Crystalline Substance Identification and Size Determination Techniques
Identification of crystalline substances in specimens is achieved through X-ray diffraction analysis, comparing diffraction spectra with known substances. The process involves determining crystalline size using the shape factor and analyzing peak broadening for residual stress effects.
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Presentation Transcript
Phase identification Identification of crystalline substance and crystalline phases in a specimen is achieved by comparing the specimen diffraction spectrum with spectra of known crystalline substances. X-ray diffraction data from a known substance are recorded as a powder diffraction file (PDF). Most PDFs are obtained with Cu (K ) radiation (wave length = 1.54 A0)
Crystalline size determination D=K / ( cos ). K= 0.9 ( shape factor), D= crystal size, = fWHM ( full width half max of the peak) in Rad , = bragg's angle Rad = (22 * FWHM) / (7 * 180) = FWHM * 0.01746 Residual stress In real life XRD peaks can be affected by stresses inside the material which are the effect of thermal or mechanical processing, or chemical contamination. Such effects can give rise to peak broadening (especially with grain size) and if residual stresses are present, peak shifting.
