Reversible thermal behavior of the layered double hydroxide of Mg with Al: Mechanistic studies
Reversible thermal behavior of the layered double hydroxide of Mg with Al: Mechanistic studies
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DOI：
10.1039/b006610i
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发表时间：
2000
影响因子：
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通讯作者：
Michael Rajamathi;G. Nataraja;S. Ananthamurthy;P. Kamath
中科院分区：
文献类型：
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作者：
Michael Rajamathi;G. Nataraja;S. Ananthamurthy;P. Kamath
镁和铝的层状双氢氧化物(LDH)在450℃下分解，生成混合金属氧化物。在空气中冷却或在水中浸泡时，氧化物重新回到母体LDH。这种可逆的热行为归因于LDH分解时形成了不稳定的缺陷岩盐相(包括Al3+离子部分取代了MgO中的Mg2+)。然而，在摩尔比为6：1的氧化镁和氧化铝的简单混合物中，当浸泡在合适阴离子的水溶液中时，也发现了类LDH相，这表明重建是通过简单的溶解-再沉淀机制进行的。缺陷岩盐相的形成不是重建的必要条件。然而，重建反应的动力学取决于阴离子的性质和氧化物的热历史。碳酸盐离子和未烧结氧化物的存在加速了重构反应。
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.