Comparative structural investigations of nuclear waste glass alteration layers and sol-gel synthesized aerogels

Abstract

While various glass alteration layer formation mechanisms have been debated in recent years, the glass alteration community generally agrees that more information on physical properties of the alteration layers is needed to further the understanding of their impacts on overall glass alteration. In this work, pore volumes and solid structures of glass (International Simple Glass, ISG) alteration layers formed in solutions of various pH conditions in initially dilute conditions at 90°C are evaluated with positron annihilation spectroscopy, small-angle X-ray scattering, and scanning transmission electron microscopy. Pore volumes of alteration layers formed at pH 9 were found to be at their lowest near the surfaces of the alteration layers. Solid structures of alteration layers are compared with those of synthetic aerogels of comparable compositions produced under various pH conditions. Alteration layers formed at pH 11 on ISG were shown to contain large structures (>10 nm) similar to synthetic aerogels created under neutral and basic conditions whereas alteration layers formed at pH 9 did not. Available dissolved silica species defined by silica solubility were proposed to have the greatest impact on alteration layer structure.npj Materials Degradation (2020) 4:5 ; https://doi.

Effects of Al:Si and (Al+Na):Si ratios on the static corrosion of sodium‐boroaluminosilicate glasses

“…Reiser et al demonstrated that solution pH significantly impacts the structure of the alteration layer of ISG, where alteration layers formed in solutions at pH 90°C ~11 are more porous and composed of larger moieties than alteration layers formed at pH 90°C ~9. 58 Reiser et al attributed these effects to differences in the solubility of silica, a major network former of ISG and the alteration layers, between pH 90°C 9 and 11. 58,94 These findings suggest that compositional-structural properties certainly affect the alteration behavior of the glasses albeit through a chain of causation (e.g., high mol% Na → increased Na release → increased solution pH → Si solubility effects → more porous alteration layers with larger structural moieties).…”

“…58 Reiser et al attributed these effects to differences in the solubility of silica, a major network former of ISG and the alteration layers, between pH 90°C 9 and 11. 58,94 These findings suggest that compositional-structural properties certainly affect the alteration behavior of the glasses albeit through a chain of causation (e.g., high mol% Na → increased Na release → increased solution pH → Si solubility effects → more porous alteration layers with larger structural moieties). As glass systems become more complex (such as adjusting Al:Si and (Na+Al):Si ratios), understanding the processes affecting the alteration behavior of the glasses becomes more difficult.…”

“…The CJ4 composition was chosen for fabrication as the International Simple Glass (ISG) by the international nuclear waste glass community to study glass properties and durability behavior. 1,[55][56][57][58][59][60][61][62][63][64][65] A new series covering an extended Al compositional space based on the composition of ISG would provide valuable information regarding the effect of Al on long-term durability applicable to nuclear waste glasses.…”

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass, part I: Physical properties

“…15 ISG has been intensively researched with studies focusing on its physical 16 and mechanical properties, [17][18][19] structural insights obtained experimentally 20 and via computer simulations, [21][22][23][24] surface quality, 19,25 waste loading, 26 radiation effects, [27][28][29][30] dissolution behavior under different testing conditions, [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] dissolution kinetic models, 50,51 as well as characterization of alteration layers using advanced techniques. 34,[52][53][54][55][56] The wealth of data associated with this glass made it a logical choice to study the impact of Al 2 O 3 concentration on glass structure and properties.…”

“…A simplified representation of borosilicate waste glasses known as the international simple glass (ISG) was designed and developed by the nuclear waste glass community to synergize efforts towards understanding waste glass properties and corrosion behavior 15 . ISG has been intensively researched with studies focusing on its physical 16 and mechanical properties, 17‐19 structural insights obtained experimentally 20 and via computer simulations, 21‐24 surface quality, 19,25 waste loading, 26 radiation effects, 27‐30 dissolution behavior under different testing conditions, 31‐49 dissolution kinetic models, 50,51 as well as characterization of alteration layers using advanced techniques 34,52‐56 . The wealth of data associated with this glass made it a logical choice to study the impact of Al 2 O 3 concentration on glass structure and properties.…”