Reversible thermal behavior of the layered double hydroxide of Mg with Al: mechanistic studies

Autor:	G. D. Nataraja, P. Vishnu Kamath, Michael Rajamathi, Sharath Ananthamurthy
Rok vydání:	2000
Předmět:	chemistry.chemical_compound Reaction mechanism Aqueous solution chemistry Hydrotalcite Phase (matter) Inorganic chemistry Materials Chemistry Oxide Hydroxide General Chemistry Chemical decomposition Reversible reaction
Zdroj:	Journal of Materials Chemistry. 10:2754-2753
ISSN:	1364-5501 0959-9428
DOI:	10.1039/b006610i
Popis:	The layered double hydroxide (LDH) of Mg with Al decomposes at 450°C to yield a mixed metal oxide. The oxide reconstructs back to the parent LDH either on cooling in air or soaking in water. This reversible thermal behaviour was attributed to the formation of an unstable defect rocksalt phase (comprising Al3+ ions partially substituting for Mg2+ in MgO) on decomposition of the LDH. However a simple oxide mixture of MgO and Al2O3 taken in the 6∶1 molar ratio is also found to yield a LDH-like phase when soaked in an aqueous solution of a suitable anion, suggesting that the reconstruction occurs through a simple dissolution–reprecipitation mechanism. The formation of the defect rocksalt phase is not a necessary precondition for reconstruction. However, the kinetics of the reconstruction reaction depends upon the nature of the anion and the thermal history of the oxides. The presence of carbonate ions and unsintered oxides hastens the reconstruction reaction.
Databáze:	OpenAIRE
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