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Properties and Recrystallization of Radiation Damaged Pyrochlore and Titanite

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Properties and Recrystallization of Radiation Damaged Pyrochlore and Titanite Properties and recrystallization of radiation damaged pyrochlore and titanite Dissertation with the aim of achieving a doctoral degree at the Faculty of Mathematics, Informatics and Natural Sciences, Department of Geosciences of University of Hamburg Submitted by Peter Zietlow 2016 in Hamburg The following evaluators recommend the admission of this dissertation: Prof. Dr. Ulrich Bismayer Prof. Dr. Shrinivas Viladkar Date of the oral Ph.D. defense: 02.11.2016 PROPERTIES AND RECRYSTALLIZATION OF RADIATION DAMAGED PYROCHLORE AND TITANITE Contents Contents Contents ...................................................................................................................................... i Abstract .................................................................................................................................... iii 1 Radiation damaged materials .............................................................................................. 1 1.1 Introduction ................................................................................................................................... 1 1.2 Metamict minerals ........................................................................................................................ 5 1.3 α-decay .......................................................................................................................................... 6 2 Metamict pyrochlore ............................................................................................................. 7 2.1 Crystalline structure ...................................................................................................................... 7 2.2 Structural damage ....................................................................................................................... 10 2.3 Self-annealing .............................................................................................................................. 14 2.4 Sample description ...................................................................................................................... 16 2.5 Experimental methods ................................................................................................................ 18 2.5.1 Electron microprobe ............................................................................................................. 18 2.5.2 X-ray powder diffraction ...................................................................................................... 21 2.5.3 Raman spectroscopy ............................................................................................................ 22 2.5.4 Fourier Transform Infrared spectroscopy ............................................................................ 26 2.5.5 Differential scanning calometry / Thermogravimetry .......................................................... 27 2.6 Group theoretical analysis of the pyrochlore structure .............................................................. 27 2.7 Results ......................................................................................................................................... 29 2.7.1 Microscopy and macroscopic sample change ...................................................................... 29 2.7.2 Electron microprobe ............................................................................................................. 30 2.7.3 Powder X-ray diffraction ...................................................................................................... 35 2.7.4 Raman spectroscopy ............................................................................................................ 44 2.7.5 Newania pyrochlores ............................................................................................................ 55 2.7.6 Fourier Transform Infrared spectroscopy (FTIR) .................................................................. 55 2.7.7 Thermal analysis ................................................................................................................... 56 2.8 Discussion .................................................................................................................................... 59 2.8.1 Electron microprobe analysis ............................................................................................... 59 2.8.2 X-ray diffraction .................................................................................................................... 60 2.8.3 Raman spectroscopy ............................................................................................................ 63 2.8.4 Newania pyrochlore ............................................................................................................. 74 [i] PROPERTIES AND RECRYSTALLIZATION OF RADIATION DAMAGED PYROCHLORE AND TITANITE Contents 2.8.5 Thermal analysis ................................................................................................................... 74 3 Metamict titanite ................................................................................................................. 76 3.1 Titanite structure ......................................................................................................................... 76 3.2 Magic angle spin nuclear magnetic resonance spectroscopy (MAS NMR) ................................. 76 Experimental conditions ................................................................................................................ 77 3.3 NMR results and discussion ......................................................................................................... 78 4 Conclusions .......................................................................................................................... 83 Bibliography ........................................................................................................................... 85 Curriculum vitae ..................................................................................................................... A List of publications .................................................................................................................. B Acknowledgements .................................................................................................................. D Eidesstattliche Versicherung .................................................................................................. E [ii] PROPERTIES AND RECRYSTALLIZATION OF RADIATION DAMAGED PYROCHLORE AND TITANITE Abstract Abstract Radiation damage in minerals is caused by the alpha-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1400 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG) (Zietlow et al., in print). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia (6.4 wt% Th, 23.1·1018 α-decay events per gram (dpg)), Zlatoust/Russia (6.3 wt% Th, 23.1·1018 dpg), Panda Hill/Tanzania (1.6 wt% Th, 1.6·1018 dpg), and Blue River/Canada (10.5 wt% U, 115.4·1018 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 %, Zlatoust and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm-1 are sensitive to radiation damage (Vandenborre & Husson 1983, Moll et al. 2011), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm-1 devided by the sum of the integrated intensities of the bands between 810 and 860 cm-1. The most radiation damaged pyrochlores (Miass and Zlatoust) show an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K. The volume decrease upon recrystallization in Zlatoust pyrochlore was large enough to crack the sample repeatedly. In contrast, the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous x-ray diffraction pattern superimposed by weak Bragg- maxima that indicates the existence of ordered regions in a damaged matrix. Unlike the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm-1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1%, Blue River ca. 1.5%, Miass ca. 2.9%). [iii] PROPERTIES AND RECRYSTALLIZATION OF RADIATION DAMAGED PYROCHLORE AND TITANITE Abstract In order to elucidate
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