X-ray Diffraction Laboratory

X-ray powder diffraction is a scientific tool to elucidate structural characteristics in materials.  X-rays that are directed at crystalline powders or polycrystalline materials will scatter in a pattern that is unique to that material.  As such, a material can be identified by its scattered pattern and the pattern can be used as unambiguous evidence of discovery or for quantitative analysis.

Powder diffraction is a bulk sample procedure and can be employed to identify solids and heterogeneous samples and can be used to monitor solid-state reactions.  Amorphous materials will also scatter X-rays and the amorphous patterns are useful information to the solid-state scientist.  

The X-ray powder pattern for Vitamin C (ascorbic acid) is shown below.  Compare the Vitamin C pattern to the chemically similar compound aspirin.  It is clear that the powder patterns are different and that an investigator can employ such patterns to establish the true chemical identity of an unknown powder.

Vitamin C :   Aspirin :

A common method to compare two powder patterns is by the plot-replot method.  Below we show the comparison of Aspirin and Vitamin C powder patterns.  The patterns are bar graphs plotted in d.  The absolute height of the bars represent the relative intensities of the peaks in the powder pattern.