NanoSIMS imaging alteration layers of a leached SON68 glass via a FIB‐made wedged crater

Abstract

Currently, nuclear wastes are commonly immobilized into glasses because of their long‐term durability. Exposure to water for long periods, however, will eventually corrode the waste form and is the leading potential avenue for radionuclide release into the environment. Because such slow processes cannot be experimentally tested, the prediction of release requires a thorough understanding of the mechanisms governing glass corrosion. In addition, because of the exceptional durability of glass, much of the testing must be performed on high‐surface area powders. A technique that can provide accurate compositional profiles with nanometer scale depth resolution for non‐flat samples would be a major benefit to the field. In this study, NanoSIMS was used to image the cross section of the corrosion layers of a leached SON68 glass sample. A wedged crater was prepared by a focused ion beam instrument to obtain a five‐fold improvement in depth information for NanoSIMS measurements. This improvement allowed us to confirm that the breakdown of the silica glass network is further from the pristine glass than a second dissolution front for boron, another glass former, despite only ~50 nm distance between them. More importantly, NanoSIMS images show that the roughness majorly exists in Si corrosion layer. This novel sample geometry will be a major benefit to efficient NanoSIMS sampling of irregular interfaces at the nanometer scale that would otherwise be obscured within time‐of‐flight secondary ion mass spectroscopy depth profiles. Copyright © 2014 John Wiley & Sons, Ltd.