X-ray diffraction technique is used for elemental
analysis of crystalline particles. XRD pattern reveals the presence of specific
elements in the analyzing sample by identifying the presence of specific peaks in
the pattern. Sharpness of peaks as well as absence of noise indicates the
purity of the product. Different ways are used for the characterization of
product such as diffraction method, emission technique, scattering and
florescence.
Type of sample:
Solid samples having crystalline nature are analyzed
through x-ray diffraction technique. Amorphous solids cannot be analyzed
through XRD.
Generation of x-rays:
To generate x-rays for sample analysis divergent
procedures are used in which high energy beam of electrons is bombarded on a
metallic target. When this electron beam strikes on the surface of metal target
it emits a primary beam which ultimately generates the secondary beam through
irradiation on contact with the substance. Some radioactive elements and
synochrotron radiation sources are also used to generate a beam of x-rays.
Principle governing XRD technique:
Principle of XRD technique relies on Bragg’s law
which states that “when a monochromatic beam strikes with the surface of a
solid crystalline product with an angle theta, the atoms on the surface of the
sample scatter some portion of this beam. The penetrating portion of x-rays beam
once again results in the scattering of x-rays by inter facial atoms. The spacing
among atomic layers and wavelength of monochromatic beam should be same. It also
requires scattering planes with regular spatial arrangement. X-ray diffraction
technique basically works on the principle of constructive interference between
x-rays beam and a sample of crystalline nature which can be explained via equation
1
nλ
= 2d sinθ (1)
The required sample is
scanned at an angle of 2-theta and the diffracted x-rays are further processed
and counted. Enough lattice planes as well as d-spacing are mandatory for the
formation of peaks in XRD pattern. Figure 1 shows the working principle of XRD.
Related
questions
1.
How
XRD works?
2.
Principle
of XRD
3.
Which
law governs x-ray diffraction technique?
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