SURFACE-TENSION OF CRYOLITE-BASED MELTS

The pin detachment method has been used to obtain data on the surface tension of liquid Na(3)AIF(6) with additions of AlF3, LiF, KF, CaF2 and Al2O3 as a function of temperature. In basic melts Al2O3 and KF are surface active and decrease the surface tension, sigma, while LiF and CaF2 additions give an increased sigma. Additions of AlF3, to Na3AlF6 decrease sigma. In acidic melts (CR < 3) for CR = 1.85 and 1.52, respectively, there is a marked increase in sigma with LiF additions and a smaller increase with Al2O3 and CaF2 additions. KF is almost neutral for these melt compositions. An explanation of the observed variations in sigma in terms of the acid-base properties or the ionic-covalent character of the additives seems to be too simple.