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首页> 外文期刊>Clays and clay minerals >RELATIVE HUMIDITY-INDUCED REVERSIBLE HYDRATION OF SULFATE-INTERCALATED LAYERED DOUBLE HYDROXIDES
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RELATIVE HUMIDITY-INDUCED REVERSIBLE HYDRATION OF SULFATE-INTERCALATED LAYERED DOUBLE HYDROXIDES

机译：相对湿度诱导的硫酸盐插层层状双氢氧化物的可逆水合

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摘要

Layered double hydroxides (LDH) are extremely important materials for industrial processes and in the environment, and their physical-chemical behavior depends in large part on their hydration state, but the characterization of these hydration effects on their properties are incomplete. The present study was designed to explore the interpolytype transitions induced by variation in the ambient humidity among LDHs. The cooperative behavior of intercalated water molecules resulted in a sudden, single-step, reversible dehydration of the [Zn-Cr-SO_4] LDH. The [Zn-Al-SO_4] LDH provided an interesting contrast with (1) the coexistence of the end members of the hydration cycle over the 40-20% relative humidity range during the dehydration cycle, and (2) a random interstratified intermediate in the hydration cycle. These observations showed that the [Zn-Al-SO_4] LDH offered sites having a range of hydration enthalpies, whereby, at critical levels of hydration (20-40%), the non-uniform swelling of the structure resulted in an interstratified phase. The variation in domain size during reversible hydration was also responsible for the differences observed in the hydration vs. the dehydration pathways. This behavior was attributed to the distortion in the array of hydroxyl ions which departs from hexagonal symmetry on account of cation ordering as shown by structure refinement by the Rietveld method. This distortion was much less in the [Zn-Cr-SO_4] LDH, whereby the nearly hexagonal array of hydroxyl ions offered sites of uniform hydration enthalpy for the intercalated water molecules. In this case, all the water molecules experienced the same force of attraction and dehydrated reversibly in a single step. The changes in basal spacing were also accompanied by interpolytype transitions, involving the rigid translations of the metal hydroxide layers relative to one another.
机译：层状双氢氧化物（LDH）是工业过程和环境中极为重要的材料，其物理化学行为在很大程度上取决于其水合状态，但这些水合作用对其性能的表征尚不完全。本研究旨在探讨LDH之间环境湿度变化引起的多型转变。插层水分子的协同行为导致[Zn-Cr-SO_4] LDH突然，单步，可逆脱水。 [Zn-Al-SO_4] LDH与（1）在脱水循环中水合循环的末端成员在40-20％相对湿度范围内并存，以及（2）随机交联的中间产物的共存形成了有趣的对比。水化循环。这些观察结果表明，[Zn-Al-SO_4] LDH提供了具有一定范围的水合焓的位点，因此，在水合的临界水平（20-40％）下，结构的不均匀溶胀导致了层间相。可逆水合过程中畴尺寸的变化也是造成水合与脱水途径差异的原因。这种行为归因于氢氧根离子阵列中的畸变，该畸变由于正离子有序而偏离了六边形对称性，如通过Rietveld方法进行的结构优化所示。这种变形在[Zn-Cr-SO_4] LDH中要小得多，因此，几乎六边形的氢氧根离子阵列为插入的水分子提供了均匀的水合焓位。在这种情况下，所有水分子都会经历相同的吸引力，并且一步就可逆地脱水。基础间距的变化还伴随着多型间过渡，涉及金属氢氧化物层相对于彼此的刚性平移。

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