Calcination-induced changes in structure, morphology, and porosity of allophane
Calcination-induced changes in structure, morphology, and porosity of allophane
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煅烧引起水铝英石结构、形态和孔隙率的变化
DOI：
10.1016/j.clay.2018.03.035
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发表时间：
2018-06-15
影响因子：
5.6
通讯作者：
Guo, Haozhe
中科院分区：
文献类型：
--
作者：
Du, Peixin;Yuan, Peng;Guo, Haozhe
水热法合成了 Al/Si 摩尔比为 1.6 的水铝英石，然后在高达 1300 摄氏度的规定温度下煅烧。然后使用 X 射线衍射、傅里叶变换红外光谱、热分析、核磁共振、透射电子显微镜和 N-2 物理吸附等技术组合对加热产物进行表征。在水铝英石中，伊毛缟石局域结构（ImoLS）的热稳定性较低，吸附水在低温下被去除。概述了水铝英石的热演化过程的五个主要步骤。 (i)在200℃或更低温度下，吸附水的损失和Si-OH的部分脱羟基伴随Si-O-Si的形成导致ImoLS的损失。 (ii)随着温度升高，Si-OH进一步脱羟基以及Al-OH发生解离，由于空心球的持续团聚导致比表面积和孔隙率下降，而水铝英石的球形形态大部分保留。 (iii)在大约500至900摄氏度时，AIO八面体和SiO四面体的断开导致水铝英石结构的分解增加以及无定形氧化铝和二氧化硅的形成。 (iv)在约1000℃下，通过所产生的非晶态氧化铝与二氧化硅之间的反应，使纳米莫来石结晶。 (v)最后，随着过量二氧化硅的消耗，已经形成的莫来石晶体进一步生长并形成方英石。
Allophane with an Al/Si molar ratio of 1.6 was hydrothermally synthesized, followed by calcination at defined temperatures up to 1300 degrees C. The heated products were then characterized using a combination of techniques including X-ray diffraction, Fourier transform infrared spectroscopy, thermal analyses, nuclear magnetic resonance, transmission electron microscopy, and N-2 physisorption. In allophane, the imogolite local structure (ImoLS) had a relatively low thermal stability, and the adsorbed water was removed at a low temperature. Five major steps were outlined for the thermal evolution process of allophane. (i) At 200 degrees C or lower, the loss of adsorbed water and partial dehydroxylation of Si-OH accompanying with the formation of Si-O-Si resulted in the loss of ImoLS. (ii) As the temperature rose, further dehydroxylation of Si-OH as well as disassociation of Al-OH occurred, leading to decreases in the specific surface area and porosity due to the continued agglomeration of hollow spherules, whereas the spherical morphology of allophane was largely retained. (iii) At approximately 500 to 900 degrees C, the disconnection of AIO octahedra and SiO tetrahedra caused increased disintegration of the allophane structure and formation of amorphous alumina and silica. (iv) At approximately 1000 degrees C, nanosized mullite was crystallized by the reaction between the yielded amorphous alumina and silica. (v) Finally, further growth of the already-formed mullite crystals and formation of cristobalite occurred, with the consumption of excess silica.