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United States Department of Agriculture

Agricultural Research Service

Title: Dielectric Spectra of Bound Water in Hydrated Smectite

Authors
item Logsdon, Sally
item Laird, David

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2001
Publication Date: N/A

Technical Abstract: Typically two or three layers of water exist in the interlayer space of Ca-smectite. Cations associated with the external surface of smectite quasi-crystals adsorb additional water, but typically less than 20% of total water. Because of the discrete number of water layers at moderate hydration levels, a continuum description is inappropriate. The objective of this study is to utilize dielectric spectra to elucidate properties of various forms of bound water in Ca-smectite. The sample was Ca-saturated and prepared as oriented films. The loosely-stacked oriented films were equilibrated above saturated salt solutions to control relative humidity, then compressed with a hydraulic press, and finally packed into coaxial cells with the preferred orientation of the clay layers parallel with the center wire. The procedure maximizes parallel orientation of the smectite layers and minimizes both the amount of quasi-crystal external surfaces and air filled void spaces in the studied samples. A time domain system was used to determine the d.c. electrical conductivity, and a vector network analyzer was used to indirectly determine the complex dielectric spectra. The gravimetric water contents ranged from 0.218 to 0.267 g/g for relative humidities (RH) ranging from 54 to 98%, and electrical conductivity (EC) ranged from 0.003 to 0.054 S/m. Three distinct dielectric relaxation frequencies, 450 kHz, 1.26 MHz, and 5.4 MHz, were apparent for the smectite at 54% RH. At 98% RH, less distinct dielectric relaxations were evident at frequencies around 260 kHz, 6.8 MHz, and 10.5 MHz. Both the real and imaginary component of the dielectric were about an order of magnitude smaller at 54% RH than at 98% RH.

Last Modified: 12/25/2014
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