Anodic Overvoltage on Inert Anodes in Cryolite-Alumina Melts

摘要

The anodic overvoltage in aluminium electrolysis was studied by galvanostatic steady state current/voltage measurements with inert anodes of different composition: Cr_2O_3-NiO-CuO, NiO-Fe_2O_3-SnO_2, NiO-Fe_2O_3-Cu, and SnO_2-Sb_2O_3-CuO. Oxygen overvoltage on sintered anodes was measured in 2.7 NaF-AlF_3-Al_2O_(3(sat)) melts at 980 deg C. The investigated anodes showed several times lower overvoltage values than a traditionally used carbon anode. The process of oxygen release on the investigated inert anodes is controlled by a two-stage reaction of charge transition. At current densities of above 1.2 A/cm~2 the deviation of the overvoltage results from the straight line in Tafel system may indicate slow desorption of gaseous oxygen off the anode surface.