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Evaluation of the energy barrier for dehydration of homoionic (Li, Na, Cs, Mg, Ca, Ba, Alx(OH)yz+ and La)-montmorillonite by a differentiation method

Published online by Cambridge University Press:  09 July 2018

M. Zabat  and
H. Van Damme
M. Zabat*
Affiliation:
Centre de Recherche sur la Matière Divisée, CNRS et Université d'Orléans 45071 Orléans Cedex 02, France
H. Van Damme
Affiliation:
Centre de Recherche sur la Matière Divisée, CNRS et Université d'Orléans 45071 Orléans Cedex 02, France
*
*E-mail: [email protected]
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Abstract

The thermal energy necessary for the removal of molecular water from Li+-, Na+-, Cs+-, Mg2+-, Ca2+-, Ba2+-, Alx(OH)yz+- and La3+-homoionic montmorillonite powders was determined by thermogravimetric analysis under atmospheric pressure. The weight loss curves and their derivatives exhibit one or several features related to the various populations of water molecules. The activation energy for water removal, which is the sum of the adsorption energy and the activation energy for diffusion, was calculated in each case using a simple first-order differentiation method. The results allow the physisorbed water and the water coordinated to the cations to be clearly separated. For the later population and with the exception of the Na-clay, a good correlation was found between the temperatures and activation energies for water removal and the polarizing power of the cations. Comparison with the results of mechanical tests performed on similar samples suggests that the creep of smectite clays is not controlled by mobility of the individual water molecules but by the mobility of the interlayer cations surrounded by their hydration shell.

Keywords

dehydrationhomoionic montmorilloniteTG
Type
Research Article
Information
Clay Minerals , Volume 35 , Issue 2 , April 2000 , pp. 357 - 363
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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