Investigation of the electrochemical reduction of Na2Ti3O7 in CaCl2 molten salt

Abstract

Abstract Sodium titanate (Na 2 Ti 3 O 7 ), as an intermediate product for producing TiO 2 through alkaline process, was used as precursor to prepare Ti metal successfully by FFC Cambridge Process. For the aim to gain insight into the electro-reduction mechanism, the sintered Na 2 Ti 3 O 7 pellets(∼1.83\u202fmm thinkness, open porosity ∼20%) were electrolysed using them as cathodes against graphite counter electrode in the molten CaCl 2 . The experiments were carried out at 900\u202f°C and the applied voltage was 3.1V. Partially reduced samples were prepared by terminating the reduction process after different electrolysis times. The obtained samples were characterised by means of X-ray diffraction analysis, SEM and EDS. The results show that Na 2 Ti 3 O 7 reacts easily with molten CaCl 2 as 2Na 2 Ti 3 O 7 \xa0+ 2CaCl 2 → Ca 2 Ti 2 O 6 \xa0+ 4TiO 2 \xa0+ 4NaCl and Ca 2 Ti 2 O 6 → 2CaTiO 3 . The electrochemical reduction of sodium titanate proceeds via sequential formation of CaTiO 3 , titanium sub-oxides (such as Ti 4 O 7 , Ti 3 O 5 , Ti 2 O 3 and TiO), CaTi 2 O 4 , Ti-O solid solution and Ti. The whole reduction can be divided into three stages: the first stage is that Ca 2+ ions from electrolyte are inserted into Na 2 Ti 3 O 7 particles leading to the formation of titanium sub-oxides and calcium titanates(CaTiO 3 and CaTi 2 O 4 ); the second stage is that calcium titanates are reduced into Ti-O solid solution from outside to inside of the pellets; the third stage is that the formed Ti-O solid solution is further deoxidised to form Ti metal.