Smelting Method of Refining High Purity Tungsten

Smelting is the main method of tungsten metal refining, including arc melting, electron beam melting and regional melting. Electron beam melting and zone melting are mainly used to produce tungsten ingots or single crystals whose purity is more than 99.999.

The preparation of high purity tungsten by smelting method is mainly divided into three stages: tungstate solution purification and reduction method to prepare tungsten and tungsten metal refining. In the first stage, chemical purification processes, such as solvent extraction and ion exchange, are used to remove most of the impurities in tungstate solution, such as As, P, and Si. The second stage is the preparation of the initial tungsten powder, and the WO₃ obtained by the calcining is reduced to tungsten in the reduction process. The third stage mainly uses physical purification technology, such as electron beam melting, regional melting, vacuum degassing, etc., to further remove impurities from tungsten and obtain high-purity tungsten.

The electron beam smelting is carried out in a vacuum, also known as a vacuum melting process. Because of its high purity of metal, low cost and high energy density, the prospect of development in China is very broad. Electron beam melting technology uses the high energy electron beam emitted by the electron beam generation system to bombard the smelting metal to realize the smelting, purifying and impurity removing technology of metallic materials. In the process of smelting, the time of maintaining the liquid is long and the refining can be fully carried out, but the loss of the main metal is caused, when the electron beam smelting process is purified, the removal of impurities and the loss of the main metal should be considered.

In the production of electronic industry, the method of regional melting can increase the purity of metal to 6N. Because of its simple principle, wide range of application and mature technology, regional melting has two ways of horizontal zone melting and suspension zone melting. Multiple electron beam melting and regional melting can effectively improve the purity of W, but its processing performance is very poor and its size is small, and it needs to be strengthened by vacuum degassing process. The high vacuum degassing process can remove the impurities from the gap to produce gas volatiles, which can effectively reduce the content of interstitial impurities such as hydrogen, nitrogen and oxygen and exclude non-metallic inclusions.

Smelting process has the advantages of high temperature, no pollution, good purification and so on. It has great advantages in purifying refractory metals. But it requires high purity of APT raw material, tungsten oxide and tungsten powder and so on, so the technology cost much time and the corresponding cost is higher than chemical vapor deposition.

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