The thermodynamics and kinetics of O radical formation process in a nanoporous crystal, 12CaO▪7Al2O3, were examined by isothermal annealing experiments in dry atmospheres. It was clarified that the formation of O radicals, O2− and O−, in the crystal occurred in 3 steps; outward diffusion of extra-framework oxide ions, its oxidation by absorbed O molecules to form O− and O2− at the surface, and subsequent inward diffusion of the O radicals. The instability of the extra-framework oxide ions was essentially the driving force for the process. Further, the analyses allow to predict the total O radical content for a given annealing condition.

Effect of Stability and Diffusivity of Extra-Framework Oxygen Species on the Formation of Oxygen Radicals in 12CaO▪7Al2O3. K.Hayashi, N.Ueda, M.Hirano, H.Hosono: Solid State Ionics, 2004, 173[1-4], 89-94