Materials Science Forum Vol. 805

Abstract: The State of Paraíba, Brazil, retains about 88.5% of all Brazilian bentonite, and much of this production comes from deposits in the District of Boa Vista, PB. Nevertheless, the deposits are almost depleted. Recently, new deposits were found, which will increases the reserves of the State, in the regions of Cubati and Pedra Lavrada, PB. The objective of this work is to characterize and develop purified clays, through sieving and hydrocycloning techniques, from those recently discovered bentonites for several applications. The characterization of the sample was done through granulometric analysis by laser diffraction, X-ray diffraction, chemical analysis by X-ray fluorescence, and thermogravimetric and differential thermal analysis. The results show that the samples are typical of bentonite clays, and that the purification solely by hydrocyclone presents the best results.

Abstract: Organoclays are used as disperse agent in the composition of drilling fluids, which play important roles during the drilling of petroleum wells. This work is intended to develop several kinds of smectite from Cubati-PB for use in drilling fluids, using the ionic surfactant Praepagen WB. The following materials were used: natural Gray and Superior Green bentonite, from the town of Cubati-PB, and quaternary ammonium salts: Praepagen WB® with 45% active matter. The organoclays were characterized by laser diffraction granulometric analysis, chemical composition by X-ray fluorescence, thermogravimetric analysis, differential thermal analysis and X-ray diffraction. In general, we noticed that the clays present diffractograms and thermal behavior typical of bentonites. The results showed that the studied clay has potential for organofilization. With respect to the process variables, we observed that they do not interfere in the organofilization process.

Abstract: The traditional Ni-based anodes are capable of providing a good power output using H₂ and CO fuels, but sulfur contamination in any hydrocarbon fuel is a problem. Thus, perovskite structure materials containing lanthanum have been widely studied as electrodes for solid oxide fuel cells (SOFCs), due to its electrical properties. In this work was investigated the obtain of the perovskite structure LaCr_0.5Ni_0.5O₃, by Pechini method, and its suitability as SOFC anode. The choice of this composition was based on the stability provided by chromium and the catalytic properties of nickel. After preparing the resins, the samples were calcined at 300oC, 600oC, 700oC and 850oC. The resulting powders were characterized by X-ray, X-ray fluorescence spectroscopy, He pycnometry, specific surface area by BET isotherm and scanning electronic microscopy. The obtaining of the powders of LaCr_0.5Ni_0.5O₃ through the Pechini method proved to be effective for temperatures above 850oC.

Abstract: This work investigated the synthesis of α-alumina using dissolution and re-precipitation of aluminum nitrate and microwave heating. The synthesized powders were characterized by X-ray diffraction, thermal analysis (TGA and DTA) and surface are by BET. The dissolution process was carried out using acid solution and heat treatment. Results depicted the efficiency of the process to accelerating the synthesis of alpha alumina. The results showed that the powders have the microwave structure of α-alumina with specific areas ranging between 3 and 15m²/g and pore diameters between 190 to 485nm.

Abstract: Alumina is a material used in a wide range of applications, including refractories, structural materials, sensors, catalysts, etc. Several synthesis methods are available for the production of submicrometric and nanometric alpha alumina. However, there is few studies on the use of acetate for the synthesis of alumina. Thus, the present work has as aim the synthesis of alumina powders using aluminum acetate. The precursors were obtained from the decomposition of aluminum acetate under temperatures of 650oC and 850oC, resulting in an amorphous precursors and gamma-alumina. These materials were submitted to dissolution and calcination. Based on the results, it is observed a reduced in the temperature formation of alpha phase, at around 900^oC, when using the adopted methodology of synthesis. Amorphous precursor was more susceptible to the synthesis procedure used and generated alpha alumina in lower temperatures.

Abstract: The solid oxide fuel cell are an alternative of production clean and efficient energy, because converts chemical energy in electrical energy. A fuel cell is formed basically by an electrolyte, a cathode and an anode. The main electrolyte used for SOFC manufacturing is the ZrO₂-Y₂O₃. The materials for electrode manufacturing must possess thermal expansion characteristics close to electrolyte and have high electrical conductivity in operating temperature. Recently, the perovskite LaNi_0,6Fe_0,4O_3-δ, has attracted interest for application as cathode in SOFC ́s for has a high electronic conductivity and a thermal expansion coefficient whish for the zirconia electrolyte. This work aimed to LaNi_0,6Fe_0,4O_3-δ obtained by Pechini method. The powders were characterized by differential thermal analysis, thermogravimetric analysis, x-ray diffraction, energy dispersion X-ray fluorescence spectroscopy, helium pycnometry and scanning electron microscopy. The results showed powders obtained with perovskite formation when calcined 600°C during 2 hours.

Abstract: Low crystalline PZT powder samples were successfully synthesized using polymeric precursor method and slow decomposition steps. The polymeric resin precursor was thermal treated in a muffle type oven varying the temperature from 250 °C to 700 °C and the time from 3 to 24 hours in order to investigate the order/disorder mechanism toward the amorphous powders. Powder samples with low crystalline phases were obtained at lower temperatures and long time of thermal treatment, demonstrating a kinetic dependence for organic removal and a thermodynamic barrier for crystallization processes. Through XRD and FTIR spectroscopy characterizations the long time thermal treated samples showed to be composed of the solid solution of metal oxides in absent of organic matter, originating broad XRD peaks profiles and no carbonaceous bands in FTIR spectra. A Photoluminescence characterization showed that the peak emission is higher for disordered and homogeneous phases, which only can be reached through the long time of thermal treatment.

Abstract: The compressive strength as well as other technical properties of structural clay masonry blocks are usually significantly affected by the firing temperature. The present work studied the temperature control response of structural clay masonry blocks when changing the firing condition from 700 to 800°C. Structural clay blocks fired at 700°C in an industrial furnace were compared with those fired in a laboratory electrical muffle furnace at 800°C. Both water absorption and compressive strength tests were carried out for the different brick samples. The block sample fired at 700°C failed to attend both the water absorption and the compressive strength requirements for structural elements. By contrast, after 800°C firing, the laboratory sample attended the water absorption specifications and showed higher compressive strength within the Brazilian standards.

Abstract: The state of Rio de Janeiro, southeast of Brazil, has two poles of conventional clay ceramic production, mainly bricks and roofing tiles. In the north region of the state, the county of Campos dos Goytacazes and in the state center, the county of Itaborai, present distinct types of clay. With the aim to improve some characteristics of the Campos dos Goytacazes clay, the objective of this work was to investigate different mixtures with the Itaborai clay. Samples were press-molded with compositions of 0, 25, 50 and 75 wt% of both clays. The samples were fired at 800°C and the technical properties related to plasticity, density, linear shrinkage, water absorption and flexural strength were determined. The results indicated that the superior performance of the Itaborai clay significantly improves that of the Campos dos Goytacazes clay for any incorporated percentage. The mechanisms and reasons for these results are discussed.

Abstract: This work has as its objective to evaluate the influence of the dry bulk density in precursor body formulations developed to fabricate ceramic paver. Cylindrical specimens were uniaxial press-molded into two dry bulk density ranges, 1.99-2.05 g/cm³ and 2.18-2.23 g/cm³, from three formulations elaborated with clays, argillite and grog and then fired at 850 and 950oC. The evaluated properties were: water absorption and uniaxial compression strength. The results indicated that the packing during the forming stage is an important technological parameter that significantly influences the evaluated properties.