A Morphological Study of the Reduction of MoO_2 by Hydrogen

摘要

Influences of the reduction temperature, dew point and hydrogen content on the morphologies of produced Mo powders by reducing MoO_2 with hydrogen were investigated. It was found that at low temperatures (blow 1173 K), the reduction proceeded through pseudomorphic transformation mechanism, and the product of molybdenum kept the same platelet shape as the initial MoO_2. However, at a high temperature of 1393 K, the produced molybdenum was formed as perfect spherical-shaped crystals, which indicated that the reduction obeyed the chemical vapor transport (CVT) mechanism. The influence of dew point in the atmosphere on the morphological changes of Mo powders was also important. It was beneficial for the nucleation and growth of Mo crystals following CVT mechanism with increasing the dew point of hydrogen. However, the influence of hydrogen content (25% H_2-100% H_2) on the morphological changes could be neglected at low temperature or high temperature when one reduction mechanism was dominated.