High ionic field-strength cations in aluminoborosilicate glasses and their impact on kinetics and mechanism of glass dissolution in aqueous media
Creators: name: Qin, Qianhui
Publisher: name: No Publisher Supplied
Year: 2024

description: Chemical durability of silicate glasses is among the most intriguing topics in glass community, as multi-component silicate glasses form the basis for a wide range of modern functional glasses, and their behavior in the surrounding environment must be well-predicted for practical use. For instance, many industrial glasses, including nuclear waste glass and optical fibers, require inherently high chemical durability as they are designed to last long, while the applications of some other advanced glass materials and processing techniques, such as bioactive glass and glass etching, rely on the careful control of the glass dissolution behavior. Therefore, the underlying science that governs the dissolution mechanisms and kinetics of multicomponent silicate glasses in different environments, especially relating to the impact of common constituent oxides, must be well-understood to prompt the application and future development of advanced glassy materials.Despite a considerable effort put into understanding this topic, the existing studies often fall short in resolving actual technical challenges that are encountered during the design and processing (e.g., chemical etching) of modern functional silicate glasses, as the majority of them focus on simple glasses comprising only traditional glass components (e.g., Na2O, SiO2 and B2O3), or are tailored to a specific application. The specialty glasses, however, comprises various framework and non-framework components – especially high field-strength cations (HFSCs) – in addition to the traditional glass formers, with each component contributing its own part to the glass structure and resulting chemical durability. As a result, the current knowledge of dissolution mechanisms, which has acquired from glasses with low compositional complexity, cannot fully serve the broad spectrum of functional glasses. In this context, the present work aims to decipher the composition – structure – solubility relationship in aluminoborosilicate system, with particular focus on elucidating the effect of HFSCs on glass durability and mechanisms that lead to this effect. Accordingly, alkali/alkaline-earth aluminoborosilicate glasses containing different HFSCs, namely Nb5+, Zr4+, Ti4+, La3+ and V5+, have been selected as the subject of this research.Under extreme scenario (i.e., pH = 2 or 13), dissolution studies of aluminoborosilicate glasses indicate a dissolution – precipitation mechanisms, with Si and Ca precipitation governing the formation of passivating layer, respectively, whereas in neutral media, a partial hydrolysis – in-situ recondensation governed dissolution is observed, followed by conditional precipitation as the reaction proceeds. Combining the dissolution studies in different pH region, it can be seen the glass dissolution behavior is not governed by one single equilibrium, but a collective result of the various physio-chemical interactions happening simultaneously at the glass-water interface and may evolve with the reaction progress. While the presence of HFSCs impacts the glass dissolution behavior, the actual effect is not solely determined by the structural role of HFSCs in the glass, the solubility of HFSCs in the targeted environment, as well as the potential interactions between HFSCs and other glass/solution components also matter. It is thus important to consider every compositional/structural driver from the glass, as well as all the environment factors, in the modelling of glass dissolution. Future work recommended for this topic include: (i) In-depth investigation on the structure of versatile HFSCs in aluminoborosilicate glass, as well as exploring their interactions with common glass components and dissolution media, to narrow the uncertainty in predicting the dissolution behavior of glasses containing these HFSCs; (ii) Correlate the glass dissolution kinetics with the variation of pH and solution chemistry through systematic investigation; and (iii) utilizing in-situ/high resolution characterization and modelling techniques to investigate the fundamental science that governs glass dissolution.