Experimental methods in chemical engineering: Electron probe micro-analysis—EPMA

Electron probe microanalysis (EPMA) is a non-destructive spectroscopic technique to map the chemical composition—quantitative elemental distribution and layer thickness—with a micro-scale resolution. An electron beam illuminates the surface of a sample and produces backscattered electrons (BSE), secondary electrons (SE), characteristic X-rays, and light known as cathodoluminescence (CL). Combining energy dispersive spectrometry with wavelength-dispersive spectrometry improves trace analysis and differentiates overlapping X-ray lines, but the detection threshold is not much better than 100 ppm (parts per million). Implementing Monte Carlo simulation with better electronics and software are ongoing research areas to improve the method's precision, sensitivity, and spatial resolution. To detect Li, Be, and B ($Z<$ 11) requires wavelength-dispersive X-ray spectroscopy (WDS), or soft X-ray emission spectroscopy (SXES), or a combination of BSE/EDS method. Researchers in metallurgy & metallurgical engineering, mineralogy, geochemistry & geophysics, and mining & mineral processing apply the method most. Chemical engineering is ranked 21st among the 250 scientific categories that use the technique. It is also applied to reconstitute works of art and the antiquities. A bibliometric map identified four clusters of research and for each cluster the major nodes were: (1) geochemistry, (2) mechanical properties, microstructure, and alloys, (3) Fe, Cu, and Cr, and (4) phase equilibria.