Structure of prismatic halloysite
Structure of prismatic halloysite
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DOI：
10.2138/am.2013.4385
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发表时间：
2013-05
影响因子：
3.1
通讯作者：
T. Kogure;Kiyofumi Mori;V. Drits;Y. Takai
中科院分区：
文献类型：
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作者：
T. Kogure;Kiyofumi Mori;V. Drits;Y. Takai
埃洛石是地球表面最常见的粘土矿物之一，但其晶体结构至今仍是一个谜。本文报道了一种多方法的研究，以阐明更多的原子排列的埃洛石从奥尔洪岛，贝加尔湖，俄罗斯，它有一个棱柱形态。它已被研究使用X射线衍射（XRD），扫描电子显微镜（SEM），选区电子衍射（SAED），特别是，高分辨率透射电子显微镜（HRTEM），以揭示其原子结构和形成过程。XRD分析表明，基底间距约为。7.2在02，11带尾有两个特征峰，d = 4.28和4.03 nm。在SEM和TEM中，埃洛石颗粒的横截面呈现出从矩形到规则的18扇区多边形的各种棱柱形状。当入射光束平行于棱镜轴时，从多角棱镜的一个扇区得到的SAED图显示出规则的单层斜倒易晶格，类似于高岭石沿着Yi方向的结构。使用新的计算机辅助最小剂量系统和垂直于棱镜轴的入射光束进行的HRTEM成像显示，大多数双八面体1：1层的堆叠，其伪镜像平面垂直于棱镜轴，并且几乎随机，或者更确切地说，从前一层向右或向左交替横向交错，这对应于Zvyagin符号中的τ+和τ-的层间位移，或者用于描述高岭石中堆叠的t1和t2的层位移。这种堆叠特征解释了来自棱柱晶粒侧面的SAED图案和XRD图案中02，11带尾部的两个特征峰。基于这些结果，它是建议，管状埃洛石最初形成为一个水合的高岭石层垂直于管轴的伪镜像平面，然后脱水，可能，部分氢键夹层，最后转化为棱柱形的一个组成的扇形平面层与完整的氢键夹层。在这种转变过程中，形成了具有可比比率和τ+和τ-频繁交替的堆叠，以最小化管的形态变化。
Abstract The crystal structure of halloysite, despite being one of the most commonly occurring clay minerals on the Earth’s surface, remains elusive. This paper reports on a multi-methodological study to shed more light on the atomic arrangement of halloysite from Olkhon Island, Lake Baikal, Russia, which has a prismatic morphology. It has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), selected-area electron diffraction (SAED) and, in particular, high-resolution transmission electron microscopy (HRTEM), to reveal its atomic structure and formation process. XRD analysis indicated a basal spacing of ca. 7.2 Å and two characteristic peaks with d = 4.28 and 4.03 Å on the tail of the 02,11 band. The halloysite grain cross sections displayed various prismatic forms, ranging from a rectangle to a regular 18-sectored polygon in SEM and TEM. The SAED pattern from a sector of the polygonal prisms with the incident beam parallel to the prism axes showed a regular one-layer oblique reciprocal lattice, similar to that of kaolinite along Yi-directions. HRTEM imaging performed with the new computer-assisted minimal-dose system and an incident beam perpendicular to the prism axis showed stacking of most dioctahedral 1:1 layers with their pseudo-mirror plane perpendicular to the prism axis and an almost random, or rather, alternating lateral stagger to the right or left from the preceding layer, which corresponds to interlayer displacements of τ+ and τ- in Zvyagin symbols, or layer displacements of t1 and t2 used to describe the stacking in kaolinite. This stacking feature explains the SAED pattern from the side of the prismatic grains and the two characteristic peaks on the tail of the 02,11 band in the XRD pattern. Based on these results, it is proposed that tubular halloysite initially forms as a hydrated one with the pseudo-mirror plane of the kaolinite layers perpendicular to the tube axis, then dehydrates with, possibly, partially hydrogen-bonded interlayers, and finally transforms to a prismatic one consisting of sectored flat layers with the complete hydrogen-bonded interlayers. During this transformation, stacking with comparable ratio and frequent alternation of τ+ and τ- is formed, to minimize morphological change of the tubes.