Electrolytic Degradation Within Cathode Materials

Abstract

There are two generally accepted electrochemical processes involving the carbon of cathode blocks, these being sodium uptake and aluminium carbide formation. Both processes occur at or below the potential required for aluminium deposition, and therefore can occur at all times in blocks permeated with electrolyte — as does occur with modern cell designs and operation. Then, since the cathode carbon is at a more cathodic potential than the molten aluminium metal pad, the electrolyte filled material can sustain the electrochemical reactions, even though the rate may be very low.

A special laboratory test has been developed to identify and ascertain the extent of the carbide forming reaction within the carbon matrix of laboratory cathode specimens. Results show that this reaction is dependent on the carbon binder pitch, the carbon filler material and the cathode heat treatment. This electrochemical reaction is expected to become more prevalent at higher current densities and the growth of the carbide can potentially contribute to accelerated wear in cathode blocks.