The effect of the dispersity of silver powder on the properties of adsorbed oxygen forms
The characteristics of the surfaces of highly dispersed (HDP, d < 30 nm) and coarse-grained (CGP, d ∼ 105 nm) silver powders are studied by means of hydrogen titration of oxygen adsorbed on the silver surface. Two forms of irreversibly adsorbed oxygen are observed for both types of samples: mobile (OIads) and localized at sites of oxygen migration from the bulk of the metal (OIIads). In the case of the HDP sample, the OIIads form becomes mobile at 523 K; however, it remains immobile on the CGP sample surface up to 673 K. The concentration of OIIads sites on the HDP surface is much smaller than that on the CGP surface, and the formation of these sites on the HDP surface is characterized by a higher activation energy. These distinctions are explained by the fact that the HDP sample is composed of larger monocrystals.