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United States Department of Agriculture

Agricultural Research Service

Title: Electrical Conductivity Spectra of Smectites As Influenced by Saturating Cation and Humidity

item Logsdon, Sally
item Laird, David

Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 24, 2004
Publication Date: June 24, 2004
Citation: Logsdon, S.D., Laird, D.A. 2004. Electrical conductivity spectra of smectites as influenced by saturating cation and humidity [abstract]. Program and Abstracts of the Clay Minerals Society. p. 127.

Technical Abstract: Electrical conductivity is an important soil property related to salinity, and is often used for delineating other soil properties. The purpose of this study was to examine the influence of smectite properties on the complex electrical conductivity spectra of hydrated smectites. Four reference smectites were saturated with calcium (Ca), magnesium (Mg), sodium (Na), or potassium (K) and equilibrated at four relative humidities (RH) ranging from 56 to 99%. X-ray diffraction (XRD) was used to determine fractions of the various smectite layer hydrates (0 to 4 layers of interlayer water molecules) in each sample. A vector network analyzer was used to determine the real component of the complex electrical conductivity spectra for frequencies ranging from 300 kHz to 3 GHz. Values of the direct current (d.c.) electrical conductivity, the frequency where the slope changes in the spectra, and the slope at the high frequency end of the spectra were determined by fitting. Both d.c. conductivity and frequency of the slope change increased with the total amount of water, the amount of interlayer water, and for saturating cations in the following order; K<Mg <Ca<Na. The opposite trends were observed for the high frequency slope. Values of these parameters were influenced by the type of smectite, but the trends were not consistent for the effect of layer charge. The results indicate that interlayer water in smectites contributes to the electrical conductivity of hydrated smectites, and that polarization of water by local electrical fields has a substantial influence on the complex electrical conductivity spectra of smectites. The accuracy of salinity estimates for soils and sediments that are based on conductivity measurements may be adversely affected unless the effects of hydrated clays on electrical conductivity are considered.

Last Modified: 4/17/2014
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