Determination of the phase boundaries of the wustite solid solution within the context of reduction tests

Abstract

Oxygen reduction measurements performed isothermally on Fe203 with CO/C0 2 gas mixtures make it possible, in combination with a system of equations describing the homogeneous wustite phase FeO n, to describe also the boundaries of this solid solution mathematically.Compared with corresponding data determined by Giddings and Gordon on the basis of a literature evaluation, the boundaries of the wustite field are found to shift to a much lower reduction potential. The developed system of equations makes it possible to plot the curves of the same oxygen concentration in the homogeneous wustite phase field of the Bauer-Glaessner diagram. When comparing the reduction equilibria of the left-and right-hand wustite solid solution boundary with the appropriate literature data there is a good agreement particularly with the measurements of Darken and Gurry. Significantly lower oxygen concentrations are found in the FeO phase diagram, however, especially at high temperatures. New concentration data derived from the systems of equations are also given for the melt equilibria of the wustite phase, which lead to the assertion that the liquidus curves of magnetite, wustite and iron are also shifted to a lower oxygen concentration. The decomposition point of the wustite is found at 570°C, 49.5 %, CO~and 23.2 % oxygen.

Melting point determinations of -rich slag

“…peaks, in agreement with the relatively large temperature difference between the solidus and liquidus temperatures of the liquid oxide + magnetite phase field (Schürmann and Jahnsen 1993). The small temperature difference between the solidus and liquidus temperatures of the wüstite phase field is similarly illustrated in the peaks of figures 9(b) and (c) where only one clearly defined peak is present.…”

“…The measured liquidus temperature in argon, 1415 • C, corresponds to the melting point of wüstite at an oxygen partial pressure of some 10 −6.9 atm (Schürmann and Jahnsen 1993). This is in the range of expected oxygen contamination, since the gas was not of an extra pure grade.…”

“…The pellet was reacted in the hot zone of a vertical tube furnace with a gas atmosphere containing 50% CO and 50% CO 2 at a temperature of 1100 • C. At this CO/CO 2 ratio and temperature the equilibrium partial oxygen pressure is calculated to be 10 −12.4 atm (using the data of Kubaschewski et al (1993)). At this oxygen pressure, the equilibrium composition lies in the wüstite phase field (Schürmann and Jahnsen 1993). After 10 h of reaction time the pellet was quenched in water.…”

“…The iron-oxygen system is a useful one for testing whether a slag-gas reaction had occurred, since the liquidus temperatures of this system are well recorded as a function of partial oxygen pressure. In this work, the assessment by Schürmann and Jahnsen (1993) was used to determine the expected liquidus temperatures.…”