Durable Glass for Thousands of Years

Abstract

The durability of natural glasses on geological time scales and ancient glasses for thousands of years is well documented. The necessity to predict the durability of high level nuclear waste (HLW) glasses on extended time scales has led to various thermodynamic and kinetic approaches. Advances in the measurement of medium range order (MRO) in glasses has led to the understanding that the molecular structure of a glass, and thus the glass composition, controls the glass durability by establishing the distribution of ion exchange sites, hydrolysis sites, and the access of water to those sites. During the early stages of glass dissolution, a "gel" layer resembling a membrane forms through which ions exchange between the glass and the leachant. The hydrated gel layer exhibits acid/base properties which are manifested as the pH dependence of the thickness and nature of the gel layer. The gel layer ages into clay or zeolite minerals by Ostwald ripening. Zeolite mineral assemblages (higher pH and Al 3+ rich glasses) may cause the dissolution rate to increase which is undesirable for long-term performance of glass in the environment. Thermodynamic and structural approaches to the prediction of glass durability are compared versus Ostwald ripening.

Basic network structure of SiO2–B2O3–Na2O glasses from diffraction and reverse Monte Carlo simulation

“…Based on the above, the following conclusions can be drawn: i) the Si-O and B-O correlations are close to each other, ii) the Si-O (close to 4) and B-O ( 3 and 4) coordination number overlap with each other, iii) the bond angle distribution connected to B and Si distribution correlates with the characteristic trigonal and tetrahedral unit formations. This together here indicates that the [4] Si-O- [4] B and [4] Si-O- [3] B mixed linkages are formed, similarly, as we have found for multi-component sodium borosilicate glasses loaded with BaO and ZrO [15]. Based on our previous works [14,15] and the results presented here we can conclude that these alkaline borosilicate glasses contain relatively regular triangle BO3 and tetrahedral BO4 units.…”

“…Two characteristic contributions have been detected: peak positioned around 0 ppm and a broader quadrupolar line between 5 and 20 ppm. Based on the literature ( [20] and [21]) we assigned these two contributions to [4] B(BO4) and [3] B(BO3) structural units, as indicated in Figure 1. The peak intensities clearly show concentration dependence.…”

“…The peak intensities clearly show concentration dependence. The intensity of the [3] B peak increases with increasing boron content while the [4] B peak decreases. The maximum increase/decrease of the either peak's area was about 15% as determined by integration of the area under the two contributions.…”

Mathematical Formulation Requirements and Specifications for the Process Models

“…A recent paper by Jantzen et al (2010) reviews the thermodynamic and structural approaches to the prediction of glass durability. Mechanistic modeling of glass durability including the slowing of the dissolution rate due to affinity and/or surface layer effects was first modeled by Grambow and Müller (2001) and is referred to as the GM2001 model.…”

Communication: Resolving the vibrational and configurational contributions to thermal expansion in isobaric glass-forming systems

“…4 It is also vital for ensuring the thermal shock resistance of glass labware and cookware 5 and the long-term safety of glasses for nuclear waste storage. 6 In the design of new glass compositions and products, it is often desirable to match the thermal expansion coefficient of a glass to another coupled material. Other times the objective is to minimize or even eliminate the thermal expansion effect entirely in order to reduce dimensional changes or optical distortion.…”