X射线衍射旋转撒样法分析氟金云母多型组成与含量

合成氟金云母多型种类与含量对云母的物理化学性质具有重要的影响。然而在X射线粉晶衍射(XRD)制样过程中云母00l基面极易产生择优取向,严重制约了云母多型组成和含量的分析。传统撒样法可促使晶体取向随机分布,但制备的试样表面不够平坦。本文对传统撒样法进行改进,在撒样过程中使样品架均匀旋转,从而获得表面平坦的试样。XRD测试结果表明,旋转撒样法取向指数(OI=I_(001)/I_(060))为3.9,与无择优取向的理论值4.5接近,明显优于正压法和侧装法(OI值分别为38.7和18.1),表明旋转撒样法能够显著减弱云母择优取向。这主要是由于旋转撒样法使晶体颗粒之间形成犬牙交错分布,提高了云母各晶面随机分布概率。Rietveld全图拟合分析显示,旋转撒样法获得的XRD数据精修效果较好,计算出本文合成的氟金云母样品中1M和2M_1多型含量分别为86%和14%,8个工业合成的氟金云母样品中1M和2M_1多型含量分别为57%～72%和28%～43%,并且存在较多的堆垛层错。总之,旋转撒样法减弱择优取向效果显著,为研究云母晶体生长、多型成因以及结构与性能之间的关系提供了技术支撑。

Composition and Content of Fluorophlogopite Polytypes by X-ray Diffraction with Rotation-spraying Method

BACKGROUND: The polytype species and the content of synthetic fluorophores have a considerable influence on the physiochemical properties of fluorphlogopites. However, conventional methods (e.g., front loading and side loading) of sample preparation tend to generate a strongly preferred orientation on the 00l basal plane, limiting the X-ray diffraction (XRD) analysis of the composition and content of fluorphlogopite polytypes. The conventional spraying method was utilized to prepare samples with random orientations for XRD analysis. However, the sample surface was not flat enough to perform the analysis.OBJECTIVES: To decrease the preferred orientation and develop a method for quantitative analysis of fluorphlogopite polytypes.METHODS: In this study, the conventional spraying method was improved. The sample holder was rotated evenly during the spraying process to obtain a flat surface sample.RESULTS: XRD data suggested that the orientation index (OI=I₀₀₁/I₀₆₀) obtained by the rotation-spraying method was 3.9, which was close to the theoretical value (4.5). The OIs of the front and side loading methods were 38.7 and 18.1, respectively, which were significantly larger than the theoretical value (4.5). The results showed that the rotation-spraying method significantly decreased the preferred orientation of mica along the 00l basal plane compared with the front and side loading methods. Microscopic observations revealed that the surface of the sample prepared by the rotation-spraying method exhibited a canine tooth staggered distribution. This increased the random distribution between the crystal particles and reduced the preferred orientation. Rietveld quantitative phase analyses of fluorphlogopites were successfully performed based on the XRD data for the samples prepared by the rotation-spraying method. In this study, Rietveld refinement showed that the contents of 1M and 2M₁ polytypes of synthetic fluorphlogopites were 86% and 14%, respectively. The systematic investigations of eight commercial fluorphlogopites revealed that these samples were composed of 28%-43% 2M₁ polytype and 57%-72% 1M polytype. In addition, significant stacking faults were observed in these eight commercial samples.CONCLUSIONS: The rotation-spraying method significantly weakened the effect of preferential orientation. This study provides technical support for understanding the mica crystal growth, polymorphism, and structure-performance relationship.