IN-SITU STUDIES OF PASSIVE FILM CHEMISTRY USING X-RAY-ABSORPTION SPECTROSCOPY

The application of X-ray absorption spectroscopy to the study of passi vation of thin metal films is discussed. Data are presented which demo nstrate the effectiveness of the technique for monitoring both potenti al- and time-dependent data on valency and selective dissolution from passive films. It is shown that iron undergoes reductive dissolution f rom the passive oxide film on both pure iron and Fe-26Cr, in the latte r case leading to enrichment of chromium in the passive film. Transpas sive dissolution of chromium can take place on Al-Cr and Fe-Cr only af ter it has been enriched in the passive film by dissolution of the oth er alloying element. Rapid polarization of Al-Cr leads to trapping of electroactive chromium in the passive film.