Mechanism of the cathode process in the electrochemical synthesis of TiB 2 in molten salts—II. Chloride-Fluoride electrolytes

Abstract

The mechanism of the cathode process in the high-temperature electrochemical synthesis of titanium diboride in molten NaCl-KCl supporting electrolyte containing titanium trichloride and alkali tetrafluoroborate as electrochemically active components has been investigated by means of linear and cyclic voltammetry. The reduction of titanium from TiCl 3 was found to proceed in two steps: Ti(III) → Ti(II) → Ti(0), the kinetics of this reduction being strongly affected by the disproportionation reaction 3Ti(II) ⇌ 2Ti(III) + Ti(0). This reaction mechanism can be altered by addition of sodium fluoride to the supporting electrolyte. Boron(III) is reduced in a single step; the rate of reduction decreases with time. The conditions for a single step discharge of Ti(III) and for the rapprochement of the reduction potentials of titanium and boron were established. The electrochemical synthesis of TiB 2 proceeds in one step with a depolarization of about 0.25 V compared with the reduction potential of boron resulting from the high negative value of the Gibbs energy of formation of TiB 2.