Accelerated Electro-Reduction of TiO2 to Metallic Ti in a CaCl2 Bath Using an Inert Intermetallic Anode

Abstract

In the FFC-Cambridge process, the cathodic dissociation of oxide and CO/CO2 production on carbon anode is the basis for metal production in a CaCl2 bath. Using an inert intermetallic anode, the CO2 evolution can be eliminated altogether with acceleration in the electro-reduction kinetics. In the presence of a carbon anode, the cathodic dissociation of TiO2 suffers from slow reduction kinetics of TiO2 to Ti metal, which can be enhanced significantly by the incorporation of alkali species in the TiO2 pellet at the cathode and in the CaCl2 bath in the presence of an intermetallic inert anode. With inert anode and incorporation of K+-ion in the TiO2 matrix and in the salt bath, nearly full metallization with greater than 99% of Ti metal containing 1500 ppm of oxygen was possible to achieve in less than 16 h of electro-reduction. The microstructural and chemical analysis of the metallic phase and its morphology revealed the presence of a layer of titanium metal that forms in the fast reduction reaction step in less than 5 h, after which the reaction rate slows down significantly before terminating in 16 h. The investigation showed that two different types of microstructures of metallic titanium were evident—a thin sheet-like material on the outer periphery of the reduced pellet and the dendritic core which was found to be under the peripheral sheet of the metallic layer. The mechanism of morphological and microstructural changes in the reduced form of titanium metal is explained.