Electrochemical synthesis of ultra-dispersed tungsten powders in molten salts

Abstract

The development of energy-efficient and environmentally friendly methods for producing ultrafine tungsten powders and its compounds is an urgent task due to the wide range of their applications. The method of electrochemical reduction of W in molten salts opens up new prospects for obtaining nano-sized tungsten powders and coatings of high purity from various precursors (oxides, sulfides, nitrides) of different morphologies and structures at low temperatures (600–900°C). The article presents the results of electrolysis of tungsten oxygen-containing compounds in molten mixtures of NaCl, KCl, CaCl2 , NaF. Both the traditional reduction of tungsten from precursors (Na2W2O7 , Na3WO3F3) dissolved in the electrolyte and the deoxidation of the solid WO3 and CaWO4 (Cambridge FFC process) were used. Tungsten powders were obtained by potentiostatic electrolysis (potentials range -1 – -3 V) at 750 °C using solid Pt or liquid Ga cathodes and different electrolyte compositions. Detailed information is presented in [1-3]. Depending on the synthesis conditions and the electrolytes composition, dispersed (30–50 nm) tungsten powders with a current yield of 45–70% were obtained. It was established that the current efficiency and final product characteristics are affected by both standard electrolysis conditions (temperature, cathode potential, current density, etc.) and other conditions: tungsten precursors (the morphology of W obtained from Na2W2O7 is characterized by a well-ordered dendritic shape and from CaWO4 by a fibrous structure with spherical inclusions); cathode material (the use of a liquid Ga cathode improves the processes efficiency) and the mechanism of chemical and electrochemical reactions. Thus, the electrochemical synthesis in molten salts can become an alternative to traditional methods of tungsten obtaining. The optimization of the conditions of these processes will make it possible to synthesize of W-Co alloys or powders (coatings) of binary and ternary carbides.