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Self- diffusion of H2O in stevensite gel: effects of temperature and clay fraction

Published online by Cambridge University Press:  09 July 2018

Y. Nakashima
Y. Nakashima*
Affiliation:
Exploration Geophysics Research Group, National Institute of Advanced Industrial Science and Technology, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan
*
*E-mail: yoshito@aist.go.jp
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Abstract

Self-diffusion coefficients of water molecules (1H2O) in Na-stevensite gel were measured by pulsed-gradient spin-echo (PGSE) proton nuclear magnetic resonance (NMR). The effects of clay fraction (0.00 37.7 wt.%) and temperature (20.0 60.3°C) were studied. The results show: (1) phenomenologically, the H2O self-diffusivity in the clay gel, D, is expressed by D/D0 = exp( 0.0198w) where D0 is the H2O self-diffusivity in bulk water of the temperature and wis the clay weight fraction (wt.%). (2) The activation energy of the diffusivity in the stevensite gel is nearly equal to that in bulk water. Thus, the normalized diffusivity, D/D0, obeys a temperature-independent master curve. (3) The exponential dependence of D/D0 on wfor w <25 wt.% (≈ 12 vol.%) can be explained by a random walk model, in which unbound H2O molecules diffuse in the geometrically tortuous pore structure of randomly scattered clay mineral grains. (4) The measured diffusivity can also be explained by a model of unbound H2O diffusing in a polymer network with a specific meshsize or characteristic interval of the crosslinkage.

Keywords

clay gel structureNMRporous mediarandom walkwater molecule
Type
Research Article
Information
Clay Minerals , Volume 37 , Issue 1 , March 2002 , pp. 83 - 91
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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