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A COMPREHENSIVE CHARACTERIZATION OF DIOCTAHEDRAL SMECTITES

机译：二面体蒙片的综合表征

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The term 'montmorillonite' encompasses a wide range of chemical compositions and structures. Comprehensive and reliable characterization is essential for unambiguous classification. Twenty eight purified, Na-exchanged smectites (<0.2 μm) were characterized by layer-charge measurement using the alkylammonium method, by cation exchange capacity (CEC) measurement with Cu-triethylenetetramine, by determination of the chemical composition using X-ray fluorescence analysis, by calculation of the structural formula following determination of the octahedral structure (trans-vacant vs. cis-vacant) by simultaneous thermal analysis, and by X-ray diffraction analysis. Mossbauer spectroscopy was applied to determine the oxidation state and coordination of Fe and changes thereof during purification of the source materials.rnThe charge derived from chemical composition was considerably greater (by up to 30%) than the measured layer charge. The independently measured layer charge was used to calculate the structural formula. The measured CEC values, comprising the permanent charges and the pH-dependent edge charges, were consistent with measured layer charge but not with layer charge derived from the chemical composition. Therefore, the structural formula of smectites should be calculated using the measured layer charge.rnThe dehydroxylation temperature, which conveys information about the structure of the octahedral sheet, was correlated to the amount of Mg and Fe~(3+) and the location of charges. No relationship was found among the dehydroxylation temperature and the mean layer charge or the Mg content. In contrast, a clear relationship was observed between the Fe content and the dehydroxylation temperature. Montmorillonites with an Fe content <0.3/f.u. are cis-vacant and those containing Fe~(3+) > 0.3 mol/f.u. are trans-vacant, mostly with additional cis-vacancies. Tetrahedral substitution also appeared to be a function of the number of trans-vacancies.rnThe parameters analyzed provide the basis for a new descriptive classification system.
机译：术语“蒙脱石”涵盖了广泛的化学组成和结构。全面而可靠的表征对于明确分类至关重要。通过烷基铵法的层电荷测量，铜三亚乙基四胺的阳离子交换容量（CEC）测量，X射线荧光分析法测定化学组成，表征了28个纯化的，Na交换的绿土（<0.2μm）通过同时热分析和X射线衍射分析确定八面体结构（反式-空位与顺式-空位）后计算结构式。莫斯鲍尔光谱法用于确定原料纯化过程中Fe的氧化态和配位及其变化。来自化学成分的电荷比被测层电荷大得多（最多30％）。使用独立测量的层电荷来计算结构式。测得的CEC值（包括永久电荷和pH依赖的边缘电荷）与测得的层电荷一致，但与衍生自化学成分的层电荷不一致。因此，应该使用测得的层电荷计算蒙脱石的结构式。rn传递有关八面体片结构信息的脱羟基温度与Mg和Fe〜（3+）的含量以及电荷位置相关。在脱羟基温度和平均层电荷或Mg含量之间没有发现关系。相反，在Fe含量和脱羟基温度之间观察到明确的关系。铁含量<0.3 / f.u的蒙脱石。是顺式-空位的，并且含有Fe〜（3+）> 0.3 mol / f.u的。是空位的，大多带有顺式空位。四面体取代也似乎是反空位数量的函数。分析的参数为新的描述性分类系统提供了基础。

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