Doped Chromium Ammonium Para Tungstate Prepare Cemented Carbide

At present, the cemented carbide under submicron is prepared by mechanical mixing, chromium powder or chromium carbide is added to the ultrafine tungsten powder, and cemented carbide is prepared by carbonization and pressing sintering after mechanical mixing. The uneven distribution of the added grain growth inhibitors will lead to the abnormal growth of "WC grain", which seriously affects the performance of the cemented carbide and restricts the development of the superfine cemented carbide.

In order to overcome the inhomogeneous distribution of the inhibitor and lead to the abnormal growth of "WC grain", the researchers invented a method of adding a homogeneous Cr ammonium para tungstate to promote the distribution of grain growth inhibitors more evenly, to achieve molecular mixing, and to effectively inhibit the abnormal growth of WC grains in the process of liquid phase sintering. The steps are as follows :

(1) In the reactor, WO₃ and ammonia were added respectively, and 1H was prepared at 100°C, ammonium tungstate solution was prepared. The concentration of WO₃ was 150-350g/L and the concentration of NH₄OH was 1.8-5.0mol/L.

(2) The ammonium tungstate solution is added to the inner liner of titanium alloy. The stirring speed is 70r/min, and the soluble trivalent chromium acetate chromium is slowly added to the side. The steam valve is opened to adjust the steam to 0.10-0.30MPa; the temperature is controlled to 90-100°C, and the evaporation crystallization is heated. The mass ratio of chromium in ammonium para tungstate powder is 0.22 to 0.60%.

(3) When the liquid level in the crystallizer is completely boiling, keep stirring and turn off steam.

(4) When crystal core is present in the crystallizer, the stirring speed is adjusted to 30r/min, the steam valve is opened and the steam pressure is maintained at 0.05-0.10MPa.

(5) When the solution density is 1.1g/cm3, control the stirring speed to 70r/min, open the steam valve and maintain the vapor pressure to 0.20-0.30MPa.

(6) When the solution pH=6.7-7.0 stops heating, cool and discharge.

The above process can be used to prepare ammonium para tungstate powder with homogeneous distribution of chromium. The chromium para tungstate can effectively inhibit the abnormal growth of WC grain in the process of liquid phase sintering and greatly improve the properties of cemented carbide.

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