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Introduction to molybdenum powder production process
Hydrogen, carbon and carbon-containing gas and the silicon, aluminum, molybdenum trioxide and so may be reduced to molybdenum. But other methods difficult to obtain high purity metallic molybdenum. The molybdenum produced by hydrogen reduction has high purity and is suitable for the production of molybdenum or molybdenum-based alloys.
The chemical reaction formula of hydrogen reduction of high purity molybdenum trioxide is:
MoO 3 +H 2
450~650°C
MoO 2 +H 2 O↑ △H°298=-85kJ
→
MoO 3 +H 2 →Mo+2H 2 O↑ △H°298=105kJ
Under the reaction conditions, MoO 3 and MoO 2 may also react to form an intermediate oxide (such as Mo 4 O 11 or the like).
The standard process for hydrogen reduction of molybdenum trioxide is divided into three stages:
(1) Molybdenum trioxide is reduced to molybdenum dioxide:
MoO 3 +H 2 â†â†’MoO 2 +H 2 O
This is an exothermic reaction. The equilibrium condition at 400~600 °C is P H2O /P H2 =5.0×10 7 ~1.7×10 6 . The nickel boat containing MoO 3 powder slowly moved forward in the four-tube muffle furnace, the furnace temperature rose from 400 ° C, and the reaction was completed before 550 ° C, and the temperature was raised to 650 ° C. The MoO 2 powder was discharged. If the reaction is not completed at 550 ° C, the fusible intermediate oxide will melt at 550 to 600 ° C to cause the charge to be sintered and the reduction is insufficient.
(2) Molybdenum dioxide is reduced to molybdenum powder: this is an endothermic reaction. The nickel boat of MoO 2 slowly moves forward in the 13-tube furnace, and the furnace temperature rises from 650 ° C to 950 ° C to react MoO 2 + 2H 2 In the equilibrium of â†â†’Mo + 2H 2 O, P H2O /P H2 is small; 645 ° C is 0.234, 800 ° C is 0.398, and 927 ° C is 0.55. Therefore, the hydrogen gas to be supplied should be sufficiently dried, and the dew point is -40 to 50 ° C as a reducing agent.
(3) Supplemental reduction: To reduce the oxygen content in the molybdenum powder produced in the second stage. It should also be replenished at 1000~1100 °C. At this temperature, the chemical stability of the nickel- chromium tubes and heaters used in the first and second stages is reduced in the air. The third stage is carried out in a tubular furnace filled with hydrogen and provided with a closed furnace shell. At this point, the oxygen content of the molybdenum powder is only 0.25% to 0.3%.
In the production implementation, the three stages of the process are simplified to: (1) there is no third stage of supplementary oxidation. (2) The first and second sections are carried out in the same 13-tube furnace. (3) The first stage and the decomposition of ammonium paramolybdate are combined in one process, and the hydrogen is introduced into the decomposition furnace of the ammonium paramolybdate. The two reaction temperatures are close to each other. After the process, not the MoO 3 is produced, but directly Produce MoO 2 . No matter how it changes, it can't be separated from several stages of the above chemical reaction.
The molybdenum powder produced by reduction can be formed by powder molding, or electric arc furnace melt, electron beam melting, and the like.