Mechanism of aqueous dissolution of silicate glasses yielded by fission tracks

Abstract

Controversy continues over the mechanism of the aqueous corrosion of silicate glasses, largely because the processes by which the superficial hydrated layer is formed have not been clearly identified1. Two alternative models are current. One view2–4 is that mobile ions in the glass network (such as Na+, Li+ and K+) are exchanged with hydrogen ions (such as H+ and H3O+) and even H2O in the solution5; the other is that the hydrated layer results from the re-precipitation from solution of dissolved network material6–12. The first model is thought appropriate for simple man-made glasses and the second for more complex and natural glasses. We report here an optical and scanning electron microscope study of the corrosion of various borosilicate glasses irradiated by fission fragments. For all glass-solution combinations studied, we find that the hydrated layer embodies relics of the fission tracks, suggesting that this layer is mainly formed by in situ replacement, but in some cases a step re-precipitation is also apparent.