In Situ Infrared Reflection Absorption Spectroscopy for Studies of Atmospheric Corrosion

Abstract

A new experimental setup for in situ infrared reflection absorption spectroscopy (IRAS) studies of atmospheric corro-sion is described. It consists of units for preparation of corrosive air, an in situ cell where samples are exposed, and an optical system linked with aFourier transform infrared spectrometer. In situ infrared spectra can be recorded in humid air at ambient pressure and results are presented of the oxide formation on copper in clean air at 90 % relative humidity and 25 ~ At these xposure conditions copper(I) oxide is formed, and its growth can be monitored from the initial stages to more fully developed oxide films. The thickness of the oxide film was estimated by electrolytic cathodic reduction and a linear elationship was found between the intensity of the copper(I) oxide band measured by in situ IRAS and the thickness of the oxide. The experimentally obtained results were compared with theoretical calculations of the relationship between band size and thickness using optical constants for Cu~O. From considerations of band intensity, noise level, and oxide film thickness, the present detection limit corresponds to a 6 A thick film of copper(I) oxide. To further illustrate the applicabil-ity of the technique, the reaction of SO2 containing air at 80 % relative humidity with copper was also studied and the formation of sulfite on the surface was detected by in situ IRAS measurements. Interracial phenomena play critical roles in the perfor-mance of materials and in many processes occurring at