Reduction equilibria of the calcium ferrites in the Fe‐Fe2O3‐CaO system as a function of oxygen concentration and temperature

Abstract

The results of isothermally conducted reduction tests on the calcium ferrites CF2+F (= 20 mol. % CaO), CF2 (= 35 mol. % CaO), CF (= 50 mol. % CaO) and C2F (= 66.7 mol. % CaO) with CO/CO2‐bearing gases of changing composition in the temperature range between 700 and 1100°C lead both to a plot of the specimen's weight loss as a function of the test duration with the reduction potential CO'2 of the inlet gases as parameters, and to a preciser determination of the reduction stages by means of a plot of the reduced iron oxide oxygen as a function of the CO'2 concentration of the reducing gas. The weight losses are attributable to the three‐phase equilibria with the ternary compounds CWF and CW3F contained in the Fe‐Fe2O3‐CaO phase diagram. Further evaluation taking account of temperature‐dependent reduction reactions leads, on the one hand, to a complete reduction diagram for iron oxides with lime in the form of log CO2/CO as a function of MT with largely linear equilibrium curves and, on the other hand, to the familiar Baur‐Glaessner diagram, the reduction potential CO'2 as a function of temperature. The main finding compared with previous literature is the existence of the ternary ferrite CW3F extending into the liquid phase, and the fresh determination of the temperatures for the four‐phase equilibria in the Fe‐Fe2O3‐CaO system below 1100°C.