CATHODIC REDUCTION AND INFRARED REFLECTANCE SPECTROSCOPY OF BASIC COPPER(II) SALTS ON COPPER SUBSTRATE

Infrared reflectance spectroscopy and cathodic reduction have been use d for the characterization of copper corrosion products formed by atmo spheric corrosion. The following basic copper(II) salts were synthesiz ed: atacamite and paratacamite (Cu2Cl(OH)(3)), brochantite (Cu(4)SO(?) 4(OH)(6)), posnjakite (CU4SO4(OH)(6)H2O), malachite (CU2CO3(OH)(2)), g erhardite (CU2NO3(OH)(3)). The samples for analysis were obtained by i ncrustation of submicron particles of the compound on the surface of O FHC copper coupons. Infrared reflectance spectroscopy shows that, unli ke copper oxides, the reflection spectra of thin layers of basic coppe r(II) salts on copper are similar to those obtained by the usual KBr-p ellet method for the location of the bands. However, some differences occur in the intensities of the bands between the two modes. Infrared reflectance spectroscopy allows an easy identification of basic copper (II) salts: chlorides can be identified by their Cu-O-H bending modes; sulfates, sulfite, nitrate and carbonate by the internal mode of the corresponding anion (nu(3) region). The cathodic reduction analyses of the salts on copper display only a wide peak in the range from -0.6 t o -0.55 V vs SCE, indicating that one step is involved. The potential of this cathodic reduction peak is distinguishable from the one of cop per(I) oxides (-0.9 V vs SCE). Thereby the relative proportions of cop per(II)) salts and copper(I) oxides present in the corrosion layer can be determined.