Composition and thermal analysis of crust formed from industrial anode cover

Abstract

When the anode cover is heated up in the reduction cell, the crust formation from the anode cover commences at the bottom and the process is driven by thermo-chemical processes. It is important to study the composition and thermal stability properties of the crust in order to understand the mechanisms of crust formation and deterioration. Several crust pieces were taken from industrial prebaked anode cells. A number of vertical crust sections were sampled from these pieces, and each section was analyzed for composition and phase change temperature. Results show that the bottom layer is enriched in cryolite, consistent with results published in the literature. The upper region was found to contain more chiolite. Crushed bath-based anode crust has higher CR than alumina based anode crust. The melting of chiolite in the crust leaves substantial macro-porosity there, which contributes to the absorption of NaAlF 4 and the penetration of bath through it. The formation conditions of crystalline crust were discussed.