Different Between X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF)
Both XRD and
XRF are material characterization techniques which have gained popularity in
the past several decades.
In simple layman
terms X-ray fluorescence is a technique for determination of the elemental
composition of the sample without differentiating between the different
chemical compounds that are present in the sample. On the other hand x-ray
diffraction provides information on the sample composition in terms of
compounds present, degree of crystallinity and its amorphous content.. In a way
it can be said that both the techniques complement one another and give a total
picture of sample composition. The attractive feature common to both the
techniques is that they are non-destructive and the sample can be recovered for
frequent confirmatory tests.
In order to
understand the differences between the two techniques it is important to have
clarity on the basic principles of the two techniques
XRD
All matter is
composed of atoms which show a degree of periodicity in their structural
arrangements. The scattering of a homogeneous x-ray beam by collision with
electrons of atoms result in diffraction which is dependent on the wavelength
of x-rays and the distance between the planes of the atoms arranged in such
arrays.
The study
provides valuable details on structural arrangements of crystals in unit cells
or lattices. Qualitative confirmation of compounds present in samples can be
arrived at by matching the diffraction patterns with library collection of
standard diffraction patterns. The technique finds potential applications in:
- identification of chemical composition of
minerals and industrial products in terms of number of phases, degree of
crystallinity and amorphous content.
- phase transformations and structural changes due
to changes in temperature, stress or gas phase environment
- Texture analysis of thin films
XRF
XRF provides
the elemental composition of sample in percentages but will not differentiate
between the compounds in which a particular element exists or the phase of the
compounds.
The
bombardment of x-rays results in the eviction of electrons from inner shells.
The vacancies created tend to be filled up by the electrons from outer shells.
In the process the energy is released as x-rays which are characteristic for
each element present in the sample. XRF provides elemental composition in
diverse samples such as minerals, cements, petroleum products, polymers,
plastics and paints. XRF permits quantification of both metallic and
nonmetallic elements of the periodic table from fluorine (atomic number 9
upwards). Sensitivities of up to fractions of a percent to ppm levels are
commonly achieved.
Combined
XRD and XRF instruments
The wealth of
information provided by both XRD and XRF techniques individually has propelled
development of combined technology instruments. A single sample can be used to
provide a saving of time and space in addition to information on elemental and
phase composition. Such instruments provide comprehensive analysis information
on metals, alloys, sinters, minerals, cements and refractory materials.
*lab-training*
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