Coated Tungsten Oxide Preparation with Alumina Hydrate by Step Hydrothermal Method

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, 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 the hybrid hydrothermal method is difficult to achieve complete reaction and to form nano-scale alumina hydrate uniformly coated tungsten oxide powder composites in the existing technology, the researchers used step-by-step hydrothermal method to prepare alumina hydrate coated tungsten oxide powder. The steps are as follows:

(1)The quality fraction of alumina hydrate in the target coated powder is 0.5%, weighing 30.3g (NH₄)6H₂W₁₂O₄₀, 0.75g Al (NO₃)₃·9H₂O, 40ml dilute HNO₃, 0.18gCO (NH₂)₂ and 40ml distilled water respectively. (NH₄)6H₂W₁₂O₄₀, and HNO₃ were added to the hydrothermal kettle for hydrothermal reaction. The temperature of hydrothermal reaction was 180 ℃ and the reaction time was 10 h. The mixed solution of WO₃ and NH₄NO₃ was formed, and the mixed solution was cooled to room temperature.

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

(3)The mixed solutions of WO₃ and NH₄NO₃, AlO(OH) and NH₄NO₃, were poured into the pure beaker and stirred in turn. The stirring speed was 200 r/min for 2 hours. Then the mixed solution was precipitated for 5 hours, then washed and precipitated with distilled water for 3 times, each time for 5 hours.

(4)The static solution is filtered, cleaned and the cleaning solvent is distilled water and ethanol respectively. The distilled water is cleaned and filtered three times and ethanol is cleaned and filtered two times. The filtered powder is dried. The drying temperature is 80 ℃ and the drying time is 6 h. At this time, the hydrated alumina has uniformly coated the surface of tungsten oxide powder. The powder is uniform in size and well dispersed, and the obtained powder has a particle size of nanometer.

Alumina hydrate coated tungsten oxide powder is prepared by step hydrothermal method. Alumina hydrate and tungsten oxide are combined by van der Waals force. Because alumina hydrate is colloid and there is repulsive force between colloid and isocolloid, it can disperse particles. At the same time, alumina hydrate can uniformly coat the surface of tungsten oxide, which hinders the deposition of tungsten oxide and inhibits the growth of tungsten oxide grain. As a result, the powder prepared by step hydrothermal method has good dispersion and the grain size is smaller than that of nanometer powder.

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