Advanced reactor system for the fine control of properties of molybdenum powder

摘要

The author's intention was not to replace, but to investigate, refine and exercise greater control over the long-established, conventional two-stage reaction for producing fine molybdenum powder. In the first stage, a mmonium dimolybdate 2(NH4)-MoO_4 (ADM) or molybdenum trioxide MoO_3 is reduced by hydrogen in either a rotary reduction or a pusher-type furnace, to molybdenum dioxide MoO_2. Reaction via ADM is simpler but the final product is less desirable. In the second stage, the MoO_2 is further hydrogen-reduced to Mo metal powder in a single-tunnel or multi-tube pusher furnace. The first-stage reaction, 2(NH_4)MoO_4 + 2MoO_3->3MoO_2 + 4H_2O + N_2 or MoO_3 + H_2->MoO_2 + H_2O, is highly exothermic and therefore difficult to control. Without this control, localised hot spots of 1000 deg C or more can develop, followed by a runaway reaction. Heat of reaction at 600 deg C is 155 kcal/kg MoO_3. The rotary reactor's advantages over the older pusher furnace include diminished likelihood of hot spots, lower energy consumption, lower capital cost (higher efficiency, therefore smaller size and shorter reaction time, due to better gas-solid contact), automated materials handling, improved and simplified control of grain size and morphology, lower maintenance and labour costs, and superior product quality.