Ultrafine Tungsten Powder Preparation -- Gas Evaporation Method
In an inert gas of a certain pressure (<1.013x10--5Pa), it is heated by resistance, laser heating, electron heating, arc heating, high-frequency heating, etc.
This method is the most effective way to prepare ultrafine particles with a particle size less than 100nm by melting and evaporating materials and condensing them into ultrafine particles. Gas evaporation was first proposed by the Japanese in 1963.
In the process of studying the process of preparing nanometer tungsten powder by gas evaporation, Chinese scholars evacuated the vacuum chamber to 2.5 * 10 - 5Pa and filled the high-purity argon with purity of 99.99% to 100~500Pa, heating to make the purity of 99. 9%, diameter of 1mm tungsten wire evaporation. The vaporized gas atoms, W, collide with an inert gas atom, lose energy, agglomerate into nanometer sized clusters, and then condense in a sample grid cooled by liquid nitrogen. The nano tungsten powder structure as the body centered cubic (B.C.C) structure and A-15 alpha - W beta - W coexist, crystalline structure with different positions without condensation. The heat treatment at 700 °C can make the beta - W structure of A-15 structure irreversibly transform into B.C.C structure, this method can be used to prepare nanocrystalline tungsten powders with a grain size ranging from several nanometers to several hundred nanometers.
The preparation method of ultrafine tungsten powder were of high purity, no other impurities in the process of pollution, fast reaction speed, good crystalline structure, but in the field of China's tungsten powder production does not seem to get a wide range of popularity, the main reason is that this method requires high technical equipment, personnel requirements are also higher.
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