André De Roy

Anionic Clays: Trends in Pillaring Chemistry

Minerals of the anionic clay family are reported by mineralogists since the beginning of this century: (Kurnakov and Chernykh 1926 ; Aminoff and Broome 1930 ; Read and Dixon 1933; Frondel 1941). A great variety of names is used in relation to the composition and the nature of the polytypes of these minerals (hydrotalcite, manasseite, pyroaurite, sjogrenite, stichtite, takovite, honessite, meixnerite ... ) ; Drits et al. 1987 proposed a systematic nomenclature. Anionic clay minerals are relatively rare and are often associated with serpentinites in metamorphic formations . These minerals also occur in saline deposits which shows that high temperature and pressure conditions are not absolutely necessary for their genesis.

Lamellar Double Hydroxides

A general overview on Lamellar Double Hydroxides (LDHs) is given, includind discussions about the structure and preparative methods. A tentative development strategy illustrated by examples is suggested.

Structural results about localisation of tetrahedral oxo-anions intercalated in lamellar double hydroxides

Abstract The structure of two synthetic Lamellar Double Hydroxides belonging to the [Zn-Cr-SO4] system with basal spacings of 8.9A and 11 A, is processed by the Rietveld method on PXRD data. The localization of interlamellar species is studied and the presence of co-intercalated alkaline cations is discussed.

First EXAFS Characterisation of a Grafting Process in Layered Double Hydroxides

Abstract In this work the grafting process occurring during thermal treatments on [Ni-Al] based LDHs intercalated with CrO4 2− or Cr2O7 2− oxoanions is investigated. The irreversible decrease of the basal spacing evidenced by PXRD measurements strongly suggests the occurrence of a grafting process. EXAFS measurements are performed at very low temperature (8K) at the K-edge of the Cr atom of the intercalated anionic species. The radial density patterns clearly show the grafting of CrO4 2− or Cr2O7 2− anions on the brucitic sheets by the appearance of a new feature at about 3.40 A on the compounds calcined at 150°C.