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Influence of Composition on Structure and Caesium Volatilisation from Glasses for HLW Confinement

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Influence of Composition on Structure and Caesium Volatilisation from Glasses for HLW Confinement Influence of Composition on Structure and Caesium Volatilisation from Glasses for HLW Confinement Benjamin Graves Parkinson B.Sc. (Hons.), M.Sc. A thesis submitted to the University of Warwick in partial fulfilment of the requirement for the degree of Doctor of philosophy Department of Physics November 2007 Contents Contents (i) List of Figures (vi) List of Tables (xv) List of Abbreviations (xvii) Acknowledgements (xviii) Declaration (xix) Abstract (xx) Chapter 1...................................................................................................................1 1 Introduction....................................................................................................1 1.1 Overview................................................................................................1 1.2 Aim of the work .....................................................................................1 1.3 References..............................................................................................5 Chapter 2...................................................................................................................7 2 Immobilisation of High Level Nuclear Waste.................................................7 2.1 Introduction............................................................................................7 2.2 High-Level Nuclear Waste......................................................................7 2.3 HLW Immobilisation..............................................................................8 2.3.1 Introduction ....................................................................................8 2.3.2 The Vitrification Process.................................................................9 2.3.3 Volatilisation of Material at the Melt Stage ...................................11 2.4 Chemical Durability of Glasses Containing HLW Oxides..................... 13 2.5 References............................................................................................ 16 Chapter 3................................................................................................................. 19 3 Glass Theory................................................................................................ 19 3.1 Introduction..........................................................................................19 3.2 Glass definition and properties – glass-forming oxides ......................... 19 3.3 Simple Structural Theories and Observations of Glass Formation ......... 21 3.3.1 Borates and Borosilicates Structural Theories ............................... 21 3.3.2 Phase Separation in Glasses..........................................................23 i 3.4 Multi-component Glass Theories ..........................................................23 3.4.1 Borate Glass Theories – The N 4 Fraction, Superstructures and Multiple Four-Coordinated Boron sites ........................................................24 3.4.2 Silicate Glass Theory....................................................................32 3.4.3 Borosilicate Glass Networks – The Dell Model............................. 33 3.5 Structural and Physical Effects of Further Oxide Additions to Alkali Borosilicates .................................................................................................... 35 3.5.1 The Glass Transition and Crystallisation Temperatures................. 36 3.5.2 Borate and Borosilicate Glass Density...........................................37 3.5.3 Glass Durability and Chemical Resistance for Waste Storage........ 37 3.6 Summary.............................................................................................. 38 3.7 References............................................................................................ 39 Chapter 4................................................................................................................. 43 4 Experimental Theory and Practice: - Glass Preparation and Characterisation 43 4.1 Introduction.......................................................................................... 43 4.2 Glass Preparation.................................................................................. 43 4.2.1 Standard Borosilicate Compositions.............................................. 43 4.2.2 Oxygen-17 Enriched Borosilicate Sample Preparation .................. 46 4.3 Characterisation Techniques ................................................................. 49 4.3.1 Introduction to X-ray Diffraction .................................................. 49 4.3.2 X-Ray Diffraction Method............................................................ 50 4.3.3 Thermal Techniques...................................................................... 51 4.4 Chemical Durability ............................................................................. 53 4.4.1 Leach Testing ............................................................................... 53 4.5 References............................................................................................ 55 Chapter 5................................................................................................................. 57 5 Experimental Theory and Practice: - Structural Determination ..................... 57 5.1 Introduction.......................................................................................... 57 5.2 Density Measurements.......................................................................... 57 5.2.1 Introduction .................................................................................. 57 5.2.2 Experimental Method – Archimedes Method and Pycnometer ...... 57 ii 5.3 Nuclear Magnetic Resonance Spectroscopy [4-8] ................................. 59 5.3.1 Introduction .................................................................................. 59 5.3.2 The NMR signal – spin relaxation and RF pulses .......................... 60 5.3.3 Nuclear Spin Energy and the Larmor frequency............................ 61 5.3.4 Heteronuclear spins, dipole-dipole coupling, magic angle spinning and quadrupolar line broadening................................................................... 62 5.3.5 Multiple Quantum Magic Angle Spinning NMR........................... 68 5.3.6 23 Na, 27 Al, 11 B, 29 Si and 17 O NMR Acquisition Conditions............ 69 5.4 Raman Spectroscopy ............................................................................ 71 5.4.1 Introduction .................................................................................. 71 5.4.2 Raman spectroscopy of glassy materials ....................................... 73 5.4.3 Quantitative Raman Spectroscopy of Glassy Materials.................. 74 5.4.4 Raman Spectroscopy – Experimental Method ............................... 76 5.5 References............................................................................................ 77 Chapter 6................................................................................................................. 79 6 Results: - Glass Preparation and Characterisation .........................................79 6.1 Introduction..........................................................................................79 6.2 Glass Characteristics.............................................................................79 6.2.1 X-Ray Diffraction.........................................................................79 6.3 Thermal Analysis Techniques...............................................................80 6.3.1 Differential Thermal Analysis.......................................................80 6.3.2 Simultaneous Thermal/Thermogravimetric Analysis..................... 81 6.3.3 Volatilisation Measurements.........................................................86 6.4 Chemical Durability - Leach Testing ....................................................88 6.4.1 pH and elemental analysis of leachates..........................................88 6.4.2 Mass-Loss Measurements.............................................................90 6.4.3 Leached Glass Structure................................................................90 6.5 Summary.............................................................................................. 90 6.6 References............................................................................................ 93 Chapter 7................................................................................................................. 94 7 Results and Discussion: - Standard Borosilicate Glass Structural Determination...................................................................................................... 94 iii 7.1 Introduction.......................................................................................... 94 7.2 Density Measurements.......................................................................... 94 7.3 Nuclear Magnetic Resonance................................................................ 98 7.3.1 Borosilicate Glasses...................................................................... 98 7.3.2 23 Na MAS NMR ........................................................................... 98 7.3.3 27 Al MAS NMR.......................................................................... 100 7.3.4 11 B MAS NMR........................................................................... 101 7.3.5 29 Si MAS NMR .........................................................................
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