Environmental effects on materials: The effect of the air pollutants SO 2, NO 2, NO and O 3 on the corrosion of copper, zinc and aluminium. A short literature survey and results of laboratory exposures

Abstract

Laboratory exposures of copper, zinc and aluminium were carried out in humid air containing single air pollutants (SO 2, NO 2, NO, O 3) and laboratory air in order to investigate their role in atmospheric corrosion. Realistic pollutant supply rates as normally encountered in outdoor exposures were chosen for the experiments. Some experiments resulted in the formation of corrosion products with morphologies commonly formed during outdoor exposure. The air pollutants sulphur dioxide, nitrogen dioxide and especially ozone play a crucial role in the atmospheric degradation of the materials investigated. Ozone has the strongest effect on the corrosion of copper followed by nitrogen dioxide and sulphur dioxide. Realistic corrosion products such as cuprite (Cu 2O), basic copper nitrates and basic copper sulfates were identified in these experiments. The effect of sulphur dioxide exceeds by far the effects of the other air pollutants in the corrosion of zinc. The experiments resulted in the formation of zinc sulphates, which are water-soluble at the test conditions (relative humidity: 90%). Ozone plays a significant role in the corrosion of aluminium, while the effect of sulphur and nitrogen dioxide was considerably smaller. The present work summarises recently discovered effects of the air pollutants mentioned and presents results of a comparative study on the effects of single air pollutants on the corrosion of copper, zinc and aluminium under realistic test conditions. The microstructures of the corroded surfaces were investigated by scanning electron (SEM/EDX) and also partially by Auger electron microscopy (AES). Corrosion products were analysed using X-ray diffraction (XRD) and ion chromatography (IC). Results from gravimetric evaluation are also reported.