Síntese do padrão difratomérico de Óxido de Cério para determinação da largura instrumental

Abstract

With the use of X-ray powder diffraction, it is possible to determine physical parameters of a crystal lattice and quantify its phases. Some of these parameters are: the dimensions of unit cell (lattice parameters), volume, crystal size, microstrain, etc. However, it is necessary to be cautious with sample preparation as well as with the diffractometer alignment in order to obtain reliable parameters. For the systematic errors do not affect the values of these parameters, patterns samples are used which are denominated Standard Reference Materials¬-SRM. In X-ray powder diffraction measurement, the patterns obtained from a sample has external effects, such as the way of preparing sample or effects caused by the equipment itself. Taking into account the instrumental effects (systematic), which will always be present in a measurement, thus, the challenge is how to quantify this effect. The SRM selected for this purpose is cerium oxide (CeO_2) which were obtained from cerium sulfate tetrahydrate (Ce〖(SO_4)〗_2∙4H_2 O) purchased from Sigma-Aldrich. The major features of SRM are: crystals have dimensions on the order of µm, chemically inert, homogeneous, low microstrain, narrow and intense diffraction peaks. All these conditions are essential, especially the crystal size to determine the instrumental width. According to the Scherrer equation, the full width at half maximum (FWHM) of a diffraction peak is inversely proportional to the average size of the crystals, in other words, measurements made in thick crystals, homogeneous, low microstrain will produce narrow peaks, and consequently, the total width and profile of the diffraction peaks are associated with instrumental effects (for example: divergence, lenses, spectral dispersion, etc). The objective of this work is to synthesize CeO_2 with the conditions described earlier and to determine the instrumental width of the diffractometer. According to the results presented by the authors of this work, it was observed that cerium oxide can be used as Standard Reference Materials for X-ray Diffraction analysis.