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 Ás) 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