Alkali metals (K and Na) penetration and its effects on expansion of TiB2-C composite cathode during aluminum electrolysis

The behavior of alkali metals (K and Na) penetration in TiB2-C composite cathode and the induced electrolysis expansion under various conditions in KF melt, NaF melt and their composite melts were investigated. The most important influence factor on the electrolysis expansion properties of the cathode was revealed, and the elements micro-analysis of cathode profiles was performed. The results indicate that, under the condition of non-polarization and Al free, no electrolysis expansion occurs. The alkali metal produced by direct discharge reduction is the most important factor causing the electrolysis expansion, and the maximal expansion is 20.40%. Electrolysis expansion in electrolyte with K is higher than that in electrolyte without K, and the maximal excess magnitude is 35.13%. Compared with pure potassium salt, composite electrolyte has less destructive effects on the cathode. In addition, no matter under the condition of polarization or non-polarization, electrolysis expansion in electrolyte with Al is always greater than that in electrolyte without Al, and the increase amplitude of electrolysis expansion in non-polarization conditions with Al is significantly greater than that in polarization conditions with Al.