Étude de la chimisorption de O2 À 77 K à l'aide d'isothermes d'adsorption physique à marches: Systèmes CdOKr et CdOCF4

The evolution of stepwise isotherms of CF₄ and Kr on cadmium at 77.4 K, when increasing oxygen quantities are prechemisorbed at the same temperature, brings out some information about that chemisorption. It can be deduced from the splitting of steps that, at 77.4K, oxygen chemisorbs as rather homogeneous patches. It seems to be islands spreading in proportion to the chemisorbed quantities. As a mean, 4 oxygen atoms seem to be adsorbed for every surface cadmium atom. Such a number involves a reaction with slightly deeper Cd atoms. Over these oxidized patches, oxygen seems to physisorb (precursor state of oxidation) more readily than upon the bare part of the metal. This suggests one modification in the set of hypotheses usually acknowledged for the analysis of oxidation kinetics in that temperature range. A brief comparison is made with the somewhat different islands that are known to grow on metals when oxidization, or sulfurization, occurs at higher temperatures. Some remarks are aimed at the effects of “thermal regeneration” under vacuum.