Ionic oxygen diffusion in the cerium and cerium-thorium oxide systems

Reduction of the cerium and cerium-thorium oxide systems with H2 between 450 and 530 0C leads to an activation energy of ionic oxygen diffusion Esub(D) of 27.2 kcal/mole for CeO2 and of 17.3 kcal/mole for CeO2 containing 1 wt% ThO2. In (CeO2 + ThO2) the reduction process is most complex and may be described by means of a parabolic rate law at the initial stages of the ion diffusion process and by a cubic expression at higher reduction levels; in CeO2 only a second order rate law is observed. The effect of the dopant, i. e. higher reduction rate and reduction level, is ascribed to the lower activation energy of O2- diffusion. (author)