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The addition of V2O5 has been long known to increase the sulfur (as SO42-) solubility in borosilicate glasses. However, the mechanism governing this effect is still unknown. Although several studies have been published in the past two decades attempting to decipher the structural origins of increasing sulfur solubility as a function of V2O5 in borosilicate glasses, most of these studies remain inconclusive. The work presented in this paper attempts to answer the question, “Why does V2O5 increase sulfur solubility in borosilicate glasses?” Accordingly, a series of melt-quenched glasses in the system [30 Na2O – 5 Al2O3 – 15 B2O3 –50 SiO2](100-x) – xV2O5, where x varies between 0 – 9 mol.%, have been characterized for their short-to-intermediate range structure and the redox chemistry of vanadium using 11B, 27Al, 51V MAS NMR, Raman, and XPS spectroscopy. The impact of V2O5 on sulfur solubility in glasses has been followed by ICP-OES. The addition of ≤ 5 mol.% V2O5 results in a linear increase in sulfur solubility in the investigated glass system. Based on the results, we hypothesize that adding vanadium to the glasses increases their network connectivity, but reduces the network rigidity by replacing stronger Si–O–Si linkages with weaker Si–O–V linkages and forming (VO3)n-single chains. These modifications to the glass structure increase the flexibility of the network, thus making it possible to accommodate SO42− in their voids/open spaces. 

Understanding the corrosion behavior of glasses in near-neutral environments is crucial for many technologies including glasses for regenerative medicine and nuclear waste immobilization. To maintain consistent pH values throughout experiments in the pH = 7 to 9 regime, buffer solutions containing tris(hydroxymethyl)aminomethane (“Tris”, or sometimes called THAM) are recommended in ISO standards 10993-14 and 23317 for evaluating biomaterial degradation and utilized throughout glass dissolution behavior literature—a key advantage being the absence of dissolved alkali/alkaline earth cations ( i.e. Na + or Ca 2+ ) that can convolute experimental results due to solution feedback effects. Although Tris is effective at maintaining the solution pH, it has presented concerns due to the adverse artificial effects it produces while studying glass corrosion, especially in borosilicate glasses. Therefore, many open questions still remain on the topic of borosilicate glass interaction with Tris-based solutions. We have approached this topic by studying the dissolution behavior of a sodium borosilicate glass in a wide range of Tris-based solutions at 65 °C with varied acid identity (Tris–HCl vs. Tris–HNO 3 ), buffer concentration (0.01 M to 0.5 M), and pH (7–9). The results have been discussed in reference to previous studies on this topic and the following conclusions have been made: (i) acid identity in Tris-based solutions does not exhibit a significant impact on the dissolution behavior of borosilicate glasses, (ii) ∼0.1 M Tris-based solutions are ideal for maintaining solution pH in the absence of obvious undesirable solution chemistry effects, and (iii) Tris–boron complexes can form in solution as a result of glass dissolution processes. The complex formation, however, exhibits a distinct temperature-dependence, and requires further study to uncover the precise mechanisms by which Tris-based solutions impact borosilicate glass dissolution behavior.