This note describes the use of the Rietveld method for determining crystallite sizes of pharmaceutical powder samples. In contrast to Scanning Electron Microscopy that could hardly detect changes in the particle size, XRD clearly showed the decrease in crystallite size with increasing milling time of the model compound.
During different pharmaceutical production processes - including crystallization, granulation, micronization, milling and spraydrying for example - crystallite sizes of the compounds can vary and are dependent on the process parameters employed. X-ray diffraction techniques play an important role in the analysis of crystallite sizes, since traditional methods such as laser granulometry determine only particle size, a parameter that is not directly related to, or correlated with, crystallite size.
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