Direct electroreduction of oxides in molten fluoride salts

A new kind of electrolyte composed of molten fluorides has been evaluated in order to perform a feasibility study of the direct electroreduction reaction. The direct reduction of SnO2 and Fe3O4 was realised in LiF-NaF at 750°C and in LiF-CaF2 at 850°C for TiO2 and TiO. The electrochemical behaviour of these oxides was studied by linear sweep voltammetry: a current corresponding to the oxide reduction was evidenced for TiO2, SnO2 and Fe3O4. After intensiostatic electrolyses, a complete conversion was obtained for all oxides, except TiO, and the structure of reduced Ti and Fe samples had a typical coral-like structure while dense drops of Sn were recovered (Sn is liquid at operating temperature). After TiO electrolysis, a thin external metallic titanium layer was detected, acting as a barrier for the oxide ions diffusion and no complete reduction can be achieved. This could be explained by a Pilling-Bedworth ratio around 1 for Ti/TiO

electroreduction of oxides in molten fluoride salts

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@inp-toulouse. b s t r a c t A new kind of electrolyte composed of molten fluorides has been evaluated in order to perform a feasibility study of the direct electroreduction reaction. The direct reduction of SnO 2 and Fe 3 O 4 was realised in LiF-NaF at 750 • C and in LiF-CaF 2 at 850 • C for TiO 2 and TiO. The electrochemical behaviour of these oxides was studied by linear sweep voltammetry: a current corresponding to the oxide reduction was evidenced for TiO 2 , SnO 2 and Fe 3 O 4 . After galvanostatic electrolyses, a complete conversion was obtained for all oxides, except TiO, and the structure of reduced Ti and Fe samples had a typical coral-like structure while dense drops of Sn were recovered (Sn is liquid at operating temperature). After TiO electrolysis, a thin external metallic titanium layer was detected, acting as a barrier for the oxide ion diffusion and no complete reduction can be achieved. This could be explained by a Pilling-Bedworth ratio around 1 for Ti/TiO