Papers by Keyword: γ-Alumina

Abstract: The effect of the transformation of phase in nanopowders of transition alumina has showed to be detrimental for the final characteristics of the consolidated materials. It was found that the complete transformation from gamma (γ-Al₂O₃) to alpha (α-Al₂O₃) alumina generated larger grain sizes and lower relative densities. This work studies the effect of slip casting preformed on the transformation phase of alumina during microwave sintering of α-alumina nanopowders. The sintering of the samples was carried out in a typical unimodal microwave furnace with a 2.5 GHz frequency. Sintering was carried out under air atmosphere at temperatures vary between 1100 and 1500 °C with heating rate of 100 and 200 °C/min and with a sintering plateau of 5 minutes. Sample characterization was performed by XRD, SEM, and TEM. The phase quantification was calculated using the Rietveld software from the XRD patterns. To have a good heating control in the microwave system it is possible by using slip casting to preform compact. It was observed that the heating rate has a strong effect on the phase transformations. Secondary phases like θ, θ’(x, y) appeared in samples sintered with a heating rate of 200 °C/min no matter the sintering temperature. Meanwhile the complete alumina transformation was found when sample were heating at 100 °C/min.

Abstract: Autogenous single pass full penetration welds of 2.8 mm thick AA 2014 plates were produced by un-pulsed and pulsed gas tungsten arc welding (GTAW) process. In pulsed current mode, two levels of pulsing viz., 3 and 6 Hz were employed. In order to improve the corrosion resistance of weld metals, micro arc oxidation (MAO) treatment was given in aqueous silicate solution containing either borax or tungstate. The MAO treatment was carried out for 10, 20 and 30 minutes. Irrespective of the electrolyte composition, surface roughness increased with increasing treatment duration. However, the effect was observed to be significant with borax addition. X-ray diffraction studies showed that γ-Al₂O₃ content in the coating continued to increase up to 20 minutes and for the coating produced with 30 minutes duration the α-Al₂O₃ content was found to be more than γ-Al₂O₃. The coating treated for 30 minutes exhibited relatively poorer corrosion resistance than the other coated specimens. The better corrosion resistance offered by the coating obtained after 20 minutes, compared with the other coatings, could be attributed to the nature of the oxide and its content. Even though tungstate addition improved hardness of the coating, borax addition was found to enhance the corrosion resistance.

Abstract: Mesoporous γ-alumina with relatively high surface area of ca. 590 m2/g and pore size of ca. 2.0 nm to ca. 9.7 nm were successfully processed using facile and cost-effective method in the presence of renewable, low-cost templates. Controlled addition of water during the processing of the materials was found to control the rapid hydrolysis rate of alumina precursors resulting in mesoporous formation. In addition, these materials porosity was made up from framework porosity as well as textural porosity given rise from the aggregations of γ-alumina nanoparticulates. Regardless of the materials specific surface area value, the competitive adsorption amount of energy gas in 68 % humidity environment increased as relative crystallinity of the materials increased.

Abstract: The γ-alumina powder is a potential material for washcoat application. This paper shows the preparation of γ-alumina using ultrasonic technique in order to obtain nanocrystalline of γ-alumina powder. The 50 gr of the γ-alumina powders was treated in the 250 gr ethanol solution using ultrasonic technique within 10, 20, 30, and 60 minutes, respectively. The process of sonication was set at the fixed frequency (18.520 kHz) and current of 2 A. Crystallite size was evaluated by using X-ray diffraction (XRD) data based with Scherrer analysis and Williamson-Hall method. The microstructural characterization of the γ-alumina powders was observed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) analysis. The result shows that the optimum of nanocrystalline size of γ-alumina at ultrasonic process for 30 minutes are approximately 4.80 nm and 29.50 nm with Scherrer and Williamson-Hall calculation, respectively.