Impact of the Heat Flux on Solidification of Cryolite Based Bath

The solidification of the electrolytic bath in Hall-Heroult cells includes the formation of a sideledge, crust as well as temporary freeze layers around alumina agglomerates, new anodes or any cold object inserted into the bath. The structure and the chemical composition of solidified phases depend on the cooling heat flux (or cooling rate), which has a huge impact on the formation of crystals, amorphous phases and pores and on the extent of ion migration. The structure and chemical composition determine the heat loss through the side ledge, and the duration of the existence of a frozen bath around alumina agglomerates or new anodes. The authors of this paper created frozen bath samples under different heat flux conditions in well controlled laboratory environment in order to study the variation of the chemical composition and structure with the cooling rate. The results of this study are presented in this article.