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Annealing Induced Recrystallization of Radiation Damaged Titanite And

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Annealing Induced Recrystallization of Radiation Damaged Titanite And Annealing induced recrystallization of radiation damaged titanite and allanite Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften im Fachbereich Geowissenschaften der Universität Hamburg vorgelegt von Tobias Beirau aus Glinde Hamburg 2012 Als Dissertation angenommen vom Fachbereich Geowissenschaften der Universität Hamburg auf Grund der Gutachten von Prof. Dr. Ulrich Bismayer und Dr. habil. Boriana Mihailova Tag der mündlichen Prüfung: 29.06.2012 Hamburg, den 14. Mai 2012 Prof. Dr. Oßenbrügge Sprecher Fachbereich Geowissenschaften Contents Abstract .................................................................................................................................... 3 1 Introduction ....................................................................................................................... 5 Nuclear waste forms .................................................................................................................. 5 Radiation damage ...................................................................................................................... 6 Titanite ...................................................................................................................................... 7 Allanite .................................................................................................................................... 11 Objectives of the current study................................................................................................ 13 2 Experimental techniques and theoretical background .............................. 14 Sample characterization and preparation ................................................................................ 14 Titanite samples .................................................................................................................. 14 Reference samples ............................................................................................................... 14 Metamict titanite samples .................................................................................................... 14 Radiation Dose calculation ................................................................................................. 17 Allanite sample .................................................................................................................... 17 Raman spectroscopy ................................................................................................................ 19 Fourier transform infrared spectroscopy (FTIR) ..................................................................... 25 Group-theory analysis of pure titanite ..................................................................................... 26 X-ray diffraction (XRD).......................................................................................................... 28 Transmission electron microscopy (TEM) .............................................................................. 32 Nanoindentation ...................................................................................................................... 33 Electron microprobe analysis and X-ray fluorescence analysis .............................................. 35 3 Results ................................................................................................................................. 36 Metamict titanite ..................................................................................................................... 36 Raman spectroscopy of unannealed titanites with different degree of metamictization ..... 36 Metamict titanite sample M28696 (Cardiff) ........................................................................ 38 Raman spectroscopy ......................................................................................................... 38 Synchrotron single-crystal XRD ....................................................................................... 40 Metamict titanite sample E2335 .......................................................................................... 42 Transmission electron microscopy ................................................................................... 42 Raman spectroscopy ......................................................................................................... 45 1 Metamict titanite sample E2312 .......................................................................................... 53 Nanoindentation ............................................................................................................... 53 Synchrotron X-Ray diffraction ......................................................................................... 58 Raman spectroscopy ......................................................................................................... 60 Metamict allanite ..................................................................................................................... 64 Chemical analysis ............................................................................................................... 64 X-ray powder diffraction ..................................................................................................... 64 Synchrotron single-crystal XRD .......................................................................................... 65 Fourier-transformed infrared spectroscopy (FTIR) ............................................................ 69 4 Discussion .......................................................................................................................... 70 Metamict Titanite .................................................................................................................... 70 Relation between Raman scattering and the degree of radiation-induced damage ............ 70 M28696 Cardiff titanite ....................................................................................................... 74 E2335 titanite ...................................................................................................................... 75 The effect of annealing ........................................................................................................ 77 E2312 titanite ...................................................................................................................... 79 Metamict Allanite .................................................................................................................... 80 5 Conclusions ....................................................................................................................... 82 Metamict - recrystallization - increasing order ....................................................................... 82 References ............................................................................................................................. 85 Curriculum vitae ............................................................................................................... 97 List of publications ........................................................................................................... 99 Contributions to conferences ................................................................................................... 99 Acknowledgements ......................................................................................................... 102 2 Abstract Minerals can become metamict over geological time periods as a result of structural damage induced by α-decay events resulting from incorporated radiogenic elements. The structural state and the thermally induced recrystallization behavior of metamict titanite were studied by Raman spectroscopy, synchrotron single-crystal X-ray diffraction, nanoindentation and complementary high-resolution transmission electron microscopy. The results of the Raman spectroscopic measurements show that Raman scattering collected from metamict titanite is still anisotropic, which is typical of single crystals and indicates oriented, basically coherent structural elements. The observed Raman scattering dependence on the sample orientation is on the other hand much more pronounced for heavily metamict than for weakly metamict titanite samples. Radiation- induced anisotropic effects are related to the specific atomic arrangements in the structure of metamict titanite. This leads to the opportunity to study separately the structural transformations of the crystalline and amorphous fractions in metamict titanite by using Raman spectroscopy. That is possible because the Raman modes in the spectra collected from a plane nearly perpendicular to the chains of corner-sharing TiO6 octahedra arise predominantly from phonon modes in crystalline nanoregions with radiation-induced defects. In contrast to the contribution of atomic vibrations in radiation-induced amorphous nanoregions, which is better pronounced in spectra collected from a plane containing TiO6 chains. The results show that radiation-induced periodic faults in the crystalline matrix are related to the disturbance of SiO4-TiO6-SiO4- TiO6 rings comprising TiO6 octahedra from different chains. The radiation-induced amorphization by contrast is related to the partial change of Ti coordination from octahedral to pyramidal and/or tetrahedral, which leads to a rising Ti-O bond strength. This in turn violates the Ti-O-Ti intrachain linkages in the titanite structure. Hence, the planes containing Si-O-Ti-O
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