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Kinetics of the Thermal Dehydration of Hydrous Silicates

Published online by Cambridge University Press:  01 January 2024

J. Birch Holt ,
Ivan B. Cutler  and
Milton E. Wadsworth
J. Birch Holt
Affiliation:
Lawrence Radiation Laboratory, Livermore, California, USA
Ivan B. Cutler
Affiliation:
University of Utah, Salt Lake City, Utah, USA
Milton E. Wadsworth
Affiliation:
University of Utah, Salt Lake City, Utah, USA
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Abstract

Generally, the rate of dehydroxylation of clay minerals may be controlled by reaction at the interface between the decomposed and undecomposed mineral, diffusion through the decomposed phase and/or nucleation of the decomposed phase. Only in rare instances are mineral decomposition reactions homogenous. Some examples are presented to illustrate these principles.

For macrocrystalline muscovite the initial sample weight rather than the external surface area was found to be a parameter of the rate of weight loss. Upon grinding the muscovite to particles smaller than — 65 mesh, an internal surface area factor strongly influenced the rate. This surface area was related to dislocations shown to be present in muscovite.

A rate equation is presented that explains the observed weight loss versus logarithm of time dependence based on a model involving a systematic relief of strain during dehydration.

The rate equation for pyrophyllite was exactly the same as that formulated for muscovite. As with muscovite there was a change in free energy of activation throughout the dehydration process. In contradiction to muscovite, the contribution to the free energy of activation was at least partly enthalpy while with muscovite it was an entropy of activation contribution.

The dehydration of kaolinite was carried out in vacuum. At pressures of one micron the reaction was found to be diffusion controlled with hydroxyl ions as the likely diffusing species.

Type
Symposium on High Temperature Transformations
Information
Clays and Clay Minerals (National Conference on Clays and Clay Minerals) , Volume 12 , February 1963 , pp. 55 - 67
Copyright
Copyright © The Clay Minerals Society 1963

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