Abstract
In situ IR-RAS (Infrared Reflection Absorption Spectroscopy) is a powerful technique for investigation of the initiation of atmospheric corrosion, but the interpretation of the spectra is not always easy, because the band positions and shapes of the IR-RAS spectra possibly change from those of the transmission spectra due to an abnormal dispersion of the refractive indexes of surface layers.
To estimate the band shifts, IR-RAS spectra of corrosion products and related compounds were theoretically calculated by using their optical constants which were derived from the transmission spectra and the Kramers-Kronig analysis. In this procedure a three phase model (air/surface layer/copper) and a four phase model (air/water layer/corrosion product layer/copper) were employed and the results were compared.
The band of IR-RAS spectra shifted to higher wavenumber region by 10, 64, 20, and 18cm-1 for CuSO4⋅5H2O, CuSO4, Na2SO3, and Chevreul's salt (Cu2SO3⋅CuSO3⋅2H2O), respectively. A spectrum obtained on copper in air containing 10 ppm SO2 and 80% relative humidity of water was analyzed based on the calculated IR-RAS spectra.
