Reduction of tungsten halides

Chlorination of scheelite or wolframite ore concentrates according to the equations 

Based on a patent of Jonsson and Svanstrom [3.56], chlorination of tungsten scrap and subsequent fractional distillation to purify the crude WClg was used by Sandvik Co. 

The most advanced installation was made in the USA in the early 1970s. L. Ramquist of the Axel Johnson Institue of Industrial Research in Sweden described an on-line, computer-controlled industrial-scale process for tungsten powder production frxjm ore concentrates and scrap. The process included ehlorination, treatment of the chlorides formed to prepare pure WClg, and reduction by hydrogen to tungsten powder. Based on this concept, R R. Mallory and Co. Inc. in the USA installed a new plant, which was, however, closed shortly after start-up. 

The two important halide compounds which are technically in use today are WFg and WClg. They can be easily prepared by direct combination of the elements. High purity is achieved by using pure starting materials. The total exclusion of moisture is very important. 

WFg is the predominant precursor for the production of tungsten thin layers in microelectronics via CVD. Because of its electromigration resistance and low resistivity of 5.6 pQ cm, tungsten is and will be the most promising material for integrated circuit metallization. 

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