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Title: A high resolution multinuclear magnetic resonance study of ceramic phases
Author: Smith, Mark Edmund
ISNI:       0000 0001 2440 8164
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1987
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The applicability of magic angle spinning (MAS) NMR to the study of crystalline ceramic phases is investigated. Aluminium-27 and silicon-29 chemical shifts from the crystalline phases of the (Sc,Y,La)-Si-Al-O-N systems are reported. The chemical shift information differentiates between distinct local environments so that the structures of phases containing elements of similar scattering factor can be refined. The utility of MAS-NMR in phase characterisation of complex mixtures is demonstrated by comparing MAS NMR results with X-ray diffraction of different phase preparations. This shows that a much more complete description of the phase distribution is obtained by using a combination of these techniques. The results of preliminary investigations of the usefulness of other less commonly studied nuclei (14N, 25Mg, 45Sc and 139La) for multinuclear NMR studies of ceramics are given. The Si(O,N)4 tetrahedra in oxynitride ceramics allow 29Si chemical shifts to be given for the complete range of SiOxN4-x (0 < x < 4) units. The expected paramagnetic shift with increasing nitrogen content is observed and, although there is extensive overlap of the shift ranges from different units, MAS-NMR spectra allow different atomic arrangements to be distinguished (e.g. in Y4Si2O7N2 and Y2Si3O3N4). The problems associated with long spin-lattice relaxation times (~ a few hours), encountered for 29Si in some of these materials are discussed, together with a calculation of signal-to-noise optimisation. A more efficient spectral accumulation procedure for such samples is suggested. The 27Al chemical shift ranges for different structural units (e.g. AlN4, AIO4, AlO6) in ceramics are investigated which allows the aluminium distribution in these materials to be refined. This is shown in the case of some non-stoichiometric spinels (Mg0.xAl2O3) and β'-sialon. In NMR spectroscopy of quadrupolar nuclei (I > 1), and in particular 27A1 (I=5/2), extensive broadening of the NMR signal occurs at some sites due to the quadrupolar interaction. Its effect on the quantitative nature of 27Al NMR spectroscopy is discussed.
Supervisor: Not available Sponsor: Science and Engineering Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics