Characterizing the Alteration Layers on Nuclear Waste Glasses by Solid-State Nuclear Magnetic Resonance
Open Access
- Author:
- Murphy, Kelly Ann
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 31, 2014
- Committee Members:
- Karl Todd Mueller, Dissertation Advisor/Co-Advisor
Karl Todd Mueller, Committee Chair/Co-Chair
Carlo G Pantano, Dissertation Advisor/Co-Advisor
Miriam Arak Freedman, Committee Member
Danny Glynn Sykes, Committee Member
James David Kubicki, Committee Member - Keywords:
- NMR
Alteration layers
Surface structure
Nuclear waste glasses
Corrosion - Abstract:
- One of the most promising options for long-term storage of radioactive waste is vitrification, or immobilization in a glass matrix. The viability of this storage method is evaluated by exposure of the glass to corrosive conditions. Previous work has indicated that alteration layers, which may be protective in nature, form on the glass surface. Solid-state nuclear magnetic resonance (NMR) spectroscopy is an ideal tool to study the alteration layers because this technique provides structural and (indirectly) compositional information. Moreover, inherent properties of the glass can be exploited to differentiate between the alteration layers and bulk glass via cross-polarization magic angle spinning (CP-MAS) NMR. Initial characterization suggested the alteration layers formed on two glass compositions were comprised of a hydrated glass layer (barrier between pristine glass and gel layer) and a nano-porous gel layer (directly in contact with solution). The former contained hydrated versions of all components in the pristine, non-corroded glass. Only certain components such as silicon and aluminum, however, were retained in the gel layer. Experimental conditions such as glass composition and form (powder versus fiber) have been shown to influence the composition and structure of the alteration layers. After formation, the alteration layers continue to interact with solution species due to an established dynamic equilibrium. Through isotopic labeling and solution swapping experiments, recondensation of aqueous silicon onto the powder surface was observed at short and long equilibration periods. Boron sorption after release to solution was also observed for one glass composition. The questions probed in these studies suggest that the solution-surface interface is constantly evolving. Therefore, future work in the field should continue to strive towards mimicking environmental conditions and attempting to answer fundamental questions about water-glass interactions.