ADVANCED REACTOR SYSTEM FOR THE FINE CONTROL OF PROPERTIES OF MOLYBDENUM POWDER

摘要

Extensive investigation in the two-stage hydrogen reduction process for fine molybdenum powder synthesis has been conducted. Reaction thermodynamic, kinetics, grain morphology transformation mechanism, grain morphology and grain size control have been studied in detail. Pilot scale development work has been performed. Stage one reduction is highly exothermic and it proceeds as MoO_3 → Mo_4O_(11) → MoO_2. Mo_4O_(11) exists as an intermediate product which is a stable phase and has needle shaped grain morphology. Desirable MoO_2 morphology can be obtained if exothermic reaction is properly controlled in stage one reduction. The second stage reduction, MoO_2 +H_2 → Mo + 2H_2O is an endothermic reaction. The final product Mo inherits MoO_2's morphology. Mo product grain size and size distribution is determined by stage two reduction. In both stages, grain morphology transformation mechanism follows nucleation of product phase and product phase crystal growth via chemical vapor transport. Volatile molybdenum oxide monohydrate, MoO_2(OH)_2, is the gas phase responsible for the chemical vapor transport of Mo. Complete reduction system was designed and engineered based on this pilot development work. Optimized process parameters developed in pilot scale have been successfully scaled-up by 35 times, up to a production rate of 2.4 tons quality Mo powder product per day. The system consisted of rotary (stage one) +18 tube pusher (stage two) system which is superior to a traditional pusher + pusher system from both product quality control and cost saving.