Ionic Oxygen Diffusion in the Cerium and Cerium‐Thorium Oxide Systems

Abstract

Reduction of the cerium and cerium‐thorium oxide systems with H2 between 450 and 530°C leads to an activation energy of ionic oxygen diffusion ED 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.

Bulk Reduction and Oxygen Migration in the Ceria-Based Oxides

“…Bulk oxygen diffusion has been inferred from isotope exchange measurements in Ce 0.1 Th 0.9 O 2 . 23 Moreover, the value of 0.75 eV for the activation energy for oxygen migration in a Ce 0.993 Th 0.007 O 2 solid solution, derived from thermogravimetric measurements 24 is comparable with the value of 0.57 eV which can be linearly extrapolated from our calculations. We were not able to find any comparative experimental activation energies for the Ce 1-x Hf x O 2 system.…”