Characterization of the anomaly in immediate aqueous interactions of sodium borate glasses by dynamic vapour sorption with in-situ Raman

Abstract

This study applied a novel technique; dynamic vapour sorption (DVS) with in-situ Raman spectroscopy, as well as complementary techniques of attenuated total reflectance-Fourier transform infrared spectroscopy and X-ray diffraction, to investigate the effect of sodium content on the immediate aqueous reactivity and reactions of a range of melt-quench-derived binary sodium borate glasses (SBGs): xNa2O-(100-x)B2O3 (x = 18, 23, 30 and 35 mol%). DVS gravimetrically measured the effect of controlled relative humidity (RH) values on SBGs, while in-situ Raman monitored their structural changes in real time. It was found that the glass boron coordination, glass transition temperature, as well as weight change and percentage of crystallinity post exposure to vapour, along with threshold % RH to initiate sorption, and threshold time to initiate crystallization under 90% RH demonstrated the anomalous variation with increasing sodium content in glasses. Relative to other formulations, 30Na2O–70B2O3 showed the lowest weight change and crystallinity after vapour desorption, and highest threshold % RH and longest threshold time. There was also a correlation between vapour- and water-induced reactions, as determined by reaction rates and structural changes. Specifically, lower glass network connectivity or non-bridging oxygen formation fostered their crystallization when exposed to either vapour or water, leading to higher weight change in aqueous environments. In sum, the results of this study validated the coupling of DVS with in-situ Raman spectroscopy in characterizing the reactivity and mechanisms of aqueous interactions of SBGs.