Preparation of ultrafine Mo powders via carbothermic pre-reduction of molybdenum oxide and deep reduction by hydrogen

A novel route to synthesize molybdenum (Mo) powders via carbothermic pre-reduction of molybdenum oxide followed by deep reduction by hydrogen was proposed. The pre-reduced Mo powders containing a small amount of molybdenum dioxide (MoO2) were produced first by reacting molybdenum trioxide (MoO3) with insufficient carbon. Then the pre-reduced Mo powders were further reduced by hydrogen at 1173 K to remove the residual oxygen. Mo particle with a much smaller size could be obtained by the carbothermic reduction owing to the absence of Mo-O-H gaseous intermediate phase which leads to the increase of particle size during the hydrogen reduction process. In the carbothermic pre-reduction process, the existence of a few MoO2 can avoid the residue of carbon in the prepared pre-reduced Mo powders which is hard to remove during the following hydrogen reduction process. It was observed that increasing the C/MoO3 molar ratio was beneficial for the decrease of the particle size of Mo powders. Mo powders with submicron-size could be obtained after further hydrogen reduction. This new method provides a simple and low cost route to prepare ultrafine Mo powders.