Abstract
Hydrogen bonding interactions play an important role in many chemical and physical processes occurring in bulk liquids and at interfaces. In this study, hydrous species (H2O 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. 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. The nano-porous gels formed on corroded glass surfaces enhance hydrogen bond strength between hydrous species as revealed by attenuated total reflectance infrared spectroscopy. Sum frequency generation spectroscopy showed some significant differences in hydrogen bonding interactions on alteration layers formed at pH 7 and pH 9. 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. 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.
Highlights
The thickness and depth profiles of alteration layers formed on International Simple Glass (ISG) samples corroded for 7 days and 2046 days in silica-saturated solutions at pH 7 and pH 9 are given in Table 1 and Fig. 1, respectively
The results show that the thicknesses of altered layers on ISG corroded for 7 days and 2046 days in pH 7 solutions are ~750 nm and ~2400 nm, respectively
The alteration layers on ISG corroded for 7 days and 2046 days in pH 9 solutions, are much thinner in comparison to those on ISG corroded in pH 7 solutions for the same corrosion times
Summary
Borosilicate 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.[1,2,3] 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.[4,5,6] Nuclear glass corrosion occurs at a rate on the order of 0.1–1 μm/day at 90 °C in the first stage (Stage-I) and 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.[6,7] The corrosion process enters the second stage (Stage-II) when the corrosion solution is saturated with respect to soluble siliconcontaining species.[8]. To understand the mechanism of glass corrosion in the second stage, it is very important to obtain information on interfacial behaviors of hydrous species (molecular water and Si-OH) on the alteration layer; hydrogen bonding interactions between these species are expected to affect the transport of water molecules in the alteration layer. A comprehensive study of the alteration layer combining elemental analysis, poresize characterization, and analysis of hydrogen bonding interactions of hydrous species (H2O and SiOH) in both centrosymmetric and non-centrosymmetric media is critically needed to understand aqueous glass corrosion mechanism and transport of molecular water and other mobile species within the nanoporous alteration layer. Dynamics, and structure in nano-porous materials have been shown to be different from those in the bulk.[9,20,21,32,59] It was shown for alteration layers formed on ISG corroded in aqueous solutions that there is an evolution of pore size in the layers with corrosion time and it is accompanied by a structural rearrangement of the alteration layer.[9,40] In consequence, the transport and behavior of water and
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