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Results for specimens of the refractory lining sampled from the bottom of an aluminum electrolysis cell with a service life of 3.5 years examined by methods of petrography, chemical analysis, and electron probe x-ray microanalysis are reported. The main products of conversion are sodium aluminosilicates, sodium silicates, a glassy phase of variable composition, oxyfluoride glasses, and eutectics. Some of the specimens analyzed are high in β-alumina (20 – 50%). Fluorides are represented by NaF (about 7%), cryolite Na3AlF6 (2 – 5%), malladrite Na2SiF6 (2%), and NaF ⋅ MgF2 (1 – 2%), and the metallic phase, by aluminum (2 – 7%) and ferrosilicon (3 – 10%). The apparent density of the used refractory material is 2.5 – 2.62 g/cm3. [ABSTRACT FROM AUTHOR]

Specimens of post-service ShA-5-grade chamotte refractory are analyzed for total elemental aluminum and silicon. Products of the electrolysis of cryolitic melt Na (gas), AlF, Al2O, and, possibly, Na2F are shown to diffuse through pores of the carbon refractory bottom lining blocks of an aluminum electrolysis cell. The lower compounds and Na(gas) as they reach the refractory layer enter into a reaction with the refractory material. The Gibbs free energy of hypothetic reactions in the Al - Si - O - F - Na system involving a gas phase has been calculated. It is inferred that the performance characteristics of the ShA-5 refractory fail to meet standard operational requirements. [ABSTRACT FROM AUTHOR]