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'Images of Clay'
'Images of Clay'
EMU Notes in Mineralogy - volume 9
Advances in the Characterization of Industrial Minerals
Chapter 3: X-ray powder diffraction with emphasis on qualitative and quantitative analysis in industrial mineralogy
D.L. Bish and M. Plötze
Powder X-ray diffraction is the method of choice for characterizing the nature of crystalline solids and it can also be applied to non-crystalline solids. The method is ideal for analysing crystalline phases (e.g. minerals) because diffracted X-rays are direct probes of the repeating atomic units in solids. Qualitative analysis is based on the fact that each crystalline structure has a certain distribution of repeat distances which results in a diffraction pattern that is much like a fingerprint. The particular distribution and intensity of diffraction peaks is uniquely characteristic of each material. Quantitative analysis, i.e. determination of the amounts of more than one phase in a mixture, can be done because the diffraction intensities are directly related to crystal structure and the amounts of each phase. Quantitative analysis methods range from those using one or a few reflections to those using the entire diffraction pattern. The latter can employ either measured standard patterns or patterns calculated based on the crystal structures of the component phases, known as the Rietveld method. These full-pattern methods have important advantages as they use all intensity data in a pattern rather than one or a few of the most intense reflections. Some of the most troublesome systematic errors, including sample displacement, zero-point shift, and preferred orientation, can be refined, and the method yields unit-cell parameters of accuracy comparable to that obtained when using an internal d-spacing standard. The method finds wide application in industry, including modal analysis and compositional determinations of individual components using unit-cell parameter systematics. In addition, modern quantitative analysis methods can often be sensitive to amounts of 0.1 wt.%.
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