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X-Ray Diffraction Technique

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X-Ray Diffraction Technique

X-Ray Diffraction Technique

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  • 1. X-RAY DIFFRACTION TECHNIQUE
  • 2. What is X-ray diffraction? non-destructive analytical technique for identification and quantitative determination of the various crystalline forms, known as ‘phases’. Identification is achieved by comparing the X-ray diffraction pattern
  • 3. What is X-ray diffraction? 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
  • 4. History of X-Ray Diffraction 1895 X-rays discovered by Roentgen 1914 First diffraction pattern of a crystal made by Knipping and von Laue 1915 Theory to determine crystal structure from diffraction pattern developed by Bragg. 1953 DNA structure solved by Watson and Crick Now Diffraction improved by computer technology; methods used to determine atomic structures and in medical applications
  • 5. Basic Components Of XRD Machine  Monochromatic X-ray source ()  Sample-finely powdered or polished surface-may be rotated against the center – (goniometer).  Data collector- such as film, strip chart or magnetic medium/storage.
  • 6. How Diffraction Works?  Wave Interacting with a Single Particle  Incident beams scattered uniformly in all directions  Wave Interacting with a Solid  Scattered beams interfere constructively in some directions, producing diffracted beams  Random arrangements cause beams to randomly interfere and no distinctive pattern is produced  Crystalline Material  Regular pattern of crystalline atoms produces regular diffraction pattern.  Diffraction pattern gives information on crystal structure
  • 7. How Diffraction Works: Schematic
  • 8. How Diffraction Works: Schematic
  • 9. Crystal Lattice A crystal lattice is a regular three dimension distribution (cubic, tetragonal, etc.) of atoms in space. These are arrange so that they form a series of parallel planes separated from one another by a distance d, which varies according to the nature of the material. For any crystal planes exist in a number of different orientations- each with its own specific d- spacing
  • 10. 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!!
  • 11. Applications of X-Ray Diffraction  Find structure to determine function of proteins  Convenient three letter acronym: XRD  Distinguish between different crystal structures with identical compositions  Study crystal deformation and stress properties  Study of rapid biological and chemical processes  Crystallographic applications
  • 12. X-ray diffraction is important for:  Solid-state physics  Biophysics  Medical physics  Chemistry and Biochemistry