Powder X-ray Diffraction
Powders of crytalline materials diffract x-rays. A beam of x-rays passing through a sample of randomly-oriented microcrystals produces a pattern of rings on a distant screen. Powder x-ray diffraction provides less information than single-crystal diffraction, however, it is much simpler and faster. Powder x-ray diffraction is useful for confirming the identity of a solid material and determining crystallinity and phase purity.
Modern powder x-ray diffractometers consist of an x-ray source, a movable sample platform, an x-ray detector, and associated computer-controlled electronics. The sample is either packed into a shallow cup-shaped holder or deposited as a slurry onto a quatz substrate, and the sample holder spins slowly during the experiment to reduce sample heating. The x-ray source is usually the same as used in single-crystal diffractometers, Mo or Cu. The x-ray beam is fixed and the sample platform rotates with respect to the beam by an angle theta. The detector rotates at twice the rate of the sample and is at an angle of 2theta with respect to the incoming x-ray beam.
/chem-ed/diffract/powder.htm, updated 10/14/96
Copyright © 1996 by Brian M. Tissue, all rights reserved.
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