PROPERTIES AND PRODUCTION CONDITIONS AFFECTING CRACK FORMATION AND PROPAGATION IN CARBON ANODES

The objective of the present work is to achieve a better understanding of anode thermal shock fracture in the early stage after an anode change in the electrolysis cell. In order to show the mechanisms leading to anode fracture and crack propagation, a thermo-mechanical model of the thermal shock experienced by an anode when it is positioned in the pot was developed. The model allows calculation of stresses and strains within the anode, as function of time. The time interval of the modelling lasts for 1 hour after the anode change. Baked anodes are inhomogeneous and anisotropic due to the raw materials and production process. Core samples from industrial scale anodes were analysed and the results provided gradient plots of physical and mechanical properties. The results were used as input to the model and together with a set of boundary conditions, the thermal shock resistance was calculated. The highest main tensile stress occurred 1 hour after the anode is immersed in the cell. The stress seems then to level out and decrease. The stress calculated is at a level where cracks may be initiated, matching the tensile strength tests.