α-Hematite powder of 8.1 μm in average diameter was packed in a quartz tube and was reduced by feeding pure hydrogen toward the upper surface of the packed bed at 900°C and the pressure increase within the bed was measured. Midway through the reduction, hydrogen-inert gas mixtures were fed instead of pure hydrogen and the variation of the pressure increase ΔP within the bed with increasing mole fraction of inert gas in feed gas, x_{I, 0}, was investigated. Nitrogen, argon, and helium were used as the inert gas and it was found that the relationship between ΔP and x_{I, a} varied with each inert gas.
To interpret those phenomena, the concept of the multicomponent dynamic effective diffusivity is proposed. It will make the nonisobaric analysis of solid-multicomponent gas reactions possible.