Use of the Rietveld Method for Describing Structure and Texture in XRD Data of Scale Deposits Formed in Oil and Gas Pipelines: An Important Industrial Challenge

摘要

Texture, or crystallographic preferred orientation, in crystalline materials is a common feature of experimental X-ray powder diffraction (XRD) data. Preferred orientation can cause serious systematic errors in both quantitative phase analysis and crystal structure determination. Studies show that the generalized spherical harmonic (GSH) description provides a better Rietveld fit than the March model for the uniaxially pressed molybdite and calcite powders. Therefore, it Was recommended to use the GSH description for correction of the preferred orientation in XRD and neutron diffraction analyses, for both crystal structure refinement and quantitative phase analysis. In the present study, the GSH description was extended to describe crystal structure and texture in the XRD data of scale deposits formed in an amine trim cooler. The results revealed that the structural refinement parameter obtained from the Rietveld refinement with the GSH description agreed well with the corresponding single crystal structure. Additionally, the GSH description provided better results for the materials investigated in the present study than the March model. Therefore, the GSH approach should be used for preferred orientation correction in XRD Rietveld analysis, for both crystal structure refinement and phase composition analyses.