Corrosion SIMS images

Imaging of elemental and isotopic distributions on surfaces has proved useful for diffusion measurements, corrosion and reactivity studies, contamination identification, and many other applications. SIMS imaging is particularly useful because of its high sensitivity. An example was the application to a problem in which a U-... 

The compositions of the.se films have been probed as a function of depth using a three-dimensional (3D) SIMS imaging procedure I5. Images of the spatial distributions of secondary ions from the film arc recorded. sequentially, as a function of depth, and are stacked" to form a 3D or volumetric image. The latter can be very effective in visualizing both the consistencies and variations expected in a typical corrosion film structure. 

SIMS systems capable of imaging can be used to. study corrosion samples in plan view or in cross section. The choice of primary ion should be of one that enhances the detection of the major products Cs is the most suitable since it enhances the production of electronegative species such as O. H and oxide molecular fragments. The beam currents used should be such that the entire oxide thickness can be profiled in a reasonable time typical sputter erosion rates in oxides are 3-5 pm/h for a I pA beam rastered over a 250 pm- area. Ion images collected should reflect the possible oxide combinations, e.g.. FeO for a simple Fe oxide, or FeCrO" for an oxide believed to contain both Fe and Cr. 

Where experiments are conducted which simulate process conditions, the effectiveness of electrochemical testing is more controversial. Postreaction EIS studies of alloys exposed to autoclave corrosion were not able to illuminate differences in the performance of the alloys. By contrast, imaging SIMS provided u.seful insight into the structural and compositional differences, leading to a characterization that might possibly be used to qualify other alloy specimens. Alternatively, one could consider the surface techniques to be at their best when performing a postfailure analysis. 

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