ENVIRONMENTAL-EFFECTS ON MATERIALS - THE EFFECT OF THE AIR-POLLUTANTSSO2, NO2, NO AND O-3 ON THE CORROSION OF COPPER, ZINC AND ALUMINUM - A SHORT LITERATURE SURVEY AND RESULTS OF LABORATORY EXPOSURES

Laboratory exposures of copper, zinc and aluminium were carried out in humid air containing single air pollutants (SO2, NO2, NO, O-3) and la boratory air in order to investigate their role in atmospheric corrosi on. Realistic pollutant supply rates as normally encountered in outdoo r exposures were chosen for the experiments. Some experiments resulted in the formation of corrosion products with morphologies commonly for med during outdoor exposure. The air pollutants sulphur dioxide, nitro gen dioxide and especially ozone play a crucial role in the atmospheri c degradation of the materials investigated. Ozone has the strongest e ffect on the corrosion of copper followed by nitrogen dioxide and sulp hur dioxide. Realistic corrosion products such as cuprite (Cu2O), basi c copper nitrates and basic copper sulfates were identified in these e xperiments. The effect of sulphur dioxide exceeds by far the effects o f the other air pollutants in the corrosion of zinc. The experiments r esulted in the formation of zinc sulphates, which are water-soluble at the test conditions (relative humidity: 90%). Ozone plays a significa nt role in the corrosion of aluminium, while the effect of sulphur and nitrogen dioxide was considerably smaller. The present work summarise s recently discovered effects of the air pollutants mentioned and pres ents results of a comparative study on the effects of single air pollu tants on the corrosion of copper, zinc and aluminium under realistic t est conditions. The microstructures of the corroded surfaces were inve stigated by scanning electron (SEM/EDX) and also partially by Auger el ectron microscopy (AES). Corrosion products were analysed using X-ray diffraction (XRD) and ion chromatography (IC). Results from gravimetri c evaluation are also reported. (C) 1997 Elsevier Science Ltd.