CHARACTERIZATION OF LAYERED DOUBLE HYDROXIDE Mg-Al-CO3 PREPARED BY RE-HYDRATION OF Mg-Al MIXED OXIDE

Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy (SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize the Mg-Al-CO3 LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxide. The mixed oxide was obtained after heating of the intial Mg-Al-CO3 LDH compound in air at 500 degrees C for 2 h. The samples were re-hydrated by two ways namely in a distilled water at 20 degrees C for 5 days or by moistening at 60 degrees C in air with RH 80% during 10 days, respectively. The characteristics of the re-hydrated LDH samples were compared with the initial Mg-Al-CO3 compound. The influence of the re-hydration conditions on the microstructure, surface morphology and thermal stability of the regenerated Mg-Al-CO3 LDHs samples is discussed. It was demonstrated that the re-generation of the layered structure by the hydration of the mixed oxide in water or in air, respectively, took place via the dissolution-crystallization mechanism and that the layered double hydroxide with different surface area and thermal behavior were formed after re-hydration in water or humid air, respectively. The emanation thermal analysis revealed differences in the microstructure changes of the re-hydrated sample during heating. XRD patterns and results of the methods used supported the ETA results.