Electrodeposition of titanium from chloride melts

Abstract

The kinetics of the electrodeposition and electrocrystallisation of titanium were studied in alkali chloride melts. Voltammograms showed two distinct anodic peaks for the oxidation steps Ti/Ti(II) and Ti(II)/Ti(III) at 70 mV and 300 mV, respectively, referred to titanium. The cathodic reduction Ti(III)/Ti(II) was very irreversible, showing an extended cathodic wave and a shoulder on the Ti(II)/Ti reduction peak. The Ti(II)/Ti reduction was found to be quasi reversible. The rate constant at 450'C was ∼ 5 × 10−3 cm s−1 . The diffusion coefficient in KCl-LiCl eutectic was ∼ 1 × 10−5 cm2s−1 at 450° C rising to 3.5 × 10−5 cm2s−1 at 650° C. Potential step measurements gave curves indicating slow instantaneous nucleation and growth (I against t1/2) followed by slow diffusion control (I against t−1/2). During constant current steady state deposition the nature of the deposit depended on the composition of the melt, the temperature and the cd. In KCl-LiCl melts coherent deposits were obtained for cds of 60–120 mA cm2 while higher current densities gave dendritic and spongy deposits.