Oxygen inward diffusion and complex reorganization of the reaction layer in ion-exchanged glasses evidenced by Auger electron spectroscopy

Abstract

Alkali silicate glasses subjected to low-temperature ion exchange in molten salt are being probed by Auger electron spectroscopy (AES). Spot analyses and elemental line scans across fresh fracture surfaces of broken glass specimens reveal oxygen enrichment of reaction layer where Na+-for-K+ ion exchange occurred and exceptional similarity in shapes of concentration depth profiles of potassium and oxygen. The probe provides the first direct evidence that smaller-for-larger ion replacement is accompanied by inward oxygen transport into reaction zone where potassium cations rearrange former sodium sites in accordance with their steric demands. Such chemical and structural rearrangements entail defect formation and glass network depolymerization and fragmentation, which define stress buildup and relaxation, residual stress intensity and profile in the surface layer of chemically strengthened glasses.