Effect of TiC on TiB2-carbon inert cathodes for aluminum electrolysis

This study employs a modified Rapoport apparatus to measure sodium expansion during aluminum electrolysis to elucidate the role of titanium carbide (TiC) in the graphitization of TiB2‑carbon composite cathodes comprising a TiB2-rich bottom layer, a functional TiB2/C middle layer, and a graphite (carbon base) top layer. The results indicate that TiC crystallites catalyze the graphitization of TiB2‑carbon composite cathodes during aluminum electrolysis. Transmission electron microscopy (TEM) analyses reveal three types of residual TiC in the TiB2‑carbon composite cathodes after aluminum electrolysis; these TiC particles indicate two distinct catalytic graphitization mechanisms. The regular morphology of TiC is a result of the dissolution-precipitation mechanism, whereas the eroded TiC corresponds to a carbide formation-decomposition mechanism. The voltage drop in the TiB2‑carbon composite cathodes was reduced by approximately 120 mV compared with that observed using simple carbon cathodes. This work provides key insights regarding the mechanism that hinders Na penetration into the carbon/TiB2 cathodes during aluminum electrolysis. [Display omitted] •TiC acted as a catalyst can accelerate the graphitization of carbon cathodes.•TiB2 can improve the resistance of carbon cathodes to the melt and sodium.•TiB2 can reduce the cathode voltage drop.