Preparation Method of Ultra-fine Tungsten-aluminum Powder

It is well known that, alumina has the characteristics of high hardness, high melting point, good wear resistance and stable high-temperature chemical properties, and is widely used in industrial production. Due to its high hardness, it can be used in the abrasive grinding industry to produce abrasives, polishing powders, etc.; due to its high temperature chemical properties, it is the main raw material for refractory bricks, enamels, porcelain and artificial gems in the refractory and ceramic industries.

Tungsten powder is a raw material for preparing tungsten deep-processed products by powder metallurgy. It is usually prepared by reducing hydrogen peroxide with ammonium paratungstate (APT) or calcined tungsten trioxide (WO₃). Tungsten has the advantages of high melting point, low expansion coefficient, good electrical and thermal conductivity, but its has a poorer wear resistance at high temperature.

Based on the respective advantages of alumina and tungsten, a high-temperature wear-resistant aluminum oxide and tungsten composite material can be produced by powder metallurgy. In this process, the preparation of the powder is the key to the powder metallurgy process. At present, the preparation methods of metal powder mainly include mechanical methods and physical chemical methods, specifically to the preparation of mixed powders of aluminum oxide and tungsten (Al₂O₃/W), and the obtained powders are different due to the difference in physical properties between the two. It is easy to agglomerate and has a limited effect on the performance of composites after high temperature sintering.

In order to solve the above problems, some scholars have proposed a preparation method of ultra-fine tungsten-aluminum powder, and the final product can be used in new materials such as aviation. The specific details of the preparation method are as follows:

The liquid-liquid mixing method is applied, according to the mass ratio of the mixed powder to be finally prepared, weigh aluminum nitrate, ammonium tungstate and citric acid, and weigh distilled water according to the mass of citric acid and the concentration of 1.35 mol/L;

1) The aluminum nitrate is dissolved in distilled water to prepare a magnesium nitrate solution having a mass concentration of 70%, and then the citric acid and APT are added to the remaining distilled water to form a suspension, and the aluminum nitrate solution is added to the suspension. After stirring for 20 minutes, a mixed liquid is obtained;

2) The mixed liquid is heated and stirred at 85 °C until a viscous fluid is formed, and then dried and dried at 120 °C, and a dry powder is obtained after 14 hours;

3) The dry powder is calcined in an air atmosphere at 550 °C for 8 hours to remove the organic matter to obtain a mixed powder of aluminum oxide and tungsten trioxide;

4) The mixed powder of aluminum oxide and tungsten trioxide is placed in a hydrogen reduction furnace for two-stage reduction, a reduction temperature of 520 °C, a time of 3 hours, a second stage reduction temperature of 950 °C, a time of 5 hours, and a volume fraction of 1 is obtained.  % of ultrafine tungsten-aluminum mixed powder having an alumina particle size of 80 nm and a tungsten particle size of 0.8 μm.

The preparation of the above ultrafine mixed powder adopts liquid-liquid mixing method to achieve uniform mixing of the prepared raw materials on the molecular level, and is advantageous for preparing a superfine and uniformly distributed mixed powder of aluminum oxide and tungsten, and satisfies preparation high performance.  Requirements for ultra-fine tungsten-aluminum composites.

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