Surface Tension of the System NaF –AlF3–Al2O3 and Surface Adsorption of Al2O3

Abstract

Part of the molten system NaF-AlF3-Al2O3 was studied by surface tension measurements, which were performed at cryolite ratios (CR) between 1.5 and 3 [CR = n(NaF)/n(AlF3)]. The maximal bubble pressure method was applied. The surface adsorption of alumina (Al2O3) was also calculated. The obtained results were discussed in terms of the anionic composition of the melt. The addition of AlF3 to melt with CR= 3 decreases the surface tension, as AlF3 is surface-active in molten Na3AlF6. The concentration dependence of the surface tension and the surface adsorption of alumina in the title system are influenced by the formation of surface-active oxofluoroaluminates. An increase of the difference between the surface tension of NaF-AlF3 mixtures and the surface tension of pure alumina was observed with decreasing cryolite ratio.