ROLE OF MELT BASICITY ON THE COMPOSITION OF ELECTRODEPOSITS IN TUNGSTEN-CARBON SYSTEM

The role of basicity of the melt during electrodeposition of tungsten carbide from the Na2WO4-Na2O-B2O3-NaCl system using the graphite elect rode has been studied by UV-vis reflectance spectroscopy of tungsten s pecies formed. It has been shown that tungsten in the melt is predomin antly found as W6+ at low basicity, as ditungstate in an intermediate basicity range and as monomeric (WO4)(2-) species in highly basic melt s leading to deposition of W, W2C and WC during electrolysis depending upon the Na2O:B2O3 ratio of the melt. Addition of NaCl was found to p lay no direct role in changing the tungsten species in the melt; its r ole probably is to increase the electrical conductivity or to decrease the viscosity/surface tension of the melt.