X-Ray Diffractometre (XRD)
X-rays, being electromagnetic waves, are susceptible to diffraction.
Having wavelengths similar to the inter atomic distances in crystals,
they interact with a crystal lattice in the same way that light
interacts with a conventional diffraction grating. In other words, they
are dispersed in different directions according to wavelength. An
important difference is that X-rays penetrate below the surface of the
crystal and rays reflected from successive atomic layers may or may not
be in phase. The condition for a maximum of reflected intensity is that
the contribution from successive planes should be in phase. If the
interplanar spacing is d, the condition is expressed by the well known
|where l is the wavelength of the incoming X-rays, q is the diffraction angle which is equal to the angle of incidence of the incoming X-rays and n is an integer.
If the X-ray beam is monochromatic and l is known, the beam will undergo diffraction by the crystals to form a
diffraction pattern of sharp reflections. Measurements of the various q angles can be used to determine the interplanar spacing d
characteristic of the diffraction crystal. X-ray powder diffraction
provides a powerful technique for mineral identification.
The sample has to be crushed to a fine powder, but very little is
necessary for an identification. The technique can be used for
identification of all crystalline materials.