Texture Analysis of Earth Materials. Comparison of EBSD With Other Diffraction Techniques

Abstract

An important feature of polycrystalline materials is the orientation distribution of crystallites also known as crystallographic preferred orientation or texture [1]. Conventionally it is measured by x-ray diffraction, averaging over sample surfaces. With demands for more quantitative material characterization, both in engineering and earth sciences, new methods have been developed. Two dimensions are of interest: Averages over larger sample volumes give a better representation to estimate bulk physical properties. Here neutron diffraction is advantageous. Because of minimal absorption large sample volumes (1-50 cm3), rather than surfaces can be analyzed [2]. If textures are locally heterogeneous, it may be of importance to analyze small regions. With a synchrotron microfocus beam volumes as small as 5 μm3 can be characterized [3]. These methods have been quantified and are extensively applied in metallurgy and geology. They provide good statistics for appropriate sample grain size but they analyze bulk textures and contain no information on local orientation correlations. Furthermore, for geological samples with low crystal symmetry, the diffraction patterns are often very complex with many overlapping peaks, making identification difficult. In such cases orientation imaging, using electron backscattered diffraction patterns (EBSD) in the SEM is useful [4]. Though grain statistics are generally much inferior, new information can be gained.