J. Phys. IV France 7 (1997) C2-1183-C2-1184
XANES Study of Ce and Mo Containing Conversion Coatings on AluminiumJ. Wan1, G.E. Thompson1, T.K. Ng1, K.Q. Lu2 and C.J.E. Smith3
1 Corrosion and Protection Center, UMIST, Manchester M60 1QD, UK
2 Institute of Physics, Chinese Academy of Sciences, Beijing, 100080, China
3 Defence Research Agency, Farnborough, Hants, GU14 6TD, UK
Ce-Mo conversion coatings on superpure aluminium have been examined using XANES and analytical TEM to study the coating development over the electropolished surface. Ce species are predominantly in the Ce3+ state in the coating, resulting from the various steps of the process, and Mo is in the Mo6+ state. After immersion in NaCl solution, Ce and Mo species leach from the coating. Conversion coating formation develops a hydrated film with cerium species incorporated ; final anodic polarisation in MoO42- solution results in Mo species in the hydrated film. Corrosion inhibition is attributed to the coating acting as a barrier layer to environmental access to the aluminium substrate and reduced cathodic activity.
© EDP Sciences 1997