Phase identification by X-ray difraction - Parallel beam geometry

What is it?

X-ray diffraction is a versatile and non-destructive analytical technique designed to perform the characterization of materials with respect to their atomic structure, allowing to know their crystalline structure, phase composition, etc. In a wide variety of samples.
X-rays are generated by bombardment of a metal target (anticathode) with a high-energy electron beam. From the interaction of X-rays with the material to be analyzed, some of the radiation is reflected coherently. This phenomenon gives rise to diffraction based on Bragg's law, thus obtaining a diffractogram of the sample with the representation of the intensity of the diffracted radiation as a function of the angle of diffraction (20) or the characteristic interplanar distance (D).
In parallel beam geometry (with low incidence angle 0), the depth of beam penetration in the sample normally depends on the density of the material to be analyzed, the beam wavelength and the angle of incidence. The irradiated area of the sample is the maximum possible and constant throughout the angular range of the test.
A diffractogram contains several peaks that are characterized by their position, intensity and shape. Each phase / substance has a characteristic X-ray diffractogram.
Phase identification is performed by comparing the diffractogram of an unknown sample with diffractograms from a reference database. The most widely used diffraction database is the International Center of Diffraction Data (ICDD). In addition, it is also possible to construct standard records of pure phases or to use diffractograms obtained from the literature, namely when we are in the presence of phases synthesized in laboratory and, therefore, non-existent in the natural state.

What is it used for?

The main applications of this analytical technique are the analysis of the structure of materials with determination of properties such as: existing phase, grain size, preferred orientations, lattice parameters and residual stresses.
Parallel beam geometry is generally used for analysis of coatings that may be several micrometers (such as a corrosion layer on a metal) or a few nanometers (such as a thin coating on a glass substrate).

Equipment and working conditions

The XRD equipment is a Philips, X'Pert MPD with ampoule (anticathode) of Cobalt.

Example of use

X-ray analysis is used in a wide range of research areas and industrial control processes, such as:
- Characterization of new materials;
- Control processes in industries such as metallurgical for phase identification;
- Determination of the crystallinity of the constituent phases of coatings;
- Study of the structural evolution of surfaces as a function of temperature (oxidation and corrosion).