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The viscosities of high alumina blast furnace slags were experimentally determined by the rotating cylinder method using the Brookfield digital viscometer model LVDV-II+ pro. Two different slag systems were considered for the current study, the CaO-SiO 2 -MgO-Al 2 O 3 quaternary and the CaO-SiO 2 -MgO-Al 2 O 3 -TiO 2 quinary system. Experiments were conducted in the temperature range of 1650 to 1873 K. The effects of temperature, basicity, TiO 2 , and silica activity of slags on viscosity were studied. The viscosity decreases with basicity for high alumina blast furnace slags with basicity in the range of 0.46 to 0.8. At high basicity (~0.8), slag viscosity decreases even with a small amount of TiO 2 (~2 pct) addition in the slag. With an increase in silica activity in the range of 0.1 to 0.4, the slag viscosity increases, the increases being steeper below the liquidus temperature.

The sulphur partition ratio between hot metal and high alumina blast furnace slag (.18% alumina) has been examined on cast by cast basis for G blast furnace of Tata Steel. Equilibrium sulphur partition ratio was calculated from sulphide capacity with the help of oxygen activity in the melt. Oxygen activity was calculated from SiO 2 /Si, MnO/Mn and CO/C equilibria. The equilibrium sulphur distribution calculated by considering the reaction [C]z[O]5(CO) g in equilibrium for estimation of oxygen activity was very close to measured sulphur distribution ratio on cast by cast basis. Use of MnO/Mn pairs gives very high oxygen activity compared with SiO 2 /Si and CO/C pairs. List of symbolsa C activity of carbon in the hot metal a Mn activity of manganese in the hot metal a MnO activity of MnO in the slag a O activity of oxygen in the metal a S activity of sulphur in the metal a Si activity of silicon in the hot metal a SiO 2 activity of silica in the slag C S sulphide capacity of the slag e j i interaction parameter of j on i f i Henrian activity coefficient for species i in the hot metal K c equilibrium constant for the reaction equation (25) K Mn equilibrium constant for the reaction equation (19) K S equilibrium constant for reaction equation (5) K Si equilibrium constant for the reaction equation (13) L S sulphur partition ratio between slag and metal P CO partial pressure of CO p O 2 partial pressure of oxygen p S 2 partial pressure of sulphur (%S) concentration of sulphur in the slag (wt-%) ½%S concentration of sulphur in the hot metal (wt-%) T temperature of the hot metal (K) X i mole fraction of individual oxides L optical basicity of multi component slag L i optical basicity of individual oxides

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A viscosity model based on a new definition of basicity has been proposed for blast furnace type slags. Conceptually, this definition of basicity is close to Bell's definition of basicity as used for modelling of sulphide capacity of blast furnace type slags. The model developed in the present work is applicable for wide range of alumina, magnesia and titania containing blast furnace slags, while most of the models available in the literature are mainly applicable for a limited range of slag composition. Viscosity estimation by this model is close to the experimental value for all types of blast furnace slags. This model is based on the chemical composition of slag and is applicable for slags above liquidus temperature. List of symbolsg viscosity of slag g o viscosity of non network forming melts A constant E activation energy of the melt B Ã i modified basicity index