Development of a reduction process and test results of the reduction equilibria of wustite as a function of oxygen content and temperature

A new measurement technique allows the continuous measurement of the oxygen contents of the wustite as a function of temperature without having to pass through the disintegration of the wustite to iron and magnetite and have the accompanying problems during the chemical analysis by cooling the sample. Measurements are carried out in form of isothermal oxygen reduction tests, starting with pure Fe₂O₃ in a thermogravimetric balance with an upstream gas mixer which, operating with CO₂/CO gas mixtures, ensures a graduation of the input reduction potential CO'₂ in steps of 1%. Simultaneous weighing of the test material sample permits, by means of the measured weight loss and relation to the charged amount of Fe₂O₃, a very accurate measurement of the oxygen concentration within the test material at any point in time during testing. Testing was carried out along these lines in the range between 700 and 1300°C. The results show that, at constant temperatures, the wustite oxygen contents decrease linearly from the right- to the left-hand boundary of the wustite field, with the oxygen pressure of the gas phase (log p_CO2/p_CO or log pO₂). When comparing these results with the findings of Darken and Gurry, a difference becomes apparent in the curves of the log pO₂ values as a function of the temperature. While our own curves are substantiated by very many measured values, the curves of Darken and Gurry are based on only twenty-three values at four different temperatures. Based on this result, systems of equations are developed which describe the homogeneous field of the wustite in the Fe-O-C reduction system without any gaps. An equivalent system of equations can also be developed from the values of a literature evaluation carried out by Giddings and Gordon. The curves resulting from the two equations do not differ very greatly. But the differences are large enough for corresponding variances to be expected when establishing the wustite boundaries and, thus, the position of the wustite field in the phase diagram.