Observation on the Creep and Cracking of Graphite Cathode in Laboratory Aluminum Electrolysis

The uniaxial compressive creep tests for graphite cathode samples under 4 MPa constant loading have been carried out by a modified Rapoport-Samoilenko apparatus. Experimental results have been obtained for different temperatures (920, 940 and 960 °C) under both laboratory aluminum electrolysis and non-electrolysis conditions. The results indicated that the creep strain of graphite samples increased with higher temperature and electrolysis process. The compressive strength of the electrolysis samples decrease significantly (>10 MPa) compared to the non-electrolysis samples, when both have been subjected to creep tests under the same operating temperature. Some transverse cracks filled with fluoride species, extending from the contact interface of Al-cathode into the inner area of the electrolytic cathode, can be observed by SEM after uniaxial compressive strength tests. Creep-electrolysis induced cracks are also associated with reduced compressive strength. The observed results may provide direct evidence for better understanding of material deterioration and mechanical failures of the cathodes in aluminum electrolysis process.