Smith, Mark E. (1987) A high resolution multinuclear magnetic resonance study of ceramic phases. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Ceramic coating, Nuclear magnetic resonance, Nuclear magnetic resonance spectroscopy, Phase transformations (Statistical physics), Crystallization
Official Date:	October 1987
Dates:	Date Event October 1987 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dupree, Ray
Sponsors:	Science and Engineering Research Council (Great Britain)
Format of File:	pdf
Extent:	ix, 176 leaves : illustrations, charts
Language:	eng

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