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

Abstract

The reduction with hydrogen is studied thermogravimetrically over the temperature region of 260-500 °C for nickel oxide-cerium dioxide mixed systems of various composition. The overall rate of reduction increases and the maximum rate of reduction of nickel oxide decreases with increasing cerium dioxide content as a result of two counteracting processes occurring on the reaction interface and conditioned by the presence of the finely dispersed unreducible component. The dependence of the degree of reduction α on time t obeys the relation (α + 0.3)/(1 - α) = Aekt over the entire system composition region. Previous exposition of the samples to gamma does 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 rate of reduction for region with excess nickel oxide, but as the concentration of cerium dioxide is increased, inversion of the radiation-induced effect takes place and the rate of reduction becomes higher than for the initial, unexposed samples. The effect of temperature and system composition on the phenomena under study is examined and discussed.