Scielo RSS <![CDATA[Materials Research]]> http://www.scielo.br/rss.php?pid=1516-143920150003&lang=en vol. 18 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Study of the TiC Coating on Powder Metallurgy Diamonds Tool's Performance]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300441&lng=en&nrm=iso&tlng=en Some diamond tools use iron in their composition, and it is known that iron is a strong catalyst for the graphitization of diamonds. This graphitization occurs mainly during the processing of composite materials - conventional sintering or hot pressing, and during cutting operations. This work studies the effect of TiC coating on diamond, on structure, microstructure and mechanical properties of the processed composites. Samples were prepared by mixing powders of Fe (40 μm) and diamond (425 μm), and subsequent hot pressing at 35MPa/900 °C, during 3 minutes. Microstructural aspects were observed by SEM, and iron diffusion on diamond was studied by EDS. Structural analyses were performed by X-ray diffraction and Raman spectroscopy. Compressive tests were carried out, as well as the wear resistance of the diamond composites. The importance of employing coated diamonds was stablished. It was observed that iron did not activated the graphitization of diamond crystals. <![CDATA[Hot Consolidation of Partially Amorphous Cu-Ti Based Alloy: a Comparison Between Hot Extrusion and Hot Compaction by Sintering]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300448&lng=en&nrm=iso&tlng=en Consolidation of amorphous powders, which take advantage of the supercooled liquid region, is an alternative way to overcome the size limitation in marginal metallic glasses. Cu36Ti34Zr22Ni8based amorphous powders were obtained during high energy ball-milling. The analyses revealed that amorphous structures of powders and ribbons are quite different and this led to a different thermal behavior being the powders more thermally stable than the ribbons. Extrusion was initially proposed as a consolidation process; however, the decrease in viscosity in remainder amorphous matrix was not sufficient for that process, but certainly sufficient for sintering the sample during hot consolidation. An amorphous/nanocrystalline microstructure known for enhancing the mechanical properties of their fully amorphous counterparts was obtained. Evaluation of mechanical properties by microhardness revealed the relatively high hardness of HV 768. From these results, consolidation by sintering seems a promising route to produce bulk metallic glasses nanocomposites. <![CDATA[Topics in Present-day Science Technology and Innovation: Ultrafast Relaxation Processes in Semiconductors]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300453&lng=en&nrm=iso&tlng=en The nowadays notable development of all the modern technology, fundamental for the progress and well being of world society, imposes a great deal of stress in the realm of basic Physics, more precisely on Thermo-Mechanical Statistics. In electronics and optoelectronics we face situations involving physical-chemical systems far-removed-from equilibrium, where ultrafast (in pico- and femto-second scale) and non-linear processes are present. Here we describe in an extended overview the question of ultrafast relaxation processes in the excited plasma in semiconductors. <![CDATA[On the Formation of Hydroxyapatite Nano Crystals Prepared Using Cationic Surfactant]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300468&lng=en&nrm=iso&tlng=en Being a major constituent of hard tissues found in humans, synthetic hydroxyapatite (HA) as a substitute to natural bone and teeth is gaining importance. In particular, nano hydroxyapatite is expected to impart considerably superior properties. The current research focuses on identification of mechanism of the formation of HA nano-crystals during its preparation when surfactant nano reactors are used for their nucleation and growth. In addition to having a rod-shaped morphology, high resolution electron microscopy has revealed the presence of 2-5 nm crystals within individual particles of HA. The HA particles were not completely hollow, rather nano sized spherical pores of about 5 nm size, have been observed in TEM. These pores are suggested to have formed due to evolution of gases during processing. <![CDATA[Enhanced Photocatalytic Activity of Pure Anatase Tio<sub>2</sub> and Pt-Tio<sub>2</sub> Nanoparticles Synthesized by Green Microwave Assisted Route]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300473&lng=en&nrm=iso&tlng=en High-yield, rapid and facile synthesis of elongated pure anatase titania nanoparticles has been achieved through a nonaqueous microwave-based approach. The residual organics onto nanoparticles surfaces were completely removed through a new treatment under ozone flow, at room temperature in air. Such an ozone cleaning method revealed an effective inexpensive dry process of removing organic contaminants from nanoparticles surfaces. The TiO2 elongated nanoparticles having a length of 13.8 ± 5.5 nm and a diameter of 9.0 ±1.2 nm were characterized by powder X-Ray diffraction, transmission electron microscopy, selected area diffraction, BET surface area analyzer and FT-IR spectroscopy. Photocatalytic evaluation demonstrated that the as-synthesized ozone-cleaned TiO2 nanoparticles and TiO2 nanoparticles loaded with platinum possess excellent Rhodamine B performance with respect to both commercial spherical nanotitania P25 and P25 loaded with platinum. This could be attributed to the anatase phase purity, small size, large specific surface area and clean surfaces of the prepared nanoparticles. <![CDATA[CSA Doped Poly(aniline-co-o-toluidine) and Dispersed Zinc Oxide Nanoparticles: a Promising Material for Photovoltaics]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300482&lng=en&nrm=iso&tlng=en Copolymerization of aniline and o-toluidine is achieved by chemical oxidative polymerization with equal molar ratio of monomers in the presence of hydrochloric acid and ammonium persulphate as an oxidant. The copolymer found to be more soluble in polar solvents such as NMP, DMF and DMSO. FTIR spectroscopy confirms the copolymer chemical structure. UV spectroscopy shows π to π* transition and excitonic transition of the copolymer film. The copolymer is doped with camphorsulfonic acid (CSA) in m-cresol and then zinc oxide nanoparticles are dispersed into the copolymer and spin coated on to a glass plate. The scanning electron microscope image shows the morphology of the copolymer matrix. X-ray Diffraction shows the characteristic peaks of CSA and zinc oxide. EDAX analysis confirms the presence of CSA and zinc oxide. The dispersion of zinc oxide nanoparticles show quenching property of photoluminescence indicating that the copolymer can be used in the opto-electronics. <![CDATA[An Experimental and Numerical Approach for the Welding Effects on the Duplex Stainless Steel Microstructure]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300489&lng=en&nrm=iso&tlng=en Key microstructural changes that occur when Duplex Stainless Steels (DSS) are welded could be evaluated when bead-on-plate welding was carried out on a 2205 DSS by the GMAW process. By using numerical simulations, it was possible to calculate locally the heating and cooling rates taking place during the 2205 DSS welding and discuss its correlation to the microstructural changes experimented by the parent metal. Results showed that increasing heat input has promoted the ferritic grain growth with a slight reduction in the austenite content present at the high temperature heat affected zone (HTHAZ), whereas the cooling rates remained above from those reported as critical for sigma phase precipitation in 2205 DSS. Furthermore, nitrogen has proved to be an effective austenite former at the fusion zone (FZ), which can contributes to get a balanced microstructure in DSS welds in contrast to the effects from the elevated cooling rates. <![CDATA[Effect of Post Weld Heat Treatment Process on Microstructure and Mechanical Properties of Friction Welded Dissimilar Drill Pipe]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300503&lng=en&nrm=iso&tlng=en In this study, N80-42CrMo4 dissimilar drill pipes were welded by a roto-friction welding machine. A set of welded samples were tested as-welded condition. Another set of welded samples were post weld heat treated (stress relief annealing) at the temperature of 600 °C, for 20 min. and then tested. The microstructures of the as-welded and stress relief annealed samples were examined by optical microscope and SEM. The properties of the all welded samples were determined by hardness measurement, tension and V notch-impact tests. The high hardness especially in the weld interface resulted in low toughness. As a conclusion, the stress relief annealing treatment caused a little decrease in yield strength and ultimate tensile strength, but increase in the elongation. The ductility of samples also increased after annealing treatment which is very important for static and dynamic loads. <![CDATA[Electrospinning of Gelatin/Poly (Vinyl Pyrrolidone) Blends from Water/Acetic Acid Solutions]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300509&lng=en&nrm=iso&tlng=en Electrospinning is a versatile and efficient technique for obtaining polymeric microfibers and nanofibers with great potential for applications in tissue engineering, biosensors, filtration, wound dressings, controlled drug release and enzyme immobilization. Electrospun fibers are obtained by applying an electric field in a polymer solution resulting in non-woven fibrous mats with high surface area relative to volume and high porosity. In this work, the electrospinning of gelatin/poly(vinyl pyrrolidone) (PVP) blends was investigated. The polymers were electrospun from solutions containing different concentrations of water and acetic acid. Solutions were characterized by measuring the pH, electrical conductivity, surface tension and viscosity. The influence of acetic acid concentration in solution properties and its influence in the spinnability were investigated. The resulting non-woven membranes were characterized by using scanning electron microscopy (SEM), thermogravimetric analysis (TG) and cytotoxicity. <![CDATA[Study on Needles and Cracks of Tin-doped Indium Oxide Tablets for Electron Beam Evaporation Process]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300519&lng=en&nrm=iso&tlng=en Tin-doped indium oxide (ITO) tablets were used to deposit ITO films on p-GaN layer of light-emitting diodes. Needles and cracks in ITO tablets generated during electron beam evaporation process were deeply investigated. The formation of needles is predominantly resulted from the scanning trace, which is controlled by x and y axes scanning singles. The needles can be eliminated by controlling electron beam scanning trace. The loose microstructure with uniform grains and pores in the ITO tablets results in weak bonding strength, which leads to cracks under the thermal shock of high energy electron beam. A three-dimensional reticulated skeleton structure with strong bonding strength can restrain these cracks. <![CDATA[Properties of SiC Ceramics Sintered via Liquid Phase Using Al<sub>2</sub>O<sub>3</sub> + Y<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub> + Yb<sub>2</sub>O<sub>3</sub> and Al<sub>2</sub>O<sub>3</sub> + Dy<sub>2</sub>O<sub>3</sub> as Additives: a Comparative Study]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300525&lng=en&nrm=iso&tlng=en Silicon carbide (SiC) ceramics show excellent performance at high temperatures. Due to the high covalence of Si-C bonds, these ceramics are produced successfully only via liquid phase sintering (LPS). In this work, SiC ceramics were sintered via LPS using eutectic mixtures of Al2O3+Y2O3, which served as a standard for comparison, Al2O3+Yb2O3 and Al2O3+Dy2O3. The oxides mixtures were used to form liquid phase during the SiC sintering. Mixtures of SiC and additives were ground, pressed at 300 MPa and sintered at 1950ºC for 2 hours. All mixtures showed similar hardness, fracture toughness and flexural strength slightly different. Also the microstructure and crystalline phase were similar, showing that the ytterbium's and dysprosium's oxides can be also used as additive as well the most used oxide, yttrium oxide. <![CDATA[Characterization of Fibers from Pineapple's Crown, Rice Husks and Cotton Textile Residues]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300530&lng=en&nrm=iso&tlng=en Fibers from pineapple's crown (PCF), rice husks (RH) and cotton textile residues (RTF) were characterized by SEM, X-ray diffraction, FTIR and thermogravimetric analysis. Moisture content, water absorption, density and the distribution of the diameter of the fibers were also evaluated. RTF showed cylindrical microstructure with smooth surface, PCF showed cellular structure and the microstructure of RH is globular, showing cell pattern of the outer surface epidermis which is well organized and has a corrugate structure. PCF and RH showed crystallographic planes of cellulose I and RTF showed a mixture of cellulose I and cellulose II. RTF showed the highest degree of crystallinity and the lower moisture content and water absorption. These results occur because the RTF has no hemicellulose, as verified by FTIR. Comparing the three fibers, the RTF presented the lowest density and diameter. Furthermore, the onset degradation temperature of RTF was 40 °C higher than the PCF and the RH. <![CDATA[Effect of the Shot Peening Process on the Corrosion and Oxidation Resistance of AISI430 Stainless Steel]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300538&lng=en&nrm=iso&tlng=en Ferritic stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. Shot peening is a process applied to add residual compression stresses in metallic surfaces with the intent of improving the material when exposed to corrosion due to stress and fatigue. Some studies about the effect of the shot peening process on the fatigue resistance, bending fatigue behavior, and residual surface stress in the ferritic stainless steels have been performed. However, the effect of the shot peening process on the corrosion and oxidation resistance of the stainless steel is not well known. In this context, the purpose of this study is to evaluate the effect of the shot peening process on these superficial properties of ferritic AISI430 stainless steel. The obtained results showed that the ferritic AISI430 stainless steel samples treated with shot peening presented a significant modification on the surface morphology and an important decrease of oxidation and corrosion resistance, evidencing that the shot peening process compromises the chemical and physical properties of the surface. <![CDATA[Particles of Coffee Wastes as Reinforcement in Polyhydroxybutyrate (PHB) Based Composites]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300546&lng=en&nrm=iso&tlng=en The objective of the present study was to evaluate lignocellulosic particles from sub-products of the coffee industry (coffee parchment - CP and husk - CH) into polyhydroxybutyrate (PHB) as a promising reinforcing filler in the biocomposites. The effects of type (CP or CH) and content (neat, 10% and 20%) of coffee wastes on the thermal, mechanical, microstructural and physical properties of the ensuing composites were evaluated. Thermal stability of the composites was improved by the coffee residues at different contents, while degree of crystallinity was decreased with the inclusion of CP. The addition of 10% of CP has not influenced significantly the tensile strength (TS) and Izod strength (IS), in relation to the neat PHB. Tensile strength (TS), MOE and Izod strength (IS) of the composites have increased significantly with the inclusion of 20% of CP. The increase in the content of coffee waste particles increased the water absorption of the composites. <![CDATA[Effect of Track Overlap on the Microstructure and Properties of the CoCrMoSi PTA Coatings]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300553&lng=en&nrm=iso&tlng=en Broadly speaking, the research and design of coatings are generally studied by way of single-track deposits; otherwise, the development of a coated part entails the understanding of how multi-track welding influences the microstructure and properties of the surface. This study evaluated the effect of track overlap on the microstructure and properties of the CoCrMoSi Tribaloy T400 alloy coatings produced on AISI 316L steel substrate. The characterization was performed by scanning electron microscopy, hardness and X-ray diffraction. The correlation between the degree of overlap and performance of the coatings was assessed by wear tests. The single track deposits showed hypoeutectic microstructure as a result of high Iron, Chromium and Nickel content. From the second track on, the chemical composition was displaced back to eutectic and then to hypereutectic with overlap of 25 and 50%, respectively. The microstructure dictated the hardness of the coatings (527 – 701 HV0.5) and the lower mass loss rate was measured for hypereutectic with primary Laves phase. <![CDATA[Corrosion of Galvanized Steel Under Different Soil Moisture Contents]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300563&lng=en&nrm=iso&tlng=en Galvanized steel has been widely applied in different applications and the industry significantly increased its production in recent years. Some galvanized structures can be completely or partially buried, such as transmission tower footings. The corrosion of these metallic structures is related to the soil chemical and physicochemical properties, which define the aggressiveness of the environment. To assess the effect of the soil moisture on galvanized steel corrosion, a comparative study was carried out. Carbon steel coupons, with or without galvanization, were buried in clay soil collected from an industrial region in the northeast of Brazil. The chemical, physicochemical and microbiological characteristics of the soil were determined. The thickness of the galvanized coating was measured by scanning electron microscopy (SEM). Corrosion tests were conducted in different soil moisture conditions using the following techniques: potentiodynamic polarization curves and gravimetric tests. The results showed the influence of soil moisture on corrosion rates. The electroplating decreased corrosion rates, especially when the coupons were exposed to low moisture soil. <![CDATA[The Effects of Cryogenic Treatment on the Corrosion of AISI D3 Steel]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300569&lng=en&nrm=iso&tlng=en It is well known that cryogenic treatment is used to improve the mechanical properties of a material. Consequently, the use of cryogenic treatment has grown beyond its successful application on tool steels. In this research, the effects of cryogenic treatment on the corrosion of AISI D3 steel in 3.5% NaCl solution were examined by electrochemical impedance spectroscopy (EIS). The surface structure of the AISI D3 steel was examined by scanning electron microscopy (SEM) after the EIS investigations. Results clearly indicated that the pre-treatment of the steel was responsible for a significant effect on corrosion. The heat treatment process prior to the cryogenic treatment and the tempering process after were shown to decrease corrosion resistance. <![CDATA[Nitrogen Surface Enrichment of Austenitic Stainless Steel ISO 5832-1: SHTPN <em>vs</em> Low-temperature Plasma Nitriding]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300575&lng=en&nrm=iso&tlng=en Specimens of ISO 5832-1stainless steel were submitted to low temperature plasma nitriding treatment and Solution Heat Treatment after Plasma Nitriding (SHTPN) process aiming to obtain a S-phase, chromium precipitates-free, surface layer. The following techniques were used for analysis: scanning electron microscopy (SEM), optical microscopy (OM), microhardness, X-ray diffraction (XRD) and wavelength dispersive spectroscopy (WDS) microanalysis. Corrosion resistance was evaluated by means of potentiodynamic anodic polarization and open-circuit measurements of corrosion potential. Results indicated that the S-phase layer with N concentrations of about 0.9 wt% and 2 µm thick was formed during low temperature plasma nitriding, while layers with concentratios of about 0.45 wt% of N and up to 200 µm thick resulted from the SHTPN process. Results proved the increase in localized corrosion resistance caused by nitrogen in solid solution for both processes, as well as the deleterious effect caused by the precipitation of chromium nitride. <![CDATA[Investigation on Physical Properties of Semiorganic Nonlinear Optical Glycine Zinc Sulfate Single Crystal]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300581&lng=en&nrm=iso&tlng=en Nonlinear optical single crystals of Glycine Zinc Sulfate (GZS) were grown by slow evaporation technique. Single crystal X-ray diffraction analysis revealed the crystal system and lattice parameter values. Powder X-ray diffraction analyses have been carried out and the diffraction patterns have been indexed. The optical properties of the crystals were determined using UV-Visible spectroscopy. Optical constants such as band gap, refractive index, extinction coefficient and electric susceptibility were determined from UV-Visible spectroscopy. The refractive index was determined using Brewster's angle method. Hardness of the GZS crystal was estimated by Vicker's hardness studies. Second Harmonic Generation (SHG) of GZS crystal was investigated by Kurtz powder technique. The dielectric constant and dielectric loss measurements were carried out for different temperatures and frequencies. The photoconductivity studies confirm that the grown crystal has negative photoconductivity nature. In order to investigate the growth mechanism and surface features, etching studies are carried out for the crystal. <![CDATA[On the Use of Special Functions for Analyzing the Steady State Creep in Short Fiber Composites Semi-theoretically]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300588&lng=en&nrm=iso&tlng=en In this paper, a novel method is presented to obtain some unknowns such as displacement rate using special and well-behaved functions for short fiber composites in the steady state creep by semi-theoretical method (STM). The creep behaviors are predicted in the short fiber composites under tensile axial stress. Also, the regions under the partial debonding are predicted by the obtained results along with the reason of the partial debonding. The main purpose of this research is the use of the mathematical model instead of the time consuming and expensive experimental methods. On the other hand, the creep unknowns are simply obtained by the special functions rather than some complex theories. The use of sensor is one of the important applications of the present method in the regions with uniform behaviors. The obtained analytical results are validated by FEM results. Average difference between the analytical method and FEM results is about 10% approximately. Finally, good agreements are found between the obtained analytical and FEM results for predicting the creep behavior. <![CDATA[Microstructural Path Analysis of Martensite Dimensions in FeNiC and FeC Alloys]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300595&lng=en&nrm=iso&tlng=en The properties of steels that undergo martensite transformation after or during processing depend on characteristics and arrangement of martensite units within the microstructure. In this work, the global microstructure descriptors of martensite transformation are related to the individual dimensions of the martensite units, the "intrinsic dimensions", – radius, thickness and aspect ratio – compensated for interactions among those units. In other words, the dimensions a martensite unit would have if it grew without impingement. This is accomplished by means of the microstructural path method. The methodology was applied to experimental data of martensite transformation in FeNiC and FeC alloys. The analysis of martensite dimensions permitted observing that the microstructural path of martensite includes a thermally activated step. We conclude that this thermally activated step does not mean that martensite itself has thermally activated growth step but that arrest of the martensite thickening process, owing to dislocation interaction with the interface motion may be thermally activated. <![CDATA[Electrochemical Stability and Bioactivity Evaluation of Ti6Al4V Surface Coated with Thin Oxide by EIS for Biomedical Applications]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300602&lng=en&nrm=iso&tlng=en To improve the implants biocompatibility many surface modifications were proposed. Investigations about the surface modification on Ti alloys by anodic oxidation are reported. This research presents a study on the stability of thin titanium dioxide grown by potentiodynamic method on Ti6Al4V surfaces up to 5.0 V. Its bioactive surface in phosphate buffer solution (PBS) and the oxide stability after immersion in artificial blood media were measured by Electrochemical Impedance Spectroscopy (EIS). Hydroxyapatite (HAP) presence was evaluated using simulated body fluid (SBF) with different immersion times. The oxides and HAP presence were analyzed by Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The oxide stability was confirmed with low dissolution rates where the Rp was around 106Ω.cm2. The results showed the TiO2 was compact and thin oxide that could prevent the severe corrosion processes and improve in few days the physical-chemical interaction of the Ti alloys with bone in physiological media. <![CDATA[Comparison of Kinetic Study of CTMA<sup>+</sup> Removal of Molecular Sieve Ti-MCM-41 Synthesized with Natural and Commercial Silica]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300608&lng=en&nrm=iso&tlng=en This work aimed to determine and compare the apparent activation energy, involved in thermal decomposition of CTMA+ from the pores of Ti-MCM-41 synthesized by two different source of silica in order to evaluate their influence in the template removal. The molecular sieves Ti-MCM-41 were synthesized using rice husk ash (RHA), as alternative low cost source of silica, and commercial silica gel, obtaining two mesoporous material by hydrothermal synthesis of gel molar composition of: 1.0 CTMABr: 4.0 SiO2: X TiO2: 1.0 Na2O: 200.0 H2O. The samples were characterized to compare its properties by X-ray diffraction, IR spectroscopy, BET method and thermogravimetric analysis (TGA). The kinetic study using the model proposed by Flynn and Wall to determine the apparent activation energy for CTMA+ removal was performed using TGA data. The thermogravimetric analysis results of the material obtained from RHA confirmed intrinsic properties of mesoporous MCM-41 as the synthesized with commercial silica gel, such as high specific area, mesoporous range of pore diameter and hexagonal structure. According to the kinetics results the RHA showed similar chemical interaction to commercial silica gel, which makes it an interesting material, since it is a low cost source of natural silica from agricultural waste. <![CDATA[Influence of Heat Treatment in Residual Stresses Generated in P91 Steel-pipe Weld]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300614&lng=en&nrm=iso&tlng=en The knowledge of residual stress arising from the welding processes is extremely important because the mechanical properties of the welded components are not only determined by the microstructures present in the joint, but also by the heterogeneous residual stresses introduced during the thermal cycle in welding processes. The aim of this work is the characterization of ASTM P91 steel-pipe welded by Metal Cored Arc Welding &amp;Flux Cored Arc Welding (MCAW/FCAW) processes, through the residual stresses evaluation associated with welding and post-weld heat treatment (PWHT). Residual stresses were analysed by X-ray diffraction technique with sin2ψ method, presenting tensile behaviour with higher magnitude at the weld metal of root region. The PWHT promoted the relief of the residual stresses in the both regions. High Vickers microhardness values were observed in the weld metal region before the PWHT, which was very efficient to reduce them. <![CDATA[Martensitic Stainless Steels Low-temperature Nitriding: Dependence of Substrate Composition]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300622&lng=en&nrm=iso&tlng=en Low-temperature plasma assisted nitriding is a very promising technique to improve surface mechanical properties of stainless steels, keeping unaltered or even improving their surface corrosion resistance. During treatment, nitrogen diffuses into the steel surface, increasing its hardness and wear resistance. In the present work the nitriding process of different martensitic stainless steels was studied. As-quenched AISI 410, 410NiMo, 416 and 420 stainless steel samples were plasma nitrided at 300, 350, 400, 450, and 500°C, for 4 h, at 3 Torr, in a gas mixture of 70% N2 + 20% H2 + 10% Ar, and flow rate of 3.33×10–6 Nm3s−1. The study of the nitrogen-rich layer thickness indicates two different activation energies, one for low (&lt;400°C) and another one for high temperature ( ≥400°C), except for the AISI 410NiMo. The surface hardness increases with temperature for all steels between 300 and 450°C. For 500°C, except for the AISI 410NiMo, the surface hardness decreases if compared to that obtained at 450°C. This hardness decrease is related to chromium nitride precipitation, also associated to the treated surface sensitization. Finally, the CrN precipitation in treated surfaces is dependent on the steel composition, with the AISI 410NiMo steel presenting the lower average chromium nitride precipitation rate. <![CDATA[Two-parameter Rigid Block Approach to Upper Bound Analysis of Equal Channel Angular Extrusion Through a Segal 2θ-die]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300628&lng=en&nrm=iso&tlng=en This article deals with a phenomenological description of experimentally determined complex geometric shape of material dead zone during Equal Channel Angular Extrusion (ECAE) through a Segal 2θ-die with a channel intersection angle of 2θ&gt;0°and 2θ&lt;180°. Taking into account the complex dead zone geometry in a 2θ-die, a two-parameter Rigid Block Method (RBM) approach to a two-parameter Upper Bound Method (UBM) has been introduced with Discontinuous Velocity Field (DVF) for planar flow of plastic incompressible continua. The two-parameter UBM has allowed us to derive the numerical estimations for such energy-power parameters of ECAE as punching pressure and accumulated plastic strain for 2θ-dies. The obtained computational data have been compared with the one-parameter analytic UBM solution. Good agreement between the two computational results has been found. <![CDATA[Rice Husk Reuse in the Preparation of SnO<sub>2</sub>/SiO<sub>2</sub>Nanocomposite]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300639&lng=en&nrm=iso&tlng=en In this study, biogenic SiO2 of high purity and high surface area obtained from rice husk was used for prepare a nanostructured SnO2/SiO2composite. The predominantly amorphous silica was extracted in an acidic route and then the nanocomposite was done via sol-gel route using ethylene glycol and citric acid followed by heat treatment. SiO2 content of the rice husk was determined by X-ray fluorescence (XRF) and its specific surface area determined by nitrogen adsorption. The composite nanostructured SnO2/SiO2 was structurally characterized by the techniques of X-ray diffraction (XRD), Raman and Fourier transform infrared (FT-IR) spectroscopy. The morphological characteristics were revealed by scanning electron microscope (SEM). <![CDATA[Simulation of the Microstructural Evolution of Pure Material and Alloys in an Undercooled Melts via Phase-field Method and Adaptive Computational Domain]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300644&lng=en&nrm=iso&tlng=en The phase-field methods were developed mainly for studying solidification of pure materials, being then extended to the solidification of alloys. In spite of phase-field models being suitable for simulating solidification processes, they suffer from low computational efficiency. In this study, we present a numerical technique for the improvement of computational efficiency for computation of microstructural evolution for both pure metal and binary alloy during solidification process. The goal of this technique is for the computational domain to grow around the microstructure and fixed the grid spacing, while solidification advances into the liquid region. In the numerical simulations of pure metal, the phase-field model is based on the energy and phase equations, while, for binary alloy, the said model is based on the concentration and phase equations. Since the thermal diffusivity in the energy equation is much larger than the diffusivity term in phase equation in pure metal system, about twenty eight times the difference between them. The computational domain growth around the microstructure is controlled according with the thermal diffusivity for pure material in the liquid region. In the numerical simulation of dendritic evolution of Fe-C alloy, the idea is similar, i.e., the solute diffusivity in concentration equation is larger than the diffusivity term in phase equation in the liquid region, in this case eleven times the difference in Fe-C alloy system. The computational domain growth is controlled via solute diffusivity in the liquid region. Hence, phase-field model is proposed with an adaptive computational domain for efficient computational simulation of the dendritic growth in a system for both pure metal and binary alloy. The technique enables us to reduce by about an order of magnitude the run time for simulation of the solidification process. The results showed that the microstructure with well-developed secondary arms can be obtained with low computation time. <![CDATA[Effect of Wood-derived Charcoal Content on Properties of Wood Plastic Composites]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300654&lng=en&nrm=iso&tlng=en The effect of wood-derived charcoal flour on the water resistance and mechanical properties of wood plastic composite (WPC) panels was investigated. The hot press molded WPC panels were produced from polypropylene (37 wt%) with maleic anhydride-grafted polypropylene (MAPP, 3 wt%) and different mixtures of wood flour and charcoal flour. The amount of charcoal flour was gradually increased up to 60 wt%. The thickness swelling and water absorption of WPC panels considerably decreased with increasing charcoal flour content. The internal bond strength and bending properties of the WPC panels significantly improved with increasing charcoal flour content. This was mainly attributed to the high amount of pores and gaps in the charcoal flour. Melted polypropylene could get into the pores and gaps during the hot press molding, which lead to a better interfacial adhesion between polymer matrix and wood filler. The results showed that the charcoal flour could be partially substituted for the wood flour in the production of WPC panels having higher dimensional stability and internal bond strength. <![CDATA[Studies of Gold Adsorption from Chloride Media]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000300660&lng=en&nrm=iso&tlng=en In this paper, adsorption of gold from chloride media using commercial sorbent (Lewatit TP 214 (L-214)) and biomass residue (rice hull (RH)) were investigated. The different adsorption parameters, sorbent dosage, contact time, temperature and pH of solution on adsorption (%) were studied in detail on a batch sorption. Before the RH was activated, adsorption (%) was poor compared with L-214. However, after the RH was activated at 1000 °C under an argon atmosphere, the gold adsorption (%) increased four-fold. X-ray fluorescence (XRF) was used to explore the feasibility this material as an adsorbent for the removal of gold from aqueous solutions. The adsorption equilibrium data were best fitted with the Langmuir isotherm model. The maximum adsorption capacities, Qmax, at 25 °C were found to be 93.46 and 108.70 mg/g for the activated rice hull (ARH) and L-214, respectively. Thermodynamic calculations using ΔH°, ΔS°, ΔG° and Ea values indicate that the adsorption process was spontaneous and endothermic.