| Cyclic oxidation of iron sheet has been studied in the temperature range of 850℃∼1050℃ at various partial pressures of O₂ and H₂. Rates of the first and second stage oxidation could be described in terms of a solid state diffusion of iron ion through wustite layer, and expressed by the equation of t/Δw=Δw/k_p+1/k₁ where t, Δw, k_p and k₁ are reaction time, weight change, and parabolic and linear rate constant, respectively. The activation energy for oxidation was found to be about 27㎉/㏖. Results revealed that rate of oxidation follows simply the flat surface geometry, whereas at the later stage oxidation was characterized by the oxidation of residual iron island in product layer. Such an effect became more significant by repeated oxidation and reduction. Reduction rate of iron oxide was faster in temperature range of 900℃∼950℃ at which the product layer had proper pore structure. At the later stage of reduction the rate was also characterized by the reduction of residual wustite island in the outer product layer. |
|
