Abstract
Autopsies of six spent potlinings with different carbon cathode block grades, amperage regimes and cell designs were conducted at three separate smelters to reveal possible mechanisms causing cathode wear. The microstructure of the cathode samples from the autopsies was investigated by optical and electron microscopy and x-ray computed tomography, while the composition of the solid bath at the surface and in the interior pores was investigated by x-ray diffraction and electron microscopy. The present findings revealed that the cathode surface was characterized by a wear pattern resembling pitting corrosion, and it is discussed that the observed variations in the bath chemistry play a major role in the wear mechanism and the pitting of the surface. A hypothesis involving initiation and termination of the main reaction causing the cathode wear is proposed based on the effect of the consumption of aluminium fluoride in the molten bath layer between the carbon and the molten aluminium pad, resulting in partial solidification of the bath and spatial variation of the current density.