FT-IR Microscopic Base Imaging System: Applications for Chemical Analysis of Zn and Ni Atmospheric Corrosion

Abstract

The possible use of an FT-IR imaging system for surface studies of atmospheric corrosion products on zinc and nickel samples has been explored. Samples have been exposed in an urban site located at Rouen in France. Corrosion products, detected by means of energy-dispersive spectrometry/X-ray diffraction (EDS/XRD) and FT-IR spectroscopy, are mainly Zn₄CO₃(OH)₆·H₂O, ZnSO₃·nH₂O, Zn₄SO₄(OH)₆·nH₂O, and NiSO₄·xH₂O. IR microspectroscopy and mapping techniques allow the observation of the heterogeneous distribution of chemical species on sample surfaces. While the zinc corroded surface seems uniform, inhomogeneity in the development of carbonate and hydroxysulfate compounds in layers is observed. The imaging chemical analysis enables the assignment of the 1550 cm⁻¹ absorption band of the corrosion product to zinc hydroxycarbonate. The corrosion mechanism observed on nickel is pitting corrosion. Pit size, chemical mapping, and 3-D visualization determined from SEM/EDS and FT-IR maps are very similar.