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-Na2SiF6SiO2 and the
Si powder. Hexagonal MoSi2 was formed as single phase with homogeneous
thickness of tens of mm above 1073 K, while the tetragonal MoSi2 phase was
additionally formed at 973 K. The growth rate of the MoSi2 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, Mo5Si3 was formed at the interface
between the Mo substrate and the MoSi2 layer.