Abstract
Hydrogen reduction of the nickel oxide under high pressure up to 31 atm was studied at 200, 220 and 240°C. The oxide powder of less than 200 mesh was reduced in a high pressure type electric furnace, and the reduction ratio was calculated from the weight change of the sample before and after reduction.
Plots of reduction ratio versus time gave sigmoid curves characteristic of the auto-catalytic reaction, and the rate equation, {1−(1−R)1⁄3}=Kt which is used for the reaction controlled by the interface reaction, was applicable in the main reduction period for about 30 to 80% reduction ratio. With rising hydrogen pressure, the reduction rate increased remarkably, and at about 10 atm it showed 3 times larger than that of one atmospheric pressure at each temperature. Moreover, the actual effect of pressure was more remarkable at higher temperature. However, a further rise of pressure exerted no significant effect on the reduction rate.
The relation between the apparent reduction rate K(min−1) and hydrogen pressure was represented by Langmuir’s type formula, K=aPH2⁄1+bPH2. Furthermore, the experimental results were discussed from a kinetic point of view, and the scanning electron micrographs showed the proceeding figures of the reduction process.
