Interfacial Tension between Aluminum and Chloride−Fluoride Melts

Abstract

Scrap and recycled aluminum have to be remelted and refined before being made into useful new products. This often involves melting the aluminum under a molten salt cover in order to prevent oxidation and to enhance the coalescence and recovery of the molten metal. A technique was developed for the measurement of the interfacial tension between liquid metals and molten salts at elevated temperatures. The technique is based on the measurement of the capillary depression occurring when a capillary, which is moved vertically down through the molten salt layer, passes through the salt/metal interface. The depression is measured by simultaneous video recording of the immersion height of the alumina capillary and the position of a liquid meniscus in a horizontal tube connected to the alumina capillary. The interfacial tension was measured for (a) aluminum and an equimolar melt of NaCl + KCl with several salt additions at 1,000 K, (b) aluminum and NaCl + NaF at 1,123 K, and (c) aluminum and NaCl + KF at 1,123 K. It was found that the interfacial tension decreases with increasing amount of NaF, increases with the increasing amount of MgCl{sub 2} additions, remains unchanged with AlF{sub 3} additions, and slightly decreases withmore » the addition of MgF{sub 2} and Na{sub 3}AlF{sub 6}.« less