th  - 1988 - 51st ENC Conference

16 0 I A 27AL MAS STUDY OF AMORPHOUS ANODIC ALUMINA: STRUCTURAL
INFORMATION COMBINED WITH QUANTITATIVE UNCERTAINTY. *I. Farnan (1)t, R.
Dupree (1), M.E. Smith (1), Y.S. Jeong (2) and G. Thompson (2). (1) Physics Department, University
of Warwick, Coventry CV47AL, U.K.; (2) Corrosion and Protection Centre, UMIST, Manchester
SK97AL, U.IL
The ability of 27A1 MAS-NMR to distinguish between aluminium in different coordination
states in aluminas and aluminosilicates has been known for some time. Here the technique is ap-
plied to technologically important amorphous anodic aluminas whose structures are poorly known.
The study reveals five-fold coordinated aluminium in these materials in addition to the more usual
aluminium coordinations of four and six, all with a symmetry comparable to crystalline alumi-
nas. The film formation conditions are observed to influence the relative amounts of this quasi-
crystalline aluminium observed in the spectrum.
Because of the range of bond lengths and angles in these amorphous materials there re-
mains a broad contribution to the spectrum associated with aluminium electric field gradients
which are not averaged by MAS. As well as causing un-narrowed lines in the spectrum, electric
field gradients can cause the aluminium signal to be broadened beyond detection, or not to be excited
by the RF pulse. This results in the need to compare signal intensities with a standard in order to
establish the fraction of the aluminium in the sample which is represented by the NMR spectrum.
Signal fractions for anodic alumina films together with signal fractions for crystalline materials
with known electric field gradients are presented. The amount of aluminium signal varies de-
pending on the anodizing conditions and the electrolyte used, which can be related to the film mor-
phology observed by electron microscopy.
t Present address: Dept. of Geology, Stanford University, Stanford, California 94305-2115
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161 I
LOCALIZED PROTON SPECTROSCOPY AND SPECTROSCOPIC IMAGING OF THE HUMAN BRAIN
* Peter Luyten and Jan den Hollander
Philips Medical Systems, PO Box i0.000
Best, The Netherlands
We have developed and optimized a pulse seouence to obtain localized
watersuppressed proton spectra in the human brain. By combining selective
excitations with phase encoding gradients one dimensional spectroscopic imaging
could be performed, resulting in the simultaneous aquisition of watersuppressed
proton spectra from different slices through the human brain. Slice selective
excitation pulses were given in three orthogonal directions. Two directions
restrict the volume of the slices and one direction parallel to the phase encoding
direction suppresses the very intens signals of subcutaneous fat and bone marrow.
These signals may obscure the metabolite resonances with.~n the same chemical shift
range. Volume selection was achieved by stimulated echo's. Watersuppression was
obtained by binomial pulses and selective dephasing pulses. Using this sequence
spectra can be obtained showing well resolved resonances of choline, creatine,
N Acetyl Aspartate and lactate in the submillimolar range. Studies are in progress
to examine cerebral infarcts and brain tumors in patients ...............
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