Thermodynamic and structural aspects of electrochemical deposition of metals and binary compounds in molten salts

Abstract

The influence of the ionic structure of electrolytes used in the electrodeposition of molybdenum, titanium and aluminium on the mechanism and kinetics of metal deposition is discussed. Using electrochemical methods of study and a complex thermodynamic and physico-chemical analysis it was determined that in all the electrolytes investigated the electro-deposition process is significantly facilitated by the formation of complex anions with lower symmetry of the co-ordination sphere. In the case of molybdenum deposition, complex heteropolyanions are probably created in the melt by the addition of B 2O 3 or SiO 2 to the K 2MoO 4-based electrolytes. The electrodeposition of titanium from the K 2TiF 6-based electrolytes is enhanced by the formation of the less stable TiF 7 3−, resp. TiF 6Cl 3− anions. In the electrolysis of aluminium from cryolite-alumina melts the creation of oxyfluoroaluminate anions facilitates the electrodeposition of aluminium.