ELECTRONIC CONDUCTION IN CRYOLITE-ALUMINA MELTS

Previous work by the authors has shown that electrons are an important constituent of cryolite melts saturated with alumina and in contact w ith aluminum. This has a negative effect on the current efficiency of aluminum production in industrial cells. In the present paper, methods used to measure electronic conduction, electron mobilities, and elect ron concentrations in cryolite alumina melts (NaF/AlF3 molar ratio=3) will be reviewed. New results will then be reported on electronic cond uction in melts with a NaF/AlF3 molar ratio of 2.4 at various sodium a ctivities. In particular, a ratio nearer to that used in industrial ce lls was examined. AC resistance measurements were performed on cryolit e-based alumina melts equilibrated with aluminum-silver alloys between 967 and 1037 degrees C. The results were used to estimate the effect of electrons on current efficiency in cells used for the production of aluminum. Equations for the current efficiency formerly used by the a uthors are reviewed and calculations based on the new results are pres ented. In general, current efficiencies between 93.5% and 99% were obt ained.