Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part II: Structure |
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| Authors: | Xiaonan Lu Joelle T Reiser Benjamin Parruzot Lu Deng Igor M Gussev Jörg C Neuefeind Trent R Graham Hongshen Liu Joseph V Ryan Seong H Kim Nancy Washton Maik Lang Jincheng Du John D Vienna |
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| Affiliation: | 1. Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA, USA;2. Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA;3. Department of Nuclear Engineering, University of Tennessee, Knoxville, TN, USA;4. Neutron Science Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN, USA;5. Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA, USA;6. Department of Chemical Engineering, Materials Research Institute, Pennsylvania State University, University Park, PA, USA |
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| Abstract: | High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and 27Al, 23Na, 29Si, and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (eg, bond distance, coordination number, etc) and medium-range (eg, oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al + Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase in tri-bridging oxygen species, whereas (Al + Na):Si substitution creates nonbridging oxygen species. Charge compensator preferences were found for Si-NBO] (Na+), 3]B-NBO] (Na+), 4]B (mostly Ca2+), 4]Al (nearly equally split Na+ and Ca2+), and 6]Zr (mostly Ca2+). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-3]B and 3]B-O-3]B linkages. These results provide insights on the structural origins of property changes such as glass-transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models. |
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| Keywords: | aluminosilicates borosilicate glass international simple glass molecular dynamics nuclear magnetic resonance scattering |
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