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X-Ray Diffraction

X-Ray Diffraction. The XRD Technique. Takes a sample of the material and places a powdered sample which is then illuminated with x-rays of a fixed wave-length. The intensity of the reflected radiation is recorded using a goniometer.

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X-Ray Diffraction

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  1. X-Ray Diffraction

  2. The XRD Technique • Takes a sample of the material and places a powdered sample which is then illuminated with x-rays of a fixed wave-length. • The intensity of the reflected radiation is recorded using a goniometer. • The data is analyzed for the reflection angle to calculate the inter-atomic spacing. • The intensity is measured to discriminate the various D spacing and the results are compared to known data to identify possible matches.

  3. Powdering Samples • The samples are powdered to give a random sampling of ALL atomic planes (crystal faces) • Statistically accurate given samples are powdered finely AND randomly oriented on sample holder • Intensities are a reflection of d-spacing abundance • Problems arise with minerals that may preferentially orient on sample holder • Micas and clays have special preparation techniques

  4. X-Rays Wavelengths used for XRD

  5. What is X-Ray Diffraction?? • Crystalline substances (e.g. minerals) consist of parallel rows of atoms separated by a ‘unique’ distance • Simple Example: • Halite (Na and Cl)

  6. Crystalline substances (e.g. minerals) consist of parallel rows of atoms separated by a ‘unique’ distance • Diffraction occurs when radiation enters a crystalline substance and is scattered • Direction and intensity of diffraction depends on orientation of crystal lattice with radiation

  7. Schematic X-Ray Diffractometer Detector X-Ray Source Powdered sample

  8. Sample XRD Pattern

  9. strong intensity = prominent crystal plane weak intensity = subordinate crystal plane background radiation

  10. Determine D-Spacing from XRD patterns Bragg’s Law nλ = 2dsinθ • n = reflection order (1,2,3,4,etc…) • λ = radiation wavelength (1.54 angstroms) • d = spacing between planes of atoms (angstroms) • θ = angle of incidence (degrees)

  11. strong intensity = prominent crystal plane nλ = 2dsinθ (1)(1.54) = 2dsin(15.5 degrees) 1.54 = 2d(0.267) d = 2.88 angstroms background radiation

  12. Factors that affect XRD data • Sample not powdered fine enough • May not give all d-spacing data (not random enough) • Analysis too fast (degrees/minute) • May not give accurate peak data • Mixture of minerals?? • Not crystalline – glass!!

  13. Mixture of 2 Minerals

  14. Applications of XRD • Unknown mineral ID • Solid solution ID (e.g. feldspars, olivine) • Mixtures of minerals • Clay analyses • Zeolites • Crystallographic applications • Material Science

  15. Created by Nicolas Barth2007Geology 114AUniversity of California, Santa BarbaraSource material by Grant Yip

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