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KMID : 1059519950390080627
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Journal of the Korean Chemical Society
1995 Volume.39 No. 8 p.627 ~ p.634
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Characterization of Layered Double Hydroxides(Mg-Al-CO3 systems) and Rehydration Reaction of Their Calcined Products in Aqueous Chromate Solution
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Rhee Seog-Woo
Kang Mun-Ja
Moon Hi-Chung
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Abstract
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Layered double hydroxides (Mg-Al-CO3 systems, LDH), which are hydrotalcite-like anionic clay minerals, having different Mg2+ to Al3+ ratio were synthesized by coprecipitation method. The subsequent products were characterized by the following methods; elemental analysis, X-ray powder diffraction, thermal analysis (DSC and TGA), FT-IR and 27Al-MAS NMR. X-ray powder patterns showed that the products formed were layered structure materials. Two heat absorption peaks were observed around 20 ∼280℃ (surface water and interlayer water) and 280∼500℃ (water from lattice hydroxide and carbon dioxide from interlayer carbonate) in DSC diagrams, and they were quantitatively analyzed by TGA diagrams (in case LDH4 16.2% and 28.6% respectively). FT-IR spectra indicate that the interlayer carbonate ions occupied symmetrical sites Between two adjacent layers in a parallel direction. 27Al-MAS NMR spectra show only single resonance (8.6 ppm) of the octahedrally coordinated aluminum similar magnesium. When LDH4 was calcined at 560℃ for 3 hours in air, its layered structure was destroyed giving a mixed metal oxide. However it readily became rehydrated in aqueous chromate solution to its original structure.
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