Materials Science Forum Vols. 798-799

Abstract: Ceramics of Pb_1.02(Zr_0.53Ti_0.47)O₃ (PZT) comprise the majority of piezoelectric devices in use today. In general, these ceramics are obtained by solid-state reaction, which favors the formation of micrometric grains. Recent studies have shown that reducing the particle size from micro to nanoscale, it generates PZT ceramics with superior dielectric properties. In this way, this study aimed to obtain nanostructured PZT ceramics from the coprecipitate method, using precursor materials as oxides reagents. From the Differential Thermal Analysis (DTA) was observed that the formation of PZT through the proposed methodology is initiated at 550^oC. However, the full phase crystallization was observed at 850^oC confirmed by X-Ray Diffraction (XRD). Spherical particles near 200nm were observed using scanning electron microscopy (SEM). This powder was sintered in conventional and microwave oven. The ceramics obtained from both sintering methods showed substantial differences in microstructure such as presence of piroclore phase and grain morphology.

Abstract: New sources of silica as a replacement for TEOS in the synthesis of SBA-15 are been performed by various research teams worldwide. The aim of this work is to describe the synthesis and characterization of SBA-15 made with chocolate B clay as an alternative source of silica by the hydrothermal method. Samples of classic SBA-15 were made with the traditional TEOS method. The samples of the two silica sources were characterized by DRX, EDX, and BET to evaluate the effects of the silica source on the synthesis of the molecular sieve. The chocolate B clay was efficient in the formation of the molecular sieve structure, but there was a great reduction in the surface area and total pore volume in comparison to the surface area of classic SBA-15.

Abstract: Bentonite clays, due to an immense variety of applications, are widely studied. Yet currently, organically modified bentonite clays studies have been increasing. The methods most studied involve addition of ionic or non-ionic surfactants to synthesize organophilic clays. The synthesis can be performed in two ways: by ion exchange (double replacement reaction chemistry), or by ion-dipole interaction where organic molecules are adsorbed on the surface of clay. The present work studies the sorption mechanisms of ionic and non-ionic surfactants to the surface of bentonite clays, thus making them organophilic. The results for the sorption experiments were obtained by adjusting the parameters of known mathematical models to the experimental data, the linear, and Freundlich models gave the best results for the sorption isotherms.

Abstract: This study aims to conduct an investigation on the performance of an organophilic clay as adsorbent in the oil/water separation process. One goal of this work is to prepare and characterize untreated sodium clay (BSN-01) from Argentina and treated BSN-01. The method used to prepare the organoclay replaces the interlayer cations of the clay (Na⁺) by quaternary ammonium cations. Tests used X-ray diffraction to verify the obtaining of organoclays. The diffractograms showed that the basal distance of the clay BSN-01 was modified, indicating that the quaternary ammonium salt was intercalated. The results of Cation Exchange Capacity suggested that the interlayer cations of the clay were exchanged with the quaternary cations of the surfactant. Finite bath tests determined the rate and capacity of oil removal by the treated clay. Up to 42.63 mg/g of oil removal capacity (92.34% efficiency) was reached, indicating that the clay treated with CTAC is an excellent alternative in the process of oil removal.

Abstract: Given the opportunities that aluminas present in relation to the broad field of applications to which they refer, the literature has reported great diversity in methodology to obtain these materials in the search of generating the best properties. In this way, the aim of this work is to evaluate the use of different citric acid and metallic cation ratio on the structural and morphological characteristics of the alumina synthesized by Pechini method and calcined at 1100°C. The samples were characterized by X-ray diffraction, thermal analysis, particle size and scanning electron microscopy. The results showed a large amount of loss of mass after pyrolysis. The α-alumina phase was achieved for the two studied ratio reaching values for crystallite size of 41.4 and 52.5 nm, crystallinity of 88 and 91.2%, agglomerates size of 12.3 and 14μm, for the synthesized samples 2:1 and 3:1, respectively. According to the SEM images, the changes in the citric acid: metallic cation ratio did not significantly modify the morphology of the alumina.

Abstract: Through the constant search by researchers to obtain materials with improved properties, literature has presented an annual increase in the number of articles that seek to optimize in the methodology used to prepare nanopowders. In this way, the aim of this work is to study how the calcined temperature (500, 600, 700, 800, 900, 1000, 1100 and 1200oC) changes the final properties of the alumina synthesized by Pechini method with citric acid: metallic cation ratio of 2:1. The alumina was characterized by thermal analysis, X-ray diffraction, particle size analysis and scanning electron microscopy. The results showed a total of mass loss of 61.6%. The alumina phase appear at 800°C of temperature, however the α-alumina only appear at 1100oC. The increase in the calcined temperature increases the crystallite size and the crystallinity of the alumina and the great value reached for the agglomerates diameter was 13μm for the alumina calcined at 1200oC. In relation to the morphology of the alumina, it was observed heterogeneous particles with different size and irregular geometry, with aspect of high density.

Abstract: Oxygen ion conductors of zirconia based ceramics are a class of materials with technological applications in several application areas: sensors of chemical species, oxygen pumps, solid oxide fuel cells among others [1]. For these applications, the zirconia must possess the fluorite type crystal structure, or close to it. Such oxides with this structure are the classic oxygen ion conductors [2]. The fluorite structure consists of a cubic lattice of oxygen ions surrounded by cations. The cations are arranged in a face centered cubic structure with anions occupying tetrahedral positions. This leads to an open structure with large empty octahedral interstices.

Abstract: This work has as main objectives to produce the ceramic Sr₂MgWO₆ and evaluate their reactivity to petroleum. Powders of SrCO₃, MgO and WO₃ were selected, taken in stoichiometric amounts and synthesized by conventional route. The synthesis was characterized by size distribution, specific surface area and thermogravimetric analysis (TGA). The synthesis was also fragmented into ball mill and characterized by specific surface. It was compacted, then was calcined at 1200 °C and analyzed by X-ray diffraction. The powders Sr₂MgWO₆ with perovskite structure were compacted and sintered at 1250, 1300 and 1350 °C. The materials produced were evaluated by microhardness, scanning electron microscopy (SEM), diffraction of X-rays and tests submersion in petroleum. The results showed that the ceramics have high microhardness and potential to be used in chemically aggressive environments such as petroleum.

Abstract: In this paper, CuCrO₂ the compound was synthesized by a route new that uses gelatin as organic precursor in order to application as ceramic pigments. The type of compound delafossite CuCrO₂ is known for its wide range of application, such as, thermoelectric devices, catalysts for the steam reforming process, ceramic pigments, NiO2 removal, among. The powders resulting from the synthesis process were calcined the 900 ^°C and characterized by X-ray diffraction (XRD), infrared spectroscopy, scanning electron microscopy (SEM), UV-Visible spectroscopy and colorimetry analysis. The results showed for the CuCrO₂ have coloring green.

Abstract: Solid electrolytes based on stabilized zirconia have been studied a long time ago in its cubic phase because of its electrical properties, which make them excellent candidates to be used in applications such as oxygen sensors and solid oxide fuel cells [1], [2]. Lambda sensor or oxygen sensor, as it is also known, is a device that measures the oxygen concentration of the gases that flow through the exhaust pipe. Physically, the lambda sensor has two electrodes. The outer which is exposed to the exhaust gases and the inner to the air (reference) [3]; these electrodes are made, generally, of porous platinum. The ceramic material, i.e., zirconium oxide, is placed in between the electrodes, so the oxygen ions can move from one electrode to another. As one of the electrodes is exposed to the reference gas, the voltage generated is a measure of the concentration of oxygen in the exhaust gases [4].