Surface Properties of Alumino-Silicates

J. J. Fripiat
The University of Louvain, Belgium

Abstract: As an approach to reviewing the surface properties of alumino-silicates, this paper considers the relationships between constitution hydroxyls, surface hydroxyls, chemisorbed and physically adsorbed water molecules and exchangeable cations. One of the main characteristics of clay minerals is, indeed, the development of hydrated high surface area, electrically charged. For this purpose the surface topography, the origin of the electrical charge, and the properties of water molecules held by Van der Waals, or stronger forces are successively studied. Chemisorbed water molecules appear to have a higher than usual degree of dissociation; this phenomenon exerts a deep influence on surface properties such as surface electrical conductivity, chemisorption of ammonia and amines, and their transformation.

When surfaces are thoroughly dehydrated, constitution protons are probably delocalized in the oxygen framework and this delocalization process probably precedes dehydroxylation.

Dehydroxylation results in a partial or a total transformation of octahedral coordinated aluminum into four-fold coordinated atoms. Stresses arising from sharing adjacent octahedral edges are probably at the origin of the Lewis catalytically active sites.

The research reports reviewed are mainly those issued from the author's laboratories, or by his correspondents.

Clays and Clay Minerals; May 1963 v. 12; no. 1; p. 327-358; DOI: 10.1346/CCMN.1963.0120133
© 1963, The Clay Minerals Society
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