Abstract:In electrolyte melts containing K at low temperature, the penetrative and migratory path of alkali metals (K and Na) in pitch, furan, phenolic aldehyde and epoxy based TiB₂-C composite cathodes during the electrolysis process were studied by EDS and self-made modified Rapoport apparatus. The electrolysis expansion rates, the diffusion coefficients of the alkali metals and the corrosion rates of the composite cathode were also calculated and discussed. The results show that no matter what kind of binder is used, alkali metals have the same penetrative path in composite cathodes: firstly in pore, then in binder and finally in carbonaceous aggregates. K and Na penetrate into both binder and carbonaceous aggregates, which leads to the expansion of composite cathodes, and K has stronger penetration ability than Na. Electrolysis expansion rate of resin based composite cathode is smaller than that of pitch based composite cathodes, and so do the diffusion coefficient and corrosion rate. Resin based composite cathode has better resistance ability to the penetration of alkali metals than pith based composite cathode, and phenolic aldehyde based composite cathode exhibits the strongest resistance ability. The penetration rate, the diffusion coefficient of alkali metals in phenolic aldehyde based TiB₂-C composite cathode and the corresponding corrosion rate are 4.72 mm/h, 2.24×10^-5 cm²/s and 2.31 mm/a, respectively.

Key words: aluminum electrolysis; penetration; migration; alkali metal; TiB₂-C composite cathode; corrosion resistance