| Abstract: | The paper describes measurements of the kinetics of iron oxidation in CO2-CO mixtures of various compositions in the temperature range of 1300 to 1450 °C. The reaction product is solid wustite below and liquid iron saturated iron-oxygen melt above 1377 °C, the incongruent melting temperature of iron saturated wustite. The experiments were carried out by measuring the weight increase during the oxidation of an iron specimen connected to a thermo-balance with a platinum wire. The specimen had the shape of a flat plate, and the oxidising gas flowed past this plate with a defined velocity. Among the experiments the flow velocities were varied. The rate law is linear in the beginning of the single experiment and later becomes parabolic. The linear law was interpreted as caused by two resistances connected in series: the transport of the oxidising gas through the adjacent gas boundary layer, and the phase boundary reaction at the oxide interface. The parabolic law was interpreted as determined by the transport of iron ions and vacancies through the growing oxide layer. The resistance of gas transport becomes negligible above a certain critical gas velocity which is 24 cm/s at 1400 °C. The critical gas velocity increases with rising temperature. The gas transport resistance was described by known theories of mass transfer in front of a solid wall. The temperature-dependent values of the phase boundary reaction rate constant were calculated with the help of known theories from the results of those experiments where the gas velocities were above the critical value for gas transport. From the parabolic law the diffusion coefficient of vacancies in wustite was calculated. The parabolic law does not appear, when the oxidation product is liquid as under these circumstances the formed oxide drops off the specimen during the experiment and hence, becomes not thicker than 22 μm. All the results join well with older results for lower temperatures known from literature. |
