In-situ synthesis of MoSi2 coating on molybdenum substrate by electro-deoxidation of a SiO2 layer in molten salt

Abstract

MoSi2 coating was fabricated in situ by electro-deoxidation of SiO2 layer pre-fabricated on molybdenum substrate in molten calcium chloride at 900°C. The characteristics of the composition and microstructure of the coating under different conditions were investigated. And the cyclic voltammograms of the silica layer in molten calcium chloride were also analyzed, aiming to achieve a better understanding of the electro-deoxidation and MoSi2 formation processes. It was found that the reduction rate increased with the cell voltage and temperature of molten salt increasing. MoSi2 coating with compact structure was obtained after the electro-deoxidation of the silica layer at 3.1V for 3h. The preliminary study on the mechanism of MoSi2 coating formation suggested that SiO2, CaSiO3 and Ca3Si2O7 were reduced directly on Mo substrate to form Si–Mo alloys. As the process continued, the ratio of Si in Si–Mo alloys increased, and finally the compact MoSi2 coating with a thickness of about 10μm was obtained. The electro-reduction of SiO2 layer was highly irreversible and controlled mainly by the slow rate of electron transfer.