POSITIVE MATERIAL IDENTIFICATION (PMI)
PMI can determine the alloy composition of materials and is a well-established technique that can either be performed in the field using handheld devices or in a laboratory.
Two methods are X-Ray Fluorescence (XRF) and Optical Emission Spectroscopy (OES)
XRF works by exposing the material to be tested to an X-ray, causing the material to emit its own secondary X-rays in response. The levels of X-rays emitted by any material are always consistent based on the composition of that material. Thus, by analysing the secondary X-rays it is possible to determine the chemical composition of any unknown material. However, it should be noted that XRF cannot distinguish between material grades in certain elements such as carbon and silicon, among others.
Optical Emission Spectroscopy (OES):
OES works by exposing the material to an electrical spark and an electrode, often in an atmosphere of Argon. This spark works in a similar way to the X-rays in that it forces the material to emit light, which will differ in colour and intensity based on the material that it is emitted from. It tends to offer a more complete view than XRF and is the only method that can distinguish between levels of carbon in a material. While OES is considered a non-destructive method, it requires grinding the material for surface preparation and the process does cause slight burning on the surface as well.