A novel green strategy for the preparation of ultrafine-grained WSi2 and W5Si3 powders

Abstract

Tungsten silicides (WSi2 and W5Si3) are important high temperature structural materials and have attracted great interest because of their excellent elevated temperatures characters, including good corrosion resistance, excellent oxidation resistance and mechanical properties. In this manuscript, a novel route for the preparation of ultrafine-grained WSi2 and W5Si3 powders via silicothermic reduction of tungsten disulfide (WS2) with CaO as the desulfurizer is proposed, and the reaction mechanism and kinetics were investigated in detail. The results show that WSi2 and W5Si3 powders can be prepared at 1100oC with a WS2:Si molar ratio of 1:4, as well as at 1200oC with a WS2:Si molar ratio of 1:2.4, respectively. In addition, it was found that gaseous SiS acts as both the product and the reducing agent during the silicothermic reduction of WS2. The reaction between WS2 and Si can be divided into two stages: in the initial stage, WS2 and Si undergo solid-solid reaction to form WSi2 and SiS; in the gas-solid reaction stage, gaseous SiS reacts with WS2 to generate WSi2 and SiS2, and meanwhile, SiS2 reacts with Si to form SiS. Additionally, both the as-prepared flake-like structured WSi2 and W5Si3 particles are composed of a large number of ultra-fine grains. Morphological observation demonstrates that the prepared WSi2 and W5Si3 powders inherit the size and flake-like structure of WS2 and are little affected by the size of Si. Furthermore, the kinetic analysis results show that the reaction between WS2 and Si should be controlled by the interfacial chemical reaction between gaseous SiS and WS2, and the extracted activation energy is about 184 kJ/mol.