Equilibrium studies between CaO-SiO 2 -10 pct MgO-Al 2 O 3 -TiO 1.5 -TiO 2 slags, carbon-saturated iron, and a carbon monoxide atmosphere were performed at 1773 K to determine the activities of TiO 1.5 and TiO 2 in the slag. These thermodynamic parameters are required to predict the formation of titanium carbonitride in the blast furnace. In order to calculate the activity of titanium oxide, the activity coefficient of titanium in carbon-saturated iron-carbon-titanium alloys was determined by measuring the solubility of titanium in carbon-saturated iron in equilibrium with titanium carbide. The solubility and the activity coefficient of titanium obtained were 1.3 pct and 0.023 relative to 1 wt pct titanium in liquid iron or 0.0013 relative to pure solid titanium at 1773 K, respectively. Over the concentration range studied, the effect of the TiO x content on its activity coefficient is small. In the slag system studied containing 35 to 50 pct CaO, 25 to 45 pct SiO 2 , 7 to 22 pct Al 2 O 3 , and 10 pct MgO, the activity coefficients of TiO 1.5 and TiO 2 relative to pure solid standard states range from 2.3 to 8.8 and from 0.1 to 0.3, respectively. Using thermodynamic data obtained, the prediction of the formation of titanium carbonitride was made. Assuming hypothetical 'TiO 2 ,' i.e., total titanium in the slag expressed as TiO 2 , and using the values of the activity coefficients of TiO 1.5 and TiO 2 determined, the equilibrium distribution of titanium between blast furnace-type slags and carbonsaturated iron was computed. The value of [pct Ti]/(pct 'TiO 2 ') ranges from 0.1 to 0.2.
In bath smelting, the FeO activity of the slag must be known to predict the equilibrium of slag-metal reactions and for effective control of the rate of reduction in the system. Also, knowledge of the solubility of MgO in these slags is useful for reducing refractory consumption. A series of measurements of the FeO activity in simulated bath smelting slags (CaO-SiO 2 -Al 2 O 3 -MgO sat -FeO) were conducted by the electromotive force (EMF) technique. The influence of the slag composition on the relationship between the FeO activity coefficient and FeO content was studied. It has been found that the measured FeO activity coefficient decreases with increasing FeO content in the slag and increases slightly with increasing slag basicity, which is defined as (CaO ϩ MgO)/(SiO 2 ϩ Al 2 O 3 ) on a mole fraction basis.The measured values of the FeO activity coefficient are in reasonable agreement with previously published data. The solubility of MgO was also measured and found to range from 16 to 30 pct and decrease with increasing basicity.
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