Formation of Al 2 O 3 –WC powders from Al–WO 3 –C mixtures

Abstract

Al₂O₃–WC powders were prepared by an aluminothermic reduction carbonisation method using Al powder, yellow tungsten oxide and carbon black or graphite as raw materials under coke. Effects of Al₂O₃ content, temperature, C/WO₃ molar ratio and atmosphere on the synthesis of Al₂O₃–WC powders were studied. The results showed that the relative content of WC and W₂C was strongly influenced by the factors mentioned above. Al₂O₃–WC composites were more easily obtained under coke than under Ar. The reaction is more feasible with carbon black owing to its higher reaction activity than graphite. The participation of CO in the coke layer is the reason that tungsten or WO₃ is feasible to be carbonised and W₂C can be easily converted into WC. Under coke, even without carbon source in the starting mixture, Al₂O₃–WC powders can also be obtained from the mixture of Al, WO₃ and 0·5 mol Al₂O₃. Scanning electron microscopy observation shows that the morphology of the reaction products varies with calcination conditions and the compositions of the raw materials. Thermodynamics is used to analyse the reaction process.