Advanced Materials & Processes

NOV-DEC 2013

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

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Page 32 of 92

Materials Characterization Primer ELECTRON PROBE X-RAY MICROANALYSIS Estimated Analysis Time Depending on the detection limits desired, a typical multi-element quantitative analysis takes a few minutes to run. 30 Electron probe x-ray microanalysis is used to qualitatively and quantitatively analyze solids containing elements with atomic numbers between 4 (beryllium) and 92 (uranium), with detection limits on the order of 100 ppm and at a lateral spatial resolution of 200 nm. Other uses include elemental compositional mapping of areas as large as 90 90 mm, or with spatial resolution on the order of 100 nm. Applications include compositional analysis of individual phases at the microstructural level in multiphase samples (e.g., analysis of individual inclusions in steels and other alloys), analysis of compositional gradients at boundaries, determination of compositional homogeneity or heterogeneity at the micrometer scale in single-phase materials, and composi- tional mapping of heterogeneous specimens to produce elemental and concentration maps. Samples Form: A bulk solid sample metallographically polished to a mirror finish is ideal for optimum analysis. Qualitative and semiquantitative analyses can also be run on rough surfaces, individual particles, and films on substrates. ADVANCED MATERIALS & PROCESSES • NOVEMBER-DECEMBER 2013 Size: Typically 25 mm in diameter by 20 mm thick (1 by ~0.75 in.), but can be as large as 90 90 20 mm (3.5 3.5 0.75 in.) depending on the configuration of the instrument stage. Limitations Routinely detects elements down to an atomic number 4 (beryllium); however, it is now possible to detect lithium (Z=4) with a new grating based WD spectrometer. Sensitivity is in the range of 100 ppm with x-ray measurement by wavelengthdispersive spectrometry; 1000 ppm (0.1 wt%) with x-ray measurement by energydispersive spectrometry. Sensitivity is lower for light elements in a heavy matrix. Lateral and depth spatial resolution of ~200 nm is limited more by electron scattering in the sample than by the focused electron beam. Quantitative analysis is limited to flat, polished specimens. Unusual geometries such as fracture surfaces, individual particles, and films on substrates can be analyzed, but with greater uncertainty. Related techniques Transmission electron microscopy extends spatial resolution of semiquantitative elemental analysis down to ~10 nm and provides high-resolution imaging and electron diffraction for crystallographic information. Secondary ion mass spectrometry, laser microprobe mass analysis provide coverage of the entire periodic table at ppm sensitivity for most elements, but it is a destructive analytical method, and has poor spatial resolution and large uncertainties in quantitative analysis. Auger microprobe analysis provides elemental analysis of the sample surface (1–5 nm deep) at the same lateral spatial resolution, and has particular sensitivity to the light elements. Raman microprobe analysis provides molecular analysis at the micrometer spatial level.

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