Materials Science Forum Vols. 727-728

Abstract: Ceria-based materials have been extensively studied due to their wide range of technological application. In this work, nanostructured powders of 20 mol% gadolinia-doped ceria pure and containing 1 mol% manganese were synthesized by the cation complexation technique. Powder materials were calcined at 600°C, uniaxially pressed and sintered in the 1200-1500°C range for soaking times of 1, 2 and 4 h. X-ray diffraction patterns evidenced a single-phase fluorite-like structure in all studied specimens. The evolution of grain sizes was evaluated by scanning electron microscopy on polished and thermally etched surface of sintered pellets. The relative density decreases for soaking times above 1300°C (with Mn) and 1400°C (without Mn). The grain size increases with manganese addition. The role of the additive on the electrical conductivity of gadolinia-doped ceria was evaluated by impedance spectroscopy measurements.

Abstract: This study aimed to assess the performance of the solid catalyst Ni_0.4Cu_0.1Zn_0.5Fe₂O₄, synthesized by combustion reaction, over the methyl esterification reaction of the fatty acids present in cottonseed oil. The catalyst was characterized by XRD, FTIR pyridine absorption, Raman spectroscopy, and SEM. The reactions were conducted at 140 and 180°C with molar ratios of 1:3, 1:6 and 1:9, with 2% of catalyst and reaction time of 2 h. The XRD results showed that the single phase ferrite was obtained with surface area of 87 m²/g and with mesoporous characteristic. It was observed from the FTIR pyridine absorption only the presence of Lewis acid sites. The Raman spectra confirm the presence of the inverse spinel phase. The results indicated that at 180°C and molar ratio of 1:9, the conversion of free fatty acids was about 87%.

Abstract: In the ceramic coating industry, color and its stability influence the visual appearance of the product. These features account for the growing interest in obtaining pigments that are stable and may optimize the process. There are different synthesis routes to obtain pigments. Obtaining glass and its subsequent crystallization is an alternative proposed in the literature. This study focuses on the possible use the glass of the Li2O-ZrO2-SiO2 system as base glass and hematite as chromophore source. Different contents of hematite (1%, 2%, 3%), from the beneficiation process of metal sheets were used. The choice of composition aimed at facilitating the devitrification process for the formation of zirconia, which is often used as an encapsulating matrix in inorganic pigments. Results showed that glass synthesis is feasible and the effect of crystallization in the presence of hematite is favored, so an effective pigmenting effect is expected.

Abstract: In this work CCTO have been synthesized in two different chemical precursors: calcium hydroxide and copper sulfate were used to compose CCTO-S powder while calcium carbonate and copper nitrate were used to form CCTO-N powder. Calcinations conditions were dramatically different in terms of shelf time and temperature. The CCTO phase was fully obtained for 3 hours of calcination in CCTO-N against the 24 hours to form the same phase in CCTO-S powder. Ceramic bodies densities values for CCTO-S samples were 95% of theoretical density (5.05 g/cm³) and 98% for CCTO-N. The dielectric constant, at room temperature, was obtained for ceramics processed by two routes. Microstructural analysis was conducted by Scanning Electron Microscopy (SEM) and it was performed to explain the dielectric constant differences between CCTO-S and CCTO-N ceramics.

Abstract: The synthesis and ceramic processing of samaria and gadolinia doped ceria - nickel oxide composites, mainly applied as Solid Oxide Fuel Cell anodes, were studied in this work. Powders with composition Ce_0.8(SmGd)_0.2O_1,9/NiO and mass ratio of 40/60%, were synthesized by hydroxide coprecipitation with CTAB surfactant, followed by solvothermal treatment in n-butanol, ethanol and n-propanol at 150 °C for 16 hours, calcination at 600°C for 1 hour and milling. Sintering of compacted samples was performed at 1300°C for 1 hour. The powders were analyzed by X-ray diffraction, scanning electron microscopy, nitrogen adsorption method (BET), laser beam scattering (Cilas) and TG/DTA. The ceramics were analyzed by scanning electron microscopy, EDS, XRD and density measurements by Archimedes method. The results showed that the powders have a high specific surface area (42 - 85 m²/g). The ceramic characterizations showed a high chemical homogeneity and density value of 99% TD for powders treated with ethanol and propanol.

Abstract: The aim of this work is to evaluate the esterification and transesterification activity of ZnAl₂O₄ catalysts obtained by different ways of heating during the combustion synthesis using glycine as fuel. Samples were prepared according to the propellants and explosives theory using a vitreous silica crucible as container, and as heating source, plate, muffle furnace and microwave oven. After synthesis, the samples were structural and morphologically characterized by: XRD, nitrogen adsorption and carbon content analysis, and employed in the esterification and transesterification reactions, the percentage of biodiesel formed (FAME) was determined by gas chromatography. The samples obtained on the plate, muffle furnace and microwave showed that even using different heating ways, led to the formation of ZnAl₂O₄ as majority phase, with crystallite sizes of 11, 15 and 10 nm, respectively. The samples present values of surface area ranging from 16 to 77 m²/g, particle size from 17 to 81 nm, and carbon content lower than 11%. The forms used for heating influenced the esterification and transesterification reactions, showing that there was a gap in the production of biodiesel, which is a promising indication that this material has potential to be used as catalysts on the biodiesel production.

Abstract: For the combustion synthesis of strontium doped lanthanum manganite (LSM), different fuels can be used influencing the phase formation and also the powder morphology. Both are important features that can improve the material performance when used in a solid oxide fuel cell cathode. Urea and sucrose are fuels used to synthesize distinct LSM powders, thus the purpose of this work was to mix these fuels in order to obtain nanocrystalline LSM powders with a differentiated morphology, more convenient for the desired application. After calcination at 750°C for 3 hours the powder generated a pure phase LSM X-ray diffraction pattern and the micrographs taken in the transmission and scanning electron microscopes revealed a very peculiar morphology with specific surface area (BET) of 13 m²/g. Calcination led to a single phase and more crystalline material but showed no influence in the powder morphology.

Abstract: Oxide ceramics show better oxidation resistance at high temperatures than other ceramics; however they are more susceptible to plastic deformation at elevated temperatures [. If their high temperature mechanical properties could be improved, they would be expected to open a wide range of applications as structural material [2, 3]. Several studies have revealed [4, 5] the potential use of YAG oxides as reinforcing component oxide in a ceramic matrix. Both YAG and Al₂O₃ have similar thermal expansion coefficient and they are chemically stable because of their low O₂ vapor pressure. In addition, there is no solid state phase transition as the temperature rises, but the eutectic reaction at 1826°C with Al₂O₃ molar concentration of 81.5% and 18.5% for Y₂O₃ which enable a fusion processing, turning the Al₂O₃-YAG composites very attractive. This eutectic reaction is possible in the restrictive composition from 18.5 to 20.5 mol% Y₂O₃ [6].

Abstract: In this paper we propose the stabilization of zirconium oxide with controlled additions of a rare earth elements concentrate, in the system ZrO2: ƞ wt% Re2O3 (with ƞ=5.36, 10.47, 13.74, 16.91 e 20) where Re₂O₃ is a rare earth elements concentrate composed mainly of 76.88% of yttrium oxide, 12.1% of Dysprosium oxide, 4.04% of Erbium oxide and 1.94% of Holmium oxide. The synthesis method used was the Pechini method. The results show that additions of 5.36 and 20 wt% of the concentrate are enough to stabilize the tetragonal and cubic zirconia phases respectively, and that zirconium oxide polymorphs can coexist with additions within these limit. In the characterization of the obtained powders are presented and discussed the following results: differential scanning calorimetry, transmission electron microscopy and X-ray diffraction. Also, it was necessary to make analysis by Rietveld refinement because they had severe overlap in the diffraction peaks. One of the most relevant results is obtaining a raw material, cheap to be used in many technological applications.

Abstract: t is well recognized that a catalyst agent is essential to synthesize diamond at high pressure and high temperature. The catalyst agent also acts as a carbon solvent and affects the properties of the final product. This is a consequence of its direct influence on the growth of diamonds crystals. The control of the growth, which is required to achieve a high quality level, is still a question open to discussion. In this work, an industrial diamond powder was synthesized from graphite using Ni-Mn as catalyst alloy added with up to 5% of iron. The synthesis was carried out at 4.5GPa and 1300°C for 10 minutes in high pressure device with central concavity. The analysis of the cubic-shaped diamond surface topography suggests that the formation of defects on the {111} faces is most likely a consequence of a complex growth process that influences the crystal productivity and morphology.