Effect of heat absorbing alumina addition on mechanochemical synthesis of WC–Al2O3 nanocomposites

Abstract

It has been shown earlier that formation of undesirable W2C phase during mechanochemical synthesis of WC–Al2O3 composites from WO3–Al–C mixture is due to high temperatures caused by the large heat release during the initial aluminothermic reduction of WO3. With the aim of preventing the formation of W2C, in this study, Al2O3 was added to lower the reaction temperature. Thermodynamic calculations showed that Al2O3 presence in WO3/2Al/C/xAl2O3 mixtures would lower the adiabatic temperature. Experimental findings revealed that with no Al2O3 addition, released heat in the mixture activates carbothermic reduction of WO3 and causes carbon deficiency, which results in W2C formation. When x = 0·6, although product consists of W2C phase, the coolant effect of alumina diminishes carbon deficiency phenomenon with a consequence of more WC formation. For the WO3/2Al/C/1·2Al2O3 mixture, carbothermic reduction reaction was prevented, which brings about complete conversion of W to WC after milling. The TEM observations showed that the produced WC–Al2O3 powder contains nanosize particles.