HIGH-TEMPERATURE OXIDATION OF ONE-COMPONENT AND 2-COMPONENT METALLIC SYSTEMS STUDIED BY IN-SITU X-RAY-ABSORPTION SPECTROSCOPY

A high-temperature oxidation technique by in-situ characterization of the oxide growth is presented. The technique has been utilised to stud y the oxidation of one- and two-component systems. Results on the oxid ation of Ni and Ni-Fe solid solution are reported for low values of th e oxygen partial pressure, namely 0.3 Pa. X-Ray absorption spectroscop y (XAS) measurements at the Fe and Ni K-edges were made in fluorescenc e mode and after each oxidation step. The atomic selectivity of XAS ma kes this technique particularly suitable when studying selective oxida tions. As indicated by the spectroscopic data, the oxidation of the Fe -Ni alloy mainly involves iron cations, and it leads to the growth of iron oxide, the formation of the ferrite being unfavourable. The oxida tion kinetics are also obtained by an appropriate analysis of the spec troscopic data, and the parabolic rate constants have been evaluated. These results indicate that the technique is particularly suitable for studying the hot corrosion of oxide film too thick for common surface spectroscopy and too thin for conventional thermogravimetric techniqu e.