Paramagnetic Fe3+: A Sensitive Probe for Disorder in Kaolinite

J.-M. Gaite1, P. Ermakoff1, Th. Allard2 and J.-P. Muller2, 3
1 Centre de Recherche sur la Matière Divisée, Université d'Orléans-CNRS, Rue de Chartres-BP 6759 - 45067 Orleans Cedex 2, France
2 Laboratoire de Minéralogie-Cristallographie, Université de Paris VI et VII, 4, Place Jussieu - 75252 Paris Cedex 5, France
3 ORSTOM, Département T.O.A. UR12, Géosciences de l'Environnement Tropical, 32 Avenue Henri Varagnat - 93143 Bondy Cedex, France

Abstract: The Fe3+ substituted for Al3+ at the 2 octahedral positions is one of the most common impurities in the kaolinite structure detected by electron paramagnetic resonance (EPR). Evidence has been provided for a relationship between the shape of EPR spectra for structural Fe and the structural disorder in kaolinite. It is proposed that the structural Fe be used as a sensitive probe for the degree of disorder of natural kaolinites. With this aim in view, an EPR disorder index (E) is defined from the width of selected EPR lines. Using reference kaolinites, it is shown that this index can account as well for long-range disorder detected by means of X-ray diffraction (XRD) as for local perturbations such as radiation-induced defects (RID). It is shown that the disorder observed through EPR has some points in common with the XRD-measured one. The influence on E of the presence of RID is shown by the study of artificially and naturally irradiated kaolinites.

Key Words: Disorder • Electron Paramagnetic Resonance (EPR) • Fe3+ • Irradiation • Kaolinite • Point Defect

Clays and Clay Minerals; August 1997 v. 45; no. 4; p. 496-505; DOI: 10.1346/CCMN.1997.0450402
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)