Clays and Clay Minerals, Vol. 56, No. 2, 155–174, 2008.
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Authors
S´rodon´, Jan
Mccarty, Douglas K.
Issue Date
2008
Type
Article
Language
Keywords
Periodicals , Geology , CEC , Charge Density , EGME , Layer Charge , Smectite , Specific Surface Area , Water Sorption
Alternative Title
Surface Area And Layer Charge Of Smectite From Cec And Egme/h2o-retention Measurements.
Abstract
The total specific surface area (TSSA) and smectitic layer charge (Qs) calculated from the structural formulae and unit-cell dimensions of 12 pure smectite samples were used as a reference in the design and evaluation of TSSA and Qs measurement techniques based on cation exchange capacity (CEC), H2O retention at 47% RH, and ethylene glycol monoethyl ether (EGME) retention. A thermogravimetric analysis-mass spectrometry (TGA-MS) technique was used to study the release of H2O from smectite on heating, and to introduce a correction for H2O remaining in the smectite after heating to110ºC, because the sample weight at this temperature has been used routinely as a reference in CEC and EGME sorption measurements. A temperature of 200ºC was found to be the optimum reference for such measurements. A good agreement between Qs from the structural formula and from CEC was obtained when this correction was applied. The TSSA of smectite was measured with similar accuracy (mean error of @5-7%) by three techniques: (1) using mean H2O coverage; (2) using mean EGME coverage; and (3) using a combination of H2O coverage and CEC. A reduction of the mean error from 5-7% to4% can be obtained by averaging these measurements, and a further reduction to 3% by introducing corrections for the dependence of H2O and EGME coverage on layer charge. The study demonstrates that Ca2+-smectite samples at 47% RH have H2O contents corresponding to 88-107% of the theoretical mass of a monolayer and offers an explanation of this variation.
Description
Clays and Clay Minerals, Vol. 56, No. 2, 155–174, 2008. Surface Area And Layer Charge Of Smectite From Cec And Egme/h2o-retention Measurements. Jan S´rodon´; Douglas K. Mccarty. DOI: 10.1346/CCMN.2008.0560203. Copyright © 2008, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 56, No. 2, 155–174, 2008.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society