Die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) Influence of...

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



Agenda

• Motivation and objectives

• Permittivity – theory

• Samples and excursus of clay mineralogy

• Summary and outlook

2



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

3

Permittivity (ε) in high MHz range (GEOPHYSICAL SURVEY SYSTEMS INC.,2001)

(CHEN & OR 2006)* Low MHz range (RAYHATNA & SEN, 1986)

w = f(εr)



Permittivity of clays and soils

4



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)

5

increasing frequency



Permittivity – theory

6

εr’ = real part of relative permittivity (dispersion)

εr’’ = imaginary part of relative permittivity (absorption), dielectric loss

Relative permittivity of water (AGILENT TECHNOLOGIES ,2009)

workingrange



Permittivity of multi-phase-mixtures

7

α = geometry factorRoth et al. 1990: α = 0.46

ε : permittivityv: volumetric weight

aasswwb vbulk water soil air

mixing rules



Samples and excursus clay mineralogy

8

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



Smectites

9

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)



Interaction of smectites and water

10

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



Cation Exchange Capacity (CEC)

11

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



Grain size of clays and soils

12

sandsandsiltsilt

clayclay



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.

.

13



Thank you for your attention!

14



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.

15

Die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) Influence of...

Documents

Transcript of Die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) Influence of...