Nano-alumina Coated Tungsten Powder Preparation by Freeze-drying

In order to ensure the uniformity of the dispersion of the composite particles and to improve the properties of the materials to the greatest extent, it is often required that the doped phase particles be coated on the surface of the matrix particles to form a coating to achieve the best mixing degree.

In view of the existing technical problems, some scholars have proposed a freeze-drying method to prepare nano-alumina coated tungsten powder, which includes the following steps:

(1)Ammonium metatungstate white crystal powder and aluminium sulfate crystal powder were weighed according to the molar ratio of alumina to tungsten in the target composite powder, respectively, and they were dissolved in distilled water for clarification.

(2)Using general nitrogen spray gun, the clarified mixed solution was dispersed in general liquid nitrogen to pre-freeze, and the frozen substance was obtained. The spray gun pressure was 1.5-3.5 atmospheric pressure.

(3)Freeze-dried mixtures of freeze-dried powders were obtained by vacuum drying of freeze-dried materials using liquid nitrogen.

(4)The freeze-dried powders obtained in step (3) were reduced by staged incineration in hydrogen atmosphere with flow rate of 0.1-0.5m³/h, and the composite powders coated with nano-alumina were obtained. The fineness of alumina was about 20 nm, and that of tungsten powder was about 1 micron.

The amorphous freeze-dried powder was prepared by liquid nitrogen pre-freezing and freeze-drying at low temperature and low pressure, which can effectively prevent the segregation of single-phase particles. Then the nano-alumina coated tungsten powder was obtained by staged calcination reduction. The whole preparation process is simple, less steps, cheap and easy to obtain raw materials, and no need to add matrix particles in advance.

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