ELECTRICAL CONDUCTIVITY OF CRYOLITE ELECTROLYTES DURING THE LIQUID-SOLID PHASE TRANSITION

摘要

It is generally accepted that flow of current during aluminium electrolysis may take place through the layer of side ledge (frozen electrolyte) to the carbon side lining of cathode. It may lead to current losses and this way contribute to decrease of current efficiency. Interesting from this of point of view is the recognition of changes of electrical conductivity of the sodium cryolite melts during the liquid-solid phase transition and in solid state. In this work electrical conductivity measurements were performed on natural cryolite and its binary solutions with AlF_3, CaF_2, MgF_2, LiF. In solidified mixtures of cryolite with additions of AlF_3, CaF_2, MgF_2, the conductivity is higher than in pure cryolite in the same temperature range. This observation suggests that in solid state additives of AlF_3, CaF_2, and MgF_2 cause changes in structure of solid cryolite by introducing cation vacancies which facilitate the ion transport.