Abstract
Activity measurement of FeTO in molten blast furnace(B.F.) type slags by the method of equilibrating molten slag with iron melt or gas involves great difficulties due to fairly low oxygen potential or a small content of FeTO in molten slags.
Then, in this work, EMF method was adopted for aFeTO measurement in B.F. type slags. The activity of FeTO (aFeTO) was calculated from EMF of the following cell.
Fe(pure solid)/CaO-SiO2-Al2O3(-MgO)-FeTO/O2, Pt. Oxygen pressure in the cell at EMF measure-ment was kept at approximately 10-10 atm, at 1400°C by CO-CO2 mixture.
A Pt-O2 electrode with a Pt ring was employed as the standard electrode.
The results obtained are summarized as follows:
(1) aFeTO in the melt of CaO-SiO2-Al2O3-FeTO (CaO/SiO2=0.41.2 mol% ratio, Al2O3=12.5 mol%) indicates a positive deviation from the ideality in the range of FeTO content 0.210 mol% at 1400°C. Activity coefficient (γFeTO) at 1 400°C increases from 1.4 to 2.0 with increase in CaO/SiO2 ratio from 0.4 to 1.2.
(2) The value of aFeTO in the melts of CaO-SiO2-Al2O3-MgO-FeTO indicates less positive departure from the ideal solution behavior in the range of FeTO content 0.22 mol% at 1400°C than those in the melts without MgO.
(3) Thermodynamic quantities of mixing of FeTO were calculated by using the data of log aFeTo versus reciprocal absolute temperature (1/T). Gibbs's partial molar free energy of mixing of FeTO in the melts of CaO-SiO2-Al2O3 increases from-17 to-5 kcal/mol with increasing FeTO content in the range of 0.310 mol%.
