Electrochemical Siliciding of Nickel and Molybdenum in Molten Fluoride

Abstract

Electrochemical siliciding of molybdenum in a molten fluoride bath was attempted with the aim of producing an oxidation-resistant MoSi2 film. Prior to this study, the electrochemical siliciding of nickel was investigated. As a result, a nickel silicide film composed of Ni3Si2 and NiSi was obtained. At a high current density of over 50 mA⋅cm−2, irregular needle-like crystals were observed and the preferential growth phase was Ni3Si2, which was consistent with the results of a previous study on diffusion coefficient determination using a diffusion couple. On the other hand, at low current density of 10 mA⋅cm−2, a nickel silicide film with a smooth surface and smooth interface was formed, which was not observed previously. In the electrochemical siliciding of molybdenum, a dense MoSi2 film was formed along with the deposition of pure silicon. The thickness of the MoSi2 film did not change significantly even when the current density was varied, which indicated that the film growth rate was determined by the diffusion rate of silicon in MoSi2. The film growth rate was significantly higher than that estimated from the diffusion calculation. This may be because not only body diffusion but also fast diffusion, such as grain boundary diffusion, occurred.