Cathodic overvoltage and the contents of sodium and lithium in molten aluminium during electrolysis of cryolite-based melts

The cathodic concentration overvoltage in Na3AlF6-AlF3-Al2O3(sat.) melts wa s investigated at the temperature of 1000 degreesC. The melts contained 10 and 20 wt.%;, of AlF3. Experimental data on the cathodic overvoltage agreed well with values calculated from the content of sodium in aluminium. The d ependence of the cathodic overvoltage on temperature was studied as well. I t was shown that the addition of 5 wt.% CaF2 or 5 wt.% MgF2 does not influe nce the overvoltage significantly, while the addition of 2 wt.% LiF decreas es the overvoltage by 20 mV at a cathodic current density of 0.25 A cm(-2) and by 50 mV at 0.75 A cm(-2). These results are consistent with the influe nce of these additions on the content of sodium in aluminium. (C) 2001 Else vier Science Ltd. All rights reserved.