Nano-alumina Coated Tungsten Powder Composite Preparation

High strength, high toughness, high hardness, light weight, high temperature resistance and corrosion resistance are the main development directions of high performance structural materials. Tungsten, with its excellent high temperature resistance, high strength and hardness, is an irreplaceable key material in many fields, especially in the field of national defense, military industry, aviation and aerospace.

Compared with pure tungsten, alumina coated tungsten and tungsten alloy can greatly increase the strength of tungsten, refine grain size, reduce particle size, increase the toughness and tensile strength of materials.

In order to solve the problem that it is difficult to form a nano-alumina-coated tungsten powder composite material by the mechanical alloy method in the prior art, the researcher improves the existing process, and the steps are as follows:

(1) According to the target coated powder, the quality fraction of hydrated alumina is 0.5%, weigh 30.3g (NH₄) 6H₂W₁₂O₄₀, 0.75g Al(NO₃)₃•9H₂O, 40ml diluted HNO₃, 0.18g CO(NH₂)₂, Distilled water 40 ml. (NH₄)₆H₂W₁₂O₄₀ and HNO₃ were added to the hydrothermal kettle for hydrothermal reaction, and the temperature of the hydrothermal reaction was 180 °C for 10 hours to form a mixed solution of WO₃ and NH₄NO₃, and the mixed solution was cooled to room temperature;

(2) Al(NO₃)₃, CO(NH₂)₂ and distilled water were placed in another hydrothermal kettle. The temperature of the hydrothermal reaction was 180 °C for 10 h, and the reaction formed a mixed solution of AlO(OH) and NH₄NO₃. Cooling the mixed solution to room temperature;

(3) The mixed solution of WO₃ and NH₄NO₃ and the mixed solution of AlO(OH) and NH₄NO₃ are successively poured into a pure beaker and mixed and stirred. The stirring speed is 200r/min for 2h, then the mixed solution is allowed to stand for 5h, and then Washed with distilled water, allowed to settle for 3 times, and each time of standing for 5 h;

(4)The solution after standing is filtered, washed, and the solvent is distilled water and ethanol respectively, wherein the distilled water is washed and filtered 3 times, the ethanol is washed and filtered twice, and the filtered powder is dried, and the drying temperature is 80 °C, drying time is 6h, at this time, the hydrated alumina has been uniformly coated with the surface of the tungsten oxide powder, the powder size is uniform, and the dispersion is good, and the obtained powder has a particle size of nanometer;

(5)Alumina hydrate coated tungsten oxide powder is put in muffle furnace for scorching. The scorching temperature is 300 ℃, the holding time is 12 h, and the heating rate in the heating stage is 20 ℃/min. After scorching, the powder is cooled to room temperature and taken out.

(6)The powder after calcination is reduced, and the first reduction is carried out. The reduction atmosphere is hydrogen, the flow rate of hydrogen is 1.5 m³/h, the reduction temperature is 600 ℃, the reduction holding time is 7 h, and the heating rate of the heating stage is 10 ℃/min.

(7)After one reduction, the powder needs to be reducted twice. The reductive atmosphere of the second reduction is still hydrogen. The reduction temperature is 900 ℃, the reduction holding time is 4 h, and the heating rate of the heating stage is 5 ℃/min. After this reduction process, tungsten oxide is reduced to tungsten. At this time, alumina has been uniformly coated with the surface of tungsten powder. The size of the powder is uniform and there is no agglomeration. The particle size is nanometer.

Alumina coated tungsten powder composites were prepared by incineration and secondary reduction of alumina hydrate coated tungsten oxide powder, which can inhibit the growth of tungsten particles and refine the grain size in the reduction process, thus obtaining nano-alumina coated tungsten powder composites.

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