Synthesis of WSi2 from Scheelite (CaWO4) by Self-Propagating High-Temperature Synthesis (SHS) Process

Abstract

In this research work, tungsten silicide (WSi2) intermetallic and tungsten silicide (WS12-W5Si3) intermetallic alloy were prepared via self-propagating high- temperature synthesis (SHS) from two aluminothermic and magnesiothermic reactant systems. The equilibrium compositions of the reactions were calculated by standard Gibbs energy minimization. The phase separation with and without the sand mold to produce these materials was applied. The resulted products properties such as phase separation, density, and micro-hardness were examined. The phase constituents and microstructure morphologies of the products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX)- capability. In the first part, tungsten silicide (WSi2) intermetallic was prepared via SHS from two aluminothermic reactant systems using scheelite (CaWO4-Si-Al) and pure oxide (CaO-WO3-SI-AI). The effects of high-energy milling of reactants, for the duration of 0.5, 2, 4 and 8 hr, and the effects of sand mold on the result products were studied. According to the experimental results, intermetallic WSiz was successfully synthesized with both systems. Using pure oxide (CaO-WO3-Si-Al) reactant gave a higher yield of WSi2 than that of scheelite mineral (CaWO4-Si-Al), and the yield can be optimized by increasing the proportion of Si in the (CaWO4-Si-Al) reactant system. Moreover, it was found that the use of a sand mold helped the phase separation of the oxide slag and its intermetallic. The second part, tungsten silicide (WSi2-W5Si3) intermetallic alloy was synthesized using SHS from the magnesiothermic reaction. The raw materials used were WO3, Si, and Mg as fuel. The SHS process successfully synthesized with higher weight percentage and dense alloy product of the WS12-W5Si3 intermetallic alloy. In addition, the true density (p) of intermetallic alloy has 8.97 g/cm3 which is 96.42% of the theoretical true density. Furthermore, it is important to notice that the magnesiothermic reaction can produce the dense and homogeneous distribution of WSi2 and WsSi3 intermetallic alloy in the as-SHS product.