BACKGROUNDThe 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.

OBJECTIVESTo decrease the preferred orientation and develop a method for quantitative analysis of fluorphlogopite polytypes.

METHODSIn this study, the conventional spraying method was improved. The sample holder was rotated evenly during the spraying process to obtain a flat surface sample.

RESULTSXRD 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.

CONCLUSIONSThe 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.