Tungsten Hexafluoride Purification Method

Tungsten hexafluoride is tungsten and fluorine to form a two element compound WF₆. In the fluorides of tungsten, WF₆ is the only stable and industrialized product.

The tungsten hexafluoride is a white solid at no more than 2.0 ℃. It is a light yellow liquid between 2.0-19.9 ℃, and is a colorless gas at less than 17.5 ℃ the density is 3.44g / cm³, 12.9 times as much as the air, is one of the heaviest known gas, and the relative molecular mass of WF₆ is 297.84. Its molecules have symmetric positive eight - hedral structure at normal temperature and have anti magnetic properties.

Due to the influence of raw materials and processes, the synthesized primary tungsten hexafluoride contains a lot of impurities, which are mainly classified into two volatile and non volatile impurities. The volatile volatile gases are light components, mainly N₂, CO, CO₂, CF₄, SF₆, HF, non-volatile impurities such as K, Na, Fe, Cr, Mo and other metal impurities. The most difficult to remove in the impurity is hydrofluoric acid (HF), which is close to the boiling point of tungsten hexafluoride. It is found that the use of six tungsten chloride (WCl₆) can effectively react with HF in WF₆, thus the purpose of removing HF can be achieved.

The purification of tungsten hexafluoride is mainly divided into three processes. 1. Initial filtration of HF. WCl₆ is added to WF₆ and reheated to 60 ℃ and under the condition of vibratory stirring and HF reaction to achieve the purpose of removing HF. 2. Remove impurities from light components. By using WF₆ and the melting point of each impurity component, the saturated vapor pressure at the same temperature is also different. In the distillation kettle, the volatile components, namely the light component impurities, are separated for gas separation. 3. Distillation and purification. Since tungsten and molybdenum belong to the associated ore, tungsten powder is one of the raw materials for the preparation of primary WF₆, which contains a trace of molybdenum. Therefore, the prepared WF₆ contains a small amount of molybdenum hexafluoride, it is a more effective way to remove metal impurities by rectifying the packed distillation column. The purity of tungsten hexafluoride products after purification can reach more than 99.999%.

After purification, the purity of tungsten hexafluoride powder will be increased again by chemical vapor deposition. It can easily achieve the purity above 5N. This method is simple and low cost. It has become one of the main ways to extract high purity tungsten from modern industry.

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