• journal_title：Clay Minerals
• Contributor：Y. NAKASHIMA
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2002-
• Format：text/html
• Language：en
• Identifier：10.1180/0009855023710019
• journal_abbrev：Clay Minerals
• issn：0009-8558
• volume：37
• issue：1
• firstpage：83
• section：Articles

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 w is 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 w for 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 mesh-size or characteristic interval of the crosslinkage.