Formation of Aluminium Carbide in Hall H

The formation and dissolution of aluminium carbide under conditions similar to the chemical and electrochemical environments in the Hall-Héroult process were studied in laboratory cells, including cells with reversed polarization. The cross sections of the various electrochemical cells after the electrolysis experiments were characterized by optical and electron microscopy. A relatively dense layer of aluminium carbide was observed on the carbon cathode surface under conventional electrolysis conditions. Aluminium carbide was also found in the pores of the cathode together with bath, while only bath was found in the anode. While the direct chemical reaction between carbon and aluminium to form Al4C3 is slow, the polarisation of the cathode and electrolysis were demonstrated to have a pronounced effect on the formation of Al4C3. The present finding is discussed with emphasis of the difference between chemical and electrochemical formation of Al4C3 and the importance of the initial presence of aluminium at the cathode.