On the Equilibrium among Silicon in Molten Iron, Blast Furnace Slag and H_2-H_2O Mixed Gas. I : Measurement of the Equilibrium among Silicon in Molten Iron, SiO_2-CaO Binary Slag and H_2-H_2O Mixed Gas

1. Measurement of Equilibrium of the Reaction, (SiO_2)^_+2H_2=Si^+2H_2O The reduction of silica from molten slag to molten iron by H_2 gas is one of the important reactions in iron and steel making process which may be expressed in the equation as follows : (SiO_2)+2H_2=Si+2H_2O……(1) When the slag is saturated with SiO_2, equation (1) becomes (SiO_2)_sat.+2H_2=Si+2H_2O……(2) As the direct measurement of the equilibrium of equation (1) was difficult, the equilibrium of equation (2) was measured, using a pure silica crucibe in the temperature range from 1, 500°to 1, 600℃. From the experimental results, it was found (a) that the relation between p^2H_2/p^2H_2O and Si% at a given temperature could be expressed by a straight line and (b) that the temperature function of the equilibrium constant could be expressed as follows : Chemical formula. 2. Measurement of the Equilibrium of the Reaction, (SiO_2)_+2H_2=Si+2H_2O The equilibrium of this reaction was measured in the temperature range from 1, 550° to 1, 650℃, using a pure CaO crucible^ and a SiO_2-CaO binary slag in which SiO_2 content was about 60% From the results of measurement, the values of the activity of SiO_2 on the liquidus line at 1, 550°, 1, 600° and 1, 650℃ were calculated as follows : a_ N_ Temperature, ℃ 0.22, 0.41, 1, 550, 0.18, 0.40, 1, 600, 0.16, 0.39, 1, 650 where pure β-cristobalite was taken as the standard of the activity of SiO_2 at each temperature. Combining these results with the data of activities of SiO_2 in SiO_2-CaO binary slags reported by Chang and Derge^, the authors performed the thermodynamic calculation on the molten SiO_2-CaO binary slag and established the relation of equilibrium among silicon in molten iron, molten SiO_2-CaO slag and H_2-H_2O mixed gas