Tungsten Oxide

Ultrafine tungsten powder is superior to common coarse grain material in mechanical, therefore, the mechanical properties, physical properties and chemical properties are better than those of ordinary coarse-grained materials.  However, the preparation of ultrafine tungsten powder is more stringent than ordinary tungsten powder, not only have better quality raw materials, but also more suitable methods and equipment are required. Since 1950s, a great deal of research work has been done on tungsten smelting industry both at home and abroad, and many years of systematic research have been carried out on the preparation of ultrafine tungsten powder, and some effective methods have been developed. Hydrogen reduction is the main method of preparing ultrafine tungsten powder. It is simple, advanced, reasonable, stable and reliable, low cost and so on. With the development of tungsten powder manufacturing, great progress has been made in the selection of tungsten oxide ...

Hydrogen reduction is the main method for preparing ultrafine tungsten powder. It is a rather complicated physical and chemical process, including chemical transformation, phase change process, solid phase diffusion and chemical vapor transfer. In W-O-H there are 6 solidification phase, which are: tungsten trioxide (WO 3 ), beta tungsten oxide (WO 2.9 , W 20 O 58 , blue tungsten) gamma tungsten oxide (WO 2.72 , W 18 O 49 , Purple Tungsten) two tungsten oxide (WO 2 ), -W alpha and beta -W. Therefore, the process of hydrogen reduction reaction of tungsten oxide is complex, and different reduction processes will occur with the change of temperature and humidity: In a high temperature and a humid reducing atmosphere, the reduction proceeds in distinct stages ( WO 3  → WO 2.9  → WO 2.72  → WO 2 → W ); In low temperature and dry hydrogen, it is possible to reduce tungsten oxide to tungsten powder directly from high valence tungsten oxide ( WO 2...

The hydrogen reduction process of tungsten oxide, is a very complex physical and chemical processes, including chemical conversion, phase transformation, solid diffusion and so on. The process generally is: tungsten oxide, hydrogen reduction, sifting, blending, tungsten powder. Different tungsten oxide reduction process of reaction pathways, the reaction speed is different, in general, the reduction reaction pathway and to avoid the simple single reaction generated in the process of WO 2  is beneficial to preparing fine tungsten powder uniformly. That is to say, the tungsten powder obtained by route WO 2.9  → W or WO 2.72  → W would be more satisfactory. Hydrogen reduction of tungsten oxide is usually carried out in a multiple tube furnace or a rotary furnace. Multiple tube reduction furnace has 3 to 5 containers used for loading, use artificial way in accordance with the order of loading and unloading material, excessive hydrogen or against the tungst...

Tungsten oxide hydrogen reduction process is generally carried out in a multiple tube furnace, in the tubular reduction furnace, the most used in China are the thirteen tube reduction furnace and the four tube reduction furnace. Four tube reduction furnace is commonly used as a tungsten oxide hydrogen reduction unit, the furnace shell is welded by ordinary steel plates, and the four tubes are placed at the same level on the same hearth. Compared with the old four tube muffle furnace up and down the structure, the temperature uniformity is much better. The automation level of the four tube reduction furnace is higher than the thirteen tube reduction furnace, and it is easier to realize mechanization and electrification, in addition, the capacity of the four tube reduction furnace is large, but the unit energy consumption is lower than the thirteen tube reduction furnace. The furnace temperature of the four tube reduction furnace is between 600 °C and 1000 °C centigra...

Self Propagating High Temperature Synthesis (SHS) is a new technology which uses the high reaction heat produced between reactants and synthesis of materials in a short time. In 1967, Soviet scientists began to study the SHS technology system and apply it to industry. Self propagating high temperature synthesis is the reaction with certain gases in vacuum or filled (N 2 , H 2 , Ar 2  etc.) combustion reaction container, then the combustion products were crushed and grinded by different specifications of powder technology. The technological process is as follows: material preparation, briquetting, preheating, ignition, self propagating, high temperature synthesis, mechanical fragmentation, product performance test. The process of preparing tungsten powder by SHS is carried out in a home-made reactor and argon atmosphere, and tungsten filament parallel to the surface of the sample is used as the ignition source. After combustion, the product was soaked i...

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 cu...

High energy ball milling method is used in low temperature, in the protective atmosphere, by using the rotation or vibration of the ball mill. The hard sphere is subjected to strong impact, grinding and stirring, and the metal is crushed into nanometer particles. At present, high energy ball milling mainly uses vibrating ball mill, planetary ball mill and stirred ball mill to prepare nanometer powder. In the nano structure formation mechanism study, that high energy ball milling is a process in which the particle circulation shear deformation, in this process, a large number of lattice defects ever produced within the great grain particles, leading to the re-combination of particles in the grain boundary. In the system of cells, the formation of nanocrystals is only the evolution of structures under mechanical driving. In the multivariate system, low temperature solid state reaction components will occurred during ball milling grinding, crushing, col...