INSITU INFRARED REFLECTION ABSORPTION-SPECTROSCOPY FOR STUDIES OF ATMOSPHERIC CORROSION

A new experimental setup for in SitU infrared reflection absorption sp ectroscopy (IRAS) studies of atmospheric corrosion. is described. It c onsists of units for preparation of corrosive air, an in situ cell whe re samples are exposed, and an optical system linked with a Fourier tr ansform infrared spectrometer. In situ infrared spectra can be recorde d in humid air at ambient pressure and results are presented of the ox ide formation on copper in clean air at 90% relative humidity and 25-d egrees-C. At these exposure conditions copper(I) oxide is formed, and its growth can be monitored from the initial stages to more fully deve loped oxide films. The thickness of the oxide film was estimated by el ectrolytic cathodic reduction and a linear relationship was found betw een the intensity of the copper(I) oxide band measured by in situ IRAS and the thickness of the oxide. The experimentally obtained results w ere compared with theoretical calculations of the relationship between band size and thickness using optical constants for Cu2O. From consid erations of band intensity, noise level, and oxide film thickness, the present detection limit corresponds to a 6 angstrom thick film of cop per(I) oxide. To further illustrate the applicability of the technique the reaction of SO2 containing air at 80% relative humidity with copp er was also studied and the formation of sulfite on the surface was de tected by in situ IRAS measurements.