EFFECTS OF MGO CONTENT AND TEMPERATURE ON THE REDUCTION RATE OF NIO-MGO SOLID-SOLUTION BY HYDROGEN

In order to obtain proper reduction conditions of the pellets of NiO-MgO solid solution, some pellets were prepared by the sintering of the NiO powder containing MgO of 0 to 20mol% and reduced by H-2 over a temperature range of 873 to 1373K. The results were summarized as follows. 1)The reduction rate of NiO containing MgO was decreased with an increase in MgO content at lower temperature than 1073K. In addition, the reduction mechanism of the pellets changed from the topo-chemical reaction to the homogeneous reaction with an increase in MgO content. However, at higher temperature than 1073K, the reduction rate of NiO containing 2.5mol%MgO was higher than that of pure NiO. 2)The reduction mechanism of the pellets could be explained by the unreacted core model at higher temperature than 1073K. The chemical reaction rate constant, kc, was decreased with an increase in MgO content, and the activation energies of kc increased with an increase in MgO content, On the other hand, the maximum of the intraparticle diffusion coefficient, De, was obtained at NiO containing 2.5mol%MgO. 3)The effects of MgO on the reduction rate were discussed, referring results of the reduction rate of the wustite containing MgO.