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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. 

Abstract For over 40 years, measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the Classical Nucleation Theory at temperatures below that of the peak nucleation rate. The data show that instead of steadily decreasing with decreasing temperature, the work of critical cluster formation enters a plateau and even starts to increase. Many explanations have been offered to explain this anomaly, but none have provided a satisfactory answer. We present an experimental approach to demonstrate explicitly for the example of a 5BaO ∙ 8SiO 2 glass that the anomaly is not a real phenomenon, but instead an artifact arising from an insufficient heating time at low temperatures. Heating times much longer than previously used at a temperature 50 K below the peak nucleation rate temperature give results that are consistent with the predictions of the Classical Nucleation Theory. These results raise the question of whether the claimed anomaly is also an artifact in other glasses. 

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. 

Abstract Nucleation is generally viewed as a structural fluctuation that passes a critical size to eventually become a stable emerging new phase. However, this concept leaves out many details, such as changes in cluster composition and competing pathways to the new phase. In this work, both experimental and computer modeling studies are used to understand the cluster composition and pathways. Monte Carlo and molecular dynamics approaches are used to analyze the thermodynamic and kinetic contributions to the nucleation landscape in barium silicate glasses. Experimental techniques examine the resulting polycrystals that form. Both the modeling and experimental data indicate that a silica rich core plays a dominant role in the nucleation process.