Phase Transformations and Deoxidation Kinetics during the Electrochemical Reduction of TiO₂ in Molten CaCl₂

Abstract

There are still some different understandings about deoxidization process from TiO₂ to Ti by FFC Cambridge process. Herein, an investigation was carried out on the phase transformations and deoxidation kinetics of the electrochemical reduction of TiO₂ to Ti in molten CaCl₂. The reaction goes through four different stages involving several phase transformations. The first stage is the deoxidation of TiO₂ with the formation of CaO and CaTiO₃. At this stage, Cl₂ is forcibly released from the anode because of the consumption of Ca²⁺ on the cathode, balanced with Cl⁻ at the anode. The second stage is the deoxidation of CaTiO₃ and titanium suboxides. These two stages take 45% of the entire deoxidation time from TiO₂ to Ti_[O]. The third stage is the deoxidation of titanium suboxides. This stage takes about 55% of the total time. The final stage is further deoxidation of Ti–O solid solution by electrochemical reduction or by calcium thermal reduction. There are no obvious kinetic barriers in the formation of CaTiO₃, but the rate of deoxidation of titanium suboxides and CaTiO₃ is relatively slow. Therefore, the limiting step from TiO₂ to Ti by the FFC process in molten CaCl₂ is deoxidation of titanium oxides and the interphase of CaTiO₃.