Viscosity of molten Al2O3-Cr2O3-CaO-CaF2 slags at various Al2O3/CaO ratios

Calcium fluoride, known as fluorspar is a very good flux in steel making and also has been reported to increase the alloy yield and metal recovery in aluminothermic melts for production of ferrochrome. The present investigation is therefore carried out to study the effect of CaF2 additions on the viscosity of synthetically prepared aluminothermic slags pertaining to the production of ferrochrome, with the composition approximating that of ferrochrome slag generated in the industry. The viscosities of these slags have been measured at four different Al2O3/CaO ratios with the broad composition of the slags varying between 50-62 mass% Al2O3, at various temperatures. Calcium fluoride additions decreased the viscosity of aluminothermic ferrochrome slags at all temperatures. It is observed that the decrease in viscosity is different at different Al2O3/CaO ratios and that at all temperatures there is fast decrease in viscosity initially at lower CaF2 contents, the rate of decrease diminishing at higher mole percent of CaF2, The viscosity is found to obey the Arrhenius equation of viscous flow at two different temperature ranges and not throughout the temperature range above liquidus. The activation energy at the two temperature ranges have been estimated and it is found to be strongly dependent not only on the CaF2 content but also on the Al2O3/CaO ratio. From the analysis of results it is suggested that the decrease of viscosity with increasing additions of CaF2 content may be due to both depolymerisation and decreasing intensity of interactions among various anions and cations in the melt.