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

Abstract

Part of the molten system NaF-AlF 3 -Al 2 O 3 was studied by surface tension measurements, which were performed at cryolite ratios (CR) between 1.5 and 3 [CR = n(NaF)/n(AlF 3 )]. The maximal bubble pressure method was applied. The surface adsorption of alumina (Al 2 O 3 ) was also calculated. The obtained results were discussed in terms of the anionic composition of the melt. The addition of AlF 3 to melt with CR= 3 decreases the surface tension, as AlF 3 is surface-active in molten Na 3 AlF 6 . 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-AlF 3 mixtures and the surface tension of pure alumina was observed with decreasing cryolite ratio.