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-A l2O3-SiO2 systems. In this work the results of surface tension, density and viscosity of some calcium aluminate slags, in the temperature range of 150 0 to 1600 degrees C are presented and the results are discussed based upon recent structural characterisation results of crystalline aluminates. The c ompositional range investigated was from 45 to 53 weight-% alumina. The res ults indicate a reduction in density as the molar ratio CaO-Al2O3 decreases . Surface tension falls on increasing either the molar ratio CaO-Al2O3 or t emperature. Conversely, viscosity increases with increasing molar ratio CaO -Al2O3, and decreasing temperature. The compositional dependence of both su rface tension and viscosity data may be associated with the presence of som e aluminium ions in octahedral co-ordination, and a concept of surface beha viour is proposed which involves surface activity of aluminate anions conta ining aluminium ions in a reduced valence state, such as Al2+.