Positive Material Identification-PMI Methods

The two main technologies used for alloy identification in PMI are :

  • X-ray Fluorescence (XRF)
  • Optical Emission Spectroscopy (OES).

X-ray Fluorescence (XRF) Method

XRF instruments work by exposing a sample to a beam of X-rays. The atoms of the sample absorb energy from the X-rays, become temporarily excited and then emit secondary X-rays. Each chemical element emits X-rays at a unique energy. By measuring intensity and characteristic energy of the emitted X-rays, an XRF analyzer can provide qualitative and quantitative analysis regarding the composition of the material being tested.

Optical Emission Spectroscopy (OES)

In the OES technique, atoms also are excited; however, the excitation energy comes from a spark formed between sample and electrode. In this case, the energy of the spark causes the electrons in the sample to emit light, which is converted into a spectral pattern. By measuring the intensity of the peaks in this spectrum, the OES analyzer can produce qualitative and quantitative analysis of the material composition. Although OES is considered a nondestructive testing method, the spark does leave a small burn on the sample surface.