Alkali borosilicate glass is used to immobilise high-level radioactive waste generated from the reprocessing of spent nuclear fuel. However, poorly soluble waste products such as molybdenum present issues for long-term storage of the material, whereby phase separation of water-soluble crystalline aggregates truncate the glass network and offer leaching opportunities for the escape of radionuclides into the environment. Solid-state NMR is an effective technique for studying the phase separation in nuclear waste glasses, as it is able to distinguish glassy and crystalline environments using nuclei-specific probes. The presence of paramagnetic transition metal cations within the waste glass compromises the efficacy of NMR, as unpaired electrons can cause broadening and chemical shift effects. This work engages in a multinuclear magnetic resonance characterisation of paramagnetically-doped (by Cr2O3, MnO2, Fe2O3, NiO, or Nd2O3) model nuclear waste glasses and explores the partitioning of transition-metal components. Characterisation of the separated heterogeneous crystalline phase was accomplished principally by 133Cs, 23Na, and 95Mo NMR, where it was determined that Cr substitutes into mixed-alkali molybdates. Furthermore, paramagnetic broadening and relaxation effects were observed and quantified by 11B and 29Si NMR.

Coordination compounds involving stable radicals represent a promising avenue toward the design of new magnetic materials. In this respect, a series of new metalverdazyl radical complexes has been prepared and their magnetic properties reported. These systems can be envisioned as model systems designed to help elucidate the fundamental electronic interactions between one paramagnetic metal ion and one verdazyl radical that lead to magnetic exchange. A new chelating verdazyl diradical has also been prepared and fully characterised. The electronic ground state of this diradical species has been established through magnetic and variable temperature electron paramagnetic resonance (VT-EPR) studies. In an effort to expand the metal-radical model systems beyond simple 1:1 metal:radical complexes, this verdazyl diradical was employed as a ligand to prepare a succession of first row transition metal complexes. The magnetic properties of the resulting coordination compounds have been studied in an effort to understand how the nature of the metal-diradical magnetic exchange changes with the metal used. In addition to the wide-spread interest in the magnetic properties of stable organic radicals, there is a growing awareness of the redox properties of this class of compounds. Electrochemical and spectroelectrochemical techniques were utilised to probe the redox properties of a verdazyl diradical and a structurally similar verdazyl monoradical. Coordination compounds involving the redox-inert metal zinc were also prepared and their redox properties investigated. While the addition of zinc to the verdazyl diradical had no significant impact on the magnetic properties of the diradical, there is a distinct difference between the redox properties of the diradical itself and its zinc complex. Coordination to zinc also affected the redox properties of the verdazyl monoradical, although to a lesser extent than what was observed for the diradical. / Graduate / 0485

Graduate / 0607

I have studied two magnetic properties of superconductors using different neutron scattering techniques. Due to their magnetic moment and lack of electrical charge, neutrons can provide an extremely sensitive probe into magnetism on a small scale. Unusual magnetic structures have previously been observed in the non-superconducting PrBa₂Cu₃O₆+_δ, in particular showing a coupling between the rare-earth and the Cu-O₂ planes. For comparison, I have used elastic neutron scattering to measure the temperature dependent magnetic structure of the high-T_c superconductor NdBa₂Cu₃O₇, and its nonsuperconducting reduced form NdBa₂Cu₃O₆. The magnetic structures of both the Nd and Cu sub-lattices are presented. Measurements are shown for single crystals of both the oxygenated and reduced form, and also for a non-stoichiometric single crystal with Nd substituted on the Ba sites. I present a quantitative analysis of the magnetic moments, with account taken of the instrumental resolution including sample mosaicity and intrinsic peak shapes. No evidence was found for any coupling of the type seen in PrBa₂Cu₃O₆+_δ. Many of the underlying properties of superconductors are evidenced in the way magnetic fields are excluded in the different states. I have used polarized neutron reflectometry to measure the magnetic field profile in thin film superconductors. I present measurements for pure niobium and preliminary measurements for YBa₂Cu₃O₇. The samples studied are much thicker than those previously measured, to provide a closer match to the bulk superconductor properties and allow meaningful measurements of the higher field states. For niobium, the applied field dependence is measured for fields covering the Meissner and mixed states, and models are compared for these states and the surface superconductivity state.

The purpose of this thesis is to describe research into the extension and development of methods in solid state NMR, and their application to chemical systems where, for various reasons, analysis was difficult, incomplete, or impossible by other spectroscopic techniques. In particular silicon-29, sodium-23, fluorine-19 and proton nuclei have been used as molecular probes in inorganic silicates, macrocyclic polyether crown complexes and fluoropolymer chemical systems. The sodium-23 chemical shift and lineshape have been shown to be sensitive to coordination and local symmetry. The cross-polarization experiment has also been applied to the sodium-23 nucleus, and shown to exhibit the same steric selectivity which has been observed in carbon-13 andsilicon-29 experiments. A probe has been configured at 4.7 Tesla to perform proton and fluorlne-19 CRAMPS experiments. Multiple pulse sequences and CRAMPS experiments have been used to investigate the molecular motions and chemical environments of the systems investigated. Conclusions are drawn upon the results which support the utility of these methods in application to difficult solid state systems.

A range of 1D and 2D MAS NMR experiments have been carried out in conjunction with X-ray diffraction experiments on a number of materials from the AM(_2)O(_7) family, which exhibit the unusual phenomenon of negative thermal expansion. It has been shown that ZrP(_2)O(_7) and HfP(_2)O(_7) exist with space group Pbca rather than Pa3 as proposed in the literature, and a full structure solution has been possible for ZrP(_2)O(_7) from a combination of NMR and X-ray and neutron powder diffraction. 2D MAS NMR has been used to differentiate at least 108 unique phosphorus sites within the asymmetric unit of SnP(_2)O(_7), supporting a recent powder diffraction study presented in the literature. PbP(_2)O(_7) has been shown, by NMR, to exist as an incommensurate phase at room temperature. ZrW(_2)O(_8), a material which also shows negative thermal expansion, has been studied here primarily with variable-temperature (^17)O MAS NMR. The results presented shed important new light on oxygen migration processes occurring at the a I β-phase transition of this material. A full structure solution is presented for 2-[4-(2-hydroxy-ethylamino)-6-phenylamino-[1,3,5]triazin-2-ylamino]-ethanol from powder X-ray data, an organic material investigated as part of a study of ink-jet-dyes.

No description available.

Fibre-reinforced polymer-matrix composite materials have highly attractive physical properties which justify the present rapid increase in applications within industry. However, composite materials suffer, like every structural material, from a failure to achieve their design properties. Therefore this research project has investigated the processing of resin used in composite materials. Initially the research programme has been concerned with the cure of epoxy resins (specifically Araldite MY750 epoxy resin system), the behaviour of the resin as it cures and how the extent of cure can affect the mechanical properties of components. Therefore, investigations have been carried out into how resin cure can be monitored by the NMR spectra and the relaxation time properties. There were four methods of analysing the data investigated, overall transverse relaxation time (T2) and free induction decay data (FID) data using the Oxford QP NMR analyser, transverse relaxation time data and spectral changes for the individual chemical environments using the Jeol EX270 NMR spectrometer, curemeter investigations using the vibrating needle curemeter (VNC) and finally Barcol hardness investigations during the later part of the cure cycle. Both the Jeol NMR spectrometer and the Oxford QP NMR analyser are designed for use primarily with liquid-state experimentation, however for the spectral, relaxation time, and FID investigations results were obtained far longer in the cure than expected. Also for the T2 investigations a transition period was noticed in the data obtained that corresponded to the gel of the resin as determined by known viscosity data for that resin mix at that cure temperature. The use of NMR as a curemeter technique was verified by repeating the analysis of the resin cure at 40, 60, 80 and 100°C. This data was then compared to known viscosity data and cure profiles obtained by the VNC curemeter and Barcol hardness readings on similar sized samples.

No description available.

No description available.