ANALYSIS OF PHASE AND CHEMICAL EQUILIBRIUM IN THE SYSTEM OF MELT (Fe – Si – C) – SLAG (CaO – Al2O3 – SiO2 ) – GAS (O2 – SiO – CO)

Abstract

The equilibrium compositions of high-silicon metal melts, which
coexist with the slag of the CaO – Al2O3 – SiO2 system, have been determined. Dependences of the activity of silicon in iron-silicon melts have been represented as lines of isoactivities on the Fe – Si state diagram. Equilibrium with the metal melt relationships lg PO2
= f (xSi , T) for temperatures of 1823, 1873, 1973 K and influence of aSiO2 = f (xSi , T) on the equilibrium composition of the gas phase (PO2= f (xSi , T, aSiO2)) have been calculated. Data on the activity of silicon dioxide in the CaO – Al2O3 – SiO2 slag system have been analyzed and corrected. It has been shown that each alloy of the given composition at a fixed temperature corresponds to only one value of aSiO2 , which is represented on the concentration diagram of the lines of isoactivity. It has been established that in the presence of carbon all high-silicon alloys can be obtained at temperatures of T ≥ 1973 K at the values of aSiO2 > 0.8; at
1873 K and aSiO2 > 0.9 can be obtained only alloys with silicon content, which is less than 25 %, and the decrease of aSiO2
up to 0.4 to less than 20 %. At lower temperatures (≤ 1823 K) under acidic slag (aSiO2> 0.5) only low-silicon alloys can be obtained (< 15 % Si).