X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely ground, homogenized, and average bulk composition is determined.
Fundamental Principles of X-ray Diffraction
Max von Laue, in 1912, discovered that crystalline substances act as three-dimensional diffraction gratings for X-ray wavelengths similar to the spacing of planes in a crystal lattice. X-ray diffraction is based on constructive interference of monochromatic X-rays and a crystalline sample. These X-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation, collimated to concentrate, and directed toward the sample. The interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy Bragg's Law nλ=2d sin θ
By scanning the sample through a range of 2θangles, all possible diffraction directions of the lattice should be attained due to the random orientation of the powdered material. All diffraction methods are based on generation of X-rays in an X-ray tube. These X-rays are directed at the sample, and the diffracted rays are collected.
Figure 1. X-Ray Diffraction
How X-Ray Diffraction Works:
When a sample is irradiated with a beam of monochromatic X-rays, the sample atomic lattice acts as a 3-dimensional diffraction grating causing the X-ray beam to be diffracted to specific angles.
Analysis and Quantization
Figure 2. X-ray powder diffractogram
Good instrument resolution resolves overlapping diffraction peaks in complex patterns.
Applications of XRD
Quantitative analysis of actual minerals in topsoils and subsoils. Classification of soils in terms of weatherable minerals: soil fertility potential. Use in...
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