Interaction of a polycrystalline silver powder with ozone

Abstract

The interaction of a polycrystalline silver powder with ozone (5 mol.% O 3 in O 2 ) was investigated over the temperature range 300-923 K. Silver powder samples were reacted with ozone for 30 min at specified temperatures in this range. All experiments were performed at atmospheric pressure. Following treatment, samples were cooled rapidly to room temperature under a nitrogen gas purge and then characterized by scanning electron microscopy, powder x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. The morphology, structure and chemical composition of the oxide products formed at different reaction temperatures were examined. The silver powder blackened immediately upon contact with the reaction gas mixture at 300 K, due to the formation of silver (I) oxide (Ag 2 O). After reaction with O 3 for 30 min at 300 K, a mixed-oxide phase comprised of Ag 2 O and monoclinic silver (I, III) oxide (AgO) was formed. The AgO was formed at the gas/oxide interface via the oxidation of Ag 2 O. A tetragonal AgO polymorph was formed when the silver powder was reacted with ozone at 473 K. The only product of silver oxidation by O 3 at 673 K was Ag 2 O, which remained stable in the reaction gas to temperatures in excess of 773 K. The silver powder was not oxidized by ozone at 923 K, although the powder did sinter extensively during the treatment. The experimental data presented are in good accord with available thermodynamic data pertaining to the thermal stability of Ag 2 O and AgO in ozonized oxygen at atmospheric pressure.

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