Scielo RSS <![CDATA[Materials Research]]> http://www.scielo.br/rss.php?pid=1516-143920160003&lang=pt vol. 19 num. 3 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Energetic and electronic properties in a multilayered ZnO graphene-like nanostructure]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300497&lng=pt&nrm=iso&tlng=pt Nanostructures based on ZnO have been widely studied due to their electronic and piezoelectric properties. Experimental studies have shown that thin films based on ZnO can be used as chemical and optoelectronic sensors. The great goal of this work is to study of the role of the number of graphene-like layers in the physical properties of the ZnO. Therefore, the geometrical and electronic properties of graphene-like structures will be compared with the wurtzite one. In this work, the pn-type semiconducting behavior of the graphene-like structures and its relationship with the number of layers will be also analyzed. <![CDATA[Growth of Large Size Lithium Niobate Single Crystals of High Quality by Tilting-mirror-type Floating Zone Method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300505&lng=pt&nrm=iso&tlng=pt Large size high quality LiNbO3 single crystals were grown successfully by tilting-mirror-type floating zone (TMFZ) technique. The grown crystals were characterized by X-ray diffraction, etch pits density measurement, Impedance analysis, Vibrating sample magnetometry (VSM) and UV-Visible spectrometry. The effect of mirror tilting during growth on the structural, electrical, optical properties and defect density of the LiNbO3 crystals were investigated. It was found that the defect density in the crystals reduced for tilting the mirror in the TMFZ method. The chemical analysis revealed that the grown crystals were of high quality with uniform composition. The single crystals grown by TMFZ method contains no low-angle grain boundaries, indicating that they can be used for high efficiency optoelectronic devices. <![CDATA[Characterization of Mullite Ceramic Membranes and their Application in the Removal <em>Escherichia Coli</em>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300513&lng=pt&nrm=iso&tlng=pt This paper aims the morphological and structural characterization of ceramic membranes of mullite and their application in the removal of Escherichia coli. A complex irregular structure presented by the pores of the membrane was verified by scanning electron microscopy (SEM). The average pore size and distribution were determined by mercury intrusion porosimetry. The average pore size of the material presented was 0,39 µm. Microfiltration tests resulted in a protein retention of 46, 76 and 89% for trypsin (TR), egg albumin (EA) and bovine serum albumin (BSA), proving the efficiency of the membrane microfiltration tests for molecular weight of 69 kDa. The application of the membranes on the retention of gram-negative bacterium E. coliresulted in a 66% efficiency at a pressure of 200 kPa and a 98% efficiency when applied a pressure of 50 kPa. Therefore, the use of mullite membranes show limited efficiency towards bacteria retention. Nevertheless, they present fluxes similar to other materials proposed in the literature. <![CDATA[Numerical Predictions for the Thermal History, Microstructure and Hardness Distributions at the HAZ during Welding of Low Alloy Steels]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300520&lng=pt&nrm=iso&tlng=pt A phenomenological model to predict the multiphase diffusional decomposition of the austenite in low-alloy hypoeutectoid steels was adapted for welding conditions. The kinetics of phase transformations coupled with the heat transfer phenomena was numerically implemented using the Finite Volume Method (FVM) in a computational code. The model was applied to simulate the welding of a commercial type of low-alloy hypoeutectoid steel, making it possible to track the phase formations and to predict the volume fractions of ferrite, pearlite and bainite at the heat-affected zone (HAZ). The volume fraction of martensite was calculated using a novel kinetic model based on the optimization of the well-known Koistinen-Marburger model. Results were confronted with the predictions provided by the continuous cooling transformation (CCT) diagram for the investigated steel, allowing the use of the proposed methodology for the microstructure and hardness predictions at the HAZ of low-alloy hypoeutectoid steels. <![CDATA[Synthesis and Characterization of 1-Methyl-3-Methoxysilyl Propyl Imidazolium Chloride – Mesoporous Silica Composite as Adsorbent for Dehydration in Industrial Processes]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300534&lng=pt&nrm=iso&tlng=pt Ionic liquid – mesoporous silica composite was synthesized as a new adsorbent for dehydration in industrial processes. An ionic liquid (IL) with proved dehydration properties has been covalently anchored to mesoporous silica. The parameters of the synthesis were studied to produce a solid and stable composite. The material was then characterized by SEM, BET, FTIR, NMR, Raman, XRD, XRF, MALDI and LDI confirming the presence of a covalent bond between the ionic liquid and the solid matrix. Evaluations have shown that the material kept the IL dehydration property. <![CDATA[Influence of Stacking Sequence on the Mechanical and Dynamic Mechanical Properties of Cotton/Glass Fiber Reinforced Polyester Composites]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300542&lng=pt&nrm=iso&tlng=pt This study focuses on the use of waste cotton fiber from the textile industry to produce composites with unsaturated polyester and to evaluate the performance of glass (G) / cotton (C) fiber laminates, particularly their mechanical and dynamic mechanical properties. Distinct stacking sequences were studied but the overall fiber content was kept constant. In general, hybrid laminates exhibited intermediate mechanical properties compared to those of the pure laminates, and optimum performance was obtained when the glass fiber mats were placed on the surfaces of the composite. Furthermore, some hybrid laminates exhibited superior dynamic mechanical performance, even compared to the pure glass laminate. Lower tan delta peak height (related to better fiber-matrix interaction) values and higher Tg were reported for the [C/G/ G ¯]s and [G/C/ C ¯]s samples which, together with the [G/C/ G ¯]s sample, exhibited the best results for reinforcement effectiveness and loss modulus peak height. Therefore, it is found possible to partially replace the glass fiber by waste cotton fiber considering that the final product may be optimized for mechanical property, which requires glass fiber at the surface of the laminate, or for dynamic mechanical properties, that allows higher cotton fiber content. <![CDATA[A study on the microstructural parameters of Zn <sub>(1-x)</sub>La<sub>x</sub>Zr<sub>x</sub>O nanopowders by X-ray line broadening analysis]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300548&lng=pt&nrm=iso&tlng=pt In the present study, the pure and La-Zr co-doped ZnO nanoparticles were prepared by sol–gel technique using zinc acetate dehydrate (Zn(Ac)2·2H2O), lanthanum nitrate hexahydrate (La(NO3)3 ·6H2O) and zirconium chloride (ZrCl4) as precursor. The structure and morphology of the prepared nanoparticle samples were studied using X-ray diffraction and transmission electron microscopy measurements. X-ray diffraction results indicated that all the samples have crystalline wurtzite phase. TEM showed that powder was polycrystalline in nature with random distribution of the pure and La-Zr doped ZnO nanoparticles. We demonstrate strain-size evaluations for pure and doped ZnO nanoparticles from the x-ray line profile analysis. The microstructural effects of crystalline materials in terms of crystallite sizes and lattice strain on the peak broadening were investigated using Williamson-Hall (W-H) analysis and size- strain plot (SSP) method. The average crystallite size of Zn (1-x)LaxZrxO nanoparticles estimated from the W–H analysis and SSP method varied as the doping concentration increased. The incorporation of Zr4+ ion in the place of Zn2+ caused an increase in the size of nanocrystals as compared to undoped ZnO. The average particle sizes of co-doped ZnO nanoparticles estimated from the USDM model is in good agreement with the TEM results. <![CDATA[Effect of Process Parameters on the Microstructure of Semi-solid ZL101 Aluminum Alloy]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300555&lng=pt&nrm=iso&tlng=pt Aluminum alloy is the important alloy which has been widely used. To reduce waste, it is necessary to thixoform these alloys in near net shape. Semi-solid slurry is the key in process. In this work, the semi-solid slurry of ZL101 aluminum alloy was prepared by using serpentine channel. Effect of process parameters on the microstructure of semi-solid ZL101 aluminum alloy produced by serpentine channel was investigated. The results show that, the morphology of primary α-Al grains transformed from rosette to spheroid with decreasing pouring temperature. Satisfied semi-solid slurry of ZL101 aluminum alloy was prepared with pouring at 630°C to 670°C. Increasing curve number can improve the morphology of primary α-Al grain and decrease grain size with same pouring temperature. Desired slurry can be obtained with the lower pouring temperature when serpentine channel is preheated. It can make the primary nucleus gradually evolve into spherical and near-spherical grains with the effect of “self-stirring” in serpentine channel and chilling. <![CDATA[Fabrication and High Temperature Friction Behavior and Oxidation Resistance of Ni-Co-ZrO<sub>2</sub> Composite Coating]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300562&lng=pt&nrm=iso&tlng=pt Ni-Co alloy and ZrO2 micron particles were codeposited on 45 carbon steel by electrodeposition. The composition and microstructure of the composite coating were characterized. The high temperature tribological properties were carried out by a pin-on-disk tribo-tester. Additionally, the oxidation resistance was evaluated via high temperature circulating oxidation test. The results indicated that the deposited composite coating showed dispersed ZrO2 particles and continuous Ni-Co matrix, and there were no obvious pores, cracks and other defects at the interface between the composite coating and the substrate. The embedded ZrO2 particles changed the friction mechanism from adhesive wear to abrasive wear, the wear loss rate and friction coefficient of Ni-Co-ZrO2 composite coating were lower in comparison with that of Ni-Co alloy coating and carbon steel substrate. In addition, the embedded ZrO2 particles exerted a reactive-phase effect on the growth of nickel oxide and cobalt oxide, and effectively reduced the oxidation rate of the substrate at high temperature. Therefore, the Ni-Co-ZrO2 composite coating presents better oxidation resistance, when compared with Ni-Co coating. <![CDATA[Effect of Heat Input on Mechanical and Metallurgical Properties of Gas Tungsten Arc Welded Lean Super Martensitic Stainless Steel]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300572&lng=pt&nrm=iso&tlng=pt Welding of 6mm thick AISI: 410S lean super martensitic stainless steel (LSMSS) under different heat input of 7.97, 8.75 and 10.9 kJ/cm was carried out by gas tungsten arc welding process. The influence of heat input on metallurgical and mechanical properties in weld and HAZ region was studied. The tensile tests were carried out at different temperatures, namely at room temperature, at 600ºC, 7000C and 8000C. It is observed that rise in the heat input and temperature decreased the tensile strength of the weld joint. Further it is noticed that rise in the heat input enhanced the toughness of weld deposit but hardness of weld joints showed insignificant variation in it. This was primarily due to the increase in ferrite content in the matrix of martensite by enhancement of the heat input. In general, the microstructures of weld consisted of mixture of martensite and austenite as well as some amount of ferrite. Whereas, HAZ near to the fusion line consisted of larger and more elongated bright phase of banded delta ferrite in a matrix of martensite irrespective of change in heat input. <![CDATA[Effect of Spun Velocities and Composition on the R‒phase and Thermomechanical Behavior in Ti‒Ni Ribbons Electrically Heated]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300580&lng=pt&nrm=iso&tlng=pt This work deals with structural, electrical and mechanical characterization of Ti‒50.13Ni and Ti‒49.62Ni (at.%) shape memory alloys (SMAs) fabricated at different circumferential wheel velocities. The effect of wheel velocity, chemical composition and heat treatments are investigated. The characterization of crystallographic phases of the Ti‒Ni ribbons was carried out using X-ray diffraction. Electrical resistance variations as function of temperature (∆R/R %) were analyzed using a non-commercial technique, which consists in a thermal-adjustable bath apparatus revealing the temperatures of B2→R→B19´ two stage transformation, whereby the presence of R‒phase can be definitively confirmed. The Stress-Assisted Two-Way Memory Effect was measured by an own designed apparatus with an Linear Variable Differential Transformer captor and a current controlled heating, and results indicate that the as-spun condition, promotes the Stress-Assisted Two-Way Memory Effect. On the other hand, increments in Ni content tend to decrease transformation temperatures and high wheel velocities help to the R‒phase formation. <![CDATA[Biomechanical Analysis of Locking Reconstruction Plate Using Mono- or Bicortical Screws]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300588&lng=pt&nrm=iso&tlng=pt This experimental in vitro study evaluated the influence of screw length on the mechanical properties of a locking reconstruction plate designed with locking rings inserted into plate holes. Synthetic bone cylinders with 10 mm fracture gap and seven-hole locking reconstruction plates were used. Two groups of bone-plate constructs were assembled: Group 1 – three monocortical screws on each fracture side, Group 2 - three bicortical screws on each fracture side. In each group nine bone-plate constructs were tested until failure, three each in bending, compression and torsion. In each group, 21 bone-plate constructs were tested for failure in fatigue testing, seven each for bending, compression and torsion. In all static testing no significant differences were found between G1 and G2, except ultimate moment in torsion test (G2&gt;G1; P=0.008). Statistical analysis revealed significant differences between groups in axial compression fatigue testing (G1&gt;G2; P&lt;0.05) and four-point bending fatigue testing (G1&lt;G2; P&lt;0.05) in maximum load, minimum load, maximum moment, and minimum moment. In conclusion, screw length can affect the mechanical properties of locking reconstruction plate. Compared to bicortical screws, monocortical screws were less resistant to bending than axial compression. This must be considered when choosing implant, particularly in fractures under high axial loads. <![CDATA[Combustibility and reactivity of coal blends and charcoal fines aiming use in ironmaking]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300594&lng=pt&nrm=iso&tlng=pt Charcoal is a very important reducing agent in Brazil, the world’s largest steel industry based on charcoal blast furnace. Charcoal generates large amounts of charcoal fines during its production and processing. A good alternative for harnessing this fuel is the injection into coke-based blast furnaces via PCI process (Pulverized Coal Injection), a key technology for reducing use of coke in ironmaking. This study aimed to evaluate the combustibility and reactivity to CO2 of binary blends of charcoal fines and coals with purpose to PCI. Moreover, it was also attempted to identify the reasons for the different behavior of coals. The work was carried out by thermogravimetric analysis (TGA). The proportions of charcoal used were 10, 20 and 50% in mass. Charcoal showed the highest combustibility and reactivity among tested fuels and the blends formulated had higher combustibility and reactivity than single coals. <![CDATA[CFD 2D Description of Local Flow of Polymer Workpiece through a modified U-Shaped Die During Equal Channel Multiple Angular Extrusion]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300602&lng=pt&nrm=iso&tlng=pt The present article is focused on a 2D computational fluid mechanics study of local viscous flow dynamics and the formation character of rotary modes of deformation during Equal Channel Multiple Angular Extrusion (ECMAE) of a polymer workpiece fluid model through a U-shaped die with parallel slants in channel intersection zones. The present local flow problem was experimentally analyzed using physical simulation methods and theoretically studied with numerical fluid mechanics techniques. The computational approach has been grounded on the numerical finite difference solution of the boundary value problem for the Navier-Stokes equations in the curl transfer form for the local viscous flow of incompressible Newtonian fluid through a U-shaped rectangular die with parallel slants. The derived research results allow us to draw a conclusion that the implementation of a geometric design of parallel slants within a 2-turn U-shaped die results in localization of the maximum tangential stresses within the workpiece volume to the vicinity of these parallel slants during ECMAE. <![CDATA[High Temperature Oxidation Behavior of Yttrium Dioxide Coated Fe-20Cr Alloy]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300611&lng=pt&nrm=iso&tlng=pt Long term isothermal and cyclic oxidation behavior of yttrium dioxide (Y2O3) coated Fe-20Cr alloy was studied. Oxidation tests were carried out in air for periods of up to 200 hours at 1000°C and the oxidation behavior of the alloy was evaluated gravimetrically. The Y2O3 coating reduced markedly the mass gain of the alloy. Energy dispersive spectroscopic analysis of scale sections on oxidized Y2O3 coated specimens revealed a Cr rich layer close to the metal/oxide interface and the presence of Y and Cr near the oxide/air interface, indicating diffusion of Cr through the Y2O3 layer. Further evidence of this diffusion was seen as change in colour of the Y2O3 coating from white to green after prolonged oxidation. X-ray diffraction analysis of the scale revealed perovskite-type YCrO3.This study attributes the increased oxidation resistance of the Y2O3 coated Fe-20Cr alloy to increased oxygen ion diffusion through the Cr2O3 scale due to YCrO3 formation and grain boundary segregated Y ion blocking alloy cation diffusion. <![CDATA[Hydrolytic and Thermal Degradation of PCL and PCL/Bentonite Compounds]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300618&lng=pt&nrm=iso&tlng=pt Poly(Ɛ-caprolactone)/montmorillonite (PCL/MMT) and Poly(Ɛ-caprolactone)/organo-modified montmorillonite (PCL/OMMT) compounds at 3% w/w clay content were prepared by melting mixing. The effect of MMT and OMMT on the degradability of PCL injected specimens was investigated in vacuum at 40oC for up to 45 days and in aqueous medium at 40oC for up to 45 days. Selected specimens were collected after 15, 30 and 45 days of exposure. Microstructural changes were monitored during the degradation experiment by means of melt flow rate (MFR), weight loss, X ray diffraction (XRD), mechanical properties, and scanning electron microscopy (SEM). PCL and its compounds revealed not to be prone to hydrolytic degradation with similar results for MFR of samples exposed in vacuum and water. Gain and loss of weight were observed during experiments, probably due to swelling mechanism taking place in two stages, with the amorphous phase being the first to be swelled followed by the crystalline one. By XRD a new peak corresponding to (002) plane was evident for PCL/OMMT. PCL proved to be resistant to degradation since experiments carried out in vacuum or in aqueous medium for up to 45 days were not enough to affect the mechanical integrity of PCL samples. <![CDATA[Fractal analysis of the heat treatment response for multiphase Al alloys]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300628&lng=pt&nrm=iso&tlng=pt The present work shows the fractal analysis for the microstructure of Al-6Si-3Cu-xMg (x = 0.59, 3.80 and 6.78 wt.%) alloys, solution heat treated at 480 °C for times ranging from 4 to 72 h. Microstructural changes were examined using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), and quantified by measuring conventional characteristics of second phases. The fractal analysis of the microstructures was also carried out using fractal dimension (Df). Results shown important variations in the microstructure when Mg content is increased, being the eutectic Al-Si and Cu-rich phases the predominant phases for the alloys with low Mg content, while for higher Mg contents predominant phases were Mg2Si and Cu-rich phases. The analysis of Df showed that this parameter could be used in order to compare the microstructural solution response of the Al alloys. Besides, it was possible to correlate the fractal dimension with the shape factor of the second phases, mainly for the alloys with only one second phase remaining after heat treatment. <![CDATA[An Investigation on the Deformation Heating in Billet and Die During Equal-Channel Angular Pressing and High-Pressure Torsion]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300640&lng=pt&nrm=iso&tlng=pt This work aims to investigate the temperature rise in Aluminum alloy 6061 due to deformation heating in equal channel angular pressing (ECAP) and high-pressure torsion (HPT) processes using finite element method. The roles of various parameters are investigated and the heating of ECAP die due to billet deformation is included in the simulations. The results show that while the work-piece moves in the exit channel, the generated heat is transferred to die via conduction and therefore the temperature isosurfaces in die are extended in the direction of inlet and exit channels. The dependency of maximum work-piece temperature to velocity is more than its dependency to friction. Increasing the plunger velocity increases the difference between maximum and minimum temperatures. Additionally, the maximum work-piece temperature is attained at the deformation zone. The temperature rise in HPT is less than ECAP due to the small size of the HPT work-piece compared to ECAP. Not only the work-piece size, but also the good heat conduction of aluminum makes the temperature distribution roughly uniform in HPT. <![CDATA[Dip coating of a carbon steel sheet with Ni reinforced TiO<sub>2</sub> nanoparticles]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300648&lng=pt&nrm=iso&tlng=pt In this work carbon steel plates were dip-coated with a composite film obtained from a colloidal suspension of Ni-TiO2. Suspensions with different solids contents were used to evaluate the adherence of the film and the microstructural features. The samples were characterized using both optical and scanning electron microscopy, energy dispersive spectroscopy and microhardness. The microstructural analysis revealed that the films have high porosity at the surface. However, an interfacial region was observed demonstrating that there was good adhesion between both materials. This region shows an increased hardness that can be attributed to diffusion mechanism of nickel from the composite film to the steel matrix. Besides the interface, there was an abnormal grain growth, followed by a region of smaller grains of austenite and at longer distances near the center of the plate some colonies of pearlite appear. <![CDATA[Influence of Gd, Nd and Ce Additions on Microstructures and Mechanical Properties of Ultra-light Dual Phase Mg-9Li-0.4Zr Alloys]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300654&lng=pt&nrm=iso&tlng=pt Effects of various rare-earth elements (RE: Gd, Nd and Ce) additions on microstructures and mechanical properties of ultra-light dual phase Mg-9Li-0.4Zr alloy were investigated. The results indicated that Mg-9Li-5RE-0.4Zr alloys exhibited α-Mg, β-Li and RE-containing intermetallic compound structures. 5 wt.% Gd, Nd and Ce additions enhanced the strength properties of as-extruded Mg-9Li-0.4Zr alloy, but greatly deteriorated the ductility. The final mechanical properties of Mg-9Li-5RE-0.4Zr alloys were 161MPa∼167MPa in ultimate strength, 141MPa∼156MPa in yield strength and 20.8%∼32.5% in elongation. Heat treatment was hardly able to improve the mechanical properties for Mg-9Li-5RE-0.4Zr alloys. <![CDATA[Synthesis and Characterization of Boehmites Obtained from Gibbsite in Presence of Different Environments]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300659&lng=pt&nrm=iso&tlng=pt In this study, results related to boehmite synthesis by hydrothermal processes starting from a Bayer commercial gibbsite are reported. The processes have been conducted from aqueous suspensions with initial acidic or alkaline pH, without or with acetate ion, at 160oC for 72h to 168h. The final materials were characterized by X-ray diffraction (XRD), thermal methods (DTA and TGA) and scanning electron microscopy (SEM). The influence of the synthesis conditions on the morphology of the boehmite crystals obtained from the gibbsite at different hydrothermal processes are discussed. <![CDATA[Characterization of Thin Carbon Films Produced by the Magnetron Sputtering Technique]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300669&lng=pt&nrm=iso&tlng=pt Thin carbon films containing both amorphous and crystalline structures were produced by RF magnetron sputtering. The depositions of the carbon films were performed on Co buffer layers previously deposited on c-plane (0001) sapphire substrates. The thin carbon films were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscope (FEG-SEM). The Raman spectra confirmed the presence of amorphous and crystalline structures by the existence of an intense D band separated from the G band, indicating early stages of crystallization. The interplanar distance corresponding to the graphite structures was determined by using HRTEM micrographs. <![CDATA[Novel Ag<sub>3</sub>PO<sub>4</sub>/CeO<sub>2</sub> p-n Hierarchical Heterojunction with Enhanced Photocatalytic Performance]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300673&lng=pt&nrm=iso&tlng=pt The composite Ag3PO4/CeO2 photocatlyst, a novel p-n type heterojunction, has been successfully fabricated through a facile hydrothermal process combined with a successive in situ precipitation technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and UV-visible diffuse reflectance spectra (DRS) were used to characterize the as-obtained products. The SEM and TEM image show that CeO2 particles have been successfully loaded and well distributed in the surface of Ag3PO4. The photocatalytic activities of the p-Ag3PO4/n-CeO2 heterojunctions were investigated for their efficiency on the degradation of Rhodamine B (RhB) under ultra-violet light and visible light irradiation, and the results showed that the p-Ag3PO4/n-CeO2 heterojunctions possessed remarkable photocatalytic activities. The enhanced photocatalytic activity can be attributed to the extended absorption in the visible light region resulting from the Ag3PO4 and the effective separation of photogenerated carriers driven by the internal electrostatic field in the junction region. <![CDATA[Removal of Methyl Tertiary-Butyl Ether via ZnO-AgCl Nanocomposite Photocatalyst]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300680&lng=pt&nrm=iso&tlng=pt ZnO-AgCl nanocomposites with different mass ratios were synthesized via a one-pot wet chemical method. The synthesized nanocomposites were characterized by SEM, XRD and photoluminescence spectroscopy. The ZnO-AgCl nanocomposites exhibited a significant enhancement of photocatalytic activity towards degradation of methyl tertiary butyl ether in aqueous solution due to the effective carrier separation performance. In addition, the proposed ZnO-AgCl also exhibited an excellent photostability. <![CDATA[Micro Abrasive Wear Behaviour Study of Carburization and Ion Plasma Nitriding of P20 Steel]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300686&lng=pt&nrm=iso&tlng=pt P20 steel, which is mainly used in plastic molds, was thermochemically treated by ion plasma nitriding and solid and gas carburization. In this work, the solid and gas carburization were performed at 925 ºC for four different durations. The ion plasma nitriding was performed at 520 ºC for four different durations. The thermochemical treatment increased the micro abrasive wear resistance of the studied material. The gas carburizing treatment resulted in a greater surface microhardness. Longer treatment times increased the effectiveness of the thickness layer in all cases. The solid carburization produced a larger thickness layer than the gas carburization and ion nitriding. <![CDATA[Effect of Storage Time on Microtensile Bond Strength of Self-Adhesive and Multi-Step Resin Cements to Dentin]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300695&lng=pt&nrm=iso&tlng=pt The purpose of this study was to evaluate the effects of long-term storage on the microtensile bond strength (µTBS) to dentin of two self-adhesive and three multi-step resin cements. Two self-adhesive cements RelyX U100 (U100) and seT PP (SET), and 3 multi-step resin cements, one using 2-step etch-and-rinse adhesive AllCem (ALC), and two conventional resin cements with self-etching primer Panavia F (PAN) and Multilink (MULT) were used. Human molars were restored (n=5), sectioned and subjected to the μTBS test after 24 h and 6 months. Fractured specimens were examined by stereomicroscope and SEM. The µTBS were analyzed by one-way ANOVA and Tukey test (α=0.05). ANOVA revealed a difference between groups (p&lt;0.0001). All multi-step resin cements ALC, MULT and PAN showed statistically similar bond strength values that were higher than those of the U100 and SET groups. The bond strength value of ALC, MULT and PAN decreases significantly after 6 months. The majority of the failures were adhesive for all the groups. The µTBS produced by the self-adhesive cements were significantly lower than those observed for multi-step luting agents. Regardless of the numbers of steps of resin cements, the storage time reduces µTBS values to dentin only to multi-step luting agents. <![CDATA[Mechanical Properties of Woven Mat Jute/Epoxy Composites]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300702&lng=pt&nrm=iso&tlng=pt Natural fibers combine technological, economic and ecological aspects. However, a major restriction on their successful use in long term composite applications is their high moisture absorption and poor dimensional stability. This paper is aimed at establishing a link between the mats grammage and the mechanical properties of the epoxy/jute fibers laminates. Composites reinforced by coarse, medium and fine (C, M and F) mats were processed by vacuum bagging. Some batches were immersed in water up to 60 days in order to study the hydro-degradation. Mechanical tests were performed to obtain the bending strength and impact response. The mechanical response to bending and impact loadings was conditioned not only by the percentage of fiber, but also by the thickness of the specimens, which leads to composites F having lower strength than composites C despite having a higher percentage of fiber. Immersion in water causes a marked loss of mechanical properties in the first days of immersion, especially for thinner fiber grammage composites. A strong influence of the mats grammage on the impact response was observed. Increasing mats grammage promotes a strong increase in peak load, restored energy and impact energy for perforation and also a marked reduction of the deformation. <![CDATA[Mechanical Characterization of Synthetic Macrofibres]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300711&lng=pt&nrm=iso&tlng=pt The present study proposes a methodology to characterize the mechanical properties of synthetic macrofibres, which are used as a reinforcement of new composites applied in civil construction industry. Some standards suggest that this characterization should be performed on original filaments and others propose using the current methodology used to characterise metallic fibres. These recommendations turn difficult the quality control procedure, so it was developed a methodology to characterize the mechanical properties of the macrofibres as they are supplied in the construction site, using the tensile test. In that sense, two types of macrofibres were evaluated obtaining their tensile strength and elastic modulus. Additionally, the macrofibres were mixed with aggregates in order to study how the abrasion affects their mechanical properties. Summing up, the proposed methodology is feasible, especially to estimate the tensile strength allowing its application in ordinary laboratories. Regarding the elastic modulus results, they may be underestimated using this method. Finally, it was observed that the abrasion between the macrofibre and the aggregates during the mixing process compromises the mechanical properties decreasing both the tensile strength and the elastic modulus. <![CDATA[Evaluation of Residual Stresses and Mechanical Properties of IF Steel Welded Joints by Laser and Plasma Processes]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300721&lng=pt&nrm=iso&tlng=pt Interstitial free (IF) steel has an extensive application in the automotive industry where the Laser Beam Welding (LBW) process is widely used due to its high productivity. Similarly, the other used process, Plasma Arc Welding (PAW), is characterized by a greater energy concentration and current density and therefore lower distortion, higher welding speeds and higher penetration may be obtained. However, while the traditional welding processes have been extensively studied with regard to the generation of residual stresses, there are few studies about residual stresses analysis and characterization of LBW and PAW joints. Therefore, the aim of the present work is to analyse the residual stresses resulting from LBW and PAW processes by X-ray diffraction technique with sin2ψ method in IF steel butt joints. For both joints, macro and microstructure were characterized and mechanical properties were determined. Tensile residual stresses in the heat-affected zone (HAZ) and in the fusion zone (FZ) were verified for both welding processes. <![CDATA[Characterization of Metallurgical Coke Produced with Coal Mixtures and Waste Tires]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300728&lng=pt&nrm=iso&tlng=pt The use of scrap tires in the coal blends is an alternative to reduction of coke production costs as well as mitigates the impact caused by tire accumulation in the environment. Tests were carried out on a pilot scale, with coal blends and waste tire in 4 levels and 3 particle sizes, in order to assess the impact on the produced coke quality, especially on the Strength after Reaction with CO2 - CSR and Drum Index (DI150-15). In addition, it evaluated the mechanical resistance to compression, punctual chemical composition by Energy Dispersive Spectroscopy (EDS) analysis beyond the carbonaceous matrix-tire interface by SEM microscopy. The results from the coking tests showed that addition of up to 3% of the average ground tire (20-30mm) with steel mesh, raised either as CSR DI150-15, making feasible added also from a technical point of view. <![CDATA[Antibacterial and Microstructure Properties of Titanium Surfaces Modified with Ag-Incorporated Nanotube Arrays]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392016000300735&lng=pt&nrm=iso&tlng=pt Although titanium (Ti) and its alloys have been widely used as implants in clinical settings, failures still occur mainly due to poor bioactivity and implant-associated infections. Here, we coated Ti implants with TiO2 nanotubes (TNTs) incorporated with the antibacterial agent Ag to produce Ag-TNTs, through anodization in AgNO3 and xenon light irradiation. We characterized surface morphology and composition of the coating with scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. We investigated surface topography of the coatings by atomic force microscopy (AFM) operated in the tapping mode. The results indicate that Ag was successfully doped onto the TNTs, and that the nanoparticles were mainly distributed on the surface of TNTs. Finally, our antibacterial experiments reveal that Ag-TNTs on Ti implants exhibit excellent antibacterial activities, which promises to have significant clinical applications as implants.