Calcined ammonium paramolybdate or MoO 3 was formed by preparing a raw material powder of molybdenum metal. In industrial production, pure ammonium molybdate can be reduced directly into metal molybdenum powder in a hydrogen furnace, or it can be calcined to MoO 3 at a temperature of 550 to 650 ° C, and then reduced to metal molybdenum powder.
In the production of molybdenum products by powder metallurgy, molybdenum powder is required to have high purity, low oxygen content, and fine and uniform particle size. Production of molybdenum powder in tube or muffle furnace or kiln with hydrogen back through the secondary reduction of ammonium paramolybdate or MoO 3 is reduced to MoO 2, the second reduction at higher temperatures, the MoO 2 Reduced to metal molybdenum powder. The various reduction process parameters are listed in Tables 1 and 2. At present, some manufacturers use the direct hydrogen reduction method of ammonium paramolybdate to reduce the calcination process and avoid the impurities brought in by calcination. In order to ensure the quality of molybdenum powder, in addition to the reduction temperature, the flow rate and humidity of hydrogen, the thickness and pushing speed of the layer, and the particle size of the raw materials are all factors that affect the particle size of the molybdenum powder. Usually, the H 2 flow rate is large, and the powder having a low dew point reduction is fine, whereas the powder is coarse. Therefore, these factors must be strictly controlled in the production process to obtain a qualified powder.
 Table 1 Main parameters of primary reduction of ammonium paramolybdate | ||||||||
Equipment | Feeding amount kg/h  | Hydrogen flow rate m 3 /h | Furnace tube inclination (o)  | Each belt temperature, °C | ||||
1 | 2 | 3 | 4 | 5 | ||||
Rotary furnace φ400/384mm | 60 to 80 | 20 to 30  | 3 to 5  | 360 ~ 380 | 420 ～ 440 | 500 ~ 540 | 550 to 580 | 550 to 580 |
Four tube muffle furnace 260*60mm  | 5kg / boat / 60min | 7m 3 /h·tube | 　 | 440 | 440 | 500 | 500 | 440 |
Table 2 Reduction process parameters of molybdenum in tubular furnace  | |||||||||||
Reduction phase | equipment | Boat size mm | Loading amount g/boat | Push speed min/boat | hydrogen | Furnace temperature in each zone, °C | |||||
Flow rate m 3 /h  | Dew point °C | 1 | 2 | 3 | 4 | 5 | |||||
The first stage | 4-tube furnace | 300*60*65 | 250 to 280  | 20 | 0.2 to 0.3 | < -10  | 　 | 500 to 550 | 　 | 　 | |
11 tube furnace | 250*40*35  | 150 to 180 | 20 | 　 | < -10  | 350 | 450 | 520 | 540 | 520 | |
second stage | 11 tube furnace | 250*40*35  | 200 to 220 | 15 | 　 | 　 | 850 | 920 | 920 | 920 | 880 |
13 tube furnace | 250*40*35 Â | 250 | 20 | 0.8 to 1.0 | < -10 Â | 750 | 850 | 920 | 920 | 880 | |
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