The System Iron-Oxygen. I. The Wüstite Field and Related Equilibria

Abstract

By measuring the temperature corresponding to the position of the sharp boundary between phases produced by holding a strip of iron or iron oxide in a known small temperature gradient in contact with a gas of definite composition, the CO2/CO ratio in equilibrimn with iron and wüstite was obtained at temperatures from 1038 to 1365°, and that in equilibrium with wüstite and magnetite from 1096 to 1388°. Between these boundaries the composition of wüstite in equilibrium with various gas mixtures was determined, and that at the boundaries derived by short extrapolation at constant temperature to the gas compositions at these points. From these measurements the activities of iron and FeO in wüstite have been calculated, and therefore the activity of any other iron-oxygen complex is available. The partial molal heat of solution of oxygen and of iron in wüstite, as well as the heat of formation of wüstite, is recorded at various compositions. The heat of formation of magnetite has been computed to be −260,930 cal. at 1250° and −267,200 cal. at 25°, in excellent agreement with the best calorimetric values. © 1945, American Chemical Society. All rights reserved.