2019 Volume 60 Issue 3 Pages 416-421
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.