The nature of disorder in montmorillonite by simulation of X-ray powder patterns
The nature of disorder in montmorillonite by simulation of X-ray powder patterns
复制标题
DOI：
10.2138/am-2002-0720
复制
发表时间：
2002-07
影响因子：
3.1
通讯作者：
A. Viani;A. Gualtieri;G. Artioli
中科院分区：
文献类型：
--
作者：
A. Viani;A. Gualtieri;G. Artioli
摘要用X射线粉末衍射结构模拟方法研究了钙基蒙脱石（漂白土）的平面无序。使用化学、显微镜和衍射方法对标准样品进行充分表征。从文献和新制定的组合模型的早期模型的障碍被用来生成模拟粉末图案与实验光谱进行比较。一个新的模型的无序与随机位移的-a/3和±B/3，与75%的总密度的缺陷，给出了最好的拟合观察到的数据。因此，该样品不能归类为乱层结构（完全无序），因此乱层无序并不总是适用于所有蒙皂石样品。这些研究结果开启了一场关于乱层无序的性质和应用的争论：蒙皂石样品是否有可能在完全无序的堆积（乱层）和高度断层但定义明确的堆积之间具有中间程度的无序，或者对于Ca-蒙脱石获得的结果只是一个例外？该无序模型可用于基于Rietveld方法的X射线粉末衍射定量相分析，这将受益于更可靠的钙蒙脱石初始结构模型，并将提高重量分数估计的准确性
Abstract The planar disorder of Ca-montmorillonite (Fuller’s earth) has been investigated using structural simulations of X-ray powder patterns. A standard sample was fully characterized using chemical, microscopic, and diffraction methods. Earlier models of disorder taken from the literature and newly formulated combined models were used to generate simulated powder patterns to be compared with the experimental spectrum. A new model of disorder with random shifts of -a/3 and ±b/3, with a total density of defects of 75%, gives the best fit to the observed data. Thus, the sample cannot be classified as a turbostratic structure (fully disordered) and consequently turbostratic disorder does not invariably apply to all smectite samples. These findings open a debate on the nature and application of turbostratic disorder: is it possible for smectite samples to have intermediate degrees of disorder between a fully disordered stacking (turbostratic) and a highly faulted but well-defined stacking or is the result obtained for the Ca-montmorillonite just an exception? This model of disorder is useful for the quantitative phase analysis by X-ray powder diffraction based on the Rietveld method, which can now benefit from a more reliable initial structure model for Ca-montmorillonite and which will improve the accuracy of the weight-fraction estimates