The rates of reduction of hematite to magnetite and of magnetite to iron in hydrogen /nitrogen /water vapor atmospheres were each studied with respect to variation in temperature, gas composition, and solid pore structure. It is shown that at temperatures below 35OoC, the reactions are under chemical kinetic control, and diffusional limitations are negligible. The activation energies for the reduction of hematite to magnetite and of magnetite to iron were found to be 185 kJ/mol and 76.6 kJ /mol, respectively. Both reactions exhibit first-order behavior for hydrogen partial pressures less than 76 kPa. The conversion and rate data for each reaction were interpreted in terms of the random pore model of Bhatia and Perlmutter (1980), which takes into account the detailed pore structure of the starting material as well as the changes that occur as the reaction proceeds. The model predictions of conversion with time agree with the measured data to within 2010, and the rate vs. conversion predictions agree to within 5%.
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