Transport of Sodium in TiB 2 Materials Investigated by a Laboratory Test and DFT Calculations

Inert, wettable cathodes have a significant potential for improving the Hall-Heroult electrolysis cell. With good wetting properties towards aluminium, the anode—cathode distance may be significantly reduced, leading to lower energy consumption and potentially extending the lifetime of the cathode. TiB2 is one of the most promising inert cathode candidate materials; however, the implementation of the material is not straight forward, partly due to the challenges of understanding the degradation mechanisms. Sodium vapour, which has proved to have great impact on the traditional carbon cathodes, has drawn less attention for TiB2 materials. Thermogravimetric tests with various sodium vapour activities have been used to study the effect of sodium vapour on commercial TiB2 materials. The chemical stability of TiB2 towards sodium and the transport properties of sodium in TiB2 materials have been investigated by atomistic calculations based on density functional theory. Finally, a possible degradation scheme of TiB2 materials subject to sodium environments is proposed.