Abstract
The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na3AlF6, A1F3, NaF, A12O3, CaF2, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF3 ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF3 ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A12O3 increased the interfacial tension for a given NaF/AlF3 ratio. KF was found to be surface active, while CaF2, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.
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