What Are Preparation Methods of Ultra-Coarse Tungsten Carbide Powder?
The main preparation methods of ultra-coarse tungsten carbide powder include high-temperature reduction, high-temperature carbonization, high-temperature carbonization by adding alkaline earth metal or alkali metal elements, high-temperature carbonization of ultra-fine tungsten powder, mixed carbonization of coarse and fine tungsten powder, aluminothermic method, etc.
(1) APT rapid calcination and rapid reduction method: APT is rapidly heated and calcined in oxidizing atmosphere at 850-1000 ℃, and then rapidly heated to 1100-1300 ℃ in hydrogen furnace for reduction. The particle size of 25-36 can be prepared by this method μ M of tungsten powder.
(2) Hydrogen reduction method of halide boiling layer: reduce tungsten chloride or fluoride in boiling layer with H2. Firstly, H2 and original tungsten powder are sent to the bottom of the reactor to form a boiling layer of tungsten, while halide vapor is introduced into the reactor from the upper part of the reactor, which is reduced to tungsten powder by H2 at the given optimum temperature, and deposited on the original tungsten powder to gradually coarsen the original tungsten powder, and tungsten powder is periodically discharged from the reactor. The particle size of tungsten powder prepared by this method is greater than 40 μm.
(3) Coarse crystal aluminothermic process: WC is directly produced from tungsten concentrate through high endothermic reaction. This process can produce high-purity, coarse particles, large blocks and single-phase WC grains.
(4) Tungsten concentrate molten salt carbonization method: at a high temperature of 1050-1100 ℃, the tungsten concentrate is decomposed with Na2SiO3-NaCl molten salt, and the resulting Na2WO4-NaCl molten salt is separated from the silicate phase containing Fe, Mn, and Ca, and then methane is sprayed into the molten salt phase to generate coarse WC.
The low-cobalt coarse-grained alloy WC made from ultra-coarse tungsten carbide powder has coarse grains and small specific surface area, which thickens the cobalt layer in the alloy, relieves the impact between WC grains during use, thus improving the impact toughness of the alloy, correspondingly reducing the cobalt content in the alloy, increasing the WC content in the alloy, and improving the wear resistance of the alloy.
Free carbon will greatly reduce the strength and wear resistance of tungsten carbide cemented carbide. The C-shaped hole in the phase detection indicates the degree of carburization.
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