Effect of heat absorbing alumina addition on mechanochemical synthesis of WC–Al₂O₃nanocomposites

Abstract

It has been shown earlier that formation of undesirable W 2 C phase during mechanochemical synthesis of WC-Al 2 O 3 composites from WO 3 -Al-C mixture is due to high temperatures caused by the large heat release during the initial aluminothermic reduction of WO 3 . With the aim of preventing the formation of W 2 C, in this study, Al 2 O 3 was added to lower the reaction temperature. Thermodynamic calculations showed that Al 2 O 3 presence in WO 3 /2Al/C/xAl 2 O 3 mixtures would lower the adiabatic temperature. Experimental findings revealed that with no Al 2 O 3 addition, released heat in the mixture activates carbothermic reduction of WO 3 and causes carbon deficiency, which results in W 2 C formation. When x50?6, although product consists of W 2 C phase, the coolant effect of alumina diminishes carbon deficiency phenomenon with a consequence of more WC formation. For the WO 3 /2Al/C/1?2Al 2 O 3 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-Al 2 O 3 powder contains nanosize particles.