Resumo em Inglês:

Abstract The use of polymer blends and composites based on fossil-based and bio-based polymers has become an important environmentally protective alternative for common use and disposable plastics applications such as packaging, bottles and trays. The disposal of these more degradable products, however, may also harm the environment and, therefore, recycling these systems becomes relevant. Recycling involves reprocessing which can significantly change the morphology and properties of polymeric products. Therefore, this study deals with the effects of reprocessing cycles on the properties and morphology of blends and nanocomposites based on fossil and bio-based polymers. The systems investigated were: a) neat polypropylene (PP), b) a polypropylene/poly(3-hydroxybutyrate) (PP/PHB) blend and c) PP/PHB/organoclay nanocomposite compatibilized with polypropylene-g-maleic anhydride (PP-g-MA) and erucamide. These materials were submitted to up to seven extrusion cycles in a single screw extruder operating at 60 rpm. Samples were taken after the first, third, fifth and seventh extrusion cycles and their tensile properties and morphology were determined. Scanning electron microscopy indicated that two phases were observed in the blend which showed spherical PHB domains. The addition of clay, PP-g-MA and erucamide improved the adhesion between the nanocomposites components. X-ray diffraction analysis showed that crystallinity tended to increase with the number of reprocessing cycles for all systems investigated up to the fifth cycle and then tended to decrease. A 10% crystallinity increase was observed for neat PP in the fifth cycle. In general, the tensile properties of all systems decreased with reprocessing and the highest losses were observed for the PP/PHB blend after seven processing cycles with 50% and 37% decreases in stress at break and elastic modulus, respectively. Impact strength of the PP matrix and of the PP/PHB blend tended to decrease with reprocessing, except for the nanocomposite which showed a slight increase especially after the seventh processing cycle in which an 18% increase in impact strength was observed.

Resumo em Inglês:

Abstract The properties of aluminum alloys can be improved by the processing conditions that cause changes in the microstructure and by the addition of alloy elements. In order to understand the physical behavior and mechanical properties of aluminum alloys, it is important to be aware of some of the microstructural characteristics. Some of these characteristics are the morphology, alloy elements, volume and size, and second phase. In this study, we analyzed the effect of annealing on the mechanical and microstructural properties of the laminated AA 5182 aluminum alloy, when subjected to different annealing conditions. The alloy was heated to temperatures of 50º C, 100º C, 150º C, 200º C, 250º C and 300º C for 10 minutes and left to cool naturally. The evolution of the microstructure was characterized by optical and electronic microscopy with EDS, and, to obtain the mechanical properties, a tensile test was performed and the fractures were subsequently analyzed. The results showed that the heat treatment used reduced the amount of second phase particles and this influenced the mechanical properties.

Resumo em Inglês:

Tolyltriazole (TTA) is a well-defined corrosion inhibitor for copper and copper alloys. However, there is little literature about its corrosion inhibition performance for mild steels in corrosive environments. This paper studied the electrochemical behavior of TTA in 0.5 M HCl solutions. Also, the morphology and nature of TTA layers on the steel surface were investigated. Electrochemical results showed that TTA is an excellent corrosion inhibitor for mild steel in acidic media with an efficiency of 91% for 0.07 M concentration. The results also indicated that TTA is a mixed-type inhibitor. XRD analysis revealed that the inhibition mechanism of TTA is based on the formation of an organic film due to the physically adsorbed molecules of TTA. AFM and EDS results showed that the formed layers decrease the adsorptivity of corrosive elements (Cl-) on the steel surface. Density Functional Theory (DFT) study confirmed the experimental results.

Resumo em Inglês:

InSe based heterojunction devices gain importance in optoelectronic applications in NIR range as multipurpose sensors. For this reason, InSe/Sb2Te3 heterojunctions are constructed as NIR sensors by the thermal evaporation technique. The structural, optical, dielectric and photoelectric properties of InSe/Sb2Te3 heterojunctions are explored by X-ray diffraction and ultraviolet-visible light spectrophotometry techniques. The structural analyses revealed the preferred growth of polycrystalline hexagonal Sb2Te3 onto amorphous InSe as a major phase. Optically, the coating of Sb2Te3 onto InSe enhanced the light absorbability of InSe by more than 18 times, redshifts the energy band gap, increased the dielectric constant by ~5 times and increased the optical conductivity by 35 times in the NIR range of light. A conduction and valance band offsets of 0.40 and 0.68 eV are determined for the InSe/Sb2Te3 heterojunction devices. In addition, the Drude-Lorentz fittings of the optical conductivity indicated a remarkable increase in the plasmon frequency values upon depositing of Sb2Te3 onto InSe. The illumination intensity and time dependent photocurrent measurements resulted in an enhancement in the photocurrent values by one order of magnitude. The response time of the devices is sufficiently short to nominate the InSe/Sb2Te3 heterojunction devices as fast responding NIR sensors suitable for optoelectronic applications.

Resumo em Inglês:

NiAl composite coating strengthened by ZrC and ZrB2 phases is synthesized by the plasma cladding process. The influence of cladding speed on microstructrue and properties of coatings is studied. The main phases of coatings are NiAl, γ-(Fe,Ni), ZrC and ZrB2 phases. ZrC is in the shape of points and small blocks, ZrB2 shows long strips and needle bar. The slower the cladding speed, the larger the size of the reinforcing phases. With the increase of cladding speed, the wear resistance of the coatings improves. Coating with the cladding speed of 10mm/s has excellent wear-resistance property owing to high hardness and low friction coefficient. ZrC and ZrB2 strengthening phases play an important role. The main wear mechanism of NiAl composite coating is adhesive wear.

Resumo em Inglês:

Critical pitting temperature (CPT) is one of the most accepted criteria for alloy classification concerning pitting corrosion. The techniques used nowadays to determine CPT have different parameters for alloys of different material classes, preventing the comparison between stainless steels and nickel based alloys. This study aims to compare the corrosion resistance of nickel based alloys and stainless steels with high corrosion resistance through potentiostatic tests for CPT determination, using a 3M MgCl2 aqueous solution. CPT values were effectively determined for the stainless steels studied but the technique did not have the same efficiency for nickel based alloys due to the occurrence of crevice corrosion, even considering the higher PRE of nickel based alloys.

Resumo em Inglês:

This research work investigates a new type of polymer-based magnetocaloric composite. Using PMMA as polymeric matrix and the magnetocaloric material Gd5.09Ge2.03Si1.88 as reinforcement,no influence of the presence of polymer on the magnetic properties of Gd5.09Ge2.03Si1.88 were observed. Three types of composites with different PMMA content were fabricated by mixing the components and curing the composite. The composites were evaluated by their mechanical, physicochemical and morphological properties.The proposed PMMA composite MC10 presented the smallest elastic modulus but highest Vickers hardness (6.61 ± 0.08 GPa and 22.10 ± 1.29 HV, respectively). The composites showed asatisfactorymagnetocaloriceffect (MCE)“peak” of -7 J/kgK. With the results, this composite can be a potential candidate for applications as Active Magnetic Regenerator in magnetic heat pumps.

Resumo em Inglês:

The Fano resonance and EIR properties in different topological one-dimensional superconductor photonic crystals has been investigated theoretically using the Transfer Matrix Method (TMM). Different types of periodic heterostructures are studied and they are designed by alternating pairs of superconductor materials such (Nb/BSCCO), (Rb3C60/ YBa2Cu3O7) and (K3C60/(BiPb)2Sr2Ca2Cu3Oy). All artificial periodic structures are sacked by dielectric cap layer at different induced fields. To exam the efficiency of the reported structures, different parameters are used for analysis such as layers thicknesses, temperature, angle of incidence, the kind of superconductor materials and the dielectric constant of the cap layer. The investigation results exhibit the presence of tunable Fano resonances and EIR resonance peak accompanied by asymmetrical line shape and they are very sensitive to the dielectric cap layer, the superconductor materials and the wave incidence angle.

Resumo em Inglês:

Abstract This work investigates the mechanical behaviour of a sustainable sandwich panel, consisting of bamboo rings core, treated aluminium skins and epoxy adhesive. A Design of Experiment (DoE) is used to identify the effects of bamboo diameters (30 and 45 mm) and aluminium skin treatments (alkaline degreasing and application of primer) on the mechanical and physical properties of sandwich panels. The aluminium skins treated with the wash primer significantly increase adhesion to the polymer, resulting in greater maximum load, flexural strength, maximum skin stress and maximum core shear stress; while the skins treated with NaOH resulted in a greater flexural and core shear modulus. Relatively more rigid and resistant structures are obtained with Ø30 mm rings, due to the increased surface contact area and the number of constraints on the core. The samples fail due to the skin fracture, implying an efficient face-core bond that is attributed to the proper absorption of the polymer by bamboo and the treatment of the aluminium surface. The proposed panels present good mechanical performance, proving to be a feasible and promising alternative for secondary structural applications.

Resumo em Inglês:

Abstract Wear resistance is a fundamental property which defines the lifetime of cutting tools, but the investigation of wear performance of alternative hard materials for traditional WC-Co composites are recent. The present work evaluated the pin-on-disk wear behavior and mechanical properties, i.e., hardness and fracture toughness of spark plasma sintered Al2O3 matrix composites with additions of 5, 15, 25 or 30%wt of niobium carbide NbC. The wear resistance was observed to increase as a function of the NbC content, even though the hardness reached a plateau at 25%wt NbC. The composite behavior was compared to that of other alumina composite tool materials proving to be a promising material for applications such as ceramic cutting tools. The composition A95N5 presented the best combination of values of wear rate: 8.9 mm3/N.m, hardness equal to (17.36±1.72) GPa and fracture toughness of (3.2±0.6) MPa. m1/2.

Resumo em Inglês:

This paper presents the study of the addition of the polyaniline polymer (PANI), at the junction of the cadmium telluride and cadmium sulfide (CdTe/CdS) layers in order to improve the contact between the layers, to decrease the air gap that limit the conversion photovoltaic. The morphology of CdS, CdTe and polyaniline (PANI) were characterized with multiple techniques including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and optical absorption. The Metrohm Autolab LED Driver Kit system was used for data collection, and it was possible to obtain the current and voltage parameters of the cells. The inclusion of PANI thin film in CdS/CdTe hybrid solar cells increases the energy conversion efficiency from 0.0075% to 0.15%, this gives a 20-fold increase in efficiency.

Resumo em Inglês:

Grain refinement in Al-Si alloys improves their mechanical properties. Research available in the literature shows the search for refinement efficiency through heterogeneous nucleation of the grain, involving the stoichiometric ratio between the alloy elements, the inoculant, and process parameters. In these surveys, there are divergences of information. However, this study does not aim to contradict this information but present an investigation made with the Al-4Nb-0.5B master alloy, where Nb >> B, used via sticks, with variations from 0 to 1 Wt.% of Nb and B according to a stoichiometric calculation added to the alloys cast with Al (7, 9, 12) Wt.% of Si and 1 Wt.% of Fe. The study also enabled an investigation into the morphology behavior of the β-Fe precipitates arising from Fe-critic in the alloy. Samples cast according to the TP1-2012 mold standard. The alloy microstructure analyzed was by energy-dispersive X-ray spectroscopy. The small addition of Nb-B can efficiently and significantly refine the size of the primary α-Al grain and has caused changes in the morphology of Fe-rich intermetallic, which became very refined spheroidised, suggesting an improvement in the mechanical properties of the material.

Resumo em Inglês:

In this study, tubular ceramic membranes were prepared from a mixture of ball clay, talc and alumina. The mixture was characterized by the following techniques: particle size analysis, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and thermal analysis. Tubular membranes were produced by extrusion process and thermal treated at temperatures between 1025 °C and 1175 °C. The membranes were characterized by XRD, linear shrinkage, apparent porosity, flexural strength, mercury porosimetry, scanning electron microscope (SEM) and contact angle. To evaluate the efficiency of the membranes, permeability tests with distilled water and oil-in-water emulsion were conducted in a tangential flow system. The results showed that the sintering of the specimens promoted the formation of α-cordierite phase and directly influenced the physical and mechanical properties such as linear shrinkage, porosity and flexural strength. Separation tests revealed that these membranes promoted high oil-water separation efficiency with values above 99.0%.

Resumo em Inglês:

In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma nitrided with a nitrogen rich gas composition was investigated. To evaluate the influence of processing time and temperature on mechanical and microstructural characteristics of nitrided layer, the samples were nitrided at 400, 450, 500 and 550 °C for 3, 6 and 9 h. The produced nitrided layers were characterized concerning the microstructure, phase composition, microhardness and surface roughness. The samples were tested by ball-on-flat reciprocating dry sliding for friction coefficient and wear analysis. The tests were stopped after a given damage criteria involving the rapid growth of the friction coefficients and wear. The correlation of the different treatment parameters and resulting case depths and surface hardness with sliding distance at the time of microcracks formation or delamination of the surface layer was evaluated statistically by the analysis of variance (ANOVA). The plasma nitrided samples at 550 °C showed better wear performances in the ball-on-flat tests than the other groups investigated, since these samples have a thicker compound layer and diffusion zone higher than the other conditions investigated. In general, the beginning wear is slower because of the hardest region of the compound layer.

Resumo em Inglês:

Abstract In this work, we presented the synthesis and characterization of poly-melamine-formaldehyde-silica (PMF‑Si) composite from poly-melamine-formaldehyde (PMF) and previously purified commercial sodium silicate used as a precursor of silica nanoparticles (Si‑NPs). The materials were characterized by several physicochemical techniques such as XRD, FTIR, SEM, TEM, AFM, TGA, and DTG analysis to access their properties. We also studied hydrogel dehydration, rehydration, the potential of zero charge (PZC), and the adsorption capacity of the dye methylene blue (MB) in the hydrogel. From XRD analysis, PMF and PMF‑Si materials presented amorphous profiles. AFM, SEM, and TEM images revealed a fibrous PMF structure and homogeneous dispersion of Si-NPs through the PMF-Si composite. The Si‑NPs exhibited an average diameter between 10 to 15 nm. The first PMF-Si hydration reached 93% after synthesis, and complete rehydration is possible up to 70% of dehydration. PMF-Si has the PZC at pH = 1.22 and, at superior values of pH, the composite exhibits superior adsorption rates of MB. The adsorption tests performed to remove MB dye using PMF-Si hydrogel showed a qmax of 140 mg/g, which is superior to other materials routinely used for MB dye removal.

Resumo em Inglês:

In this paper, NiMoO4 powder was synthesized by the complexation method combining EDTA-Citrate. The behavior of the NiMoO4 material in the ethyl transesterification reaction was evaluated by analyzing the acidity index under specified reaction conditions. The results showed that NiMoO4 crystallized at 800 °C with a total mass loss of 85%, presenting a monoclinic structure, free of secondary phases, high degree of crystallinity and average crystallite size of 140 nm. The particles had heterogeneous sizes and shapes, but with well-defined contours. The increase in the mass of NiMoO4 in the reaction medium reduced the acidity index (0.8 mgKOH.g-1 with 15 wt.%). Despite the use of the minimum molar ratio (1:3), the ethyl route being less reactive and the use of the operating temperature close to the alcohol evaporation temperature, NiMoO4 showed promising catalytic potential in the transesterification process.

Resumo em Inglês:

Abstract We have obtained kefir biofilms loaded with Maytenus rigida extract. The main goal was to evaluate the influence of the addition of the extract on the biofilms microtexture using stereometric and fractal parameters. Atomic force microscopy, Fourier transform infrared spectroscopy, and contact angle tecniques were used to evaluate the topography, chemical interation and wettability of the biofilms. Chemical evaluation showed that the extract interacts with the polymeric matrix of the biofilms, changing their structure. This behavior affected the surface energy because the wettability decreased when the Maytenus content increased. The surface morphology was also affected and suggested the prevalence of bacteria and yeast at lower and higher extract concentrations, respectively. The surface roughness increased according to the increase in the extract concentration. Texture parameters revealed that the biofilm with lowest concentration had deeper furrows than for higher concentration. Advanced fractal parameters revealed that topographic uniformity, percolation and texture homogeneity were more suitable for the biofilm with 0.25 g.L-1 of extract. These results indicate that this biofilm have promising 3D micromorphology for regenerative medicine application. Furthermore, the physics tools used revealed to be very useful for characterizing of the microtexture of polymeric-based biological materials.

Resumo em Inglês:

Abstract The addition of pozzolans has a potentially important role in the cement industry since using waste from other industries has important environmental benefits, including reduced CO2 emissions from cement production. This study evaluates the pozzolanic activity of the glass powder in three different particle sizes (150 µm, 75 µm, and 45 µm, upper limits) and compares the results with those of other added pozzolans and technical standards found in the literature. Pozzolanicity was determined by four methods: Pozzolanic Activity Index (PAI) with lime, Performance Index (PI) with Portland cement, electric conductivity, and modified Chapelle. The results of the Chapelle and electrical conductivity trials indicated the pozzolanic activity of glass powder in all three particle sizes studied. The results of PAI with lime revealed pozzolanic activity of the 45 µm fraction while the performance index with cement showed the pozzolanicity of the 75 µm and 45 µm fractions according to ASTM C 618-05 (2005). It is concluded that the smallest glass fractions provided better reaction rates due to larger contact surfaces and are, therefore, considered pozzolans.

Resumo em Inglês:

Abstract Pure ZA27 alloys and ZA27 alloys with Cu and Mg additions were cast and deformed by compression. Samples of both alloys were heat treated at 460°C after deformation and the evolution of the microstructure as a function of time measured. The results showed that the average grain size increases with the increase of time for both alloys, with a coarsening rate which is 55% lower for the alloyed ZA27 alloy than the rate of the pure ZA27 alloy. X-ray diffraction analysis indicated that the ZA27 alloys containing Cu and Mg additions present the ε phase which is not present in the non-alloyed ZA27 alloy; and that the α and η phases transform to the β phase during heat treatment. Microhardness measurements showed that the ZA27 alloy with Cu and Mg additions has higher microhardness than the pure ZA27 alloy.

Resumo em Inglês:

Abstract The aim of this work was to analyze the properties and shear bond strength (SBS) of lithium disilicate to resin cement before and after etching the glass-ceramic surfaces. Lithium-metasilicate samples were heat treated and characterized by Scanning Electron Microscopy, X-ray diffraction and roughness measurement. For the analysis of the shear bonding strength (SBS) of lithium disilicate to dental resin cement, three groups (n = 12) of Li2Si2O5 were prepared: 1°)without treatment (NT); 2°)surface etching with hydrofluoric acid(HF), followed by silane agent and adhesive treatment; 3°) surface treatment with a self-etching ceramic primer (SECP). After the heat-treatment, the samples had Li2Si2O5 crystalline phase dispersed in a residual amorphous phase. Roughness of the NT and SECP samples was smaller that of the HF samples. Samples without surface treatment (NT) had the lowest SBS (5.5MPa). HF(24.2MPa) and SECP(24.8MPa) samples has similar SBS. Weibull statistics showed that HF-samples are more reliable than NT and SECP. The SBS was significantly increased by either HF etching and SECP surface treatment. While the chemical characteristics of the surface submitted to SECP treatment are considered to be responsible for the SBS increase, the main adhesion mechanism after HF etching is the increase in surface roughness.

Resumo em Inglês:

Composites of biodegradable polymers/bioactive glasses (BG) are of particular interest in bone repair, where ceramic phase can improve osteogenic features. This work reports the development of organic–inorganic beads based on alginate prepared by incorporating at polymer suspension different contents (25, 50 and 75 wt% with respect to alginate) of BG present at precursor solution, whose system (SiO2–CaO–P2O5) was obtained by hydrolysis of both tetraethoxysilane (TEOS) and triethylphosphate (TEP) alkoxides, molar ratio TEOS:TEP of 1:0.1317, and which calcium source came from the same cold CaCl2 solution used to gelling the hybrids. Beads were synthesized by extruding mixtures, drop by drop, in CaCl2 solution. Were also investigated the behavior resulting upon soaking of hybrids into SBF. Samples were characterized by SEM, ATR-FTIR, TGA and XRD analysis. Results indicated decrease in spheres size with increase of glass and presence even pos-immersion, of Si, Ca and P associated to BG phase.

Resumo em Inglês:

Chromium nitrides CrXN have attracted research interest due to their excellent wear and corrosion properties when are deposited on steels. Nevertheless, due to the considerable difference between CrXN and steel expansion coefficients, microcracks and delamination are still persistent problems. In this regard, this research addressed the generation of CrNX nanolayers, through an ion nitriding process, carried out on hard chromium coated AISI 1045 steel. The effect of nitriding temperature (500°C-550°C) and nitrogen content in plasma (25, 50, and 75%) on corrosion performance and layer characteristics were studied. Grazing Incidence X-ray Diffraction analysis revealed that modified surfaces are composed of nanolayers, constituted by a mixture of CrN, Cr2N, Cr, and Fe4N. Rietveld quantification shows that the fraction of chromium nitrides in the region analyzed increased with increasing both temperature and nitrogen content in plasma, resulting CrN as the predominant phase for all evaluated conditions. The electrochemical behavior of the modified nanolayers was studied by potentiodynamic polarization technique, revealing an enhancement in corrosion performance of chromium coated 1045 steel by the nitriding treatment, showing a corrosion current density 10 times lower than the untreated sample and more positive corrosion potentials for the nitrided samples concerning chromium coated 1045 steel.

Resumo em Inglês:

Abstract Plasma nitriding is a plasma-activated thermochemical method widely used to increase the fatigue strength, hardness and wear resistance of low-alloy steels. In this work, a new structure consisting of a hollow cathode metal plate can produce a hollow cathode discharge and heat the workpiece by radiation. This principle is used to perform hollow cathode source plasma nitriding (HCSPN). Herein, 42CrMo steels were treated by conventional plasma nitriding (CPN) and HCSPN treatments. The 42CrMo steels were nitrided at 525 °C for 6 h in NH3 atmosphere. The mechanical and dry wear properties were measured by nano-indentation, Vickers micro-indentation and ball-on-disk tribometer, respectively. The H3/E⁎2 ratio was 0.0274 GPa (H=11.51 GPa and E⁎=235.84 GPa) for the CPN sample and 0.0276 GPa (H=10.87 GPa and E⁎=215.54 GPa) for the HCSPN sample. Compared with the untreated 42CrMn steel, all the nitrided samples possess increased fracture toughness. Because the workpiece was not used as a discharge cathode, this HCSPN treatment overcame the disadvantages of the conventional CPN treatment. Additionally, results showed that the surface of the HCSPN sample was smoother than that of the CPN sample, and its tribological performance was better.

Resumo em Inglês:

Abstract This work established the fracture probability equation for JIS SM490A steel using the computational model supported by the local approach and the standard Crack Tip Opening Displacement (CTOD) fracture toughness experiments. As the experiments were conducted at a low temperature providing conditions for the brittle fracture, the specimen suffers a small plastic deformation until its failure. The computational model tries to represent the experiment results, estimating the scale and shape parameters of the Weibull distribution for the cumulative fracture probability equation. A procedure based on the local approach was executed to find the optimum values for the fracture probability equation. In addition, a plot was provided to show the distribution of likelihood values according to assumed values for the shape and scale parameters. In the end, a comparison between the experimental and predicted statistical distribution of critical CTOD was done successfully, indicating that material toughness can be predicted by the present model.

Resumo em Inglês:

Abstract Ni-W-P ternary coating was successfully deposited on AZ91D magnesium alloy by electroless plating with low energy consumption. The effect of Na2WO4 concentration on the microstructure, deposition rate, corrosion behavior, adhesion force, porosity test and micro-hardness of Ni-W-P ternary coatings were evaluated. Results reveal that when the concentration of Na2WO4 is 15 g/L in the plating solution, the coating with the average thickness of 17 μm is uniform and dense, and the content of phosphorus and tungsten reached 9.63 wt.% and 1.14 wt.% respectively, which presents amorphous structure. Meanwhile, when the concentration of Na2WO4 is 15 g/L, the amorphous Ni-W-P ternary coating has the best corrosion resistance, among which Ecorr is -0.326 V, Icorr is 0.003 A/cm2 in 3.5 wt.% NaCl solution. In addition, the mechanisms of corrosion resistance for the substrate and the coating were exploded.

Resumo em Inglês:

Abstract Optical thermometry is a growing technological field which exploits the ability of certain materials to change their optical properties with temperature. In this work, poly(glycerol dendrimer) microspheres (PGLyD) encapsulating cobalt-doped hopeite (CoHo) was synthesized for its potential use as optical thermometer. The structure of the CoHo:PGLyD was studied using scanning electron microscopy (SEM), infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). On the basis of SEM images, the CoHo:PGLyD exhibited a spherical shape in which around 80% of the microspheres were within 0.82 µm. A multilayer feed-forward artificial neural network (MLP-ANN) was used to extract the chromaticity profile dependence of the CoHo:PGLyD with temperature. A color change was observed for the CoHo:PGLyD, going from dark blue (490-550 nm) to pale pink (650 nm) when the temperature changed from 20-200 °C, respectively. These results suggest that CoHo:PGLyD is a promising material for temperature sensing applications.

Resumo em Inglês:

Abstract This study aimed to analyze the wettability characteristics applied to the surface of heat-treated pure titanium grade 2. Titanium is widely used for applications in implants produced by incremental sheet forming (ISF), where the 3D model resulting from tomography was used to produce the part. Since the ISF process creates residual stresses in the sheet, heat treatments were applied to relieve them. Also analyzed were roughness, researching what the literature recommends to enable surface wettability. Tests were conducted to assess geometric discrepancy using 3D scanning. The results obtained prove the efficacy of the experiment in assessing wettability as a characteristic of bioactivity, which is necessary for applications involving the human body. In addition, geometric discrepancy analysis enables the prosthesis to be used with the best esthetic and functional comfort possible.

Resumo em Inglês:

Abstract In this work, the residual stress study by XRD was carried out after martensitic transformation of a 304L steel subjected to plastic strain by rolling and tensile test, at room and cryogenic temperatures. This article intents to contribute with the understanding of residual stresses generated by martensitic transformation induced by plastic deformation due to its complexity. From the experimental conditions employed, it was possible to obtain high martensite volumetric fraction and it was possible to observe the influence of existing phases on the performance of residual stress measurements. In general, compressive residual stress was observed for both austenite and martensite phases. The samples rolled at cryogenic temperature showed higher magnitudes of compressive stresses, between -123 and -231 MPa, for martensite volumes between 98 and 100%. It was also clearly displacement and widening of diffraction line due to the presence of residual macro and microstresses when compared to the as-received material.

Resumo em Inglês:

Abstract Carbon-black nanoparticles (CBN) have been incorporated into cement-based materials for improvement of mechanical or self-sensing properties. There is no previous research focused on the microstructural evaluation of effects of CBN on both parameters. In this work, mortars containing different CBN contents were produced, cured for 28 days, and subjected to electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Tests for determination of compressive strength, modulus of elasticity and piezoresistivity response were developed. SEM indicated that lower CBN contents refined the cementitious matrix, while higher contents increased the volume of voids. XRD and Raman spectroscopy indicated hydration improvements for CBN contents between 0.375% and 3%. The best mechanical improvements were provided by concentrations of CBN up to 3%. CBN contents of 5% and 6% provided the best sensing properties. The optimal concentration was found to be 5% of CBN, since it provided excellent piezoresistivity, without significant mechanical properties loss.