Sodium and Bath Penetration Into TiB2-Carbon Cathodes During Laboratory Aluminium Electrolysis

Abstract

TiB2-carbon cathodes with varying amount of TiB2 were prepared by pressing and baking. The TiB2 bonded strongly to the carbon matrix, the crushing strength being better than that of pure carbon. The shrinkage during baking was found to decrease with increasing amount of TiB2. Penetration of sodium and bath was studied in a laboratory aluminium electrolysis set-up, the cathode being on top of the melt. The penetration velocity increased with increased TiB2 content, current density and cryolite ratio, but reached a plateau at CR=3 or at 0.7 A/cm2, respectively. The sodium concentration was lower in the TiB2 area than that in the carbon matrix, and bath constituents were found on the TiB2 grain boundaries. AIF3 was depleted in the carbon area while NaF preferentially migrated to the TiB2 area enhancing sodium generation and penetration.