High energy ion beam studies of ion exchange in a Na20-Al2O3-SiO2 glass

As part of understanding the processes leading to sodium release and ion exchange, the surface and near surface reaction regions on several specimens of a Na2O–Al2O3–SiO2 glass have been examined after exposures to isotopically labeled aqueous solutions. The majority of the analyses described here have been carried out using energetic ion beam analysis. Rutherford backscattering spectrometry (RBS) has been used to measure the overall glass composition and to determine the profiles and amounts of Na released from the surface. An important part of the ion exchange process is the uptake and incorporation of hydrogen and oxygen in the glass from the solution. To facilitate this analysis, the glasses were exposed to a solution containing 18O and D and analyzed by accelerator based nuclear reaction analysis. To confirm some of the RBS depth profile data very near the surface, x-ray photoelectron spectroscopy depth profiles were collected on some samples. Although the Na concentration is decreased in the near surface region, it is not totally removed from the outer surface. In this same region, there is also a significant amount of 18O incorporated demonstrating considerable interaction between the water and the glass. Deeper into the material the amounts of D and 18O are more consistent with water or D3O+ diffusion. These results suggest that there exist an outer reaction layer and an inner ion-exchange layer in the surface region of the reacted glass.