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Thermal evolution of Mg-Al-CO3 hydrotalcites

Published online by Cambridge University Press:  09 July 2018

Ts. Stanimirova ,
N. Piperov ,
N. Petrova  and
G. Kirov
Ts. Stanimirova
Affiliation:
Department of Mineralogy, Sofia University, 15 Tzar Osvoboditel, Sofia 1000
N. Piperov
Affiliation:
Institute of Inorganic Chemistry, Bulgarian Academy of Sciences, Academic G. Bonchev Str. bl. 11, Sofia 1113
N. Petrova*
Affiliation:
Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Academic G. Bonchev Str. bl. 107, Sofia 1113, Bulgaria
G. Kirov
Affiliation:
Department of Mineralogy, Sofia University, 15 Tzar Osvoboditel, Sofia 1000
*
*E-mail: [email protected]
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Abstract

The thermal decomposition of hydrotalcite (HT), with chemical composition Mg1-xAlx(OH)2(CO3)x/2.(1-3x/2)H2O, (0.20 < x ≤ 0.33), is a complex sequence of dehydration, dehydroxylation and decarbonization and leads to the formation of a series of metaphases: HT-D (dehydrated HT), HT-B (partially dehydroxylated HT) and MO (mixed oxides with periclase-like structure). The evolution of water and CO2 in natural and synthetic hydrotalcites (a Mg/Al ratio between 2:1and 3.7:1), heated to 800°C, was investigated by differential thermal analysis, thermogravimetry and evolved gas analysis. At least six endothermic and two exothermic effects were established by computer-aided resolving of the curves. The formation of each HT metaphase was related to the release of a discrete number of water molecules depending on the Al content in the samples and each appeared as a corresponding endothermic peak in the DTA curves. The exothermic processes associated with the crystallization of HT-B and MO metaphases were specified by decomposition of DTA curves. The evolution of CO2 during the thermal decomposition of the carbonate groups was found to be different for the samples studied. The preservation of CO3 even at high temperatures was established for synthetic samples with a high Al content. The release of volatile H2O and CO2 (which comprise ~40% of the sample mass) provokes fine cracking both along and across the layers.

Keywords

hydrotalciteDTATGevolving gas analysis
Type
Research Article
Information
Clay Minerals , Volume 39 , Issue 2 , June 2004 , pp. 177 - 191
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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