The controversial role of inter-diffusion in glass alteration: Implications for Current Long-Term Modeling

International audienceCurrent kinetic models for nuclear waste glasses (e.g. GM2001, GRAAL) are based on a set of mechanisms that have been generally agreed upon within the international waste glass community. These mechanisms are: hydration of the glass, ion exchange reactions (the two processes are referred as inter-diffusion), hydrolysis of the silicate network, and condensation/precipitation of partly or completely hydrolyzed species that produces a gel layer and crystalline phases on surface of the altered glass. Recently, a new idea with origins in the mineral dissolution community has been proposed that excludes inter-diffusion process as a potential rate-limiting mechanism. To understand how the so-called interfacial dissolution/precipitation model can change the current understanding of glass behavior, an in-depth review of the current knowledge with a special focus on inter-diffusion processes is considered. Also discussed is how experimental conditions change the predominant mechanisms and how one model may not be sufficient to explain the glass dissolution behavior under a wide range of geochemical conditions. In addition to the review of the above subjects, a key experiment used to account for the interfacial dissolution/precipitation model was replicated to further revisit the interpretation. It is concluded that the selected experiment design may lead to ambiguous conclusions and that, under the conditions investigated (dilute conditions, deionized water), evidence of inter-diffusion exists

Effects of Al:Si and (Al+Na):Si Ratios on the Static Corrosion of Sodium-Boroaluminosilicate Glasses

International audienceUnderstanding alteration mechanisms of borosilicate glasses in aqueous media is essential to nuclear waste performance assessments to ensure radioisotopes are contained for extended durations. Aluminum is typically added to glass compositions to reduce the extent of alteration. However, previous work on 7-day durability tests has suggested that Al has a non-linear relationship with extent of alteration. The effects of Al:Si and (Al+Na):Si substitutions on glass durability were evaluated using series of glasses based on the International Simple Glass corroded in static conditions up to 13 months in deionized water at 90 °C. The alteration behavior was determined by measurement of element release in solution. The ⁓7-day alteration trends across the series were consistent with predicted trends. The 13 month results indicated overall alteration decreased as Al:Si ratios increased and was unaffected by changes in (Al+Na):Si except for the glass with the highest (Al+Na):Si ratio (ISG-A23N), which completely altered within 14 days. Frequent sampling and in-situ Raman measurements revealed ISG-A23N experienced several distinguishable alteration rate regimes within 7 days, forming a ⁓100 µm alteration layer and a NaSiAlO4 zeolite

Natural Glasses

International audienceNatural glasses have been used since prehistoric times and are strongly linked to human evolution. On Earth, glasses are typically produced by rapid cooling of melts, and as in the case of minerals and rocks, natural glasses can provide key information on the evolution of the Earth. However, we are aware that natural glasses are products that are not solely terrestrial and that the formation mechanisms give rise to a variety of natural amorphous materials. On the Earth's surface, glasses are scarce compared to other terrestrial bodies (i. e., the Moon), since the conditions on the surface give rise to devitrification or weathering. In order to provide an exhaustive overview, we shall classify natural glasses based on the mechanisms by which they were formed: temperature related, temperaturepressure related, temperature-pressure-volatile related, and others. In this chapter, we will review the most common natural glasses and their technological applications and also the scientific and technological advancements achieved from the study of these natural amorphous materials. Finally, we will provide some insights into the structure and properties of natural glasses and melts