APPLICATION OF X-RAY-ABSORPTION NEAR-EDGE SPECTROSCOPY AT THE S K-EDGE TO THE STRUCTURAL CHARACTERIZATION OF SURFACE REACTED METALLIC ALLOYS

X-ray absorption spectroscopy has been used to study the interaction o f H2S at 700-degrees-C with a protective oxide layer on a Ni-20Cr allo y. Both fluoresence and electron yield detection modes, applied simult aneously, enabled structural information from 100nm and 5nm respective ly to be probed which allowed the processes at the air/oxide and oxide /alloy interfaces to be monitored as a function of corrosion time. The data revealed sulphur to be in a high 6+ oxidation state in the early stages of the corrosion process, changing to 2- with the formation of a thicker sulphide-like surface film.