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In situ transformation of amorphous gels into spherical aggregates of kaolinite: A HRTEM study

Published online by Cambridge University Press:  09 July 2018

F. J. Huertas ,
S. Fiore  and
J. Linares
F. J. Huertas*
Affiliation:
Department of Earth Sciences, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
S. Fiore
Affiliation:
Laboratory of Geochemistry and Environmental Mineralogy, Istituto di Metodologie per l'Analisi Ambientale, CNR, 85050 Tito Scalo (PZ), Italy
J. Linares
Affiliation:
Department of Earth Sciences, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
*
*E-mail: javier.huertas@eez.csic.es
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Abstract

Initial stages of the gel-to-kaolinite transformation were studied using HRTEM. Spherical aggregates of kaolinite crystals were produced during the synthesis of kaolinite by hydrothermal treatment of Si-Al amorphous gels. Prior to sphere formation, gels transform into pseudospherical domains that have a Si/Al ratio of one and display no SAED pattern. The spherical particles consist of radially arranged sectors of stacks of planar crystallites. Crystals display nonbasal spacings of 4.5, 4.2 and 3.8 Å and a basal spacing of 7.1 Å , the c* axis following the radius of the sphere.

Interpretation of the 3D nanostructure of the spheres is difficult. The c* axis exhibits a radial disposition, but the relative orientation of the a* and b* axes in neighbouring crystallites may produce bent layers or incoherent contacts. In addition, curved layers with a d spacing of 7.4 Å may be attributed to halloysite layers collapsed under microscopy conditions. The disappearance of the spheres during the hydrothermal treatment is probably due to preferential dissolution of either highstress areas near bent layers or non-crystalline material filling crystal boundaries. Dissolution leads to sphere disaggregation and allows the component columnar crystals to continue to grow. Observations of the gel matrix suggest that under our experimental conditions kaolinite crystallizes via an in situ transformation of the gel.

Keywords

kaoliniteTEMspherical aggregatessynthesis
Type
Research Article
Information
Clay Minerals , Volume 39 , Issue 4 , December 2004 , pp. 423 - 431
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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