MoSi 2 coating on molybdenum using molten salt

Abstract

For obtaining oxidation resistance of molybdenum in air, molybdenum silicide was non-electrolytically coated in the molten salt, where a disproportion reaction occurs between the salt composed of NaCl–KCl–NaF–Na 2SiF 6–SiO 2 and the Si powder. Hexagonal MoSi 2 was formed as single phase with homogeneous thickness of tens of μm above 1073 K, while the tetragonal MoSi 2 phase was additionally formed at 973 K. The growth rate of the MoSi 2 layer and its morphology at the sample corner were affected by this phase formation. The protective layer on the siliconized sample proved to be effective for preventing oxidation that occurs for pure molybdenum at low temperatures. During the oxidation at the high temperature, Mo 5Si 3 was formed at the interface between the Mo substrate and the MoSi 2 layer.