HR: 1330h
AN: T42A-0266    [PDF]
TI: Reduction of ionic diffusivity in nanopore water of geomaterials
AU: * Hirono, T
EM: hirono@jamstec.go.jp
AF: Japan Marine Science and Technology Center, Natsushima 2-15, Yokosuka, 237-0061 Japan
AU: Nakashima, S
EM: satoru@geo.titech.ac.jp
AF: Tokyo Institute of Technology, Ookayama 2-12-1, Tokyo, 152-8551 Japan
AU: Spiers, C J
EM: cspiers@geo.uu.nl
AF: Utrecht University, Budapestlaan 4,E^ PO Box 80.02, Utrecht, 3508 TA Netherlands
AB: Recent molecular dynamics simulations and spectroscopic approaches indicated that water molecules confined in nanometre scale has a constrained structure with shorter hydrogen bond distances. In order to verify a hypothesis that ionic diffusivity in rocks should be affected by the constrained molecule structure of water in nanopore, we measured the effective diffusion coefficients of iodine ion in undeformed rocks by through-diffusion experiments. We also studied the quantitative relationship between the diffusion coefficients and the pore structures. Most of effective diffusion coefficients (De) for rocks can be explained by the power law with effective porosity (p), while De values for the sample involving abundant nanopores were much lower than this relation. These could be resulted from that De depends not only on porosity and tortuosity (t) but also on inonic diffusion coefficient in nanopore water (Dn). By simultaneous equation of Dn and t with known De and porosity in two nanopore-type rocks, Dn and t can be deduced independently, leading the equation (De = 9.0 x $10^{-10}$ x p$^3$ ). This means that Dn is 9.0 x $10^[-10]$ m$4^{24}$/s. This Dn values is about two-times lower than the diffusivity in free pure water. This result can be applied for hydraulics, structural geology and new discipline of nano technology.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
SC: Tectonophysics [T]
MN: 2003 Fall Meeting