Surface tension, densities and viscosities of some CaO-Al₂O₃ slags

The metallurgical concepts with regard to the structures and properties of calcium aluminate melts have been based upon analogies within ternary CaO-Al₂O₃-SiO₂ systems. In this work the results of surface tension, density and viscosity of some calcium aluminate slags, in the temperature range of 1500 to 1600°C are presented and the results are discussed based upon recent structural characterisation results of crystalline aluminates. The compositional range investigated was from 45 to 53 weight-% alumina. The results indicate a reduction in density as the molar ratio CaO-Al₂O₃ decreases. Surface tension falls on increasing either the molar ratio CaO-Al₂O₃ or temperature. Conversely, viscosity increases with increasing molar ratio CaO-Al₂O₃ and decreasing temperature. The compositional dependence of both surface tension and viscosity data may be associated with the presence of some aluminium ions in octahedral co-ordination, and a concept of surface behaviour is proposed which involves surface activity of aluminate anions containing aluminium ions in a reduced valence state, such as Al²⁺.