Journal Article

PreJuSER-5532

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png A Fast Field Cycling Nuclear Magnetic Resonance Relaxometry Study of Natural Soils

Pohlmeier, A.FZJ* ; Haber-Pohlmeier, S.FZJ* ; Stapf, S.

2009
SSSA Madison, Wis.

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Please use a persistent id in citations: doi:10.2136/vzj2008.0030

Abstract: This study used nuclear magnetic resonance (NMR) relaxometry at different Larmor frequencies to investigate water dynamics in the pore space of natural porous media. Spin-lattice NMR relaxation times (T-1) were determined in purified fine sand and two natural soils, Kaldenkirchen sandy loam and Merzenhausen silt loam, by means of fast field This technique investigates relaxation processes as a function of the Larmor frequency. in the 0.005 and 20 MHz, yielding so-called relaxation dispersion curves (1/T-1 vs. log.). The data were further by means of inverse Laplace transformation to calculate the T-1 relaxation time distribution functions. Only sand was characterized by monomodal distribution with T-1 of about 1 s at 20 MHz, whereas the natural soil showed multi modal distribution functions in the range between 2 and 70 ms. With decreasing Larmor frequency, all distribution functions kept their shapes but were shifted to faster relaxation times. The corresponding relaxation dispersion curves indicate predominance of two-dimensional diffusion of water in the soils, whereas in the sand, diffusion behaved like unrestricted three-dimensional diffusion. In terms of the Brownstein-Tarr model, in the T-1 relaxation times with increasing silt and clay content can be explained by an increase of the volume ratios (S/V) of these porous media, i.e., by a decrease in the pore sizes. Finally, distribution functions of size parameter V/S were obtained from the spin-lattice relaxation time distributions by normalizing on the specific surface area. They ranged from submicrometers in the Merzenhausen soil to micrometers and submillimeters in soil and fine sand, respectively.

Keyword(s): J

Note: The authors thank the German research fund (DFG) for financial support (Sta 511/4- 1, PO 746/2-1, and Transregio/SFB32), F. Pauly and U. Lesten (ZAT, Research Center Julich) for the recording CT images, C. Walraf (ICG-4, Research Center Julich) for the BET measurements, and J. Koestel and A.-P. Schmidt-Eisenlohr (ICG4, Research Center Julich) 360 for the water retention curves of the soils.

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Research Program(s):

1. Terrestrische Umwelt (P24)

Appears in the scientific report 2009

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