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Investigating simultaneous microwave dielectric and structural characterisation of heterogeneous gas sorption processes

Barter, Michael ORCID: 2019. Investigating simultaneous microwave dielectric and structural characterisation of heterogeneous gas sorption processes. PhD Thesis, Cardiff University.
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The main aim of this thesis is to design, simulate, build, and conduct and interpret experiments using simultaneous microwave dielectric and structural measurements. These measurements will be used to characterise solid state materials during polar gas sorption processes. The gases reviewed in this thesis are ammonia and sulphur dioxide. Metal-organic frameworks are investigated for use as both ammonia and sulphur dioxide solid state storage materials. Metal halides are also investigated for absorption of ammonia. These sorption processes are investigated using microwave dielectric characterisation. This is combined with structural characterisation from either neutron or X-ray diffraction. The combination of these techniques is used to monitor changes in bulk material properties along with changes in molecular structure during the gas sorption processes. A sample environment is designed for simultaneous neutron diffraction and microwave characterisation of materials at varying temperatures. The developed equipment uses heating coils to heat a flowing gas, which is used to heat the sample. A cylindrical cavity is designed and constructed for this experimental rig with a thinned section of cavity wall to minimise neutron scattering from the sample environment. This equipment is tested by successfully monitoring the activation of a MOF sample at 150 °C to remove water present in the sample. A hairpin style resonator is also developed for use with simultaneous dielectric characterisation and Xray diffraction. The open structure of the hairpin geometry of this resonator allows the X-ray beam to be unimpeded by the resonator, maximising the resolution or X-ray data. This is used to investigate the absorption of ammonia by halides salts. Also in this thesis, a new method for correcting for changes in frequency caused by changes in temperature is developed for cylindrical microwave cavities. Temperature correction is often required during microwave characterisation where changes in temperature caused by changes in ambient conditions, exothermic/endothermic reactions, or while examining dielectric properties over a range of temperatures. TMm10 modes consist of two symmetrical mode patterns with identical resonant frequencies. This technique uses a strategically placed sample to split vi the frequencies of these degenerate modes. The higher frequency, unperturbed mode is used as a local reference and the lower frequency, perturbed mode as the measurement mode. The effectiveness of this technique is proved by heating water sample from 20 ºC to 60 ºC, calculating its permittivity and comparing against literature values.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Microwave Characterisation; Energy Storage; Structural Characterisation; Gas Sorption.
Date of First Compliant Deposit: 21 August 2019
Last Modified: 04 Nov 2022 13:04

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