Scielo RSS <![CDATA[Materials Research]]> vol. 5 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<B>Materials Research - Revista Ibero-americana de Materiais</B>: <B>Criteriosa, justa e educativa!</B>]]> <![CDATA[<B>Synchrotron SAXS Studies of Nanostructured Materials and Colloidal Solutions</B>: <B>A Review</B>]]> Structural characterisations using the SAXS technique in a number of nanoheterogeneous materials and liquid solutions are reviewed. The studied systems are protein (lysozyme)/water solutions, colloidal ZnO particles/water sols, nanoporous NiO-based xerogels, hybrid organic-inorganic siloxane-PEG and PPG nanocomposites and PbTe semiconductor nanocrystals embedded in a glass matrix. These investigations also focus on the transformations of time-varying structures and on structural changes related to variations in temperature and composition. The reviewed investigations aim at explaining the unusual and often interesting properties of nanostructured materials and solutions. Most of the reported studies were carried out using the SAXS beamline at the National Synchrotron Light Laboratory (LNLS), Campinas, Brazil. <![CDATA[<B>Transição de Fase Difusa e Propriedades Dielétricas de Cerâmicas Ferroelétricas de (Pb, Ba)Nb<SUB>2</SUB>O<SUB>6</B></SUB>]]> Tungsten bonze structured lead barium niobate (Pb1-xBa xNb2O6) ferroelectric ceramics were prepared by the conventional mixed oxide method and their dielectric properties were carefully investigated. All studied samples presented elevated values of maximum dielectric constant (epsilon'm) and its corresponding temperature of maximum (Tm) in comparison with perovskite structured ones. The phase transition features indicate that the PBN samples do not present a complete diffuse phase transition. Indeed, the diffuseness degree of the ferroelectric phase transition is highly dependent of the ions Pb2+ content in the sample compositions. The diffuseness of the ferroelectric phase transition is enhanced while the temperature of maximum dielectric constant is decreased with the Pb2+ content decreasing. In addition, the maximum dielectric constant shows an opposite behavior. <![CDATA[<B>Crystallization Mechanism and Kinetics of BaO-Li</B><SUB>2</SUB><B>O-ZrO</B><SUB>2</SUB><B>-SiO</B><SUB>2</SUB><B> Glasses</B>]]> Differential thermal analysis and scanning electron microscopy were used to determine the influence of the addition of BaO on the crystallization mechanism of Li2O-ZrO2-SiO2 systems. As the concentration of BaO in the samples increased, a transition occurred in the predominant crystallization mechanism, which passed from superficial to volumetric. To determine the maximum nucleation rate, the crystallization kinetics of the sample containing 20 mole % BaO, which showed the most uniform crystallization, was studied by counting the nuclei with an image analyzer. The first nuclei appeared at the first endothermic inflection point (at the start of Tg, at 440 °C), while the maximum number of nuclei was counted at the midpoint of the glass transition region (446 °C). These results are similar to those observed for other materials that crystallize in volume, and confirm scanning electron microscopy data. <![CDATA[<B>Structural Evaluation and Performance of Portland Cement Concretes After Exposure to High Temperatures</B>]]> We evaluated the "residual" thermal conductivity of Portland cement concretes (with characteristic compressive strength at 28 days, f ck, of 20 MPa and 50 MPa) at room temperature after heat-treating at 180 °C, 300 °C and 600 °C. The description of the geometry of the structure was carried out using mercury intrusion porosimetry and nitrogen sorption. The results showed a decreasing tendency of residual thermal conductivity, which we attributed to heat-induced concrete degradation. Furthermore, the results from mercury intrusion porosimetry and nitrogen sorption tests showed that a coarser pore structure is produced with the raise of heat-treatment temperatures. <![CDATA[<B>Surface Modification of Polymeric Materials by Plasma Treatment</B>]]> Low-temperature plasma treatment has been used in the last years as a useful tool to modify the surface properties of different materials, in special of polymers. In the present work low temperature plasma was used to treat the surface of asymmetric porous substrates of polysulfone (PSf) membranes. The main purpose of this work was to study the influence of the exposure time and the power supplied to argon plasma on the permeability properties of the membranes. Three rf power levels, respectively 5, 10 and 15 W were used. Treatment time ranged from 1 to 50 min. Reduction of single gas permeability was observed with Ar plasma treatments at low energy bombardment (5 W) and short exposure time (20 min). Higher power and/or higher plasma exposition time causes a degradation process begins. The chemical and structural characterization of the membranes before and after the surface modification was done by AFM, SEM and XPS. <![CDATA[<B>Electrochromic Properties of Sol-gel Coating of Nb</B><SUB>2</SUB><B>O</B><SUB>5</SUB><B> and Nb</B><SUB>2</SUB><B>O</B><SUB>5</SUB><B>:Li</B><SUP>+</SUP>]]> Thin solid films of Nb2O5 and Nb2O5:Li+ were prepared by the sol-gel process using the sonocatalytic method. The films reported here were prepared from a NbCl5 as precursor and butanol as solvent. Through the addition of lithium salt LiCF3SO3 to the precursor solution, films with different electrochemical performance were obtained. The electrochemical and optical responses of the films were determined from the cyclic voltammetry and chronoamperometry measurements using a 0.1 M LiClO4/PC as electrolyte. The electrochromic properties of the films were investigated using in situ spectroelectrochemical method. They exhibit a gray coloration under Li+ insertion with a reversible variation of the transmittance in the visible and near infrared range between 20% and 80%. <![CDATA[<B>Influence of Calcification Solution on <I>in vitro</I> Chitosan Mineralization</B>]]> The influence of the calcification solution on the mineralization of chitosan membranes was analysed. Two factors were studied: pH and chemical composition (excess of calcium or phosphate ions) of solutions. Substrates (membranes) of chitosan underwent mineralization by soaking in calcification solutions for 7 days at 36.5 °C. As expected, SEM-EDS analyses demonstrated that higher pH and concentration of ions increases deposition, however, the morphology and composition of these deposits varies depending on which ion (phosphate or calcium) is in excess. Larger spherical deposits are observed when a calcium-rich solution is used instead of a phosphate-rich one. In the latter, the interconnectivity of the inorganic and organic (matrix) phases is very different, suggesting a different mechanism of deposition for each situation. <![CDATA[<B>Ultrasonic Measurements In Brazilian Hardwood</B>]]> This paper reports on a study of the application of ultrasound waves in wood with the purpose of evaluating the latter's mechanical properties. The evaluation is based on the correlation between the speed of sound, modulus of elasticity and density. The speed of transmission is sensitive to the material's quality-determining factors; hence, this technique is an important industrial tool to improve the quality control of processes. The species used in the experimental procedure were "cupiúba" (Goupia glabra) and "jatobá" (Hymenaea sp). Tests were carried out to determine the properties of apparent density at 12% humidity content (rhoap,12%), modulus of elasticity in static deflection (E M), and modulus of rupture (MOR). Ultrasound tests were also performed to find the stiffness matrix coefficient (C LL), for purposes of comparison with the static findings. The results and analyses lead us to conclude that the nondestructive ultrasound method can be employed to obtain reliable evaluations of the mechanical properties of dicotyledons. <![CDATA[<B>Structure Refinement of (Sr,Ba)Nb</B><SUB>2</SUB><B>O</B><SUB>6 </SUB><B>Ceramic Powder from Neutron and X-Rays Diffraction Data</B>]]> The structure of polycrystalline strontium barium niobate at room temperature was refined by the Rietveld method. Sintered ceramic samples were used to collect powder neutron and X-ray diffraction data. The ratio Sr/Ba ~ 64/36 was found from the initial batch composition Sr0.61Ba0.39Nb2O6, corroborating with the quantitative X-ray dispersive spectroscopy (EDS) measurements. The structure is tetragonal with cell parameters a, b = 12.4504(3) Å and c = 3.9325(1) Å and space group P4bm. It was not necessary to introduce any positional disorder for the oxygen atoms. Cation Nb+5 displacements not parallel to the c direction are presented, which can influence the behavior of the ferroelectric properties. <![CDATA[<B>Susceptibility to Stress Corrosion Cracking of 254SMO SS</B>]]> The susceptibility to stress corrosion cracking (SCC) of solubilized and sensitized 254SMO SS was studied in sodium chloride, and sodium fluoride solutions at 80 °C and sulfuric acid solutions in presence of sodium chloride at 25 °C. The influence of salt concentration, pH values and the addition of thiosulfate was examined. The susceptibility to SCC was evaluated by Slow Strain Rate Tests (SSRT), at 1.5 x 10-6 s-1 strain rate. The behavior of 254SMO was compared to those of AISI 316L SS and Hastelloy C276. 254SMO showed an excellent resistance to SCC in all conditions, except in the more acidic solutions (pH <= 1) where, in the sensitized conditions, intergranular stress corrosion cracking occurred. <![CDATA[<B>Hydrous Tantalum Phosphates for Ion Exchange Purposes</B>: <B>A Systematic Study</B>]]> This work describes two methods of preparation of hydrous tantalum phosphates and their characterization as ion exchangers. The hydrous metallic phosphate compounds were chemically and physically characterized by thermal gravimetric analysis, X-ray diffractometry and surface area measurements. By the first method, tantalum phosphate was prepared by alkaline fusion of Ta2O5 with an excess of K2CO3, followed by lixiviation of the tantalate fusion product with hot water, and precipitation with diluted H3PO4. Preparation II was performed using metallic Ta dissolved in concentrated HF/HNO3 acidic mixture followed by hydrolysis of fluortantalic acid intermediary and precipitation with diluted H3PO4. Both freshly prepared materials (I and II) were exaustively refluxed with concentrated H3PO4, in its boiling point temperature, resulting respectively in Ta2O5. 2.1 H2O, (IR) and Ta2O5. 1.3 H2O, (IIR). Characterization of the prepared products have presented the following values: surface area of 108.27 ± 2.80; 220.14 ± 2.67; 117.07 ± 5.25 and 141.61 ± 0.27 m².g-1 respectively for I, IR, II and IIR. All these materials were amorphous. The ion exchange behavior for all four hydrous tantalum phosphates was studied using Na+, K+ and Ba+2 as the exchanged species. The values for typical ion exchange capacity were 1.64; 1.23; 1.47 and 1.01 miliequivalent.g-1, respectively for I, IR, II and IIR products. <![CDATA[<B>Correlation between Corrosion Potential and Pitting Potential for AISI 304L Austenitic Stainless Steel in 3.5% NaCl Aqueous Solution</B>]]> We investigated the effect of surface finish of two AISI 304L (UNS S30403) stainless steels on the corrosion potential (Ecorr) in 3.5% NaCl aqueous solution and its value was compared with the pitting potential (Ep) value and the type of anodic potentiodynamic curve obtained for determination of Ep in this solution. Five different surface finishes were examined. Ecorr and its standard deviation are strongly affected by the type of surface finish. Moreover, there are evidences of a linear correlation between Ecorr and Ep, as well as between the percentage of anodic curves with a well-defined pitting potential and the uncertainty in the determination of Ecorr.