Inglês:

The developed novel Nanoclay (NC) filled bamboo fibre (BF) /glass fibre (GF) reinforced unsaturated polyester (USP) hybrid composites were subjected to static and dynamic mechanical studies. Effect of NC on mechanical properties of the neat and NC filled BF/GF hybrid composites were tested in accordance with the ASTM standards. Dynamic mechanical analysis was performed on the composites to evaluate their viscoelastic properties like, storage modulus (E’), loss modulus (E”) and damping factor (Tanδ). Outcomes of the mechanical results revealed that, NC filled BF/GF-USP hybrid composites showed superior mechanical performance over the neat hybrid composites particularly 5 wt.% NC filled BF/GF hybrid composite (HC4) outperformed other composites. From the dynamic mechanical it was found that the addition of NC filler in the hybrid composites enhanced the E’, E” and glass transition temperature (Tg). Fractured specimens of the hybrid composites were examined using Field emission electron microscope (FESEM). Matrix fracture, micro-cracks, fibre pullouts, stretching of fibres and delamination of the fibre layers were significantly noted in the fractography analysis. Therefore, from the obtained results, NC filled BF/GF USP hybrid nanocomposites can be employed for automotive applications.

Resumo em Inglês:

Nitrocarburized coating by plasma electrolytic saturation, PEN/C coatings, have been proposed to increase the corrosion and wear resistance of steel by using a process of low-temperature hydrostatic plasma. The objective of this work is to analyse the wear and corrosion resistance of PEN/C coatings on SAE 1045 steel, using the electrochemical slurry erosion wear test (ESEWT). This test allows the evaluation of the simultaneous effect of erosion wear and electrochemical behaviour on this coating. Thus, it was possible to evaluate the erosive and corrosive effect and the synergy of these phenomena on the PEN/C coated SAE 1045 mass loss rates. ESEWT tests were performed at different times and under different electrochemical conditions: under cathodic protection and open circuit potential (OCP). The PEN/C coating increased the corrosion resistance of SAE 1045. Synergy between the erosive wear and corrosion was the main factor in the mass loss rates of both analysed systems. The synergistic mechanism of the substrate occurred by removing the corrosion product and by activating the surface generated by the erosive process of the particles. The synergistic mechanism of the PEN/C coating occurred with the removal of inherent surface irregularities through the erosive process, combined with localized corrosion.

Resumo em Inglês:

Powder metallurgy is an attractive method for cost effective production of near net shape Ti-Nb alloys, and, when elemental powders and coarse HDH powders are used, a higher flexibility in alloy composition and low processing costs can be achieved. In this study, manufacturing of (α+β) Ti-Nb alloys by powder metallurgical techniques using coarse HDH Nb (D50= 110 μm and D50= 255 μm) and HDH Ti (D50= 22.6 μm) powders as starting materials was described. Tape casting was applied for the production of porous sheets while warm compaction of Metal Injection Molding (MIM) feedstock was applied for the production of dense parts. Microstructural and mechanical tests were employed to investigated the effect of coarse Nb powders on the sintering behavior and mechanical properties. Tape casting enabled to produce porous sheets of Ti16Nb alloy with an interconnected porosity varying from 14 - 31 vol.%. Warm compaction enabled to produce Ti-Nb parts with less than 2% porosity and Yield strength in compression of 975-1100 MPa, which is similar to the values reported for Ti-Nb based alloys produced by powder metallurgy of finer powders. A dynamic Young’s Modulus of 37-52 GPa, significantly lower than that of cp-Ti was achieved. These results might provide guidelines for the use of coarse Nb powders as starting materials for the powder metallurgical development of low-cost Ti-Nb based alloys.

Resumo em Inglês:

Ti alloys have been developing through the years, aiming the biomedical application since it has suitable properties. Among Ti alloys, the Ti-Nb systems are a pronounced group to biomedical applications due to its low elastic modulus, good corrosion resistance, and mechanical properties. Although this system is quite well-known regarding its phases, structure and properties, there is not plenty of information about wear available in the literature. To investigate the wear resistance, the samples were submitted to x-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the phases formed. Hardness and elastic modulus were measured by microhardness Vickers and dynamic Young modulus by excitation impulse. Additionally, wear volume, wear resistance, and H/E ratio were calculated to understand the wear material’s performance. This study aims to investigate the wear resistance of Ti-xNb (x = 15, 25 and 40wt.%), one of each type of Ti alloys and phases formed: Ti-15Nb (α´), Ti-25Nb (α”) and Ti-40Nb (β) and the influence of cooling rate after solution heat treatment on wear properties through ball cratering. It was possible to find that the harder the alloy, the higher the wear resistance. Thus, in the case of Ti-xNb (x = 15, 25 and 40wt.%), alloys the hardness plays a significant role in wear resistance. Besides that, the samples that have presented the α´ or α”phase have the lowest wear resistance. Therefore, not only the hardness influences the wear resistance but also the combination of phases formed.

Resumo em Inglês:

In this study, we hypothesized that microtextured titanium (Ti) surfaces produced by laser metal fusion (LMF) 3D printing may play an important role in osteoblastic differentiation of mesenchymal stem cells (MSCs). For that, MSCs derived from mouse bone marrow were cultured on Ti discs produced in two different ways: microtextured produced by acid etched (Ti-Ac, control group) and microtextured produced by LMF 3D printing (Ti-3D-LMF, test group), in which it was evaluated: (1) cell proliferation, (2) alkaline phosphatase activity and (3) extracellular matrix mineralization. The results showed that both groups allowed cell proliferation over time (p<0.001). Additionally, there were no statistically significant differences between groups in the assessments of alkaline phosphatase activity (p=0.385) and extracellular matrix mineralization (p=0.234). Although both groups evaluated induce cell proliferation and osteoblastic differentiation similarly, the technology used in the Ti-3D-LMF group may prove advantageous as it produces specific dental implants for patients through customization.

Resumo em Inglês:

This research investigates optimizing the properties of 2024 aluminum alloy using the Extreme Vertices Design (EVD) method and linear regression. It examines the oxidation behavior of the alloy during solubilization heat treatment, specifically focusing on the effect of magnesium addition leading to a dark oxide layer. The study employs a comprehensive experimental design and regression models to estimate the specific oxidation rate constant (k). Analysis of results reveals variations in oxidation behavior among alloys and the influence of aluminum, copper, and magnesium concentrations on the oxidation rate. The regression analysis yields a comprehensive equation: k = -0.01Al - 4.06Cu - 15.71Mg + 4.52Al·Cu + 17.01Al·Mg + 418.5Cu:Mg - 447.7Al·Cu·Mg, with statistically significant results (p < 0.05) for all terms. An increase in magnesium concentration was found to enhance the oxidation rate, implying a higher alloy susceptibility to oxidation. These findings underline the value of the EVD method and regression analysis in alloy property optimization, thus aiding in the design of aluminum alloys with improved oxidation resistance.

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Additive manufacturing (AM) technology depends on the implemented selective laser melting (SLM) process. A good comprehension of its parameters is required to perform an efficient SLM process. Therefore, this study develops a computational fluid dynamic (CFD) model to simulate the SLM process based on a novel approach (particle by particle) and analyze its operating parameters. The model is based on the classical physics laws to formulate the governing equations and solve them in the ANSYS FLUENT software WORKBENCH R19.1. Melting of stainless steel 316L powder particles was considered a case study where laser power, scanning speed, and spot diameter were considered steady parameters. A User Define Function (UDF) is written in C-language to define the heat source and its parameters, and then it is run over the cell face center in every time step. A parametric study was conducted for three of the SLM main parameters; laser power, spot diameter, and scanning speed. The model was verified through the validation process, which confirmed the model's accuracy and reliability. The model outcomes revealed a proportional relationship between the laser power and each melting temperature and liquid mass fraction for a fixed spot diameter and scanning speed. Moreover, a higher energy density is achieved for a smaller laser spot diameter, which yields a higher liquid fraction and melt temperature.

Resumo em Inglês:

The corrosion behavior of Al0.8CrFeCoNiCu0.5Six (x=0, 0.2, 0.3) high-entropy alloy laser cladding coatings in a 3.5% NaCl solution was investigated using polarization tests, impedance spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. As the Si content increased, the over-passivation potential and the width of the passivation zone for the Al0.8CrFeCoNiCu0.5Six coating expanded, while the corrosion current density tended to decrease, enhancing the stability of the passivation film and the corrosion resistance of the coating. The Al0.8CrFeCoNiCu0.5 coating underwent selective corrosion, with some pitting corrosion distribution showing no apparent regularity. The Al0.8CrFeCoNiCu0.5Si0.2 coating exhibited a distinct grain profile with a tendency towards intergranular corrosion. The aggregation of Cu-rich and Al-Ni intergranular phases in the eutectic structure led to preferential erosion at the grain boundaries by corrosion ions in the Al0.8CrFeCoNiCu0.5Si0.2 coating. The Al0.8CrFeCoNiCu0.5Si0.3 coating presented corrosion pits, although their distribution did not display apparent regularity. The Al0.8CrFeCoNiCu0.5Six high-entropy alloy coating demonstrates superior corrosion resistance in solution compared to 5083 aluminum alloy.

Resumo em Inglês:

This study synthesized mixed matrix membranes (MMMs) using PEBAX® MH-1657 and ZIF-67 with varying particle concentrations (1, 3, and 5 wt%) to assess permeability and selectivity. ZIF-67 nanoparticles were prepared using the solvothermal method with methanol and characterized. Permeation tests were conducted at 10 and 15 bar using N2 and CO2. The analysis revealed ZIF-67 particles with an approximate diameter of 280 nm and confirmed characteristic sodalite peaks. The ideal CO2/N2 selectivity reached 67 (CO2 permeability = 132 ± 3.5 Barrer) at 15 bar. The impact of ZIF-67 varied with pressure and composition; at 10 bar, CO2/N2 selectivity decreased compared to pure PEBAX®; however, at 15 bar, the 1 wt% ZIF-67 membrane exhibited superior selectivity, surpassing Robeson's upper bound. The results indicate that ZIF-67 enhances the permeability and selectivity of PEBAX®, with superior performance observed at lower concentrations.

Resumo em Inglês:

Biocomposites have gained attention in the packaging industry due to their potential as sustainable alternatives to conventional synthetic materials. In this study, novel cotton incorporated poly(lactic acid)/thermoplastic starch biocomposites were developed for packaging applications using in short shelf life products the extrusion method. Pelletized samples obtained by extrusion were stamped from plates obtained by compression and were characterized through measurement of density, hardness, contact angle and water absorption, as well as Fourier transform infrared spectroscopy (FTIR), thermal analysis and scanning electron microscopy (SEM). No significant changes in the density results were observed. A slight increase in the hardness of formulations in relation to the PLA was associated with the presence of cotton fiber in biocomposites. The FTIR results revealed physical interaction of PLA, TPS and cotton fiber. By DSC analysis, for all formulations the melting exhibited only one peak, suggesting good homogeneity and interaction among the components, as observed by TG/DTG results, and corroborating SEM analysis. The biocomposite PLA/TPS/Cotton 85/10/5 wt.% displayed greater increase in water absorption than both 95/5/0 and 90/5/5 wt.% formulations, which can be attributed to the increase in starch proportion, confirming the contact angle results. The hydrophilic tendency corroborated the biodegradation process in the packaging end-of-life.

Resumo em Inglês:

A novel, efficient, and cost-effective coating method was developed for fabricating highly conductive cotton yarn loaded with reduced graphene oxide (rGO). This method is straightforward, rapid, scalable, and amenable to solution processing. The key innovation involves pretreating the cotton yarn with chicken egg albumin (CEA) before applying the rGO coating through a simple dip-and-dry process. This method significantly reduces the electrical resistance of the cotton yarn, achieving an optimal specific resistance of 80 Ω.g/cm2 with just five coating cycles. Additionally, the coated samples exhibit exceptional reliability, enduring 104 bending tests and 5 washing tests without compromising conductivity. Notably, the study reveals consistent proportional variations in response to changes in relative humidity, regardless of the initial reference resistance value or yarn characteristics. These stable and conductive rGO-coated cotton yarns (rGOCY) might be seamlessly integrated into textiles and garments, enabling the development of flexible and wearable electronics, as well as sensors.

Resumo em Inglês:

Blending finer powders of Ti, Zr, Ta, Sc, and Nb compounds as inoculants have been a promising strategy to modify precipitation-hardened aluminum alloys for laser-based powder bed fusion, promoting a crack-free equiaxed microstructure. However, there is still a lack of comprehensive understanding of the influence of these fine Al-Nb-B inoculant particles on the AA 2017 powder's physical characteristics and flowability during the process. The results indicate that blended powder has a similar PSD to AA 2017 powder. Furthermore, the circularity, smoothness, and morphology of the particles indicate that both inoculant and AA2017 powders do not exhibit high sphericity, but the blended powder showed slightly more agglomerated particles. Regarding rheological properties, it was observed that a higher flow energy was required to move the blended powder in unconfined conditions compared to the AA 2017 powder. Additionally, the blended powder exhibited higher compressibility and tendency to retain air in packed conditions during the deposition and spreading process. In conclusion, the physical characterization techniques combined with rheological tests have proven to be a rapid and reliable approach for assessing the impact of the finer inoculant particles' characteristics on the laser-based powder bed fusion.

Resumo em Inglês:

The accumulation of tramp impurities, particularly Fe, during recycling of Al alloys frequently leads to the production of coarse intermetallics during solidification, which affect final product mechanical properties. Because lowering the Fe concentration and/or using thermomechanical processing to subdivide the particles is expensive, it is preferred to modify the morphology, size, and distribution of the IMCs during solidification. Benefiting the properties of Al-contaminated alloys entails increased recyclability and a reduction in the usage of virgin primary Al and downcycled alloys. The Al-8%Si-0.8%Fe-2.5%Cu-1.0%Zn (in wt.%) alloy was modified with 0.7%Ni and 0.7%Co. Both dendritic growth and tensile properties were evaluated for the three alloys. The secondary dendrite arm spacing values (λ2) were found very refined for all alloys. The λ2 in the modified alloys was even more reduced. The Co addition of 0.7% reached higher values of tensile strength (220 MPa) as compared to the others without major losses in ductility. The addition of Co can enhance strength by up to 15%, considering more refined microstructures.

Resumo em Inglês:

Austenitic and lean duplex stainless steels, such as AISI 317L and SAF 2304, present high mechanical and corrosion resistance, which make them alternative materials for biodiesel plant equipment. Because there is not sufficient research about these stainless steel-specific applications, this work aims to evaluate AISI 317L and SAF 2304 stainless-steel pitting corrosion resistance in a chloride-containing acidified glycerin solution, collected directly from a biodiesel plant. The SAF 2304 presented a higher pitting potential than the AISI 317L, at room temperature and at service temperature, 337 K. However, the SAF 2304 passive layer was more reactive than the AISI 317L, showing a higher passive current density in the polarization and chronoamperimetric tests. Furthermore, the Mott–Schottky technique showed that the passive layer of the AISI 317L steel contained a lower concentration of defects than the passive layer of the SAF 2304, and the oxides of the passive layers are n-type semiconductors.

Resumo em Inglês:

The surge in deep and ultra-deep water oil exploration in Brazil, particularly in the pre-salt layer, necessitates the advancement of materials and engineering components to meet sectoral challenges. To enhance the longevity and corrosion resistance of pipelines and structures, welded cladding of stainless alloys onto structural steels has been deployed. However, dissimilar welding often leads to the formation of Partially Diluted Zones (PDZ), marked by discontinuous, high-hardness regions at the interface. This study employs Electron Microscopy via Backscattered Electron Diffraction (EBSD) to characterize these zones, addressing limitations in conventional metallographic techniques. By cladding ASTM A36 steel test plates with AWS E 309L (309L stainless steel) through automated MIG welding, metallurgical-mechanical properties were assessed using Field Emission Scanning Electron Microscopy (FEG-SEM), EBSD, SEM-EDS, and Vickers Microhardness. The Heat-Affected Zone (HAZ) displayed low hardness, while the PDZ exhibited varied morphologies with significant concentrations of iron, chromium, and nickel, accompanied by elevated microhardness and a characteristic martensitic microstructure. In comparison between single and double-layer depositions, the latter substantially reduced hardness in the PDZ and HAZ. This study provides critical insights into the microstructural attributes of welded cladding, offering valuable guidance for optimizing materials in deepwater applications.

Resumo em Inglês:

A solution blow spinning (SBS) process was utilized to create nanofibers of TiO2/C and TiO2/C/N with potential applications in photocatalysis and dye adsorption. Polyvinylpyrrolidone was used as a carbon and nitrogen source. Their content in the TiO2 structure decreased as the temperature increased from 350 to 550 °C. Physical-chemical, morphological, and structural features were investigated. Adsorption and photodegradation experiments revealed that the material calcined at 400 °C had higher dye removal (98%) under dark settings, whereas the greater photodegradation efficiency under visible and UV light was 56% and 98%, respectively, for the sample calcined at 550 °C. The results suggest that the SBS has the potential to develop an efficient adsorbent and photocatalyst for use in treatments of contaminated water.

Resumo em Inglês:

This study used an aqueous dispersion of silanized colloidal silica (SCS), whose particles’ surfaces were modified with an epoxysilane-based coupling agent, as the liquid medium and binder for MgO-Al2O3-containing suspensions. Fine calcined alumina and magnesia sinter particles were dispersed in SCS to form a 65 vol% solids suspension. Equivalent silica-free compositions containing calcium aluminate cement or unsilanized colloidal silica were tested as references. After mixing, the SCS-suspension showed low viscosity and suitable workability and, after curing, a thin protective coating of magnesium silicate hydrate (MSH) was formed, thus preventing MgO hydroxylation and improving bonding strength, generating green-dried structures of significant flexural strength (8 MPa). During initial heating, the decomposition of MSH and the softening of amorphous silica particles reduced the overall expansion of spinel (MgAl2O4) formation. After sintering at 1600ºC, the structure showed intense densification (total porosity of 8%) high flexural strength (73 MPa) and large spinel crystals surrounded by a thin layer of amorphous silica and magnesium silicates.

Resumo em Inglês:

This study investigated the impact of adding graphene oxide (GO) and iron oxide (II) (Fe3O4) nanoparticles individually and in combination on the morphology, thermo-mechanical, and dielectric properties of a Polypropylene/High-Density Polyethylene (PP/HDPE) blend. By adding these nanoparticles separately or as a mixture, we can determine if both mechanisms have a synergistic effect and how they impact the dielectric constant values of their nanocomposites. The nanoparticle mixture was prepared in both an alkaline and a neutral medium. The mixture in the alkaline medium contained lower quantities of iron nanoparticles than in the neutral medium, and they were localized on the surface of GO. The nanocomposites showed significant differences in dynamic-mechanical and dielectric properties. The system with Fe3O4 exhibited a higher storage modulus, while the system with GO had a higher dielectric constant. However, no synergistic effect was observed in the nanoparticle mixtures.

Resumo em Inglês:

In this study, nanostructured coatings of VN2/Fe3N/Fe4N are synthesized by Plasma Deposition (CCPD) using a vanadium cathodic cage and subject to cathodic and floating potential treatments. Microstructural and mechanical properties of coated SAE 1080 steel samples are investigated using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vickers microhardness (HV), and surface roughness analysis. The coating produced under cathodic potential treatment exhibited a nitride-based microstructure (VN2, Fe3N, Fe4N), with surface morphology consisting of clusters of granular structures with varied particle sizes. The coating produced under floating potential predominantly exhibited the iron nitride phase (Fe3N) with a morphology composed of uniformly sized grains. Microhardness testing showed that both layers exhibited more excellent plastic deformation resistance than the substrate. Roughness measurements confirmed a more organized microstructure profile for the sample treated under floating potential. This study demonstrates that the CCPD-produced cathodic potential coating can be utilized in tribological applications.

Resumo em Inglês:

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Fifty million people today are affected by this disease globally. AD has had a tremendous impact on the affected individual, caregiver, and society, in both developed and developing nations. Donepezil—chitosan-gold nanocomposite (Donz-CS-AuNPs) was prepared by co-precipitation technique. Placket-Burman experimental design was used in this work to estimate the effect of the three independent variables (concentration of chitosan, gold, and donepezil) on the dependent variables (loading efficiency, and particle size) by using Minitab 18.1 software. The quantities for the independent variables used were: 10 and 40 mg of donepezil, 24.6 and 73.8 mg of gold, and 500 and 1500 mg of chitosan. The Donz-CS-AuNPs were characterized using energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and release study. The results of EDX showed strong signals of Au (1.5–2, 2–2.5 and 9.5–10 keV), which confirmed the specific gold peaks from the Donz-CS-AuNPs. The XRD pattern of Donz-CS-AuNPs nanocomposites showed the existence of AuNPs peak at 2θ= 38.2°, 43.8° and 64.5°. The SEM images demonstrated spherical shapes of the AuNPs. In the in vitro release study, the release increased steeply and reached 75% after 1440 min.

Resumo em Inglês:

A device with a controllable atmosphere has been designed and fabricated to sinter metal particles in the manufacturing processes of metallic components (porous or non-porous parts). The device avoids the employment of an expensive controlled atmosphere furnace (a furnace in which it is possible to produce a vacuum or through which a constant flow of highly pure inert gas is maintained to protect the specimen). Metallic powders of pure metals or alloys with sintering temperatures (Ts) up to 1300°C and different forms and particle sizes can be used. The device consists of two chambers (an upper chamber for the atmosphere control and a lower chamber for the sintering processes) which are coupled by a sealed system composed of an O–ring and a clamp. The device is designed to be utilized with any conventional vertical electrical furnace (a furnace without the possibility of producing a vacuum inside or maintaining a constant flow of inert gas inside) and can be operated in three different ways: i) with a vacuum inside, ii) with a static atmosphere of inert gas inside, and iii) with a dynamic atmosphere of inert gas inside.

Resumo em Inglês:

The aim of this paper was to analyze the passivation of the rear face of silicon solar cells by TiO2 thin films produced by atmospheric pressure chemical vapor deposition (APCVD). A compact high-throughput APCVD system was employed to deposit the TiO2 films. Silicon solar cells with a n+pp+ PERT (passivated emitter rear totally-diffused) structure were produced and characterized. The use of TiO2 on the rear face resulted in a 0.5 mA/cm2 increase in short-circuit current density and a 0.5% absolute improvement in efficiency compared to devices without a passivation layer. Analyzing the internal quantum efficiency of the devices, we concluded that this economically technique provides passivation on the p+ surface, doped with boron, similar to that obtained with thermally grown silicon oxide films.

Resumo em Inglês:

The demand for oil and its derivatives has driven the oil and gas sector to explore deep waters. Nickel-based alloys, like Inconel, are used due to their corrosion resistance properties. Cladding structural steels with these alloys is a cost-effective solution. However, dissimilar metal welding poses challenges, including the formation of Partially Diluted Zones (PDZ). This work highlights the use of Electron Backscatter Diffraction (EBSD) as a very adequate technique for the microstructural characterization of dissimilar anticorrosive materials. The MIG process was utilized to perform cladding of Inconel 625 onto the A36 steel substrate. The samples were prepared for analysis using techniques such as EDS, FEG-SEM, EBSD, and Vickers microhardness testing. The results demonstrate the effectiveness of the EBSD technique in characterizing dissimilar metal cladding. The combination of EBSD with EDS analysis and microhardness testing provided comprehensive insights into the microstructure and mechanical properties of the material. EDS mapping analysis confirmed the formation of PDZ with a distinct beach-like morphology, indicating localized compositional variations. The uniform thickness of the PDZ, approximately 20 µm, highlights the convective motion and solidification behavior of the partially diluted zone. Phase map EBSD analysis revealed different crystal structures in the cladding zone, including a FCC structure for the nickel cladding layer and a BCC structure for the ferritic steel base metal. The PDZ exhibited the same crystal structure as the base metal, indicating chemical element diffusion without altering the ferritic steel structure. Contrast band EBSD analysis provided detailed microstructural information, revealing solidification structures and potential hardness variations. The observed martensite formation in the PDZ highlights its susceptibility to cracking and detachment of the coated layer. The hardness results support the microstructural findings, demonstrating significant variations in hardness across the cladding structure, particularly in the PDZ and at the interface between the Inconel alloy and the base metal. These findings contribute valuable insights into the microstructural and compositional gradients within the joint region, reinforcing their implications for material performance.

Resumo em Inglês:

Electrospinning, an economical technique, is widely used for biomedical scaffold fabrication, crucial in tissue and organ regeneration, particularly with biomaterials. Polymers, either pure or reinforced with ceramics, aid in cell proliferation and tissue formation. Polyhydroxybutyrate (PHB) is a promising biopolymer for tissue engineering, offering biocompatibility comparable to petroleum-derived polymers. Combining PHB with hydroxyapatite (HAp) enhances mechanical strength and osteoconductivity. This study aims to produce electrospun PHB microfibrous webs reinforced with HAp for scaffold fabrication. Morphological variations are analyzed through manipulation of electrospinning parameters. The study observed microfibrous webs with diameters ranging from 2 to 9 µm. Mechanical and microstructural evaluations demonstrate superior strength of PHB/HAp microfibrous webs compared to pure PHB, 1.23 MPa and 0.58 MPa respectively, demonstrating the efficacy of HAp reinforcement. These findings highlight the potential of PHB/HAp microfibrous webs in bone tissue engineering.

Resumo em Inglês:

Magnesium stannate (Mg2SnO4) samples with 0.003, 0.004, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.5, 1, 2, and 5 at. mol% of Co2+ were prepared by wet chemical method. The samples were investigated using X-Ray diffraction and photoluminescence techniques at room temperature. The results indicate that Co2+ occupies tetrahedral sites in the inverse spinel structure of Mg2SnO4, replacing Mg2+. The material exhibited a red-infrared luminescence associated with Co2+ spin-allowed transitions. Crystal field parameters were calculated using Tanabe-Sugano theory for d7 systems in tetrahedral environment. In the range studied, optimum divalent cobalt concentration for emission applications was found to be 0.08 at. mol%.