Molybdenum carbide powders obtained from the vapor phase reaction of the MoCl 4-CH 4-H 2 system

Abstract

The formation of fine molybdenum carbide powder by the vapor phase reaction of the MoCl 4-CH 4-H 2 system was studied at 800–1400 °C. The mixing temperature of MoCl 4 and H 2 had a significant effect on the properties of the powders. After low temperature (600 °C) mixing (method A), Mo 2C powders free from Mo with a particle size of about 0.08 μm were produced by the reaction at 1200 °C and [CH 4] ≧ 0.5%. After mixing at the reaction temperature (method B), pure Mo 2C powders with a particle size of 0.15–0.2 μm were produced at 1000 – 1200 °C and [CH 4] = 1 – 2%, but MoC was formed as the major carbide phase at [CH 4] ≧ 2.5%. The Mo 2C particles produced by method A were polycrystalline and those produced by method B were single crystalline. It was concluded that the formation of molybdenum carbide powders in the present reaction system occurs as follows: formation of Mo particles and their subsequent carburization in method A, and growth of carbide particles by the deposition of Mo and its immediate carburization in method B.