Characteristic microstructure underlying the fast hydration- dehydration reaction of b-La2( SO4) 3: " fine platy joints" with " loose grain boundaries"
Characteristic microstructure underlying the fast hydration- dehydration reaction of b-La2( SO4) 3: " fine platy joints" with " loose grain boundaries"
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DOI：
10.1039/c8ta06721j
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发表时间：
2018-12-28
影响因子：
11.9
通讯作者：
Uda, Tetsuya
中科院分区：
文献类型：
--
作者：
Shizume, Kunihiko;Hatada, Naoyuki;Uda, Tetsuya
β-La-2(SO4)(3)的快速水合/脱水（水插入/脱嵌）反应有望应用于热化学储热，但其动力学尚未得到很好的理解。在这项工作中，我们研究了 β-La-2(SO4)(3) 的微观结构及其对水合反应速率的贡献。通过比表面积测量和透射电子显微镜，在板厚数百纳米的β-La-2(SO4)(3)颗粒中发现了一种独特的精细微观结构，类似于地质学中的板状节理。晶界松散，甚至氮气也可以扩散。这种微观结构是通过La-2(SO4)(3)9H(2)O脱水合成β-La-2(SO4)(3)时形成的。通过热重分析法定量评价β-La-2(SO4)(3)的水合反应速率。基于这些结果，我们建立了β-La-2(SO4)(3)中水扩散的合理机制：水优先通过板状节理中的松散晶界扩散并被各自的晶粒吸收。片状颗粒上的表面反应可能决定了水合反应的速率。这表明，如果我们能够在β-La-2(SO4)(3)的合成过程中增加片状颗粒的总表面积，则可以预期更快的水合反应速率。
The fast hydration/dehydration (water insertion/deinsertion) reaction of beta-La-2(SO4)(3) is expected to be applied to thermochemical heat storage, but its kinetics have not been well understood. In this work, we investigated the microstructure of beta-La-2(SO4)(3) and its contribution to the hydration reaction rate. From specific surface area measurements and transmission electron microscopy, a unique fine microstructure that looks like platy joints in geology was found in beta-La-2(SO4)(3) particles with a plate thickness of several hundred nanometers. There are loose grain boundaries where even nitrogen gas can diffuse. This microstructure is formed when beta-La-2(SO4)(3) is synthesized through dehydration of La-2(SO4)(3)9H(2)O. The hydration reaction rate of beta-La-2(SO4)(3) was quantitatively evaluated by thermogravimetry. Based on these results, we established a reasonable mechanism for water diffusion in beta-La-2(SO4)(3): water diffuses preferentially through the loose grain boundaries in the platy joints and is taken in respective crystal grains. The surface reaction on the platy grains presumably determines the rate of the hydration reaction. It is suggested that if we can increase the total surface area of platy grains during the synthesis process of beta-La-2(SO4)(3), a faster rate for the hydration reaction can be expected.