(Invited) Structural Control of Molybdenum Silicide By Electrolytic Silicification of a Mo Substrate

Abstract

Metal silicides are attracting attention as environment-friendly functional materials because they are composed of abundant elements in the earth’s crust. However, conventional processes for preparing silicides from SiO2 as the starting material consume a lot of energy and utilize hazardous materials through the reduction process of SiO2. Against this background, the electrochemical process in molten salt become key technology for fabricating silicon materials in an environmentally friendly, simple, and inexpensive process. We have already reported the electrodeposition of metallic silicon films from SiO2 in high temperature molten salt. This process has the potential to develop environmentally friendly and sustainable systems for fabricating silicon materials by combining non-consumable oxygen-evolving anodes. In this study, we focused on the electrochemical formation of molybdenum silicide from SiO2 in molten chloride because the molybdenum silicide are promising materials for ultra-high temperature protective coating, heating element, and thermoelectric conversion element. We report here the electrochemical formation of molybdenum silicide in CaCl2-based molten chloride containing SiO2 system. A Mo substrate was used as the working electrode. From the results of characterization by XRD, SEM, and EDS analysis, a metastable β-MoSi2 phase and stable α-MoSi2 phase were obtained by controlling applied potentials during potentiostatic electrolysis. In addition, since the nucleation and growth process of the silicide is very important to control its structure, composition and morphology, the electrolytic time transient between molybdenum substrate/molten chloride interface were carefully observed by SEM analysis. The fundamental research on formation process of silicides in molten salt will greatly contribute to materials science in high temperature environment and developing the novel rout for fabricating silicon materials.