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Folding in Sepiolite Crystals

Published online by Cambridge University Press:  01 July 2024

C. Serna ,
J. L. Ahlrichs  and
J. M. Serratosa
C. Serna
Affiliation:
Instituto de Edafologia y Biologia Vegetal, C.S.I.C. Madrid, Spain and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA
J. L. Ahlrichs
Affiliation:
Instituto de Edafologia y Biologia Vegetal, C.S.I.C. Madrid, Spain and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA
J. M. Serratosa
Affiliation:
Instituto de Edafologia y Biologia Vegetal, C.S.I.C. Madrid, Spain and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA
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Abstract

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Fibrous sepiolite crystals derive much of their commercial value from their molecular size channels and grooves. The crystals fold upon drying and these channels and grooves are lost. A model for the folding and unfolding of the crystals is presented. Extensive i.r., X-ray and thermogravimetric evidence shows that folding occurs when approximately half of the water of hydration, which is coordinated to the edge magnesium atoms inside of the channels, is removed. This occurs near 175°C under vacuum and near 300°C in air. When the crystals fold, all remaining water molecules enter a new environment, that of the hexagonal holes of the neighboring silica surface. A true anhydride is produced at about 500°C under vacuum when the final water is lost, but this final dehydration produces no important structural change. Rehydration of the anhydride to the normal hydrated sepiolite does not occur at room temperatures in 100% r.h. However, above, 60°C rehydration does occur.

Type
Research Article
Information
Clays and Clay Minerals , Volume 23 , Issue 6 , December 1975 , pp. 452 - 457
Copyright
Copyright © 1975, The Clay Minerals Society

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