X-ray diffraction analysis of mineral crystals

1. Principle of Mineral Crystal X-ray Diffraction

There are regular lattice in mineral crystal. The lattice can be divided into a group of parallel and equidistant planar lattice (dot). The plane spacing of two adjacent lattice is dhkl, in which the subscript hkl is the surface net index.

When X-ray irradiates the mineral crystal, every lattice in the crystal will scatter the incident X-ray.The distance between any adjacent planes is dhkl.When X-ray irradiates on this crystal plane, the incident angle and scattering angle are equal, both are θ. When the optical path difference is an integral multiple of the X-ray wavelength (λ), the scattered X-rays strengthen each other and produce diffraction rays,that is 2dsinθ=nλ. This is the famous Bragg formula.At present, X-rays are usually produced by high-voltage power source to excite copper target (Cuk α) and iron target (FEK α) in vacuum tube, some are produced by synchrotron radiation.

Bragg formula shows that when n λ is constant, D is inversely proportional to sin θ, that is, D is inversely proportional to θ. The change of crystal plane spacing directly reflects the size and shape of crystal cell. Each crystalline material has its own specific structural parameters, including symmetry, lattice type and cell size. The position and intensity of the diffractive rays of each mineral crystal are the characteristics of mineral crystal and the physical basis of mineral crystal identification.

2. The Principle of Mineral Powder Diffraction is as Follows:

The mineral crystal powder is randomly oriented, and the probability of having various crystal orientations is equal.Therefore, there are diffraction lines with the same intensity in all directions of a certain diffraction angle θ.Therefore, the mineral crystal powder forms a series of cone-shaped diffraction line cones under X-ray irradiation.

In the actual detection, the diffraction angle θ value and the intensity of the diffraction line are recorded, and the D value of the diffraction line is calculated according to the Bragg formula, and the hkl value of each diffraction line is determined by indexing each diffraction line.Mineral X-ray powder diffraction card or database was checked to get the name of mineral species.