ELECTROCHEMISTRY OF TITANIUM IN NACL-KCL MIXTURES AND INFLUENCE OF DISSOLVED FLUORIDE IONS

Transient electrochemical techniques show that in NaCl-KCl melts the reduction of TiCl4 occurs through a three-step reaction, Ti(IV) --> Ti(III) --> Ti(II) --> Ti. The diffusion coefficients of the electroactive species and the standard potentials, E(43)(d)egrees, E(32)(d)egrees, and E(26)(d)egrees for the couples, Ti(VI)/Ti(III), Ti(III)/Ti(II), and Ti(II)Ti were measured by chronopotentiometry and cyclic voltammetry. The influence of the melt composition has been examined. The addition of fluoride ions, a common ligand for titanium ions, induces a negative shift of about I V in the potentials, E(43)(d)egrees and E(32)(d)egrees. It results in a decreasing influence of the disproportionation process 3Ti(II) --> Ti + 2Ti(III) which depends on the F/Ti ratio and on the concentration of titanium ions.