Corrosion and Oxidation of Silicon Carbide Based on a Nitride Binder in an Aluminum Electrolyzer Side Lining

Abstract

The main question for understanding the corrosion of a side lining made from silicon carbide based on a silicon nitride binder is whether corrosion of Si₃N₄–SiC material by gases (and, in particular, oxidation) is preceded by corrosion by molten electrolyte, or corrosion by molten electrolyte plays its own role in material degradation during service. It is more probable that reactions of SiC and Si₃N₄ with molten cryolite pass through a pre-oxidation stage. Calculations show that the majority of possible reactions of SiC and Si₃N₄ with oxygen, carbon monoxide, and carbon dioxide have a positive volumetric effect, which reduces material porosity, but may cause crack development within it. In this case the silicon oxide formed is dissolved in molten electrolyte and may also react with electrolyte components in the gas phase.