Materials Science Forum Vols. 727-728

Abstract: One suitable material candidate to improve B₄C mechanical properties is SiC. B₄C-SiC ceramic composites are very promising armor materials because B₄C and SiC are intrinsically very hard. In this work a pressureless sintering study of B₄C-SiC ceramics was made. B₄C-SiC mixtures were prepared with SiC concentration from 10 to 50 wt%. Without the external applied pressure during sintering it was necessary to add sintering aid. The additive system AlN-Y₂O₃ was investigated as sintering aid. Samples were densified by pressureless sintering at 2000 °C/30 min in an argon atmosphere. B₄C-SiC composites were analyzed by XRD and SEM. Bulk density and total weight loss were also measured. Density higher than 93 % of the theoretical value was determined and microhardness of 30.3 GPa was achieved for composite with 10 wt% of SiC sintered with AlN-Y₂O₃ additive.

Abstract: The solochemical method was applied to prepare ZnO nanocrystals at low temperature, using sodium hydroxide and zinc chloride as starting materials. In this work, different addition times of the precursor solution were adopted and their effects on the crystalline domains (or crystallite) size and particle morphology of the obtained samples were investigated. The synthesized products were characterized by X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) techniques. The XRPD results revealed that all samples produced have a single ZnO hexagonal wurtzite phase (space group P6₃mc) under anisotropic strain. The parallel to perpendicular crystallite size ratio was about 1.21 for the sample produced with instantaneous addition of the precursor solution and 1.19 for 1 h longer addition time. The anisotropic strains become about 12% smaller for the sample produced with longer addition time. The TEM results of the samples showed ZnO nanometric particles with nearly rounded and rod-like morphologies.

Abstract: Advances in scientific research in the field of nanotechnology sparked an increase in technological and industrial applications involving nanoparticles, Moreover, there was increasing concern about the control of nanoscale particles released to the atmosphere, driven by concerns over air quality and human health. In this context, this study aims to determine the size distribution of TiO₂ nanoparticles generated by the commercial TSI Atomizer Aerosol Generator model 3079 for different solution concentrations and air flow rates. The concentrations of the TiO₂ solutions used in the generator were 0.0125, 0.025 and 0.05 g.L^-1, while the aerosol flow rates were 1.27, 2.55 and 3.82 L.min^-1. The size distribution was measured with the TSI Scanning Mobility Particle Sizer (SMPS) equipment, which provides the number of particles per size range. The results showed that even changing the concentration of TiO₂ in solution, peak concentrations of nanoparticles remained in the same range between 15 to 45 nm. Moreover, it was observed that particle concentration in the gas stream decreased with increasing flow rate.

Abstract: Biopolymers are a growing research issue since they appear as a solution to the emerging environmental concerns that have risen in recent years. They represent an interesting alternative to synthetic polymers for a short-life range of applications. Recently, great attention has been paid to the association between biopolymers with nanosized llers, in particular, to those in which layered silicates are dispersed at a nanometric level in a biopolymer matrix. Surch materials called nanobiocomposites. In this work, Brazilian bentonite clay was organophilized with three organic intercalants by ion-exchange reactions for use in nanobiocomposites. The clay was characterized by X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and Thermogravimetry (TG). The XRD results confirmed the increased spacing basal because the presence of intercalant molecules in the clay, too confirmed by FTIR. The organoclay showed greater weight loss than the clay without modification. The structure had produced nanobiocomposites exfoliated and/or partially exfoliated.

Abstract: The development of solid oxide fuel cell with thin film concepts for an electrode supported design based on the yttria-stabilized zirconia has demonstrated favourable results due to its high chemistry stability in oxidization and environment reduction. The spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on different substrates. The precursor solution was obtained by zirconium and yttrium salt dissolutions in a mixture of water and glycerine in several ratios to study the solvent influence. The substrate was initially heated at 600 °C and during the deposition it ranged from 260-350°C, finishing at a fast increase in temperature of 600°C. The heat treatment was carried out in four different temperatures: 700 °C, 750 °C, 800 °C, and 900 °. The precursors were characterized by thermal analysis. The microstructures of the films were studied using scanning electron microscopy and X-ray diffraction. The results obtained showed that the films obtained were crystalline before the heat treatment process and have shown ionic conductivity above 800°C.

Abstract: Based on recent studies this research aims to continue the studies on nanocomposites obtained by blending polypropylene (polymer matrix) and bentonite clays of Paraíba, with emphasis on issues related to the surface modification of clays (charges), with the aim of stimulating the compatibility between the inorganic and organic components, since after the modification with organic surfactants, is easier for the clay to interact with the polymer. First was evaluated the effect of the concentration of clay (0.5, 3 and 5 phr - parts per hundred resin) on the properties of polypropylene and then a compatibilizer was used in order to further increase the properties of the composites. The results showed a very significant increase in both mechanical and morphological properties of the material as a function of clay content in the polymer matrix and dispersed systems with compatibilizer showed even higher properties, such as a significant gain in impact strength of polypropylene without loss in modulus of elasticity.

Abstract: Various methods have been reported to obtain nanosized ferrite particles such as chemical coprecipitation, sol-gel, spray-drying, microwave plasma, sonochemical, hydrothermal synthesis, reverse micelle technique and mechano synthesis. In this work Nickel Ferrite nanoparticles are produced using coconut water or pectin extracted from apple peel (using sulfuric or chloridric acid) as precursor for the proteic sol-gel (PSG) method. The samples are prepared by drying and subsequent isothermal treatment of the sol gel at 873 or 1173 K during 2 hours. The resultant materials were analyzed by Fourier Transform Infrared Spectroscopy (FTIRS) and discussed with emphasis in the purity of the samples produced.

Abstract: Among the researches on preparation and test of nanostructured materials, titanium dioxide and zinc oxide have been the most frequent studied oxides. In order to extend their properties, composites have been prepared using three different methods: Polyol Method, Sol-gel Process and a combination of the two processes (hybrid process). Recent research showed best properties in composite materials than in pure oxides. In this work is presented the preparation and the structural characterization of ZnO-TiO₂ composite nanostructures to be tested for their performance in electrocatalysis and in further trial on photovoltaic cells.

Abstract: Polymers nanocomposites are a class of materials where inorganic substances with nanometrics dimensions are modified and used as dispersed loads in polymers matrices. In this work, polyamide 6.6 was chosen because of its excellent chemical, mechanical and thermal properties. The bentonite clay was treated with quaternary ammonium salt (Cetremide®) to make it organophilic and to improve the interaction with the polymer matrix. It was verified by the Torque Rheometry that the system with salt presented a bigger torque in relation to the torque of the system with untreated clay and pure polyamide 6.6. The nanocomposites presented an exfoliated and partially exfoliated structure, as evidenced by XRD. By DSC, it was observed that the treated clay increases the decomposition temperature of the nanocomposite.

Abstract: Bentonites are the most used fillers in the development of nanocomposites, due to their characteristics that provide nanosized particles, contributing to a large contact area between the clay and the polymer. In general, the additions of small amounts of organoclay improve the mechanical and thermal properties of nanocomposites. Bentonite clays and organoclays were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). The results of XRF, XRD and FTIR confirmed the presence of quaternary ammonium salt in the organoclay structure. From TG, it was observed that the organoclay showed better thermal stability when compared with bentonite clay.