Orientation and Motion of
Water Molecules in Cordierite:
A Proton Nuclear Magnetic Resonance Study
Douglas G.
Carson, George R. Rossman2,
Robert W Vaughan1
1Division of Chemistry and Chemical Engineering
2
Division of Geological and Planetary Sciences
California Institute of Technoogy
Pasadena, CA 91125
Abstract
Conventional and solid state proton nuclear mag-netic
resonance (NMR) techniques have been used to examine water molecules in
the channels of a single crystal of cordierite, (Mg, Fe)2A14Si5O18,
as a function of temperature, magnetic field, and orientation. Only one
type of water was found rather than water in two distinct rigid
orientations which were indicated by earlier infrared spectral studies.
However, the measured dipolar splittings indicate that this water is in
rapid motion. Shifts in the dipolar doublet due to Fe2+
impurities indicate that the water molecules are not moving among
adjacent channel sites along a channel cavity. A two-site hopping model
is proposed involving the major residence time spent with the
hydrogen-hydrogen vector par-allel to the channels, a minor residence
time spent with the hydrogen-hydrogen vector perpendicular to the
channels, and a short time (<1 µs) in transit. This model fits
both the present NMR data and previously reported infrared absorp-tion
data and is compared to previously reported neutron diffraction data
last updated: 3-Sep-2017