In a nutshell, X-ray Powder Diffraction is a fast scientific analytical technique which is used, primarily for phase identification of crystalline material. It can identify information on the dimensions of unit cells.
The material analysed is finely ground. homogenized in order to determine the bulk composition.
Diffraction occurs when light bends slightly as it passes around the edge of an object or if it comes across an obstacle or opening.
Powder Diffraction, in contrast to individual crystal diffraction methods, works best with an individual well-ordered crystal.
How Does it Work?
In order to set out how it works, we must first look at X-rays. These are a form of radiation which includes wavelengths which are measured in nanometres (one nanometre equals one billionth of a metre). When monochromatic x-rays are caused to scatter from a substance, interference is caused, which results in a pattern of higher and lower intensities due to destructive and constructive interferences in accordance with what is known as “Bragg’s Law”.
Braggs Law states that diffraction will only happen if the interaction between the X-rays meets the conditions of Braggs Law, which are:
- The angle of incidence is equivalent to the angle of scattering
- The difference in the length of the path equals an integer number of wavelengths
The above makes for a condition of maximum intensity which enables a calculation to be made abut the crystal structure under examination.
What is X-ray Powder Diffraction Used to Measure?
X-Ray Diffraction can be used for the following applications:
- To measure the average spacings found between layers of rows of atoms that are found in a substance.
- To determine how a particular or individual crystal or grain is orientated.
- To measure the shape, size and internal stress of minute crystalline areas.
- To identify the crystal structure of a substance
What Equipment is Needed for X-Ray Powder Diffraction?
The process is executed using an instrument called a X-ray diffractometer. It is made up of three main constituent parts: a holder for the sample, a detector for the X-rays, and cathode tube.
The cathode tube is used to generate X-rays by applying heat directly to a filament. Electrons are thereby produced and these are the pointed towards a target by the application of a voltage. The target is bombarded, thereby dislodging inner shell electrons and producing X-rays. These X-rays are then directed towards the sample. The X-ray detector and the source then rotate. Once Bragg’s Law has been satisfied, constructive interference happens, resulting in a peak in intensity. The detector then records and processes the signal and converts it into a form called a count rate which is output to a computer.
What are the Uses for X-ray Powder Diffraction ?
This highly valuable technology is used in many areas including Geology, biology, engineering., environmental science, electronics, research into batteries, material science, thin-film coatings, pharmaceuticals, forensic science, glass industry and many more progressive industries.
