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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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the xrd technique
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.
powdering samples
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
x rays
X-Rays

Wavelengths used for XRD

what is x ray diffraction
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)
slide6
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
schematic x ray diffractometer
Schematic X-Ray Diffractometer

Detector

X-Ray Source

Powdered sample

slide9

strong intensity = prominent crystal plane

weak intensity = subordinate crystal plane

background radiation

determine d spacing from xrd patterns
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)
slide11

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

factors that affect xrd data
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!!
applications of xrd
Applications of XRD
  • Unknown mineral ID
  • Solid solution ID (e.g. feldspars, olivine)
  • Mixtures of minerals
  • Clay analyses
  • Zeolites
  • Crystallographic applications
  • Material Science
slide16

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