47, 48 In these studies, however, the porous structure of leached layer was unknown and only hydrous species in non-centrosymmetric medium (a medium without an inversion center) were analyzed. 44, 45, 52 To the best of our knowledge, there are only two reports studying hydrous species on glass surfaces leached in pH 1 aqueous solutions using SFG spectroscopy. 46, 47, 48, 49, 50, 51 For hydrous species at interfaces, SFG has been shown to be a powerful tool. 44, 45 While IR spectroscopy has been used to study the ingress of water into glass surface upon leaching/corroding in aqueous solution, only changes in total amount of hydrous species were considered in most studies. That is because the OH stretch band is very sensitive to the strength of hydrogen bonding interactions. 37, 38, 39, 40, 41, 42, 43 One of the most efficient methods to probe hydrogen bonding interactions of hydrous species is vibrational spectroscopy, especially infrared (IR) and sum frequency generation (SFG) spectroscopy. 9, 21, 34, 35, 36 The alteration layer formed on glass upon corrosion in aqueous solution has been shown to be nano-porous and transport of water within the layer has been characterized in some experimental studies. 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 Computational studies showed that transport and hydrogen bonding interactions can be significantly altered by the confinement in nanoscale geometry. Transport properties and hydrogen bonding interactions of hydrous species in the nano-porous materials have been investigated using various analytical techniques and computational simulations. To understand the mechanism of glass corrosion in the second stage, it is therefore very important to obtain information on interfacial behaviors of hydrous species (molecular water and Si-OH) on the alteration layer particularly, hydrogen bonding interactions between these species are expected to affect the transport of water molecules in the alteration layer. The corrosion rate in Stage-II is limited mainly by the transport of mobile species within the nano-porous alteration layer, 7, 9 especially diffusion of water and solvated ionic species. 8 It would be ideal if the corrosion process remains in this stage until the radioactive decay of the nuclear waste diminishes to the safe level. 6, 7 The corrosion process enters the second stage (Stage-II) when the corrosion solution is saturated with respect to soluble silicon-containing species. ![]() 4, 5, 6 Nuclear glass corrosion occurs at a rate on the order of 0.1–1 µm/day at 90 ☌ in the first stage (Stage-I) and then it gradually slows down due to the formation of an alteration layer on the surface and the increase of solution concentrations of network former and modifier species being released from the glass matrix. 1, 2, 3 However, during its storage in repository locations, nuclear waste glass could get into contact with underground water, if the repository is damaged, leading to aqueous corrosion of glass and release of radioactive elements into the geosphere. The simulation and experimental results obtained in this study indicate that the water mobility in the gel formed at pH 9 could be slower than that in the gel formed at pH 7, and as a result, the leaching rate at pH 9 is slower than that at pH 7.īorosilicate glass has been used as a host matrix for radioactive wastes in the nuclear industry due to its good processability, chemical durability, radiation stability, and high-load capacity. The glass dissolution under the leaching conditions used in this study has been known to be ten times faster at pH 7 in comparison to that at pH 9 due to unknown reasons. Sum frequency generation spectroscopy showed some significant differences in hydrogen bonding interactions on alteration layers formed at pH 7 and pH 9. The nano-porous gels formed on corroded glass surfaces enhance hydrogen bond strength between hydrous species as revealed by attenuated total reflectance infrared spectroscopy. The simulation results revealed various possible types of hydrogen bonds among these hydrous species in nanoconfinement environments with their populations depending on pore-size distribution. In this study, hydrous species (H 2O and Si-OH) on nano-porous alteration layers (gels) formed on a boroaluminosilicate glass called International Simple Glass corroded in aqueous solutions at pH 7 and pH 9, and initially saturated with soluble silicon-containing species were analyzed using linear and non-linear vibrational spectroscopy in combination with molecular dynamics simulations. ![]() Hydrogen bonding interactions play an important role in many chemical and physical processes occurring in bulk liquids and at interfaces.
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