俄歇电子能谱（AES） can be effective in determining the quality of passivation layers used to prevent corrosion. In addition, if corrosion does occur, Auger analysis can be instrumental in determining its cause. Auger analysis is capable of detecting very localized corrosion and potential causes, as shown in the following case study.
Figure XNUMX shows a high magnification secondary electron image (XNUMXx magnification) obtained from an Auger instrument on the as-received surface of a piece of XNUMX series stainless steel sheet. The micrograph shows a series of extremely small defects, most of which being only about XNUMXnm in diameter. This SEM image was used to define points on which Auger electron spectroscopy was to be performed. One large and one small particle (points XNUMX and XNUMX, respectively) were analyzed along with a control region (point XNUMX) off of the defects. All three of the survey spectra show the presence of the expected C, O, Cr, Fe and Ni from the air-exposed stainless steel surface. In addition, the spectrum from point XNUMX (larger defect) shows the presence of a large amount of Ca along with a smaller Na peak. The Auger spectrum from the small defect (point XNUMX) shows the presence of S and Na contaminants but also shows much different Fe to Cr peak ratios than the spectrum from the control area (point XNUMX). Quantification of the elements detected from these three points is shown in Table XNUMX. Auger maps were acquired for several of the elements of interest including Ca, Cr, and Fe. The map for Ca reveals a lateral distribution of Ca within a XNUMXmm2 field of view.
Although scores of particle defects were observed in the SEM image, only a few of them appear to have significant Ca, as shown in the Ca Auger map. Most of the smaller particles correspond to larger concentrations of Fe, compared to the background area (Point XNUMX). This indicates that localized corrosion has occurred within these XNUMXnm-sized defects with an obvious potential cause being the presence of Na.