Thermal stability of silver in ion-exchanged soda lime glasses

Abstract

X-ray photoelectron spectroscopy was used to study the thermal stability of silver in ion-exchanged sodium calcium silicate glasses during heat treatment in ultrahigh vacuum. The changes in concentration, in line shape, and in binding energy as functions of sample temperature show that silver diffuses toward the surface and the chemical structure of the sample surface changes. Judging from a comparison of the line shapes and the binding energies of the samples to those of pure silver and silica, the concentration variations in bridging and nonbridging oxygens, and the binding energy shifts of nonbridging oxygens, it is concluded that the SiO2 glass network starts breaking up during Ag+ diffusion at sample temperatures below 200 °C, metallic silver clusters form, and nonbridging oxygens originally surrounded by silver atoms reconnect to silicon atoms at sample temperatures above 200 °C. The relaxation of surface stress introduced by the exchange process and the net reduction of Gibbs free energy cause the surface diffusion and segregation of silver and the reconnection between oxygen and silicon. The estimated activation energy of the silver surface diffusion is 0.16 eV.