Structural Organization in Amorphous Silico-Aluminas

P. Cloos*, A. J. LÉonard*, J. P. Moreau, A. Herbillon and J. J. Fripiat#x2021;
Laboratoire de Physico-Chimie Minérale, Institut des Sciences de la Terre, 42, de Croylaan, Heverlee-Louvain, Belgium
* The University of Louvain.
Research Associated to “Ciments Lafarge”, France.
The University of Louvain and M.R.A.C. (Tervuren).

Abstract: A structure model for amorphous hydrated or dehydrated silico-aluminas with composition varying between 0 < Al: Al+Si < 1 is presented. A central core made from a tetrahedral network in which silicon is partially substituted by aluminium carries a net negative electrical charge. This charge is balanced by more or less polymerized hydroxyaluminium cations forming a coating around the core.

As Al: Al+Si increases, the number of substitutions in the core increases as well as the complexity of the hydroxyaluminium cations in the coating.

For Al: Al+Si ≳ 0·8, a demixing is observed, leading to the formation of a crystalline pseudoboehmite and bayerite.

Upon heating, the coating as well as the demixed phases are transformed into a spinel structure containing tetrahedral aluminium, while the core structure remains unaffected.

This model could explain the solubility features, the phosphate reaction and the catalytic properties of amorphous silico-aluminas.

Clays and Clay Minerals; December 1969 v. 17; no. 5; p. 279-287; DOI: 10.1346/CCMN.1969.0170505
© 1969, The Clay Minerals Society
Clay Minerals Society (www.clays.org)