Method for the in situ Measurement of pH and Alteration Extent for Aluminoborosilicate Glasses Using Raman Spectroscopy.

Characterization of long-term processes occurring during alteration of aluminoborosilicate glasses is relevant for natural as well as man-made materials. Static dissolution tests are a common setup for such studies, but the obtained results and related errors are impacted by the frequency and protocol of samplings performed to determine release via solution analysis, e.g., ICP-OES. A noninvasive method was developed to continuously monitor glass alteration based on in situ Raman spectrometry of the solution contained in the alteration vessel. The alteration of a benchmark glass, the environment assessment (EA) glass, for 7 days at 90 °C showed that the pH and boron concentration results obtained from solution monitoring and ICP-OES quantification were similar to the pH and boron results obtained from chemometric modeling of the Raman spectra and within error of previously published results in similar conditions. The errors on altered amounts of glass based on B release were similar for both in situ Raman and ICP-OES. The new Raman method provides a more detailed picture of real time monitoring of an alteration experiment, with intervals between monitoring times as short as dozens of seconds. The in situ Raman method also helps to reduce perturbation to experiments caused by the physical sampling of aliquots (including temperature excursions, re-equilibration with atmosphere, volume variation, and potential chemical contamination) by limiting their number and frequency.