INITIAL INTERACTION OF SULFUR-DIOXIDE WITH WATER COVERED METAL-SURFACES - AN IN-SITU IRAS STUDY

In situ infrared reflection absorption spectroscopy (IRAS) has been us ed to study the initial interaction of sulfur dioxide with water adlay er covered copper, nickel, and zinc surfaces. Each metal was exposed t o 0.21 ppm SO2 in flowing air at 80% relative humidity and the formati on of sulfite was followed from submonolayer thickness to layers of co rrosion products of a few nanometers thickness. From the positions of sulfite bands in the experimentally obtained IRAS spectra and from con siderations of optically induced bandshifts in calculated IRAS spectra , it is suggested that the sulfite ions are coordinated with sulfur or sulfur and oxygen to the copper surface and with oxygen to the nickel and zinc surfaces. A fast initial growth rate was observed for the su lfite layer, which was followed by a slower growth rate after a few ho urs of exposure. A reaction sequence is suggested where bisulfite ions , formed by hydrolysis of sulfur dioxide in the water adlayer, generat e surface metal-sulfito complexes at the oxide covered metal surface w hich subsequently detach from the surface and precipitate as thin laye rs of corrosion products.