So, what is this all about? X-Ray Powder Diffraction or, in short, XRD Diffraction may be simply described as a technique used to rapidly identify the phase and unit cell of crystalline material.
The technique has enabled scientists to garner a deep insight into the structures of alloys and metallic compounds. The beauty of the process is that it is not destructive, so the sample remains intact following the execution of the process.
It has a number of valuable uses. More commonly, XRD Diffraction is used to identify crystal structure, specific phases, orientation, and structural properties such as – average grain size, percentage of crystallinity, and phase quantification.
The Process – How Does it Work?
It works by bombarding the subject sample with incident X-rays and then measuring the intensities and scattering angles of the X-rays as they pass through the sample.
X-rays are waves of electromagnetic radiation and crystals are regular arrays of atoms. Crystal mots scatter incident X-rays through interaction with the atoms of the electrons. This is known as elastic scattering which results in patterns of lower and higher intensities in accordance with something called Bragg’s Law.
In order to better understand this, we need to look at Bragg’s Law. This states that diffraction will only happen when the X-rays and subject sample interact and meet the following conditions:
- The angle of incidence is equal to the angle of scattering and
- The length of the path difference is equal to an integer number of wavelengths.
This makes for a condition of maximum intensity which will then enable a calculation about the crystal structure to be made.
What Does XRD Diffraction Measure?
- Average spacings between layers and rows of atoms in the sample substance
- The orientation of grain or crystal
- The orientation of a grain or crystal
- The size and shape of small crystal areas
- The internal stress of a sample
- The crystal structure of a substance that was previously unknown.
Equipment Required
For XRD Diffraction you would need an X-ray cathode tube, a holder for the sample, and an X-ray detector.
The cathode tube produces the X-rays by applying heat to the filament. Electrons are then produced and directed to the sample target, bombarding it and dislodging its inner electrons and thereby producing X-rays that are pointed at the sample. The sample and the detector then rotate, and the sample is analysed and measured for output to a computer.
What Are the Uses for XRD?
The main applications of XRD may be listed as follows:
Engineering Industries
Geology
Research Into Batteries
Environmental Sciences
Pharmaceuticals and generic drugs
Forensic Science and the Law
Research into various products and processes
Thin-film coatings
Glass Technologies
Lighting industries
Data
Packaging
Raw Material
This rapid and powerful technique has changed the way that crystalline samples are analyzed. It needs minimal preparation and setup; the required equipment is readily available. Checking the results, once output to a computer is a straightforward process, which is easy to interpret.
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