Electron Microprobe Analysis

EMP provides advantages over EDS/SEM in steels analysis.

• Detection limits are lower
• elements like Mo (Molybdenum) and S (Sulphur) can be resolved.

Most metals including stainless steels and aluminium alloys can be characterised quickly and cheaply by electron microprobe analysis (WDS). All elements present, except for light elements eg. Carbon and Nitrogen, which are generally not diagnostic, can be quantitatively determined down to very low detection limits as listed below.

The inability of the EDS systems to resolve the Mo and S Peaks is not a problem with the superior resolution of the WDS crystals. A scraping or small off cut (0.1mm) is all that is needed - no complex wet chemistry. The difference in Cr and Ni content as well as the 2%+ Mo in 316 make 304 and 316 easily distinguishable.

The technique is very useful in the tracing of metal contaminants in any manufacturing process to determine source. Inclusions and other impurities in metal castings can be easily identified.

Full chemical analyses are determined using a fully automated Jeol JXA5A electron microprobe incorporating computer controlled wavelength dispersive crystal spectrometers and X-Y-Z stage system, with an accelerating voltage of 20KV and beam current of 29nA. The beam is defocussed to 15µm for analysis.

X-rays are produced in the area excited by the electron beam, 3 crystals LIF, PET and RAP covering overlapping ranges of the periodic table are used to focus characteristic X-rays which are then counted by gas flow counters in each spectrometer. These counts are compared to X-ray counts from well-characterised natural and synthetic chemical standards. ZAF (atomic number, absorption, fluorescence) matrix correction procedures are then used for data reduction.

Sample Preparation Details:

Polished block

Standard Stainless Analysis  Cr | Mn | Fe |   Ni | P | Nb |  Mo | S | V | Si

Standard Aluminium Analysis  Al | Si | Ti

Other elements normally at no extra cost - pls check for element availability.

Basic Operation of an Electron Microprobe