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There are still some different understandings about deoxidization process from TiO 2 to Ti by FFC Cambridge process. Herein, an investigation was carried out on the phase transformations and deoxidation kinetics of the electrochemical reduction of TiO 2 to Ti in molten CaCl 2. The reaction goes through four different stages involving several phase transformations. The first stage is the deoxidation of TiO 2 with the formation of CaO and CaTiO 3. At this stage, Cl 2 is forcibly released from the anode because of the consumption of Ca 2+ on the cathode, balanced with Cl ¹ at the anode. The second stage is the deoxidation of CaTiO 3 and titanium suboxides. These two stages take 45% of the entire deoxidation time from TiO 2 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 TiO solid solution by electrochemical reduction or by calcium thermal reduction. There are no obvious kinetic barriers in the formation of CaTiO 3 , but the rate of deoxidation of titanium suboxides and CaTiO 3 is relatively slow. Therefore, the limiting step from TiO 2 to Ti by the FFC process in molten CaCl 2 is deoxidation of titanium oxides and the interphase of CaTiO 3 .

The crystallization processes of titanates are central to the fabrication of optical and electrical crystals and glasses, but their rich polymorphism is not fully understood. Here, we show when and how polymorphic selection occurs during the crystallization of barium titanate (BaTiO3, BT) using in situ high energy synchrotron X-ray diffraction and ab initio molecular dynamic simulation. An anomalous structure transition is found in molten BT during cooling across the cubic-hexagonal transition temperature, which enables nucleation selection of BT by manipulating the undercooling: a cubic phase is preferred if nucleation is triggered at large undercooling, whereas a hexagonal phase is promoted at small undercooling. We further reveal that the nucleation selection between the cubic and the hexagonal phase is regulated by the intrinsic structure property of the melt, in particular, the degree of polymerization between Ti-O polyhedra. These findings provide an innovative perspective to link the polymorphic crystallization to the non-isomorphic structure transition of the melt beyond the conventional cognition of structural heredity.

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