Molybdenum dioxide hydrogen reduction

Industrial common molybdenum powder manufacturing method.

Reduction reaction is endothermic reaction, reaction equilibrium constant Kp (pH ₂ O/(pH2) at 700 k is 0.076, the 918 k is 0.234, the 1073 k is 0.389, the 1200 k is 0.55, the reaction equilibrium constant smaller. Due to the reaction equilibrium constant is small and endothermic reaction, therefore need to use a higher reduction temperature. Reduction in more than four reduction furnace tube or other tube furnace, molybdenum mu through full drying hydrogen (including water under 0.5 g/m3), reduction temperature along the furnace tube length direction from the feed end of about 923 k rose to about 1253 k. The discharge end reduction of output of molybdenum powder sieving to in a timely manner and batch.

Are the major factors affecting the quality of molybdenum powder raw material quality, filling boat, reduction temperature, hydrogen flow rate and moisture, material residence time in the oven. Raw material of molybdenum dioxide purity determines the purity of the product molybdenum powder. Reduction in the boat charge tightness, material thickness, material will affect the hydrogen penetration, restore moisture out, thus can also affect the product quality of molybdenum powder. Low reduction temperature, reduction reaction is incomplete, slow reaction, the molybdenum powder obtained high oxygen content, fine granularity; Reduction temperature high contrast. Hydrogen humidity is big, molybdenum powder increased oxygen content, granularity of coarse; Hydrogen flow rate, reduction reaction speed, molybdenum powder, oxygen levels drop but seized material and heat loss increased. Material is long residence time in the oven, product molybdenum powder and granularity coarsens oxygen levels drop. Try to avoid in the process of reduction of other impurities into and prevent the oxidation of the molybdenum powder during cooling can also improve the quality of products, molybdenum powder.

To further reduce the oxygen content in the product molybdenum powder, sometimes still need the reduction in the production output of molybdenum powder in the muffle furnace or other reduction furnace at 1273 ~ 1373 k temperature with dry hydrogen reduction again to supplement. When using high pure molybdenum dioxide raw materials, strict control of milling conditions and pollution of impurities, high purity of 99.9999% can be obtained from molybdenum powder.

Molybdenum halide hydrogen reduction

With hydrogen molybdenum reduction gas halide preparing method of molybdenum powder. This method is a gas in the opposite should, thus has the characteristics of molybdenum powder particle size is easy to control. The fine-grained even can use this method, the ultrafine molybdenum powder, or on molybdenum plating coating on a substrate. This is a kind of industrial promising method. Molybdenum halide are molybdenum chloride (MoCl2, etc.) and molybdenum fluoride (MoCl5, etc.).

Usually use "flame" reduction method. Reduction in as shown in figure 1 equipment. Molybdenum in the nozzle with hydrogen halide vapor injection reaction tower, halogen elements are at the same time also injected gas and hydrogen gas burning complement insufficient heat. From the nozzle spray into the gas mixture in the reaction tower export form "flame", at the same time get molybdenum powder by gas reduction reaction. Molybdenum powder particle size is generally around 2 um. MoCl5, MoF5 reduction temperature is 798 ~ 828 k, 70% ~ 85% of the dust collected in the dust collection tower and metal yield can reach 96% ~ 96%, the product obtained fluoride 0.03% ~ 0.05%. Also has the use of flow reduction furnace.

Atomization method

Atomization method of melting, atomization metal molybdenum or molybdenum wire for making molybdenum powder, the method of main metal molybdenum wire atomization method, vacuum spray method and the metal molybdenum billet atomization method.

Metal molybdenum wire atomization method The metal molybdenum wire make it melted, and with strong pulse current in inert atmosphere of molten metal to spray powder method. Use this method to get the powder particle size range is very wide. Along with the increase of discharge voltage, molybdenum powder particle size is reduced, in a vacuum spray very fine molybdenum powder can be obtained.

Vacuum spray method Atomization device is composed of two Chambers stacked with each other, the original vacuum smelting of metal molybdenum materials in the next room first, forming a molten metal molybdenum, again under pressure ventilation with hydrogen saturation, then through specialized obturator molybdenum from the chamber will be molten metal into the chamber, the vacuum chamber. After the molten metal molybdenum is fed into the vacuum chamber, due to intense precipitation hydrogen flow of molten metal molybdenum "bang", form a very fine powder. Under the vacuum or inert medium products out of the room on molybdenum powder.

Metal molybdenum billet atomization method using rotating electrode atomization method (figure 2), the metal molybdenum billet as consumable electrode for the rotation, through the fixed tungsten electrode arc melt metal molybdenum billet, high speed (about 10000 ~ 25000 r/min) of consumable electrode due to the effect of the centrifugal force makes the molten metal to spray powder, molybdenum powder collection chamber filled with inert gas. In production of powder is very pure, size range between 10 to 500 um.

Plasma method

With a hydrogen plasma (see plasma metallurgy) reduction of molybdenum oxide powder for making molybdenum powder method. The legal system of fine molybdenum powder and spontaneous combustion, the average particle size was 0.01 ~ 0.1 / zm.