EPR SIGNAL SIMULATIONS OF NATURAL, HYDRATED AND DEHYDRATED KAOLINITE: EVOLUTION

OF THE LOCAL ORDER-DISORDER

S. Jemai1*, J. M. Gaite2, A. Ben Haj Amara1

1 Laboratoire de Physique des Matériaux. Faculté des Sciences de Bizerte 7021 Zarzouna, Tunisie

2 ISTO/CNRS, 45067 Orléans Cedex 2- France

* Corresponding author. E-mail : Samira.jemai@issatm.rnu.tn

Received : 09 May 2002; revised version accepted : 09 August 2002

Abstract 

Some kaolinite hydrates were synthesized using DMSO, NH4F and water washings. They are characterised by 8.4 and 10Å basal distances and different stabilities.

In order to evaluate the disorder in the layer (atomic bonds, distortions,…) we chose the electron paramagnetic resonance (EPR) which is a local technique. The method used to characterize the studied samples is based on the comparison between experimental signals and calculated EPR profiles.

Experimentally, we find that the EPR centres (Fe3+, Si-O-, Al-O--Al) don’t have the same sensitivity to the hydration phenomenon. In fact, the EPR signals of Fe3+ and Al-O--Al show some modifications after the hydration of kaolinite which is not the case of the Si-O- signal. These changes can’t be removed by dehydration.

Quantitative studies were made on the natural kaolinite, the 8.4Å hydrate and the dehydrated compound using the Al-O--Al octahedral centres. The obtained results let us to explain the EPR signal changes by the modifications of the line width and the superhyperfin tensor A which indicates the apparition of some octahedron distortions.

Keywords : Kaolinite; Hydrate; EPR; Simulation;

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