Hydrated Alumina Coated Tungsten Oxide Preparation by Step Hydrothermal Method

Tungsten is an irreplaceable key material in many fields due to its excellent high temperature resistance, high strength and hardness, especially in the fields of national defense industry and aerospace. Compared with the pure tungsten, the aluminum oxide coated tungsten and tungsten alloy can greatly increase the strength of tungsten, refine the grains, reduce the particle size, increase the toughness and tensile strength of the material.

In order to solve the problem that mixed hydrothermal method is difficult to achieve complete reaction, and it is also difficult to form nano level hydrated alumina coated tungsten oxide powder composite materials, researchers use step-by-step hydrothermal method to prepare hydrated alumina coated tungsten oxide powder, the steps are as follows:

(1)The mass fraction of hydrated alumina in the coated powder is 0.5%. 30.3g (NH₄)₆H₂W₁₂O₄₀, 0.75ga (NO₃) 3.9h2o, 40ml dilute HNO₃, 0.18g CO(NH₂)₂ and 40ml distilled water are weighed respectively. Add (NH₄)₆H₂W₁₂O₄₀ and HNO₃ to the hydrothermal reactor for hydrothermal reaction. The temperature of the hydrothermal reaction is 180 ℃, and the time is 10h. The reaction generates a mixed solution of WO₃ and NH₄NO₃. Cool the mixed solution to room temperature;

(2)AL(NO₃)₃, CO(NH₂)₂ and distilled water were put into another hydrothermal reactor. The temperature of hydrothermal reaction was 180 ℃, and the time was 10 hours. The mixed solution of AlO(OH) and NH₄NO₃ was formed. The mixed solution was cooled to room temperature;

(3)Put the mixed solution of WO₃ and NH₄NO₃, AlO(OH) and NH₄NO₃ into a pure beaker and mix them in turn. The stirring speed is 200R / min, and the time is 2H. Then, the mixed solution is allowed to settle for 5h, washed with distilled water and settle for 3 times, and the time for each time is 5h;

(4)After standing, the solution is filtered, cleaned, and the cleaning solvent is distilled water and ethanol respectively. The distilled water is washed and filtered 3 times, ethanol is washed and filtered 2 times, and the filtered powder is dried at 80 ℃ for 6 hours. At this time, the hydrated alumina has been evenly coated with the surface of tungsten oxide powder. The powder size is uniform and well dispersed, and the particle size of the powder is nanoscale.

The hydrated alumina coated tungsten oxide powder is prepared by step hydrothermal method. The hydrated alumina and tungsten oxide are combined by van der Waals force. Because the hydrated alumina is a colloid, there is a repulsive force between the colloid and the same-sex colloid, so it can disperse the particles. Meanwhile, the hydrated alumina can uniformly cover the surface of tungsten oxide, which hinders the deposition of tungsten oxide and inhibits the growth of tungsten oxide grains. Therefore, the powder prepared by step hydrothermal method has good dispersibility and the grain size is smaller than that of nano powder.

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