Diffraction practical: Quantifying disorder

Experiment

1. Take diffractograms (10^o to 90) of three forms of silica, SiO₂:
   1. quartz sand
   2. a slice of flint, a very fine-grained from of quartzite
   3. fumed silica powder, a glassy form of silica
2. Take a diffractogram of an empty sample holder as a background reading.

Report

1. Subtract the background from all diffractograms. Take care to scale the background reading to coincide with the baseline around the peaks in your diffractograms.
2. Use Scherrer's formula to derive the column length in different crystallographic orientations and estimate an average particle size in the flint sample.
3. Determine the characteristic length scale of the major atomic pair correlation in the amorphous sample by rescaling the diffractogram in terms of the momentum transfer, q.
4. Is the apparent particle size dependent on crystal orientation? If so, why?
5. Which pair correlation is the strongest contribution to the amorphous diffractogram? Does it relate to any of the crystalline lattice spacings?

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