Thorsten Geisler-Wierwille of the University of Bonn, Germany, is using fluid-cell Raman spectroscopy to explore silicate glass corrosion by aqueous solutions – with potential implications for the storage of nuclear waste in glass form (1). Here, he tells us more.
What prompted your research?
The idea for the in situ Raman spectroscopy study of solid–solid replacement reactions in aqueous solutions hatched in my brain 15 years ago! Five years later, I raised funding for a Raman spectrometer to dedicate to long-term measurements. PhD student Christoph Lenting and I started to develop the analytical method, enabling us to obtain the first real-time spatially resolved in situ data on glass corrosion.
How does it work?
Confocal Raman spectroscopy means spectra can be collected from tiny transparent samples by focusing a monochromatic laser beam on the region of interest. We designed the fluid cell and the sample arrangement so that reactions could be imaged with the laser beam axis parallel to the reaction front. The cell is mounted on an automated x-y-z stage so the laser beam can be positioned accurately over the solid–water interface
What was the most exciting finding?
We observed a pH gradient of about 50 μm depth at the glass surface and a water-rich zone between the corrosion product and the glass. The pH of this interface solution increases as the corrosion layer grows, confirming an interface-coupled dissolution– reprecipitation process – fundamentally different to current models for evaluating the fate of nuclear-waste-containing glasses.
Can you tell us about your industry partnerships?
Schott AG is interested in obtaining more detailed insights into glass corrosion to maximize the corrosion resistance of their glassware products. They funded Lars Dohmen’s PhD project as well as Moritz Fritzsche’s ongoing work with more stable glasses over longer timeframes.
What’s next?
We have opened up new avenues in the study of glass–water interactions, as well as mineral–water reactions and the partitioning of O and H isotope tracers among solid and solution species during reactions. In situ and real-time hyperspectral Raman imaging of solid–fluid reactions and the associated redistribution of O and H isotopes could lead to the discovery of new interface phenomena and further our understanding of solid–fluid reactions; the kinetics of individual reaction steps, such as the re-equilibration and maturation of the product phase; transport processes in dynamically evolving porous products; and the behavior of stable isotopes at solid– liquid interfaces. An exciting possibility is to study the impact of self-irradiation damage on the aqueous corrosion resistance of nuclear-waste-storing glasses. Soon, results from our experiments with heavy-ion-bombarded glass samples will be published and, in collaboration with the Joint Research Center of the European Commission in Karlsruhe, Germany, we plan to study a radionuclidecontaining glass formed during the 1986 Chernobyl accident.
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References
- T Geisler et al., “Real-time in situ observations of reaction and transport phenomena during silicate glass corrosion by fluid-cell Raman spectroscopy”, Nat Mater, [epub ahead of print] (2019). DOI: 10.1038/s41563-019-0293-8.