The subject of vacuum metallurgy encompasses various diverse areas such as the extraction of metals, refining, degassing, remelting, sintering, heat treatment, brazing and other techniques for joining under vacuum. These processes are carried out under vacuum either because the process can not be carried out under normal atmospheric conditions or the rate of process is enhanced under vacuum. Vacuum also protects the metal from the environment during processing. Removal of the volatile phases formed during chemical reactions from the reaction interface shifts the equilibrium and enhances the rate of reaction. .Sometimes, the vapour pressure of the metal produced by such a reaction is so low that unless a vacuum applied, the reaction will not take place. Chemical transport reactions are employed in the refining of highly refractory metals such as titanium, zirconium, vanadium etc. The metal is converted into a volatile compound under vacuum. The volatile material is subsequently decomposed to recover a high purity metal. Another type of refining exploiting vacuum is degassing or deoxidation of melts. The principles of thermodynamics and kinetics play a crucial role in the vacuum metallurgy operations. Application of vacuum metallurgy for extraction and refining processes is illustrated with appropriate examples.
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