Titanium, boron and titanium diboride deposition in alkali fluorochloride melts

Abstract

The mechanism of the electroreduction of K₂TiF₆ and KBF₄ in fused KCl–NaCl–NaF was determined from transient electrochemical techniques at temperatures ranging from 650 to 800 °C. The reduction of titanium occurred in a two-step reaction Ti⁴⁺ + e⁻→ Ti³⁺ and Ti³⁺ + 3e⁻→ Ti similar to that obtained in all-fluoride melts. The deposition of boron is obtained from the reduction of boron at oxidation state III: B³⁺ + 3e⁻→ B. Cyclic voltammetry showed that when KBF₄ was introduced in the KCl–NaCl–NaF–K₂TiF₆ melt a new peak appeared corresponding to the reaction Ti³⁺ + 2B³⁺ + 9e⁻→ TiB₂. Analysis by numerical simulation of the transient curves was used to obtain accurate values of the reaction parameters: rate constants, coverage factors, diffusion coefficients and standard potentials. From these measurements the thermodynamic properties of the solutions are calculated. It is shown that the Gibbs energy of formation of TiB₂ deduced from the present experiments is in good agreement with the values in the literature.