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Experimental and computational studies of the structure, thermal expansion and volume isotope effect in high-pressure ices

Baron, Geoffrey; (2022) Experimental and computational studies of the structure, thermal expansion and volume isotope effect in high-pressure ices. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Exploration by spacecraft of the outer solar system has revealed that the moons of the giant planets are geologically active worlds. Some could sup- port subsurface oceans, even life. Computer models have been designed to emulate the geological evolution of these moons but, to make useful predic- tions, reliable information about the likely layers of ice and rock within their interiors is needed. This thesis has investigated several high-pressure ice phases, namely ices II, III, V and VI, which could occur in the regime of pressure and tem- perature likely to exist in the mantle of an icy moon. Consequently, they are good candidates as ’rock forming’ materials and are likely to form icy shells surrounding a moon’s inner core. Samples of both D2O and H2O ices II, III, V and VI were manufactured in the laboratory by means of a piston-cylinder cell. Their high-pressure struc- tures were preserved at ambient pressure by recovery and storage under liq- uid nitrogen. The samples were then investigated by neutron powder diffrac- tion (at ambient pressure and temperatures from 10-150 K) using the High Resolution Powder Diffractometer (HRPD) at the ISIS facility in the UK, so as to accurately determine both their crystal structures and thermal expan- sion coefficients. All of these ice phases exhibit a ‘normal’ volume isotope effect, “VIE”, with V(H2O) > V(D2O). The effect of hydrogen ordering at low temperatures was also investigated and found to be isotope independent. To compliment the experimental work, ab initio simulations of ices II, IX and XI were made using density functional theory (DFT). These calculations broadly replicated the experimental values for thermal expansion and cor- rectly predicted the VIE for ices II and III. However, for ice XI (an ordered form of ice Ih) a normal VIE was predicted below 130 K, in conflict with ex- perimental results for ice Ih.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Experimental and computational studies of the structure, thermal expansion and volume isotope effect in high-pressure ices
Language: English
Additional information: Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10145115
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