Facile microwave-assisted fabrication of WC-Al2O3 composite powder from WO3-Al-C mixture
(1. School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran;
2. Department of Materials Engineering, Faculty of Engineering, Malayer University, Malayer 65719-95863, Iran;
3. Research Laboratory of Hydrothermal Chemistry, Kochi University, Kochi 780-8520, Japan)
Abstract: A facile and cheap method for the fabrication of WC-Al2O3 composite powder was proposed. Thermodynamic calculations indicate that aluminothermic reduction of WO3 in WO3:xAl:(4-1.5x)C mixture is accompanied by a great deal of heat, so carbothermic reduction reaction (endothermic) becomes activated in the system. By substitution of aluminum with carbon, the formation of unwanted W2C phase can be prevented because of less thermodynamic stability at lower temperatures. For the verification of the proposed reaction mechanism, various WO3:xAl:(4-1.5x)C mixtures (1.1≤x≤2) were heat-treated in a domestic microwave oven. The results showed that the type of reaction is self-propagating high temperature synthesis (SHS) when 1.4≤x≤2. Lower amount of Al in WO3:xAl:(4-1.5x)C mixtures results in a higher formation of WC. A W2C-free WC-Al2O3 composite was obtained by continuation of microwave heating in an isolated atmosphere, after the occurrence of SHS reaction in a mixture containing 1.4 mol of Al. Results also showed that when x≤1.3, type of reaction becomes gradual, which in turn brings about the incompleteness reaction and residue of initial reagents.
Key words: microwave heating; combustion synthesis; WC-Al2O3 composite