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
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 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.