Abstract
The thermal decomposition and structural reconstruction of Mg-Fe-based
hydrotalcites (FIT) have been studied through thermogravimetric
analyses, X-ray powder diffraction (XRD), Fourier transform infrared
spectroscopy and Mossbauer spectroscopy. The destruction of the layered
structure took place at about 300degreesC. The broad peaks observed in
the X-ray diffractograms suggest that the resultant oxides constitute a
solid solution. For samples treated at temperatures higher than
500degreesC, the formation of the MgO and MgFe2O4 spinel phases is
observed. Fe-57 Mossbauer spectroscopy was employed to monitor the Fe
chemical environment for the samples annealed at different temperatures
(100-900degreesC). In situ XRD experiments revealed that the HTs start
an interlayer contraction at about 180degreesC. This phenomenon is
identified as being due to a grafting process for which the
interlamellar anions attach to the layers through a covalent bond. The
reconstruction of the HTs was also investigated and its efficiency
depends on the thermal annealing temperature and the Mg/Fe ratio. The
structure of the reconstructed samples was found to be exactly the same
as the parent structure. (C) 2004 Elsevier Inc. All rights reserved.
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