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Preparation of ultrafine molybdenum powder are: evaporation state trioxide reduction, activation reduction and twelve Ammonium hydrogen reduction method.
 

1 evaporated state trioxide reduction method is MoO3 powder (purity 99.9%) is mounted on a molybdenum boat, placed in a preheated furnace 1 300 ~ 1 500 ℃ is evaporated into gas at a flow rate of 150 mL / min and a H2-N2 gas flow 400 mL / min of a mixed gas of H2 containing the folder, MoO3 vapor into the reaction zone, becoming ultrafine molybdenum powder by reduction. The method of spherical particles of uniform particle size obtained 40 ~ 70 nm molybdenum powder, but it is difficult to control the process parameters, wherein, MoO3-N2 components and the mixing temperature and MoO3 H2-N2 gas stream are of great influence on the particle size .
 

2 activation reduction to ammonium heptamolybdate (APM) as raw materials in catalysis NH4Cl, superfine molybdenum powder prepared by the reduction process, the restore process NH4Cl completely evaporate. Restore process is broadly divided into the thermal decomposition of ammonium chloride, APM decomposed into molybdenum oxide, MoO3 and HCl reaction 7MoO2Cl2, MoO2Cl2 is hydrogen reduction of molybdenum powder and superfine 4 stages. This method than the traditional method of lowering the reduction temperature of about 200 ~ 300 ℃, but only once the restore process, the process is relatively simple. Molybdenum powder having an average particle size prepared by the method of 0.1 μm, and the powder has a good sintering performance. Lingnan University in Korea proposed a similar approach, but the materials used for the high-purity MoO3.
 

3 twelve Ammonium hydrogen reduction of ammonium molybdate is twelve nickel alloy boat, and placed in a tube furnace at 530 ℃ reduction with hydrogen, and then with hydrogen at 900 ℃ reduction may a specific surface area of ​​the system 3.0 m2 / g or more of molybdenum powder, molybdenum powder such as particle size of about 900 nm. The process just described method, the analysis did not see the mechanism, its feasibility remains to be seen.
 

4 is hydroxy hydroxy molybdenum material method, at atmospheric pressure and a temperature of 350 to 1000 ℃ and N2 atmosphere, a vapor feed hydroxyl molybdenum thermal decomposition treatment. Since the decomposition of the hydroxy compound, the state of completion in the gas phase nucleation, crystal nuclei grow, so that fine particles prepared molybdenum powder, the average particle size of 1 ~ 2 μm. Method using a molybdenum powder, a hydroxyl group having a high chemical purity and good sinterability.

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