Zirconium Tungstate Preparation

Zirconium tungstate has a formula of Zr(WO₄)₂ and a molecular weight of 586.9. It is a negative thermal expansion material with excellent performance. It has negative thermal expansion performance in the temperature range of 0.3-1050.0k.

The preparation methods of zirconium tungstate include impregnation method, co precipitation method, hydrothermal method, sol-gel method, hydrothermal method and combustion method. The products of solid-phase method have impurities and need to be quenched, and the coprecipitation method also needs to be quenched. Combustion method pollutes the environment. Coprecipitation method and hydrothermal method are widely used.

1. Coprecipitation method:
Weigh ZrOCL₂·8H₂0 and H₂WO₄ in a ratio of 1:2 for standby. The experimental process is: preparation of solution, adjustment of pH value, CO precipitate, mixing, washing, dehydration, precursor, heating and synthesis.

A.H₂WO₄ is yellow powder, insoluble in water, sulfuric acid, nitric acid and hydrochloric acid, soluble in HF acid, alkali and ammonia water. In the experiment, H₂WO₄ was added into a certain amount of concentrated ammonia water and fully stirred, then placed for 24 hours, completely dissolved

B.ZrOCl₂·8H₂O is dissolved in deionized water to prepare 0.5mol·L1 solution, and impurities are filtered. ZrOCl₂·8H₂O solution is added into the ammonia solution of h2w04 according to the stoichiometric ratio, and the pH value is adjusted and controlled within the range of 2-3 to obtain the self color precipitate. The whole process is stirred by electromagnetism. The precipitate is dehydrated from the center, washed five times with anhydrous ethanol, dried and calcined at 600 ℃ for 2h.

C.Put the precursor powder into muffle furnace. Heat preservation at 1200 ℃ for 0.5h and 1H, and quench in air to room temperature to obtain 1 x and 2 x samples.

2. Hydrothermal method:
ZrO(NO₃)₂·5H₂O and N₅H₃₇W₆O₂₄·H₂O are used as raw materials. 50 ml of a 0.2 mol / L Zr solution and 50 ml of a 0.4 mol / L W solution were configured, and the two were continuously stirred for 2.5 h. Then, 35 ml of 6 mol / L HCl was added, followed by stirring for 3 hours and heating at 180 °C for 15 hours. It was filtered, washed with deionized water, and dried at 60 °C. The obtained precursor was heated at 500 °C for 6 hours to obtain ZrW₂O₈ powder.

Zirconium tungstate is difficult to synthesize, high cost and poor performance at high temperature. Usually, some substances are added to inhibit its decomposition, but the added substances need to be analyzed. Zirconium tungstate has a narrow thermodynamic stable temperature range, only between 1105-1257. It is difficult to synthesize the material. How to improve the purity of the product and reduce the production cost is the main development direction of zirconium tungstate in the future.

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