The kinetics of reduction of nickel oxide-cerium dioxide mixed systems with hydrogen and the effect of ionizing radiation on it

The reduction with hydrogen was studied thermogravimetrically over the temperature region of 260-500 degC for nickel oxide-cerium dioxide mixed systems of various composition. The overall reduction rate increases and the maximum reduction rate of nickel oxide decreases with increasing cerium dioxide content as a result of two counteracting processes occurring at the reaction interface and conditioned by the presence of the finely dispersed irreducible component. The dependence of the degree of reduction α on time t obeys the relation (α+0.3)/(1-α)=Aexp(kt) over the entire composition region. Previous exposure of the samples to gamma doses of 100 and 500 kGy from a 60Co source or to a fast neutron dose of 400 Gy from a 252Cf source results in a decrease in the reduction rate for region with excess nickel oxide. As the concentration of cerium dioxide is increased, however, an inversion of the radiation-induced effect takes place and the reduction rate becomes higher than for the initial, unexposed samples. The effect of temperature and system composition on the phenomena under study is examined and discussed. (author)