Upgrading Strategy of Tungsten-cobalt Composite Oxide Powder

The preparation method of the traditional cemented carbide is mainly to reduce the tungsten oxide by hydrogen to tungsten powder by using a fixed bed, a rotary furnace, a hydrogen plasma, etc., and the tungsten (W) powder and the carbon (C) powder are ball milled and mixed by high temperature carbonization. The tungsten carbide (WC) is ball-milled and mixed with the pre-formed cobalt powder to obtain a tungsten carbide-cobalt (WC-Co) cemented carbide mixed powder, and then the cemented carbide is prepared by press sintering.

The traditional method of preparing tungsten carbide (WC) in mixed powders is difficult to distribute uniformly in cobalt (Co) phase due to its long process and low efficiency, which affects the performance of subsequent cemented carbides. Nowadays, with the development of cemented carbide industry to produce nano-sized cemented carbides with high performance and low cost, it is difficult to produce nano-sized cemented carbide powder by traditional methods.

In view of the shortcomings of the traditional process, some enterprises have improved the preparation method of W-Co composite oxide powders. The main processes are as follows:

The solution of metatungstic acid with a specific gravity of 1.10 g/ml was prepared, and cobalt carbonate was added into the solution. The mixture of metatungstic acid and cobalt carbonate was reacted in glass-enameled reactor according to the ratio of 95% WC+5% Co. The composite solution of tungsten and cobalt was obtained by stirring and fully reacting at 90 ℃. The tungsten and cobalt composite solution was sprayed by pressure spray tower. The inlet temperature of the spray tower was set at 280 ℃ and the outlet temperature was set at 130 ℃.

The powder particles after spray granulation were dehydrated and dried in a rotary furnace. The heating temperature was 450 degrees and the heating time was 2 hours. The tungsten-cobalt composite oxide powders prepared by this method contain 74.72% tungsten and 4.21% cobalt. The bulk density of powder is 2.665g/cm³, the fluidity is 25.47s/50g, the average surface area particle size is 55.907 micron, and the average volume particle size is 81.616 micron. According to the requirement of 5% Co content in WC-Co cemented carbide, the cobalt content in W-Co composite oxide should be 4.19%, and the error of cobalt content should be 0.02%. The results show that the prepared W-Co composite oxide powder has uniform composition, less damage and good morphology.

The improved process is characterized by short process, easy control, easy operation and low investment cost. It is suitable for industrial scale production. The composite oxide powders produced are uniform in composition, less damaged and high in strength. It can be widely used in the production of nano-scale WC-Co composite powders.

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