Wetting Between Carbon and Cryolitic Melts. Part II: Effect of Bath Properties and Polarisation

An apparatus for determination of wetting angles, based on the immersion-emersion technique and adapted for use at high temperature, was used for measuring the wetting between cryolitic melts and samples consisting of standard anode carbon. Anodic polarisation of the sample and the alumina concentration were the more important factors. Polarisation strongly improved the wetting if the melt was low in alumina, and the effect persisted for a while after the current was turned off. Increasing the alumina concentration to near saturation brought about a dramatic change from non-wetting to good wetting. The advancing angle of wetting was normally larger than the receding angle, while the opposite was observed in some experiments with aqueous solutions of ethanol and sodium fluoride. The latter effect has interesting consequences for the motion of gas bubbles, and the results also demonstrate that it is necessary to be careful in the selection of liquids and materials for physical modelling of aluminium cells.