Resumo em Inglês:

The understanding of the creep behavior of silicon nitride (Si3N4) is extremely complex because of a large number of parameters influencing simultaneously the creep deformation of the materials. In general, the main creep mechanisms acting in these materials are grain boundary sliding or materials transport by solution-precipitation process. In this work, the creep behavior has been monitored by X ray diffraction analysis, determining the peak intensity ratio of the (101) and (210) planes of b-Si3N4. This characterization technical, allied the microstructural analysis can contribute to determination of creep mechanisms acting in material. The beta-Si3N4 grains are highly elongated with aspect ratios ranging between 3 and 11. Therefore, the intensity of the peaks related to the basal plane (101) tends to be higher when compared to the lateral planes (210). During creep deformation occurs alignment of the elongated beta-Si3N4 grains in the plane parallel to the direction of the applied load, reflecting in the peak intensity ratio. Crept samples presented variations in the (101)/(210) peak intensity ratio of beta-Si3N4 indicating that grain rotation can to be contributing with creep deformation. In this way, the use of X ray diffractometry as a mean to characterize microstructural changes during creep has been shown successfully.

Resumo em Inglês:

Hexametildisilazane (HMDS) plasma polymerized thin films obtained using low frequency power supplies can be used to make adsorbent films and turn surfaces hydrophobic. The aim of this work was to verify the hydrophobicity and adsorption properties of HMDS thin films (with and without the addition of oxygen, resulting in double or single layer films) obtained using an inductive reactor powered with a 13.56 MHz power supply. Single and double layer thin films were deposited on silicon for film characterization, polypropylene (PP) for ultraviolet (UVA/UVC) resistance tests, piezoelectric quartz crystal for adsorption tests. The double layer (intermixing) of HMDS plasma polymerized films and HMDS plasma oxidized surfaces showed a non-continuous layer. The films showed good adhesion to all substrates. Infrared analysis showed the presence of CHn, SiCH3, SiNSi and SiCH2Si within the films. Contact angle measurements with water showed hydrophobic surfaces. UVA/UVC exposure of the films resulted in the presence of cross-linking on carbonic radicals and SiCH2Si formation, which resulted in a possible protection of PP against UVA/UVC for a duration of up to two weeks. Adsorption tests showed that all organic reactants were adsorbed but not water. Plasma etching (PE) using O2 showed that even after 15 minutes of exposure the films do not change their hydrophobic characteristic but were oxidized. The results point out that HMDS films can be used: for ultraviolet protection of flexible organic substrates, such as PP, for sensor and/or preconcentrator development, due to their adsorption properties, and in spatial applications due to resistance for O2 attack in hostile conditions, such as plasma etching.

Resumo em Inglês:

The use of shape memory alloys (SMA) as smart structures and other modern applications require a previous evaluation of its performance under load as well as a training procedure. In general, these requirements lead to the design and assembly of a specific test bench. In this work, an experimental set-up was specially designed to perform the electro-thermomechanical characterization of SMA wires. This apparatus was used to determine the strain-temperature (epsilon - T) and electrical resistance-temperature (R - T) hysteretic characteristics curves of a Ti-Ni shape memory wire (90 mm in length and 150 µm in diameter) under mechanical load. The SMA wire is loaded by means of constant weights and a controlled system for injection of electrical power allows performing the heating-cooling cycles. The obtained hysteretic epsilon - T and R - T characteristics curves for some levels of applied loads are used to determine important shape memory parameters, like martensitic transformation temperatures, temperature hysteresis, temperature slopes and shape memory effect under load. These parameters were in accord with the ones found in literature for the studied SMA wires.

Resumo em Inglês:

Investigation of the blue cooperative luminescence in a binary composition of GeO2-PbO glasses with different Yb3+ concentrations is reported. High refractive index (1.96) and large transmission window (0.4 up to 5.0 µm) are characteristics of this vitreous system. Luminescence and lifetime measurements in the visible and near infrared regions were performed to investigate the spectroscopic characteristics of the glasses. Visible emission around 507 nm was detected in all samples. The visible emission intensity increases with the Yb2O3 content at least up to 2.0 wt. (%), that represents the maximum Yb2O3 concentration possible for this glass system. The visible lifetimes are about half of their respective near infrared ones, and the blue luminescence comes from a cooperative process. A rate equation was used to describe the behavior of the cooperative emission intensity as a function of Yb2O3 concentration; a good agreement with the calculated and measured cooperative luminescence was achieved.

Resumo em Inglês:

Aiming the development of high-performance biodegradable polymer materials, the properties and the processing behavior of poly(3-hydroxybutyrate), P(3HB), and their blends with poly(epsilon-caprolactone), PCL, have been investigated. The P(3HB) sample, obtained from sugarcane, had a molecular weight of 3.0 x 10(5) g.mol¹, a crystallinity degree of 60%, a glass transition temperature (Tg), at - 0.8 °C, and a melting temperature at 171 °C. The molecular weight of PCL was 0.8 x 10(5) g.mol-1. Specimens of 70/30 wt. (%) P(3HB)/PCL blends obtained by injection molding showed tensile strength of 21.9 (± 0.4) MPa, modulus of 2.2 (± 0.3) GPa, and a relatively high elongation at break, 87 (± 20)%. DSC analyses of this blend showed two Tg´s, at - 10.6 °C for the P(3HB) matrix, and at - 62.9 °C for the PCL domains. The significant decrease on the Tg of P(3HB) evidences a partial miscibility of PCL in P(3HB). According to the Fox equation, the new Tg corresponds to a 92/8 wt. (%) P(3HB)/PCL composition.

Resumo em Inglês:

CdTe thin films are used as absorber layer in CdS/CdTe solar cells. The microstructure of this absorber layer plays a fundamental role in photovoltaic conversion and can be controlled by the deposition parameters used during the film growth. In this work, CdTe thin films were deposited by the CSS method onto glass substrates previously covered with In2O3:Sn. The effects of pressure, source temperature and substrate temperature on the microstructural properties of the films were studied. The properties were mainly influenced by the pressure, the presence of oxygen in the reaction chamber, and the substrate temperature. For films deposited under an argon atmosphere, an increase in grain size and a reduction of the texture were observed as the pressure and substrate temperature were increased. The introduction of oxygen in the atmosphere led to a decrease in the deposition rate and affected the microstructure and composition of the film. Films deposited under an argon-oxygen atmosphere have smaller grains than those deposited under argon and are richer in Te. The addition of oxygen to the atmosphere apparently did not result in the formation of oxides.

Resumo em Inglês:

The possibility of preconcentration on microchannels for organic compounds in gas or liquid phases was evaluated. Microstructures with different geometries were mechanically machined using poly(methyl methacrylate) - PMMA as substrates and some cavities were covered with cellulose. The surfaces of the microchannels were modified by plasma deposition of hydrophilic or hydrophobic films using 2-propanol and hexamethyldisilazane (HMDS), respectively. Double layers of HMDS + 2-propanol were also used. Adsorption characterization was made by Quartz Crystal Measurements (QCM) technique using reactants in a large polarity range that showed the adsorption ability of the structures depends more on the films used than on the capillary phenomena. Cellulose modified by double layer film showed a high retention capacity for all gaseous compounds tested. However, structures without plasma deposition showed low retention capacity. Microchannels modified with double layers or 2-propanol plasma films showed higher retention than non-modified ones on gas or liquid phase.

Resumo em Inglês:

Electric arc furnace dust (EAFD) is a solid waste generated in the collection of particulate material during steelmaking process in electric arc furnace. The aim of this work is to carry out a chemical and structural characterization of two EAFD samples with different Zn contents. Optical emission spectroscopy via inductively coupled plasma (ICP), X ray diffractometry (XRD) and Mössbauer spectroscopy analysis were carried out in such EAFD samples. From XRD measurements, the samples exhibits the following phases: ZnFe2O4, Fe3O4, MgFe2O4, FeCr2O4, Ca0.15Fe2.85O4, MgO, Mn3O4, SiO2 and ZnO. The phases detected by Mössbauer spectroscopy were: ZnFe2O4, Fe3O4, Ca0.15Fe2.85O4 and FeCr2O4. Magnesium ferrite (MgFe2O4), observed in the XRD patterns as overlapped peaks, was not identified in the Mössbauer spectroscopy analysis.

Resumo em Inglês:

Unlike other thin film deposition techniques, close spaced sublimation (CSS) requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate) and a sintered CdTe powder. In this work, CdTe thin films were deposited by CSS technique from different CdTe sources: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass). The largest deposition rate was achieved when a paste made of CdTe and propylene glycol was used as the source. CdTe source-plates led to lower rates, probably due to the poor heat transmission, caused by the introduction of the plate substrate. The results also showed that compacting the powder the deposition rate increases due to the better thermal contact between powder particles.

Resumo em Inglês:

Microstructures are the strategic link between materials processing and materials behavior. A dendritic structure is the most frequently observed pattern of solidified alloys. The microstructural scales of dendrites, such as primary and secondary arm spacings, control the segregation profiles and the formation of secondary phases within interdendritic regions, determine the properties of cast structures. In this work, the influence of thermosolutal convection on dendrite arm spacings is experimentally examined in the downward vertical unsteady-state directional solidification of Sn-Pb hypoeutectic alloys. The experimental observations are compared not only with the main predictive theoretical models for dendritic spacings but also with experimental results obtained for Sn-Pb alloys solidified vertically upwards. Primary dendritic arm spacings have been affected by the direction of growth, decreasing in conditions of downward vertical solidification when compared with those grown vertically upwards. Further, the unsteady-state lambda1 predictive models did not generate the experimental observations.

Resumo em Inglês:

The development of hybrids materials has been extensively investigated in recent years. The combination of a wide variety of compositions and production processes had permitted the use of these materials in different applications like coatings for corrosion protection of metals. In this work organic-inorganic hybrid materials have been prepared from the hydrolysis of tetraethylorthosilicate and silanol-terminated polidymetilmetoxysilane using a sol-gel process. These materials have been applied on galvanized steel and on steel electroplated with a ZnFe. In order to evaluate the degradation behavior of these coatings, electrochemical techniques (Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization) were used. EIS data was fitted to an equivalent circuit from which the electrochemical parameters were obtained. Results show a good protective character of the hybrid films, when compared with uncovered specimens. The overall performance of the coating systems appears to be highly dependent on the kind of metallic coating applied to the steel.

Resumo em Inglês:

Titanium/hydroxyapatite (HAP) composites are candidate materials for biomedical applications as implants and hard tissue substitutes since they combine the good mechanical properties and biocompatibility of Ti with the excellent HAP bioactivity and osteointegration. In powder metallurgy processing of these composites, HAP decomposition promoted by Ti during powder sintering is found. In a previous work Ti-50v%HAP greens of 60% theoretical density (dT) were vacuum sintered at 1150 °C and formation of CaO and Ca4O(PO4)2 (TTCP) resulting from the HAP decomposition, as well as Ti4P3 at the Ti/HAP interfaces was obtained. In the present work those composites are compared with similar ones processed from TiH2 as a substitute for Ti which were also vacuum sintered at 1150 °C from greens with 60 to 86%dT. For the lower %dT, the compounds formed were CaO, TTCP and Ti4P3 and for the higher %dT ones, besides those same products, CaTiO3, Ti5P3 and a phase containing Ti, Ca and P were detected.

Resumo em Inglês:

This paper describes a numerical simulation and experimental study of the Vickers indentation testing of WC-6Co specimens. The numerical analysis was implemented by a three-dimensional finite element (FE) model using the commercial solver MARC™. Hardness values predicted by this model agreed well with those obtained experimentally. It was also observed that the load-displacement curves obtained numerically were quite similar to those presented by the literature for the Vickers testing. The maximum principal stress field was used to locate the most expected areas for crack formation and propagation during the Vickers indentation testing of WC-6Co.

Resumo em Inglês:

Brazil's electric power utilities have commonly employed native timbers as the main material for manufacturing cross-arms for distribution lines. However, the increasingly high costs of these timbers and Brazil's new environmental laws have contributed to change this situation, spurring research on new materials for application in transmission and distribution systems. This paper discusses two reforested wood species, Pinus elliottii and Eucalyptus citriodora, coated with castor oil-based polyurethane resins, as an alternative material for distribution line cross-arms, from the standpoint of their mechanical and electrical properties and their low cost. Numerical simulations and a complete description of the entire coating process are also part of this work.

Resumo em Inglês:

Carbon fabric/epoxy composites are materials used in aeronautical industry to manufacture several components as flaps, aileron, landing-gear doors and others. To evaluate these materials become important to know their mechanical properties, for example, the tensile strength. Tensile tests are usually performed in aeronautical industry to determinate tensile property data for material specifications, quality assurance and structural analysis. For this work, it was manufactured four different laminate families (F155/PW, F155/HS, F584/PW and F584/HS) using pre-impregnated materials (prepregs) based on F155TM and F584TM epoxy resins reinforced with carbon fiber fabric styles Plain Weave (PW) and Eight Harness Satin (8HS). The matrix F155TM code is an epoxy resin type DGEBA (diglycidil ether of bisphenol A) that contains a curing agent and the F584TM code is a modified epoxy resin type. The laminates were obtained by handing lay-up process following an appropriate curing cycle in autoclave. The samples were evaluated by tensile tests according to the ASTM D3039. The F584/PW laminates presented the highest values of tensile strength. However, the highest modulus results were determined for the 8HS composite laminates. The correlation of these results emphasizes the importance of the adequate combination of the polymeric matrix and the reinforcement arrangement in the structural composite manufacture. The microscopic analyses of the tested specimens show valid failure modes for composites used in aeronautical industry.

Resumo em Inglês:

Pulverized Coal Injection (PCI) is an important standard technology replacing coke partially by pulverized coal into the blast furnace that allows a significant reduction of hot metal costs and environmental impact, contributing to a decrease of coke requirements for ironmaking. Coals typically used in this process in Brazil are, at current time, exclusively imported from many countries, although economic important coal-measures occur in the southern part of the country. The Brazilian coals have a low rank, higher contents of inert components, proportioning nocoking properties and an expected high reactivity. Due to these caractheristics, these coals could be used for injection in the blast furnaces in order to decrease the dependency on high cost imported coals. The efficiency in the combustion and the coal reactivity are considered important parameters in the blast furnace, since a larger amount of char (unburned coal) causes severe problems to the furnace operation. The aim of the present work is to compare the reactivity of a south Brazilian coal, obtained from Faxinal mine, with two imported coals and the blends of the Brazilian coal with the imported ones. The reactivity of these coals and their blends were evaluated in a thermogravimetric analyzer. In the experiments, various mass ratios of Faxinal coal and the imported coals were used to compose the blends. The gasification reaction with pure CO2 was conducted under isothermal conditions at 1050 °C and atmospheric pressure. The experimental results show the greater reactivity of the Faxinal coal. The additive behavior was confirmed. The blends with a composition of up to 50% Faxinal coal have parameters according to the usual limits used for PCI.

Resumo em Inglês:

Based on the fact that the Ti-6Al-4V alloy has good mechanical properties, excellent resistance to corrosion and also excellent biocompatibility, however with low wear resistance, this work aims to test plasma processes or combination of plasma and ion implantation processes to improve these characteristics. Two types of processing were used: two steps PIII (Plasma Immersion Ion Implantation) combined with PN (Plasma Nitriding) and single step PIII treatment. According to Auger Electron Spectroscopy (AES) results, the best solution was obtained by PIII for 150 minutes resulting in ~ 65 nm of nitrogen implanted layer, while the sample treated with PIII (75 minutes) and PN (75 minutes) reached ~ 35 nm implanted layer. The improvement of surface properties could also be confirmed by the nanoindentation technique, with values of hardness increasing for both processes. AFM (Atomic Force Microscopy) characterization showed that the single step PIII process presented greater efficiency than the duplex process (PIII + PN), probably due to the sputtering occurring during the second step (PN) removing partially the implanted layer of first step (PIII).

Resumo em Inglês:

Equal Channel Angular Pressing (ECAP) is the most prominent SPD (Severe Plastic Deformation) method for the production of ultrafine and nanostructured metals, and has been extensively employed and analyzed. This technique was applied to a Pb-4%Sb alloy at room temperature, in order to study its effect on a low melting point and multiphase metallic material. The material was subjected to effective strains higher than 9, after 8 passes of processing, where dynamic and static recrystallization are expected during and after each pass. This eliminates any grain refinement and allows the analysis only of the microstructural effects associated with second phase redistribution and eventual precipitate dissolution. ECAP followed route C, which eliminates structural alignment after each even ECAP pass, facilitating the study of the microstructural evolution. It is shown that three ECAP passes are necessary to completely break the lamellar structure of the as cast strucure and that antimony dissolves into the lead rich matrix. Dynamic recrystallization and structural changes reduce the material strength and change the flow curve format.

Resumo em Inglês:

The increasingly design requirements for modern engineering applications resulted in the development of new materials with improved mechanical properties. Low density, combined with excellent weight/strength ratio as well as corrosion resistance, make the titanium attractive for application in landing gears. Fatigue control is a fundamental parameter to be considered in the development of mechanical components. The aim of this research is to analyze the fatigue behavior of anodized Ti-6Al-4V alloy and the influence of shot peening pre treatment on the experimental data. Axial fatigue tests (R = 0.1) were performed, and a significant reduction in the fatigue strength of anodized Ti-6Al-4V was observed. The shot peening superficial treatment, which objective is to create a compressive residual stress field in the surface layers, showed efficiency to increase the fatigue life of anodized material. Experimental data were represented by S-N curves. Scanning electron microscopy technique (SEM) was used to observe crack origin sites.

Resumo em Inglês:

The temperature induced phase transition in MnAs is analyzed in this work using X ray Rietveld refinement. The results show the presence of the hexagonal phase (P6(3)/mmc) at room temperature and the first-order structural-magnetic transition to the orthorhombic phase (Pnma) around 318 K was followed in detail. The MnAs magnetic characterization allowed to obtain the transition temperature and a maximum value of 47 J/(kg.K) for the measured magnetocaloric effect for a magnetic field variation of 5 T.