X-Ray%20Diffraction - PowerPoint PPT Presentation

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X-Ray%20Diffraction

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Takes a sample of the material and places a powdered sample which is then ... The data is analyzed for the reflection angle to calculate the inter-atomic spacing. ... – PowerPoint PPT presentation

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Title: X-Ray%20Diffraction


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
  • Braggs Law
  • n? 2dsin?
  • n reflection order (1,2,3,4,etc)
  • ? radiation wavelength (1.54 angstroms)
  • d spacing between planes of atoms (angstroms)
  • ? angle of incidence (degrees)

11
strong intensity prominent crystal plane
n? 2dsin? (1)(1.54) 2dsin(15.5 degrees) 1.54
2d(0.267) d 2.88 angstroms
background radiation
12
d-spacing Intensity
2.88 100
2.18 46
1.81 31
1.94 25
2.10 20
1.75 15
2.33 10
2.01 10
1.66 5
1.71 5
13
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!!

14
Mixture of 2 Minerals
15
Applications of XRD
  • Unknown mineral ID
  • Solid solution ID (e.g. feldspars, olivine)
  • Mixtures of minerals
  • Clay analyses
  • Zeolites
  • Crystallographic applications
  • Material Science

16
Created by Nicolas Barth2007Geology
114AUniversity of California, Santa
BarbaraSource material by Grant Yip
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