th  - 1988 - 51st ENC Conference

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I00 I NOVEL RESONATOR DESIGNS, E. Marshall, J.J. Listinsky, R.G. Bryant,
J.P. Hornak, University of Rochester, Rochester, NY 14642 and Rochester Institute of
Technology, Rochester, NY 14623
Certain flat sample geometries and anatomies are not conveniently studied by NMR in a
coil of cylindrical symmetry due to poor filling factor or on a surface coil due to signal roll-off. A
single turn solenoid is a high efficiency transmit and receive coil with a nearly homogeneous RF
magnetic field and sensitivity which may be used for NMR imaging and spectroscopy. We have
designed a single turn solenoid with rectangular symmetry called a ribbonator. The LC circuit of
the ribbonator is formed from a sheet of copper wrapped around a rectangular form. A gap
between the two edges of the sheet is bridged by the capacitive elements of the resultant LC
circuit. Ribbonators retain the favorable properties of a conventional cylindrical STS such as a
high Q and nearly uniform excitation and receive fields. As a result the ribbonator efficiently
produces MR signals from fiat objects placed within its volume. Holes may be cut in the side of
the inductor to allow easier insertion of samples and do not significantly perturb its properties.
The resonance equation for this rectangular parallelopiped shaped resonator will be discussed.
Contour maps of the RF magnetic field along with images of the hand and wrist obtained from a
ribbonator will be presented.
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THE USE OF VARIABLE ANGLE SAMPLE SPINNING TO ASSESS AROMATIC CLUSTER
SIZE IN COALS, COAL CHARS AND CARBONACEOUS MATERIALS
Mark S. Solum °, Naresh K. Sethi, Julio C. FaceUi, Warner R. Woolfenden,
Ronald J. Pugmire and David M. Grant
Deparunents of Fuels Engineering and Chemistry, University of Utah,
Salt Lake City, Utah 84112
Variable angle sample spinning and powder pattern lineshape analysis techniques have been
employed to study the 13C shielding tensov~ in bituminous coals, anthracites, inertinite macerals, and coal
cha~. The shielding tensors have been analyzed as a superposition of different bands due to benzene-
like, condensed (bridgehead and inner) and substituted carbons. A comparison of experimental data and
theoretical calculations on model compounds containing 1-4 aromatic rings plus circumcoronene (C54HIs)
support the interpretation of the shielding tensor data observed in coals and coal derived materials.
Determination of the ratio of non-protonated to protonated aromatic carbons obtained on the coals,
macerals, and chats by spectroscopic analysis are in good agreement with elemental analysis and previous
dipoar dephasing NMR experiments. The method therefore constitutes a valuable way to analyze the
strucnue of high rank coals and coal derived carbonaceous residues. The mole fraction of condensed
inner ring carbons obtained by this technique is used to estimate the average cluster size in these
polycondensed axomalic hydrocarbon materials. These data along with results from dipolar dephasing
techniques on coals ate then used as input parameters in coal devolatization modeling.
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