Surface layers formed initially on copper in air containing water vapor and SO2 as determined by IR-RAS and 2D-IR

To determine the components of corrosion products and the respective formation rates of the components, a series of in situ time-resolved IR-RAS spectra was measured on copper in air containing 8.7 ppm SO2 and 80% relative humidity, and two-dimensional correlation analysis (2D-IR), which differentiates effectively overlapping bands and gives a clue to their band positions, was applied to the IR-RAS spectra. On the basis of the 2D-IR, deconvolution of the overlapping bands was carried out and the growth rates of the respective components of corrosion products were determined. The components of the surface layer formed in the environment are discriminated successfully by using 2D-IR and it is elucidated that sulfite and sulfate grow on the surface and Chevreul's salt (CuSO3Cu2SO3·2H2O) is estimated as the main component of sulfite and CuSO4·5H2O, that of sulfate. The formation of an adlayer of water appears preceding sulfite and sulfate, and the formation rate of sulfite is higher initially than that of sulfate, but the rate declines to become nearly equal to that of sulfate within the experimental period.