Preparation of metal molybdenum powder
The method is basically the same as the method for preparing tungsten powder. The hydrogen reduction method of molybdenum oxide is still the only method for producing molybdenum powder.
The raw material for the production of molybdenum powder is generally ammonium paramolybdate 3(NH4)O·7MoO3·4H2O. Ammonium paramolybdate can be converted to MoO3 or MoO2 by calcination or hydrogen reduction. When using MoO3 as a raw material, first-stage, second-stage and third-stage method is used to produce molybdenum powder. Most plants adopt second-stage method. The first stage of the reduction temperature is performed at 450-650 ° C, and the second stage is performed at 900-950 ℃.
The factors that affect the quality of molybdenum powder are mainly the quality of raw materials, loading of the boat, reduction temperature, hydrogen flow and humidity, and the residence time of the material in the furnace. The purity of the raw material molybdenum dioxide determines the purity of the product molybdenum powder. The amount of material in the reduction boat, the thickness of the material layer, and the tightness of the material will affect the penetration of hydrogen and the elimination of reducing water and gas, and therefore the quality of the molybdenum powder. The reduction temperature is low, the reduction reaction is incomplete, and the reaction speed is slow. The obtained molybdenum powder has high oxygen content and fine particle size; the high reduction temperature is the opposite. Molybdenum powder has a high humidity, and the molybdenum powder has an increased oxygen content and a coarse particle size; a large hydrogen flow rate increases the reduction reaction speed, and the molybdenum powder has a reduced oxygen content, but the material and heat loss taken away increase. The material stays in the furnace for a long time, the oxygen content of the product molybdenum powder decreases and the particle size becomes coarse. In the reduction process, trying to avoid the introduction of other impurities and prevent the molybdenum powder from oxidizing during cooling can also improve the quality of the product molybdenum powder.
In order to further reduce the oxygen content in the molybdenum powder of the product, it is sometimes necessary to put the molybdenum powder produced by the reduction in a muffle furnace or other reduction furnace during the production to replenish it with dry hydrogen at a temperature of 1273 ~ 1373K. When using high-purity molybdenum dioxide raw materials, strict control of milling conditions and impurity pollution can produce 99.9999% high-purity molybdenum powder.
Molybdenum powder is divided into F.S.S.S. = 0.5-1μm, 1-2μm, 2-4μm, 4-6μm, 6-10μm according to different particle size. 2-4μm range is the most common one.
Molybdenum powder applications: used as raw materials for making molybdenum blanks which will be forged, rolled and machined for all kinds of molybdenum metal products, used to molybdenum silicide electric heating elements, as raw materials for thyristor wafers, molybdenum heads, etc.