On the genesis of molybdenum carbide phases during reduction-carburization reactions

Molybdenum carbide has been prepared according to the carbothermal reduction method. Carbon black substrate was used as C-source whereas a H2-flow was the reducing agent. Two different H2 consumption steps were identified during the carburization treatment. The low temperature step is related to the reduction of Mo6+-to-Mo4+, the higher temperature process accounts for the deep reduction of Mo4+-to-metal Mo0 and its subsequent reaction with C to form the Mo-carbide. The influences of the maximum carburization temperature, carburization time, gas hourly space velocity regarding Mo-loading, heating rate and temperature of Ar pre-treatment were analyzed. All these conditions are interrelated to each other. Thus, the carburization process ends at 700 °C when Mo-loading is 10 wt%, however Mo-loading higher than 10 wt% requires higher temperatures. Carburization temperatures up to 800 °C are needed to fulfill Mo-carbide formation with samples containing 50 wt% Mo. Nevertheless, Ar pre-treatment at 550 °C and slow heating rates favor the carburization, thus requiring lower carburization temperatures to reach the same carburization level.