Spinel crystallization is known to be detrimental to the operation of Joule heated ceramic melters during the vitrification of iron-rich high-level nuclear wastes (HLW) into borosilicate glasses. The literature on this subject focuses on tackling the problem by developing empirical constraints to design compositions, which limit the fraction of spinels formed in the melter or by developing empirical models to predict the settling behavior of spinels in the melter as a function of the glass composition. While these empirical models can predict the behavior of most of the compositions, they are not failsafe as there are always some compositions, whose behavior is beyond the predictive ability of these models. This can lead to undesirable situations during the vitrification of the nuclear waste, and therefore an in-depth investigation of the chemo-structural descriptors controlling the crystallization behavior in these glasses is warranted. Accordingly, the present study aims to understand the impact of non-framework cation mixing (i.e., Li + /Na + and Ca 2+ /Na + ) on the structure (through Raman spectroscopy and Mössbauer spectroscopy) and crystallization behavior (through XRD, SEM-EDS, and vibrating sample magnetometry) of iron-rich model HLW glasses in the system: (mol.%) x M y O-(25−x) Na 2 O-9.12 B 2 O 3 -6.4 Al 2 O 3 -51.25 SiO 2 -7.22 Fe 2 O 3 -0.38 MnO-0.08 Cr 2 O 3 -0.55NiO (M y O = Li 2 O or CaO).

The overarching goal of the present multiscale investigation is to unearth the kinetics and mechanisms of corrosion of borosilicate glasses in hyper-alkaline (pH = 13) environments as a function of their chemical composition. Accordingly, a series of 3- to 6-component borosilicate glasses have been designed starting from Na2O–B2O3–SiO2 ternary, wherein the compositional complexity has been added in a systematic tiered approach, finally resulting in the composition of the well-known international simple glass (ISG). Tetramethylammonium hydroxide (TMAH), one of the most widely used alkaline etchant in the glass and electronics industry, has been used as the corrosion media. A series of state-of-the-art characterization techniques including magic angle spinning nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, elastic recoil detection analysis, and high-resolution transmission electron microscopy have been employed to unearth the compositional dependence of glass corrosion in hyper-alkaline environments. The glass compositions underwent congruent corrosion in the forward rate regime, whereas the controlling mechanism of corrosion in the residual rate regime depends on the presence/absence of Ca in the surrounding environment and can be explained on the basis of the dissolution–reprecipitation model. The dependence of corrosion kinetics and the chemistry of alteration products (in the residual rate regime) on the glass composition have been discussed. The results presented in this contribution will ultimately supplement the scientific literature attempting to understand the fundamental science governing the aqueous corrosion of silicate-based glass chemistries and add to the growing database required to develop nonempirical predictive models for designing glasses with controlled dissolution rates.

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This paper presents an insight into the structural rearrangements induced by Fe 2 O 3 and P 2 O 5 in glasses designed in the Na 2 O−Al 2 O 3 −B 2 O 3 −SiO 2 quaternary system. A suite of stateof-the-art characterization techniques, including magic angle spinning-nuclear magnetic resonance (MAS NMR) (on both iron-free and iron-containing glasses), Raman, and Mossbauer spectroscopies, have been employed to study the structural evolution of glasses as a function of the Fe 2 O 3 /Al 2 O 3 ratio and P 2 O 5 content over a broad composition space. It has been shown that while P 2 O 5 tends to repolymerize the structure of Fe 2 O 3 -freeglasses, it has a minimal impact on the network connectivity of iron-rich glasses. Further, there seems to exist a strong tetrahedral avoidance between AlO 4 and FeO 4 units in the glass structure. In P 2 O 5 -free glasses, iron tends to preferentially bond with borate and silicate units, while in the presence of P 2 O 5 , iron prefers to associate with phosphate (over borate and silicate) units in the glass structure. Finally, an attempt has been made to correlate the underlying structural descriptors with the rheological and crystallization behavior of glasses with an overarching goal to establish the composition−structure−property relationships in the investigated glass system.