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THE X-RAY DIFFRACTOMETER

THE X-RAY DIFFRACTOMETER. AND OTHER XRD INSTRUMENTATION. Precession Camera. 1913 - 1914 William Henry Bragg and William Lawrence Bragg Father and Son English Physicists BRAGG’S LAW : nλ = 2 d Sin Θ λ = wavelength of X-rays n = any whole #

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THE X-RAY DIFFRACTOMETER

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  1. THE X-RAY DIFFRACTOMETER AND OTHER XRD INSTRUMENTATION Precession Camera

  2. 1913 - 1914 William Henry Bragg and William Lawrence Bragg Father and Son English Physicists BRAGG’S LAW: nλ = 2 d Sin Θ λ = wavelength of X-rays n = any whole # d = spacing between atomic planes in angstroms Θ = angle of X-ray incidence on atomic planes INSTRUMENTATION: XRD POWDER DIFFRACTION Generator 40,000 to 50,000 volts 30 to 20 milliamps Tube Rating: 2100 watts Run at 80% Water Chiller 1 liter/min flow rate 65 degree F temperature. X-ray Tube: Cu - target Mo also used Mo = 0.7107 λ K alpha avg Cu = 1.5418 λ K alpha avg Cr = 2.2909 λ K alpha avg

  3. http://epsww.unm.edu/xrd/resources.htm Constructive and Destructive Interference of waves by a regularly spaced array.

  4. Characteristic X-rays Bremstrahlung: "Breaking Radiation" Most common Scenario: High Energy Electrons have only a distant encounter. Small amount of Energy lost. Less than common Scenario: High Energy Electrons have a near encounter. Moderate amount of Energy lost. Uncommon Scenario: The High Energy Electron experiences a head on collision. Gives up just about all of its kinetic energy .

  5. Characteristic X-rays

  6. Monochromator: Absorption Edge Filters Cu Target Ni Filter Mo Target Zr Filter Cr Target V Filter Graphite Monochromater Goniometer: Sollar Plates - Divergent Slit - Sample - Receiving Slit – Sollar Plates- Scatter Slit - Detector Detector: Scintillation Detector Theta - Two Theta Rotation

  7. XRAY DIFFRACTION DATA BASE OF INORGANIC AND ORGANIC CRYSTALLINE SUBSTANCES I.C.D.D. International Centre for Diffraction Data Swathmore, Pennsylvania J.C.P.D.S. Joint Committee on Powder Diffraction Standards Hanawalt Search Method: A means of identifying elements based upon relative insensitivities of peaks. Sample printout of XRD analysis compared to database values.

  8. POWDER CAMERA FORMULA Camera diameter: 114.6 mm Camera radius 57.3 mm S = (2  r)(4) S = distance between arc set 360  on powder film (mm)  = 3.1416  = angle of incident of X-rays on lattice planes d = atomic spacing between planes in Å  = 360 S = X-ray wavelength for Cu 4(2  r) target: 1.5405 Å n = Any whole number.  = (360) Smm = S 4(2) (3.1416) (57.3 mm) 4 Example Problem: Mineral species: Titanite [ CaTiSiO5 ] has a major set of planes with a 3.21Å d-spacing. A set of arcs measured from the film strip: S = 55.5 mm  = 360 S = (360) ( 55.5) = 55.5 = 13.87 4(2  r) 8 (3.1416) (57.3) 4 d = n  = 1.5405 = 1.5405 = 2 Sin  2 Sin (13.87) 2 (0.2397) 1.5405 = 3.2 0.4794 d = 3.2 Å

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