Resumo em Inglês:

The automotive industry is constantly under several challenges in many aspects, such as development of new materials and improvement their manufacturability. In order to achieve light weight, reduced emissions and ensure conductor safety, advanced high strength steels (AHSS) are able to fulfill these requirements. Dual phase steels (DP) are well suited for light weighing car body constructions. The gas tungsten arc welding (GTAW) process is focused in literature as an alternative choice for joining AHSS steels; this study is held to disclose the exhibited microstructural constituents. In addition, quantitative determinations of the volume % of phases in the various weld regions were made. The relative amounts of lower bainite (LB), upper bainite (UB), and polygonal ferrite (PF) in the heat affected zone (HAZ) were determined by image analysis from optical microscopy (OM) and scanning electron microscopy (SEM). It was found that GTAW promoted the development of significant amounts of LB in the HAZ (50.89 %). In contrast atomic force microscopy (AFM) leads to quantify the different phases by the morphology, height and roughness, it was found that martensite (M) dropped down to 7.5% in the intercritical zone (IZ) although PF increases to 92.5% compared with the base metal (BM).

Resumo em Inglês:

In this work reports results related to growth and characterization of AlxGa1-xAs epilayers, which were grown in a metallic-arsenic-based-MOCVD system. The gallium and aluminium used precursors were trimethylgallium (TMGa) and trimethylaluminium (TMAl), respectively. By photoluminescence measurements observed, that only samples grown at temperatures above 800°C display photoluminescence. Hall measurements on the samples showed highly compensated material. Samples grown at temperatures lower than 750°C were highly resistive. Independently of the V/III ratio; the samples grown at higher temperatures were n-type. As the temperature is increased the layer compensation decreases. The AlxGa1-xAs epilayers resulted n-type with an electron concentration of 1×1017 cm-3 and a corresponding carrier mobility of ~2200 cm2/V×s. Raman spectra show vibrational bands associated to TO-GaAs-like (262 cm−1), LO-GaAs-like (275 cm-1), TO-AlAs-like (369 cm-1) and LO-AlAs-like (377 cm-1). The Raman spectra show the epilayers become more defective as the growth temperature is increased. The chemical composition was studied by SIMS exhibit the presence of silicon, carbon and oxygen as main residual impurities. The silicon concentration of ~1.0×1017 cm-3 is very close to the carrier concentration determined by the van der Pauw measurements. The residual oxygen detected on the samples maybe responsible of the weak photoluminescence signal of the AlxGa1-xAs layers.

Resumo em Inglês:

In this work, API X-65 pipeline steel non-conventionally heat treated, to enhance its mechanical resistance, was welded using the Metal Inert Gas (MIG) process with and without the application of low intensity axial magnetic fields (6 mT). Microstructural and mechanical characterization of the welds revealed that the use of the magnetic field during welding improved the toughness of the welds and therefore increased their mechanical strength. Failure of the welds occurred far from the weld beads. The electromagnetic stirring of the weld pool significantly reduced the levels of porosity in the weld beads and favored columnar grain growth due to the ferromagnetic nature of the base metal and filler wire. Impact toughness was also improved from 120 to 266 J. Hardness values measured across the welds indicate that the use of the magnetic field during welding yields welds suitable for withstanding sulphide stress cracking.

Resumo em Inglês:

This work presents the characterization of ZnTe nanolayers grown on GaAs and GaSb (100) substrates by the Atomic Layer Deposition (ALD) regime. Under certain conditions, the alternating exposition of a substrate surface to the element vapours makes possible the growth of atomic layers in a reactor where the atmosphere is high-purity hydrogen. ZnTe was grown simultaneously on GaAs and GaSb at the same run, allowing, a comparison between the effects produced by the superficial processes due to the different used substrates, thereby eliminating possible unintended changes of growth parameters. Nanolayers on GaSb maintained their shiny appearance even at temperatures near 420°C. It was found that for exposure times below 2.5 s there was not growth on GaAs, while for GaSb the shortest time was 1.5 s at 385°C. By HRXRD the peak corresponding to (004) diffraction plane of ZnTe was identified and investigated, the FWHM resulted very wide (600-800 arcsec) indicating a highly distorted lattice mainly due to mosaicity. Raman scattering shows the peak corresponding to LO-ZnTe, which is weak and slightly shifted in comparison with the reported for the bulk ZnTe at 210 cm-1. Additionally, the measurements suggest that the crystalline quality have a dependence with the growth temperature.

Resumo em Inglês:

Samples of clays from Actopan, Hidalgo employed in brick manufacturing are physical, chemical and mineralogical characterized. Transmitted polarized light microscopy showed a uniform particle size with grain morphology characteristic of euhedral crystals with quartz, feldspars, nontronite, and iron oxides particles. Scanning Electron Microscopy revealed 75 µm to 90 µm wide subhedral structures formed by particles from 2.0 µm to 5.0 µm; and rombohedrales forms 40 µm wide, 70 µm long, constituted of silicon, aluminum, iron, titanium, calcium, minor amounts of potassium, magnesium, and sodium. Minerals such as quartz, albite, cristobalite, calcium and Hematite phases were recognized by X-Ray Diffraction technique. Chemical analysis by atomic emission spectrometry with Inductively Coupled Plasma confirmed this mineralogy composition while laser granulometry method found the same particle size. Grain size analysis determined submicrometric dimensions, and multimodal type curves, that can be interpreted as the mixing of two or more different mineral phases in each sample.

Resumo em Inglês:

Bimetallic nanoparticles are of special interest for their potential applications for fuel cells, mainly for portable power applications. Among the bimetallic systems, Pt-Pd bimetallic nanoparticles have received great interest as they can be widely used as effective catalysts for various electrochemical reactions. In this work, Pt-Pd alloy bimetallic nanoparticles were synthesized through a chemical reduction method. The nanoparticles were characterized using aberration-corrected scanning/transmission electron microscopy (STEM). Also, parallel beam X-Ray diffraction analysis was carried out to evaluate the crystallographic structure. High-angle annular dark field (HAADF)-STEM images of the Pt-Pd bimetallic nanoparticles were obtained. The contrast of the images shows that the nanoparticles have an alloy structure with an average size of 7.15 nm. To understand the properties of the bimetallic nanoparticles, it is necessary to know the distribution of the elements in the nanostructure. We have used a semi-quantitative method to analyze the HAADF-STEM images, which allowed us to measure the total intensity of the scattered electrons for each atomic column. HAADF-STEM images of the Pt-Pd bimetallic nanoparticles were compared directly with image simulations, good agreement between simulation and experimental images was found. Cyclic voltammetry studies were carried out to analyze the electrochemical behavior of the bimetallic nanoparticles.

Resumo em Inglês:

In the last years, electrochemical noise (EN) has demonstrate that is capable of detect the initiation of cracks during the slow strain rate tests (SSRT). In this research, EN has been used as a tool to detect stress corrosion cracking (SCC) in low carbon steel (X52) exposed to a synthetic soil solution called NS4 at room temperature with pH of 5, 8 and 10. The electrochemical potential and current noise were measured simultaneously during SSRT. Relation between EN and SCC process was analyzed. EN readings of current consisted of transients with high intensity and frequency during all SSRT tests. EN readings of potential at the maximum strength (UTS) and before fracture, increase intensity and amplitude of the transients, attributed to beginning of cracking. Localized index (LI) values indicate a mix corrosion type (general and localized corrosion) during SSRT tests. According to SCC index obtained from mechanical properties, it is clear that X52 steel has low SCC susceptibility. Scanning electron microscopy (SEM) observations were carried out in the fracture surface and longitudinal sections. The specimens tested in NS4 solution with pH 5 were the most likely to present SCC, additionally in this condition a brittle fracture with transgranular appearance was observed.

Resumo em Inglês:

The effect of six different types of activated carbons has been studied in view of their applicability as functional fillers upon the dielectric and microwave properties of natural rubber based composites. It is found that the textural characteristics of the studied active carbons exert influence both on the real part of dielectric permittivity and dielectric loss angle tangent, as well as on the microwave properties of the studied composites. The composite containing activated carbon on the basis of wooden material possesses the highest value of the total shielding effectiveness in comparison with the composites, containing another activated carbons. It has the lowest values of specific surface area, area and volume of micropores and the highest values of external surface area, volume of mesopores and average pore diameter. With gradually increasing the values of the indices in the first group and gradually decreasing the values of the indices in the second group, the value of total shielding effectiveness decreases. It is obvious that these indices have influence on the rubber matrix-filler particle interactions, such as multicontact chain adsorption to the surface of the filler. The spatial inhomogeneities formed give rise to polarization phenomena and to a frequency dependence of the dielectric properties.

Resumo em Inglês:

This work aims to investigate the role of epoxy addition in high density polyethylene (HDPE) matrix. The block copolymer polyethylene-b-poly (ethylene glycol) (PEG-co-PE) was used as a compatibilizer. The samples were obtained by melt mixing using a torque rheometer. Instrumental nanoindentation was used to determine Young's modulus and nanohardness, thermal properties were analyzed by differential scanning calorimetry (DSC) and phase morphology was investigated through transmission and scanning electronic microscopy. The epoxy addition increased HDPE crystallinity by 13% and Young's modulus by 8%. The addition of PEG-co-PE decreased the size of dispersed phase by approximately 50% and improved phase adhesion and homogeneity compared to the blends without block copolymer. The experimental results were compared to numerical results obtained from the use of the homogenization by asymptotic expansion approach. The numerical results presented a fair agreement to the experimental values.

Resumo em Inglês:

The aim of this work was to study the use of slags to desulfurize cast iron. It was proposed to use alumina instead of fluorspar. In addition, marble waste was used instead of lime. Simulations applying Thermo-Calc® software were carried out in order to obtain the theoretical phases using thermodynamic data. Then, a comparison between theoretical data and experimental tests were performed. Cast iron was melted in induction furnace at 1550ºC. Slags composed mainly for CaO and Al2O3 were used to desulfurize cast iron. The results showed that the desulphurization reaction was favored when the liquid phase was increased. Furthermore, it was found that cast iron desulfurization occurs by top slag mechanism. Furthermore, the desulfurization tests showed a decrease up to 90.10% in the sulfur content to the mixture containing conventional lime and 87.25% to the mixture RMF15. The slags obtained from marble waste contained MgO, which it interfered negatively in the desulfurization yield. In addition, increasing the CaO particle diameter improved the desulfurization process. The desulphurization process more favored to particle size of 500-1000 µm.

Resumo em Inglês:

A [211]-oriented niobium single crystal was deformed by equal channel angular pressing (ECAP) at room temperature using the route Bc to a total strain of 9.2. A sharp cube texture develops after ECAP processing. The deformed samples were annealed in vacuum from 400ºC (673 K) to 900ºC (1173 K) for 1 h to evaluate their microstructural stability. Scanning electron microscopy (SEM) was used to image the microstructures of as-deformed and annealed specimens. Electron backscatter diffraction (EBSD) was employed to determine the respective microtextures before and after annealing. Coarsening of the microstructure occurs at a maximum rate at 550ºC (823 K) due to discontinuous recrystallization. Normal grain growth replaces discontinuous recrystallization as the main coarsening mechanism above 700ºC (973 K).

Resumo em Inglês:

Nanoelectronic is nanotechnology applied in the context of electronic circuits and systems. Molecular electronic, which is supposed to replace silicon electronic in the future, is an incipient branch of Nanotechnology which focusing on the organic molecules. Since recognizing and examining this family of Nanostructures needs a long time and very expensive, an appropriate pattern to predict electronic properties is very beneficial; Topological Indices Method (TIM) is a useful approach for this purpose. This study is to present a simple model based on graph theory to predict electronic and optical properties of Circumacenes. Therefore, it is first tried to prove a theorem for RRR index in of Circumacenes family. Then RRR index is measured for some Circumacenes family members. Electronic and physical properties of Circumacenes family (C8(n+2)/3H(2n+22)/3) including Ionization Energy, Binding Energy, Gap Energy, and Electron Affinity Energy, were measured using Gaussian 09 Software by Hartree-Fock method. Finally, the relationships described electro-optical properties of Circumacenes family achieved by RRR index.

Resumo em Inglês:

Mortar compressive strength is a standard requirement and should be tested on stand-ardized specimens with a 40 mm square cross section. However, these specimens with only one type of mortar (base-coat layer) do not represent the render traditionally ap-plied to façades since that must consist of at least two layers (base coat and top coat, with different formulations and thicknesses).The in-service compressive strength of the render is therefore currently evaluated on-site by means of indirect methods (e.g. pendulum rebound hammer or ultrasound). Addi-tionally, studies on evaluating the compressive strength in multilayer coating systems, based on the laboratory analysis of the mortar samples collected in situ, are few and far between. This paper intends to discuss the method of assessing in-service compressive strength of applied multi-coat renders systems, by testing cores collected after pull-off tests. Therefore, 422 compressive strength tests were carried out to establish a relation-ship between the compressive strength of single- and multi-coat renders and identify which render layers influence the system’s compressive strength. The experimental cam-paign results have shown the great influence of the top coat on multi-coat renders’ per-formance and the feasibility of studying the in-service compressive strength after a pull-off test; and also allowed identifying relevant parameters to evaluate the strength of samples collected in-situ.

Resumo em Inglês:

The purpose of the present study was to evaluate the antimicrobial potential of styrene-ethylene/butylene-styrene based thermoplastic elastomers (TPE) incorporated with zinc pyrithione (ZnPT) and silver nanoparticles (AgNano). Japan Industrial Standard was applied to evaluate the antimicrobial potential of incorporated TPE compounds against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Antifungal action was evaluated against Aspergillus niger, Candida albicans and Cladosporium cladosporioides. Samples prepared with ZnPT eliminated 99.9% of the E. coli and 99.7 % of the S. aureus population, and presented an inhibition zone in the fungal assay. Samples prepared with AgNano eliminated 99.7% of the E. coli and 95.5 % of the S. aureus population. There was no inhibition zone in samples containing AgNano; however, these samples did not present fungal growth on their surfaces. TPE samples containing ZnPT showed biocidal activity against the microorganisms tested and can be used to develop antimicrobial products.

Resumo em Inglês:

The purpose of the present study is to model and analyze heat treatment process of Al-Si-Mg alloy prepared by indirect squeeze casting. The combined effects of whole heat treatment process, including solution treatment temperature, solution treatment time, ageing temperature and ageing time, on Vickers hardness, were investigated. The non-linear mathematical model has been developed through Box-Behnken design based on response surface methodology. The results of ANOVA tests have proven the model is capable of making accurate predictions and statistically adequate. The significance tests show all four process parameters significantly affect response value and the relationship might be non-linear in nature. The dimensional response surface and matching contour plots are drawn, establishing an evaluation of the interaction effects of process parameters. The optimum heat treatment process is found as solution treatment temperature of 540.28ºC, solution treatment time of 7.55h, ageing temperature of 174.23ºC, and ageing time of 8.61h.

Resumo em Inglês:

In this study, the effects of the parameters such as applied potential difference, time and annealing temperature in the titania nanotubes formation were evaluated. The morphology of the nanotubes was evaluted by using Field Emission Gun - Scanning Electron Microscope (FEG-SEM), Atomic Force Microscope (AFM), contact angle and X-rays diffraction (XRD). Self-organized nano-structures were formed on the Ti-7.5Mo alloy surface from the same electrolyte (glycerol/NH4F) for all conditions. It was observed that the potential influenced the diameter while the length was changed according to the anodization time lenght. The presence of the phases anatase and rutile was altered by annealing temperature. Results showed that 20V-48h-450 ºC was the better than other conditions for application as biomaterial.

Resumo em Inglês:

One of the most significant problems in bending sheet metals is the springback behavior caused by the elastic stress formed after the bending process. In this study, the effects of forming pressure, die angle and holding time on the springback behavior were experimentally investigated for V-bending using the flexforming process. Furthermore, springback behavior was predicted using a fuzzy logic system based on unexecuted break-test parameters. The study was carried out using a thin rubber membrane instead of the thick ones normally used in flexforming processes. During the flexforming process, it was observed that springback were 60.57% and 41.92% less than those formed by a conventional die for AL1050-0 and AL5754-0 sheet metal materials, respectively. It was determined that an increase of 15 degree in the die angle increased springback values on average by 0.12 degree and 0.23 degree for AL1050-0 and AL5754-0, respectively. It was also found that an increase of 10 seconds in the holding time decreased springback values on average by 0.14 degree and 0.19 degree for AL1050-0 and AL5754-0, respectively. It was determined that there were no forming defects on the surfaces of the parts bent through the flexforming process.

Resumo em Inglês:

In this present study was evaluated the influence of heat treatment on the wear resistance of electroless high phosphorus nickel coating (9-10% P wt.). In addition, both untreated and treated Ni-P deposits were then compared to electroplated hard chromium coatings in terms of wear behaviour. Three different heat treatment conditions were performed at temperatures of 320ºC, 400ºC and 500ºC under different holding times. The selection of the heat treatment conditions was chosen considering the results obtained by a differential scanning calorimetry (DSC) analysis. The wear behaviour of the Ni-P samples was investigated through a non-lubricated "ball on plate" test carried out against an Al2O3 counter-face. After an analysis of the friction coefficient, microstructure of the worn surface, width and chemical composition of the wear track, was possible to conclude that the heat treatment affect positively the wear resistance of Ni-P coatings. Treatment conditions of 320ºC with 9 hours holding time and 400ºC with 1 hour holding time showed the best results due to a structural change from amorphous supersatured solid solution of phosphorus in nickel to a crystalline structure of nickel crystallites and nickel phosphides (Ni3P) occurred between 320ºC and 360ºC that was verified after x-ray diffraction analysis. Moreover, Ni-P heat treated coatings showed better results when compared to electroplated hard chromium deposits, hence acting as a natural alternative for chromed coatings.

Resumo em Inglês:

In this paper the synthesis of the LaBiFe2O6 material by the modified Pechini method is reported. Structural, morphologic, magnetic and optic experimental studies were performed. Rietveld refinement of x-ray diffraction patterns revealed that LaBiFe2O6 crystallizes in an orthorhombic perovskite structure (space group Pnma, # 62). Scanning electron microscopy images showed the nanometric feature of grains. X-ray dispersive spectroscopy permitted to infer the obtaining of the LaBiFe2O6 expected stoichiometry. Results of magnetic susceptibility as a function of temperature and field magnetization evidenced mixed ferromagnetism and superparamagnetism behavior at T=300 K. Mössbauer spectroscopy supported the superparamagnetic and ferromagnetic responses as a result of the nanogranular morphology and anisotropy effects. Spectrum of diffuse reflectance suggest that this material behaves as a semiconductor with energy gap Eg=2.13 eV.

Resumo em Inglês:

Magnetite was doped with rare earth ions (europium) to produce core-shell materials with both magnetic and luminescent properties, i.e., a magnetic Fe3O4 oxide core and a SiO2:phen:Eu3+ shell. The resulting material was analyzed by X-ray powder diffraction and transmission electron microscopy, and subjected to magnetic and luminescence emission measurements. All the synthesized materials exhibited superparamagnetic behavior and luminescence emission. The magnetic behavior of Fe3O4 and luminescence emission of SiO2:phen:Eu3+ of the materials were compared to precursors.

Resumo em Inglês:

This work reports the synthesis of a variety of materials with an ilmenite-type structure MTiO3 formula, where M= Fe, Co, and Ni, these materials were synthesized by the method of solvo-combustion, a simple and rapid method. These materials were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy, thermogravimetric analysis (TGA/DTA), surface area determination by the BET method and analysis of particle size. The photocatalytic activity was measured in the degradation reactions of Rhodamine B (rhB) and tetracycline (TC). The results show that the crystallinity and surface area are factors that influence significantly on the photocatalytic activity of the synthesized titanates.

Resumo em Inglês:

The use of polyethylene in sliding systems for automotive industry requires adequate mechanical properties, such as high wear resistance, besides good processing properties in conventional extrusion processes. Aiming to fulfill these requirements, crosslinks were introduced in a high molecular weight polyethylene (HMWPE) grade through a process involving grafting of vinyltrimethoxysilane (VTMOS) onto the polymer chain, promoted by dicumyl peroxide (DCP). The results obtained showed that the introduction of crosslinks improved the wear resistance of HMWPE. However, the HMWPE crosslinking led to a significant decrease in the Young’s Modulus, as a result of the reduction in crystallinity or the heterogeneous structure of the crosslinked samples. The tensile strength and the thermal properties were not affected.

Resumo em Inglês:

Cobalt blue pigments were prepared by self-propagating combustion followed by sol-gel method using aluminum nitrate and cobalt nitrate as the raw material. X ray diffraction (XRD), scanning electron microscopy (SEM), fiber optic spectrometer and colorimetric analysis were used to investigate the effect of reaction temperature, metal ion concentration and dispersant upon the gel formation. The results show that the formation of gel network could be promoted by increasing the concentration of metal ion (0.01~0.2 mol/L) and sol-gel reaction temperature (80~90°C), and the disper-sibility and stability of the pigment powder could be improved with dispersing agent. The dried gel precursor was calcined at 1250 °C to form 200~500 nm cobalt aluminum with spinel structure with highly negative value of b*.

Resumo em Inglês:

This study investigates the production of cerium sulfide (CeSx) amorphous thin films on substrates (commercial glass) by chemical bath deposition at different pH levels. The transmittance, absorption, optical band gap and refractive index of the films are measured by UV/VIS Spectrum. According to XRD analysis, the films show amorphous structure in the baths with pH: 1 to 5. It has been observed that the optical and structural properties of the films depend on pH value of the bath. The optical band gap (2.08 eV to 3.16 eV) of the films changes with the film thickness (23 nm to 1144 nm). We show that the refractive index has a positive relationship with the film thickness, where the values of 1.93, 1.45, 1.42, 2.60 and 1.39 are obtained for the former, and 34, 560, 509, 23 and 1144 nm (at 550 nm wavelength) for the latter. We compare the optical properties of amorphous and crystal form of CeSx thin films. We show that the optical band gaps of the amorphous CeSx are lower than that of crystal CeSx.

Resumo em Inglês:

The physical and mechanical properties of polytetrafluorethylene (PTFE) are greatly dependent on the degree of crystallinity and this is extremely important for the modeling of PTFE processing which is complex and costly. Differential scanning calorimetry (DSC) is one of the most important techniques for the determination of the degree of crystallinity and powder granules of the sample are generally used in the analysis. This procedure provides samples with a high surface-to-volume ratio, resulting in the formation of a considerable number of surface crystalline structures, called warts, along with the bulk crystallization, as shown by scanning electron microscopy. The presence of warts has a significant effect on the PTFE melting enthalpy and thus hinders the correct estimation of the degree of crystallinity of industrial PTFE parts, in which bulk crystallization prevails. In this study, we propose a procedure which does not lead to the formation of warts in the DSC sample and thus allows a more accurate determination of the melting enthalpy (or the degree of crystallinity) of industrial PTFE parts. We demonstrate that samples must be extracted from the core of dense (well-pressed) parts previously sintered in an oven, and the use of powder granules and/or sintering in DSC is not recommended.

Resumo em Inglês:

The mechanical properties, texture and microstructural evolution of a 6111 aluminum alloy during hot rolling and cold rolling deformation were systematically investigated in this article. The results show that cold rolling and hot rolling have significant effects on the tensile behaviors of the alloy. The shear texture and recrystallization texture mainly formed during the hot rolling deformation process, while the rolling texture mainly formed during the cold rolling deformation. The grain refinement mechanisms depend significantly on the rolling process. Movement of shear zone and recrystallization are the main grain refinement mechanisms during the hot rolling process, while dislocations tangling is the main grain refinement mechanism during the cold rolling process. The recrystallization textures and shear textures affect the anisotropy in elongation but the rolling textures affect significantly the anisotropy in yield strength.

Resumo em Inglês:

The use of FTO samples as an extended gate field effect transistor biosensor is presented. The FTO samples were produced by spray pyrolysis technique. The cleaning process is shown to have a fundamental importance for the final sensitivity of the samples when multiple re-usage is adopted. The role of electrical resistivity and morphology of the films are investigated. The influence of pH sequence of measurements from 2 to 12 is presented. Both increasing and decreasing the pH values sequence of measurements are compared. Electrical, morphological, time evolution and electrochemical experiments are correlated in the main discussion. A physical-chemical model is presented to explain the main mechanisms of charge adsorption and desorption. Parameters not commonly reported in the literature are proven to have fundamental importance in sensors behavior and characterization.

Resumo em Inglês:

The present study was to evaluate the effect of polyethylene terephthalate (PET) particle sizes on the mechanical and physical properties of extruded fiber-cement composites with different particle sizes combined to cellulose pulp in the production of fiber cement by the extrusion process. The design consisted of four formulations, one composed of 5% cellulose and the other three with 2.5% cellulosic pulp and 2.5% of PET particles with different particle sizes. Physical, mechanical and microstructural tests were performed without aging cycles and after 200 and 400 accelerated aging cycles. The degradation of vegetable fibers in the cement and the decrease of properties with aging was observed. PET particles were more resistant in alkaline environment and did not degrade. However, particle size did not exert great effect in the physical and mechanical properties of the composite. Thus, the use of PET particles shows potential as a reinforcement for fiber-cement composites.

Resumo em Inglês:

The epoxy resin is one of the matrices most employed in obtaining composites and coatings. Its properties have been modified using materials such as clays and polyhedral oligomeric silsesquioxanes - POSS. The use of POSS in the preparation of thermosetting nanocomposites has been studied in obtaining hybrid materials with higher mechanic and surface properties. The functionality of POSS cage is important, since a thermosetting is formed by a cross-linked structure that can interact at any direction, forming bonds or acting in the interface of the cages inserted. This works aims to evaluate the influence of three POSS (Glycidylisobutyl-POSS, Triglycidylisobutyl-POSS and Glycidyl-POSS) added in epoxy resin, in the mechanic and electrochemical behaviors, when applied on low alloy steel. It was observed an increase in roughness and hydrophobicity. The sample containing Glycidylisobutyl-POSS presented the best results of corrosion resistance. Glycidyl-POSS showed an inefficient dispersion, forming agglomerates, leading to a low electrochemical behavior.

Resumo em Inglês:

In this study the corrosion resistance of Ti30Ta experimental alloy was evaluated when submitted to different deformation rates. Alloys were processed in arc melting, furnace, forged and treated. The samples were machined in accordance with ASTME9-09 standard to carry out compression tests. The influence of deformation was evaluated by optical microscopy and XRD, and Eletrochemical parameters were analyzed in the most severe condition of deformation (22%). Corrosion resistance exhibited the same behavior for two conditions, 22% and without deformation.

Resumo em Inglês:

Studies of the doping process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work, we studied the doping effects on the crystal structure, electric, morphologic and magnetic properties of the BSCCO system with the nominal composition Bi1.6Pb0.4Sr(2-x)RExCa2Cu3O(10-δ). Here, the rare earth element (RE) was replaced by La in the sites of Sr. The x was ranged from 0.0 to 2.0, in steps of 0.5. The samples were prepared based on Pechini's method. The resulting powder was pressed at room temperature and the pellets were submitted to several heat treatments. The characterizations confirm the La in the sites of Sr however; the superconducting properties of the sample were not improved.

Resumo em Inglês:

Injection molding is a process used to manufacture high volumes of plastic containers of complex geometric shapes. Although CuBe has always been used, there are currently some alternative alloys such as the CuNiSiCr alloy that has lower manufacturing cost and similar properties. The objective of this paper is to characterize, by techniques of microscopy, the process of fusion and thermo-mechanical treatments of the CuNiSiCr alloy. These results indicate that the forging process manages to break the grain boundary segregation without cracking the material. The hardness achieved after heat treatments is greater than 32HRc and conductivity reaches 27% IACS. These characteristics are similar to those of CuBe alloys.

Resumo em Inglês:

To solve chipping of veneer porcelain in zirconia dental prosthesis it has been studied different cooling rates in firing schedules to control residual stresses generated by differences in thermal properties between the ceramics. However, cooling rates may affect the porcelain, irrespectively of interaction with zirconia. This study analyzed the effect of cooling rate on the three-point flexural strength (FS), residual stress, Vickers hardness (VH) and V-notch fracture toughness (SEVNB) on a feldspathic porcelain (Vita VM9) indicated for covering zirconia. Bar-shaped specimens were sintered according manufacturer's schedule firing and cooled at different rates (slow, normal or fast). Specimens were tested for FS (n=30), VH (n=15) and SEVNB tests (n=15). Weibull analysis were performed from FS values to measure reliability and probability of failure (PF). One-way ANOVA was significant for VH (p<0.001), and Tukey's test showed that slow cooling led to higher values. There was no significant difference for FS (p=0.654) and SEVNB (p=0.734). Fast cooling led to the lowest PF, but cooling rate factor was not significant for Weibull modulus. All cooling group showed residual tensile stress (MPa): Slow = 34.81; Normal = 27.04; Fast = 18,98. It was concluded that cooling rate produce minor changes in the porcelain properties.

Resumo em Inglês:

Two Cu-Zn-Al alloys with variable content of Zn (25 and 30 wt%) and constant Al content (4 wt%) prepared by induction melting of pure metals and hot rolled into strips of 0.5 mm thickness were thermally processed by using three different heat treatments: direct quenching, step-quenching and up-quenching with boiling water and room temperature water as the quenchants. The effects of composition and different methods of heat treatment on the microstructure and transformation temperatures of the investigated Cu-Zn-Al alloys were investigated using SEM-EDS and DSC techniques.

Resumo em Inglês:

The reactions that can occur on organic materials treated in plasma enviorement are strongly affected by surface temperature, thus the sharp determination of this variable is extremely important to process control. In situ temperature measurements are often employed; however, the measured point is generally under the treated surface. If in metallic materials the high thermal conductivity minimizes this problem, in non-metallic materials processing it becomes important, because its thermal resistivity besides a high sensibility to small temperature variations. The present work uses a simulation tool to extract thermal data on Ar+O2 RF plasma processing of Stearic Acid. Experimental data were obtained by thermocouples placed inside the samples. The extrapolation of surface temperature was performed by numerical simulation with Autodesk CFD software v.15.1. Results show that the temperature of the surface reaches values higher than the ones measured inside the sample holder. This difference of temperature is in good agreement with the visual observation of the phase transformations in the treated material, showing a simple and valuable tool to better control of plasma treatments.