Reduction of NiO-Mn2O3 mixed oxides with hydrogen and its affecting by ionizing radiation

Abstract

Reduction of NiO-Mn2O3 mixed oxides with hydrogen was studied thermogravimetrically at 350-440°C; in the entire composition region, 0-100% of one component, total reduction with the formation of a heterogenous Ni-MnO system was observed. The character of the kinetic curves of reduction of Mn2O3 is affected by the way of preparation and heat treatment of the samples before their reduction in inert atmosphere. In the mixed oxide, nickel accelerates the reduction of manganese sesquioxide, proceeding via Mn3O4 intermediate product. The mutual interaction of the two components appears in the pronounced dependence of the reaction rate on the composition, correlable with the analogous dependence of the apparent activation energy of reduction. The extent of the interaction, morphological changes, and some physicochemical parameters depend upon the degree of dispersion of the two oxides, which is also a function of the composition. A prior irridation of the samples by gamma radiation, dose 8 . 105 Gy, or fast neutrons, fluency 6.8 . 1015 n/m2 (Dn = 28.1 Gy), brings about a substantial increase in the content of the chemisorbed oxygen, particularly in the range of excess Mn2O3. The gamma irradiation results in an acceleration of the reduction of the mixed oxides; the extent of this positive effect is a nonmonotonic function of the composition and depends markedly on the temperature. The complex influence of fast neutrons appears as a negative effect (lowering of the reduction rate) resulting from the destruction of the existing centres (the polishing effect); in dependence on the composition the effect inverts into a positive one on the generated and stabilized new centres, which affect the rate of nucleation of the nickel metal phase.