Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Nakashima, Y. Search for Related Content GeoRef GeoRef Citation

DIFFUSION OF H₂O IN SMECTITE GELS: OBSTRUCTION EFFECTS OF BOUND H₂O LAYERS

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 address of corresponding author: nakashima.yoshito{at}aist.go.jp

In water-rich smectite gels, bound or less mobile H₂O layers exist near negatively-charged clay platelets. These bound H₂O layers are obstacles to the diffusion of unbound H₂O molecules in the pore-space, and therefore reduce the H₂O self-diffusion coefficient, D, in the gel system as a whole. In this study, the self-diffusion coefficients of H₂O molecules in water-rich gels of Na-rich smectites (montmorillonite, stevensite and hectorite) were measured by pulsed-gradient spin-echo proton nuclear magnetic resonance (NMR) to evaluate the effects of obstruction on D. The NMR results were interpreted using random-walk computer simulations which show that unbound H₂O diffuses in the gels while avoiding randomly-placed obstacles (clay platelets sandwiched in immobilized bound H₂O layers). A ratio (volume of the clay platelets and immobilized H₂O layers)/(volume of clay platelets) was estimated for each water-rich gel. The results showed that the ratio was 8.92, 16.9, 3.32, 3.73 and 3.92 for Wyoming montmorillonite (5.74 wt.% clay), Tsukinuno montmorillonite (3.73 wt.% clay), synthetic stevensite (8.97 wt.% clay), and two synthetic hectorite samples (11.0 wt.% clay), respectively. The ratios suggest that the thickness of the immobilized H₂O layers in the gels is 4.0, 8.0, 1.2, 1.4 and 1.5 nm, respectively, assuming that each clay particle in the gels consists of a single 1 nm-thick platelet. The present study confirmed that the obstruction effects of immobilized H₂O layers near the clay surfaces are important in restricting the self-diffusion of unbound H₂O in water-rich smectite gels.

Key Words: Hectorite • Montmorillonite • Porous Media • Random Walk • Stevensite • Water

This article has been cited by other articles:

				Y. NAKASHIMA H2O self-diffusion coefficient of water-rich MX-80 bentonite gels Clay Minerals, June 1, 2006; 41(2): 659 - 668. [Abstract] [Full Text] [PDF]