![]() Diffraction patterns can be searched in large databases of patterns from known materials in order to identify/quantify the material phases present in a sample. It is a must use characterization technique for almost all real world materials as it can provide valuable information for their degree of crystallinity. XRD is unique in providing a wide variety of information on crystal structures, crystalline phases, preferred crystal orientations (texture), and other structural parameters such as crystallite size, percent crystallinity, strain, stress, and crystal defects. If the material is completely amorphous no peaks will be observed in XRD. The response of amorphous, not ordered materials or domains in XRD is characterized by broad low intensity signals. The lattice spacing and crystal structure parameters can be determined from the plot. X-ray diffraction occurs at specific angles with respect to the lattices spacing defined by Bragg’s Law and the result of an x-ray diffraction analysis is a diffractogram – a plot of diffraction peak intensities versus the angles of diffraction. The 3D unit cell ordering forms crystal lattices that diffract X-rays. The crystalline parts of the materials exhibit three dimensional long range order of repeat arrangements of atoms (unit cells). In XRD analysis a collimated X-ray beam of known wavelength hits the tested sample. X-ray Diffraction (XRD) is a nondestructive technique for characterizing crystalline materials or materials with some crystalline domains in them. In addition, when appropriate, we also use the Rietveld method, which can be applied to any materials for which crystal structure details are available.Rigaku SmartLab X-Ray Diffractometer (XRD) Background This is because most clay minerals contain defects/disorder which cannot be readily modelled and so the approach of using patterns measured from real materials is often much more reliable and accurate. Our main methods of analysis, particularly for clay bearing materials are based on full pattern fitting methods that use measured diffraction patterns. The reproducibility of the diffraction data that is obtained is at the heart of the accuracy of all our quantitative methods. This is a result of the elimination of preferred orientation (texture). The major advantage of spray drying is that XRPD data become highly reproducible. Sample preparation is often the key to reliable quantitative XRPD work and a method known as Spray Drying ( watch a video here) has been further developed at The James Hutton Institute for use in the quantitative analysis of bulk materials by XRPD. Precise identification of clay minerals is the first step in any clay mineral analysis, and we base our identifications on years of experience of the interpretation of diffraction patterns from clay minerals and their responses to various ancillary treatments. These are most readily determined from calculated one dimensional X-ray diffraction patterns, using for example the NEWMOD program as described in Moore and Reynolds (1997). Following identification, quantitative analysis may be made by an intensity ratio method whereby the integrated intensity (peak area) of selected clay mineral peaks is related to their weight fraction in the mixture by means of a predetermined constant of proportionality termed mineral intensity factors (MIF) or more generally known as Reference Intensity Ratios (RIR). Peak positions, shapes and intensities and changes in these between treatments are diagnostic for the identification of different clay minerals. Other treatments may be appropriate for the identification of some clay minerals. These oriented samples are run on the diffractometer (air-dried) and then run again following various treatments such as solvation with ethylene glycol, and heating to specified temperatures for specified times. It is also the best way to make a homogenous sample, essential is quantitative results are required. This so called 'filter peel' method enhances the preferred orientation of the platy clay particles which helps to obtain a good diffraction signal from the diagnostic basal planes of the clay minerals. Once obtained the clay fraction is prepared by collecting it on a filter and transferring the layer of clay to a glass slide substrate. Typically, clay mineral analysis involves the separation of a clay sized fraction (usually < 2 micron) from the sample. ![]()
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