Tensile Stress-Induced Micro-Cracking of Ramming Paste Drives Electrical Instability in Hall-Héroult Cells

The reliability of Hall-Héroult cells is often undermined by electrical instability during start-up, which is typically addressed through prolonged preheating schedules. This study identifies a fundamental thermomechanical material failure in the cathode structure as the primary root cause. Using a validated, fully coupled finite element model, we demonstrate that high tensile stresses are generated and concentrated specifically in the carbonaceous ramming paste joints during the preheating cycle. Applying the Goldenblat-Kopnov criterion for brittle materials confirms that these local stresses significantly exceed the failure threshold, leading to micro-cracking of the ramming paste (criterion value > 1). This predicted mechanical degradation directly disrupts the uniformity of current paths, establishing a quantifiable mechanistic link to fluctuations in cell resistance and, consequently, to electrical noise. This finding enables a paradigm shift in failure analysis, moving the focus from bulk cathode behavior or thermal gradients to the critical interfacial integrity of the ramming paste. This new perspective opens avenues for material-based design improvements.