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Hill-Casey, Fraser (2018) Hyperpolarised noble gas nuclear magnetic resonance and magnetic resonance imaging studies of complex porous media. PhD thesis, University of Nottingham.

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Abstract

The ability to non-invasively probe void spaces is an extremely valuable tool for applications ranging from chemical engineering to biomedical, pulmonary imaging studies. Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) provide such a methodology. To achieve suitable signal intensity from the magnetic resonance experiment, a probe molecule such as H2O is introduced to the void space to generate enough detectable signal for an MR system. The use of liquids, however, restricts the time scales accessible and confines characterisation of diffusion to that of the molecular regime. In recent years, gas phase measurements have been made with probe molecules such as sulphur hexafluoride SF6 but such measurements typically require high pressures to achieve suitable sensitivity and as such are subject to the same limitations as liquid measurements. However, via use of hyperpolarisation (hp) techniques such as Spin Exchange Optical Pumping (SEOP) it is possible to perform measurements of noble gases at atmospheric pressure and room temperature. As such, it is possible to utilise these hp gasses to investigate low-density, gas-phase mass-transport, such that the diffusion may be studied in the Knudsen regime. Understanding of diffusion processes are particularly valuable to the design of hierarchical porous media such as catalysed diesel particulate filters (DPF) and other industrial catalytic processes. The characterisation of the structure-transport relationships of porous solids is extremely valuable for the design of new advanced catalysed materials for a range of applications.

The work within this document has applied a variety of MR techniques to the investigation of structure-transport relationships in complex porous media. Further new production methodologies have allowed for new, novel gas probes to be produced, further increasing applicability of hp noble gas MR techniques to probing void spaces within porous media.

Hp 129Xe has been shown to be a valuable probe of flow within complex porous media via MRI phase-shift velocimetry. Measurements were performed in channels with porous walls and velocity profiles were shown to provide good correlated with theoretical models.

Structure-transport relationships within the hierarchical pore structure of the DPF was probed via a multi-modal, multi nuclei-study. NMR relaxometry and MRI of gas phase 129Xe were used as to interrogate the contributions of each level of the structural hierarchy of the sample to the dispersive mass transport.

A novel methodology of SEOP for the production of highly polarised 129Xe and 83Kr spin states via use of hydrogen-noble gas mixtures is presented. Catalytic separation techniques were employed for purification of the polarised spin system from its buffer gas of H2. These developments enhance the applicability of 129Xe and 83Kr to material science applications, as well as vastly increasing viability of clinical applications.

Finally, SEOP of 21Ne was performed and for the first time produced a highly polarised sample, suitable for NMR spectroscopy and relaxometry studies. The quadrupolar relaxation of 21Ne was characterised in a range of void spaces and surface chemistries. 21Ne is shown to be a promising probe for investigations of porous media.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Rigby, Sean Meersmann, Thomas Pavlovskaya, Galina
Keywords:	MRI; NMR; Hyperpolarized; Gases; Xenon; Krypton; Porous Media; SCR; relaxation; diffusion
Subjects:	Q Science > QC Physics > QC770 Nuclear and particle physics. Atomic energy. Radioactivity T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	53321
Depositing User:	Hill-Casey, Fraser
Date Deposited:	01 Nov 2018 09:54
Last Modified:	25 Jul 2024 11:28
URI:	https://eprints.nottingham.ac.uk/id/eprint/53321

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