Powder XRay Diffraction

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Powder X-Ray Diffraction
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How do we identify/individualize minerals, rocks,
soils and other trace evidence? PLM-polarized
light microscope -identification of constituents
based on optical properties note binocular
microscope group here SEM/EDS -identification
of constituents by determination of chemical
composition characteristic x-rays
What do we do if constituents are to small to ID
by PLM, or have a chemical composition that is
non-unique??
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The Powder X-Ray Diffractometer (XRD) uses x-rays
to determine the structural fingerprint of
minerals, soils, synthetic crystalline material
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What is the difference between micro beam
chemical analysis by x-ray fluorescence XRF on
the SEM/EDS and x-ray diffraction XRD?
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Powder XRD in Criminalistic studies
Identification of soils, mineral specimens, and
gemstones Determination of fire origin
Identification of drugs and other
pharmaceuticals, poisons, synthetic fibres,
gunpowder, explosives, metals and alloys,
building materials
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What do we mean by X-ray Diffraction and why
do we call it powder xrd?
Schematic of a Powder XRD
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Diffraction and Bragg's Law Diffraction occurs
as waves interact with a regular structure whose
repeat distance is about the same as the
wavelength of the waves.
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X-rays have wavelengths on the order of a few
angstroms, the same as typical interatomic
distances in crystalline solids. That means..
-X-rays are diffracted from minerals and other
solids with crystalline or regularly repeating
atomic structures.
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W. L. Bragg recognized a predictable
relationship among several factors 1. The
distance between similar atomic planes in a
mineral. 2. The angle of diffraction as measure
in degrees. 3. The wavelength of the incident
X-radiation (e.g. Cu radiation wavelength
1.54 angstroms)
W.L Bragg
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and now, why do we call it powder xrd?
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Diffraction through a many crystals
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Minerals and other crystals produce a series of
peaks from cones of diffraction that are
diagnostic
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Powder XRD Scan of Actinolite amphibole
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The Diffractometer A diffractometer can be used
to make a diffraction pattern of any crystalline
solid. -a diffraction pattern an investigator
can identify an unknown mineral -characterize
the atomic-scale structure of an already
identified mineral.
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Siemens D5000 Powder X-Ray Diffractometer
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Goniometer Assembly on the D5000
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