The Kinetics of Isothermal Hydrogen Reduction of Nanocrystalline Fe₂O₃ Powder

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The kinetics of reduction of nanocrystalline Fe₂O₃ powder with hydrogen was investigated in the temperature range from 573 K to 813 K. A comparison between the reduction rates of the nanocrystalline powder (20–50 nm) and those of the conventional powder (200–400 nm) showed no discernible difference despite a substantially larger specific surface area of the former. Since observations under the scanning electron microscope revealed that the nanocrystalline powder forms large agglomerates, the kinetic results were theoretically tested for the possibility that the reduction of the powder was inhibited by intra-agglomerate pore diffusion. Alternatively, a potential influence of water vapor remaining in the packed powder bed is discussed. Activation energies of 47.2 and 51.5 kJ/mol were obtained for the reduction of the nanocrystalline and the as-received powder, respectively. These values show fair agreement with those obtained by previous studies.