Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder

The production of tungsten by direct current reduction has been investigated. Experimental studies involved the electrochemical reduction of the solid tungsten compounds tungsten trioxide (WO(3)) and calcium tungstate (CaWO(4)) in the form of an assembled cathode of porous pellets attached to a current collector. Molten calcium chloride and a molten solution of calcium chloride and sodium chloride at eutectic composition, 48 pct mol NaCl, were used as the electrolytes. Reduced samples were characterized by means of X-ray diffraction analyses and scanning electron microscopy. The results of X-ray analyses, supported with thermodynamic computations, showed that WO(3) cannot be used without loss in processes that involve the use of CaCl(2) at high temperatures because it reacts with CaCl(2) by releasing volatile tungsten oxychloride. In the electrochemical reduction of CaWO(4), X-ray diffraction results indicated the presence of tungsten with significant concentrations of calcium compounds. Metallic tungsten was obtained after treating the reduced samples with dilute hydrochloric acid solutions.