Tungsten powder is the main raw material for processing powder metallurgy tungsten products and tungsten alloy. Pure tungsten powder can be made into silk, rod, tube, plate and other processing materials and products of certain shape. Mix tungsten powder with other metal powders, and we can have all kinds of tungsten alloys, such as tungsten-molybdenum alloy, tungsten-rhenium alloy, tungsten-copper alloy and high density tungsten alloy. Another important application of tungsten powder is the production of tungsten carbide powder, which is in turn made into hard alloy tools, such as turning tool, milling cutter, drill bits and molds.
The purity of conventional tungsten powder is 99.95%. The residual impurities in tungsten powder will have an impact on the processing performance and usage performance of the product. Among them, Ca/Mg/P/As/Si/S/Fe/Ni/Cu/Al/Mo will reduce the strength of tungsten alloy. K/Na will facilitate the growth of tungsten carbide particles. V and Cr play the role of continuous growth.
According to the average particle size, tungsten powder can be divided into ultrafine tungsten powder, general tungsten powder, coarse tungsten powder.
The preparation method of metal tungsten powder mainly includes the hydrogen reduction of tungsten trioxide, the hydrogen reduction of halide, the carbon reduction of tungsten oxide or tungstate, the metal thermal reduction of tungsten oxide or tungstate, and the thermal dissociation of hydroxy compounds. Among them, the first method has the most mature technique and the most widely used industrial applications.
The reduction temperature, the load of tungsten oxide, the speed of the boat, the flow rate of hydrogen and the moisture content in hydrogen will all affect the final particle size of the powder.
In addition to particle size, other important parameters include particle shape, surface area, bulk density, mobility and compression, etc. If the shape of the particles is irregular or dendritic, due to the mechanical engagement between the particles, the strength of unburnt earthenware will increase.