FT-IR microscopic base imaging system: Applications for chemical analysis of Zn and Ni atmospheric corrosion

The possible use of an FT-IR imaging system for surface studies of atmosphe ric corrosion products on zinc and nickel samples has been explored. Sample s have been exposed in an urban site located at Rouen in France. Corrosion products, detected by means of energy-dispersive spectrometry/X-ray diffrac tion (EDS/XRD) and FT-IR spectroscopy, are mainly Zn4CO3(OH)(6).H2O, ZnSO3. nH(2)O, Zn4SO4(OH)(6). nH(2)O, and NiSO4. xH(2)O. IR microspectroscopy and mapping techniques allow the observation of the heterogeneous distribution of chemical species on sample surfaces. While the zinc corroded surface se ems uniform, inhomogeneity in the development of carbonate and hydroxysulfa te compounds in layers is observed. The imaging chemical analysis enables t he assignment of the 1550 cm(-1) absorption band of the corrosion product t o zinc hydroxycarbonate. The corrosion mechanism observed on nickel is pitt ing corrosion. Pit size, chemical mapping, and 3-D visualization determined from SEM/EDS and FT-IR maps are very similar.