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Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Influence of clay mineral composition on complex permittivity of clays and soils
Heike Kaden
Competence Center for Material Moisture (CMM), Karlsruhe Institute of Technology
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Agenda
• Motivation and objectives
• Permittivity – theory
• Samples and excursus of clay mineralogy
• Summary and outlook
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Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
material permittivity
vacuum 1
air 1.00059
dry soil 3-6
dry clay 4
dry sand 4-6
wet soil 29
wet clay (non-swellable) 27
swellable clays 100 – 250*
wet sands 15-25
water 81
bound water 3.6-3.8
Motivation and objectives
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Permittivity (ε) in high MHz range (GEOPHYSICAL SURVEY SYSTEMS INC.,2001)
(CHEN & OR 2006)* Low MHz range (RAYHATNA & SEN, 1986)
w = f(εr)
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Permittivity of clays and soils
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Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Permittivity – theory
Complex permittivity ε* transmissibility of materials for electrical fields, complex number
ε* = ε’ + jε’’
Relative permittivity εr
polarizability of materials, dimensionless
εr = ε* / ε0
Polarization mechanisms• interfacial polarization• orientation polarization• ionic polarization• electronic polarization (displacement polarization)
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increasing frequency
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Permittivity – theory
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εr’ = real part of relative permittivity (dispersion)
εr’’ = imaginary part of relative permittivity (absorption), dielectric loss
Relative permittivity of water (AGILENT TECHNOLOGIES ,2009)
workingrange
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Permittivity of multi-phase-mixtures
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α = geometry factorRoth et al. 1990: α = 0.46
ε : permittivityv: volumetric weight
aasswwb vbulk water soil air
mixing rules
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Samples and excursus clay mineralogy
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clay minerals
1:1 layer silicates 2:1 layer silicates
JASMUND & LAGALY (1993)
swellable non-swellablenon-swellable• smectites• vermiculites
• talc-pyrophyllite group • illites• micas• chlorites
• kaolinite• serpentine
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Smectites
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AlAlIIIIII
oxygen
hydroxyl groups
water
SiSiIVIV
M+x+y(H2O)n(Al3+, Fe3+
2-y Mg2+, Fe2+y) (Si 4-x Alx)O10(OH)2
montmorillonite, beidellite, nontronite
AlIII for SiIV
MgII for AlIII
FeII/FeIII for MgII; AlIII
EMMERICH et al. (2009) and WOLTERS et al. (2009)
Die Kooperation von Forschungszentrum Karlsruhe GmbH
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Interaction of smectites and water
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JASMUND & LAGALY (1993)
high cation exchange capacity100-120 meq/100 g
high water binding capacity
water adsorption on inner surface and outer surface
high specific surface areaup to 750 m²/g
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Cation Exchange Capacity (CEC)
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sample CEC [meq/100g]
bentonite (EXM1912) 120
bentonite (Volclay) 84
bentonite (Calcigel) 63
illite (Arginotech GI) 25
ceramic kaoline (FW830) 4
limestone 3
finesand (N45) 2
silty quartz-feldspar-mixture (FS700) 2
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Grain size of clays and soils
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sandsandsiltsilt
clayclay
Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Summary and outlook
Dielectric properties of soils can be used for volumetric water content measurements.
Permittivity of bound water (3.6-3.8) is lower than permittivity of free water (≈ 81), which can lead to underestimation of water content in highly swellable clays as they adsorb large amounts of water.
There are still phenomena to be explained: permittivity values of up to 250 in bentonite-water-mixtures
Determination of moisture in soils with high amount of swellable clays requires special calibration of moisture-permittivity-relationship.
.
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Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Thank you for your attention!
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Die Kooperation von Forschungszentrum Karlsruhe GmbH
und Universität Karlsruhe (TH)
Literature
Chen, Y. and Or, D., 2006: Geometrical factors and interfacial processes affecting complex dielectric permittivity of partially saturated porous media. Water Resources Research, 42: 1-9.
Emmerich, K., Wolters, F., Kahr, G., and Lagaly, G., 2009: Clay profiling: The classification of montmorillonites. Clays and Clay Minerals, 57: 104-114.
Jasmund, K. & Lagaly, G., 1993: Tonminerale und Tone. Steinkopff Verlag Darmstadt. 490 pp.
Klein, K. and Wang, Y.-H., 2005: Towards a Better Understanding of the Electro-Magnetic Properties of Soils, IUTAM Symposium on Physicochemical and Electromechanical Interactions in Porous Media, 241-250.
Raythatha, R. and Sen, P. N., 1986: Dielectric properties of clay suspensions in MHz to GHz range. Journal of Colloid and Interface Science, 109: 301-309.
Roth, K., Schulin, R., Flühler, H., and Attinger, W., 1990: Calibration of Time Domain Reflectometry for Water Content Measurement Using a Composite Dielectric Approach. Water Resources Research, 26: 2267-2273.
Wolters, F., Lagaly, G., Kahr, G., Nueesch, R., and Emmerich, K., 2009: A comprehensive characterization of dioctahedral smectites. Clays and Clay Minerals, 57: 115-133.
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