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X-rays were discovered in 1895 by German physicist Roentgen. X-rays are a form of electromagnetic radiation of very short wavelengths in the angstrom and nanometer region. X-rays are used to make images of the internal structure of bodies and this is done by scattering of X-rays by the internal lattices of solid objects.
X-ray diffraction is a tool for the investigation of the structure of matter and is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of natural and manufactured materials.
Applications of X-ray diffraction
Using X-ray diffraction, a wealth of structural, physical and chemical information about the material investigated can be obtained. A host of application techniques for various material classes is available, each revealing its own specific details of the sample studied besides applying in chemical analysis, stress and strain measurement, the study of phase equilibria, measurement of particle size, as well as crystal structure.
A crystal lattice is a regular three-dimensional distribution (cubic, rhombic, etc.) of atoms in space arranged in such a way that they form a series of parallel planes separated from one another by a distance which varies according to the nature of the material. For any crystal, planes exist in a number of different orientations, each with its own specific spacing.
When a monochromatic X-ray beam is projected onto a crystalline material at an angle, diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number of wavelengths.
By varying the angle, the Bragg's Law conditions are satisfied by different spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffracted peaks of radiation produces a pattern, which is characteristic of the sample. Where a mixture of different phases is present, the resultant diffractogram is formed by addition of the individual patterns.
X-ray fluorescence unit (XRF)
The wavelength-dispersive x-ray fluorescence unit (XRF) is used chiefly for the determination of major element (Si, Al, Fe, Na, K, Mg, Ca, Mn, Ti, P) in rocks, minerals, ceramics, nanocompounds, cements, clays, alloys, etc. and major trace elements such as Rb, Sr, Y, Zr, Nb, Zn, Co, Cu, Ni, Ba, and Cr. Qualitative or semi-quantitative scans can be run on elements such as carbon through uranium.
Soft X-ray Appearance Potential Spectroscopy (SXAPS)
Soft X-ray Appearance Potential Spectroscopy SXAPS is a member of the Appearance Potential Spectroscopies. The experimental apparatus has a filament mounted near the sample which emits electrons which are accelerated towards the sample. X-rays generated within the sample are detected via photoelectrons generated by the X-ray within the detector. SXAPS is not particularly surface sensitive, but as it is a threshold technique, the incident electrons will only travel a short distance before they are unable to excite the level of interest and suffers from poor signal.