Copper sulfur pollutants effect

The influence of NO on electric contact materials seems often to be due to synergistic effects with other pollutants. Whereas exposure of e.g. copper and gold contacts in an atmosphere of NO shows no corrosion effect the synergistic effect of SO and NO2 is very pronounced (, ). A possible explanation is that NO2 oxidizes SO2 to sulfuric acid according to the following reaction ... 

Air pollution sources in the United States and Canada currently emit more than 25 million tons of sulfur dioxide each year. SO2 and wet acidic deposition are believed to cause damage to aquatic life, crops, forests, and materials. The effects on materials include damages to common construction materials including galvanized steel (zinc), paint, copper, building stones and mortar, as well as damages to cultural or historic objects and buildings. 

The contaminants may be deposited on the surfaces of the materials in the form of anhydrous or hydrated species. Some pollutants, like CO2, SO, NO, and HCl, are typical of urban and industrial areas, give rise to acid rains, and might contribute to the cathodic processes, while others, such as chlorides, are typical but not exclusive of marine and coastal areas and give rise to hygroscopic salts that increase the duration of wetting of surfaces, increase the conductivity of solutions, and make less protective the corrosion products. Some others, such as the sulfides, which can result from microbiological activity, alter the composition of the corrosion products, their protective capability, and the nobility of the metal often they are semiconductors, depolarize the cathodic process of hydrogen evolution, and may be oxidized to sulfuric acid by bacteria. Ammonia alters the composition of corrosion products and the solubility of metal ions it has particularly drastic effects on copper alloys and their corrosion forms. In the transport of these contaminants toward the surfaces, an important role is exerted by the wind and by the orientation of the surfaces, which can promote or hinder the washout by the rains. 

Tables 2.3-2.6 and Fig. 2.2 give historic data on corrosion resistance of zinc classified subjectively by environment. The qualitative terms used by authors clearly have different corrosion significance in different parts of the world. Some work for which atmospheric pollution data is available is given in Table 2.7A together with a supplement. Table 2.7B. Averages of six l-year tests in the worldwide ISOCORRAG series, still in progress, have been published, however (Knotkova, 1993) the full data cover steel, copper, and aluminum as well as zinc. The interpretation of measurements of atmospheric sulfur dioxide and chloride is not clear-cut different measurement techniques can give substantially different results, and the relationship between corrosion effects and the particular method of measurement requires further interpretation.

Copper manufacture during the last part of the 20 century was influenced by an ever-increasing concern for the environment. The most significant release of pollutants in the pyrometallurgy of sulfide ores is related to atmospheric emissions of sulfur dioxide and particulate matter containing heavy metals. If not captured, some sulfur dioxide reacts with water vapor in the atmosphere to form sulfuric acid, which returns to earth in acid rain. All the effects of acidic deposition on soils, vegetation, wildlife and man-made structures are well documented. With new techniques sulfur dioxide is transformed to sulfuric acid. A must from the environmental viewpoint may thus - as is often the case - be profitable. 

The corrosion resistance of copper is good, but in polluted, humid air, containing sulfur dioxide and/or chlorides, the copper surface is oxidized. A black film, mainly cuprite, Cu O, is formed. A green patina with varying formula is formed by secondary processes. Two common types are Cu.,(OH)gSO H2 Cu lOHjjCl. These compounds have a decorative effect but serve also as protecting layers, reducing the rate of further corrosion. 

Combustion of coal produces many of the same ultimate water pollutants as combustion of petroleum does, i.e., PAHs. Coal burning, however, produces greater quantities of metals, sulfur dioxide, and haloacids. Coal combustion stack emissions contain significant quantities of arsenic, mercury, selenium, copper, and tin [25]. Sulfur dioxide is ultimately converted to sulfuric acid in the air. Sulfuric acid and the haloacids (HF, HCl, HBr, and HI) ultimately come down as acid rains and acidify surface waters [26]. Acidified water is by itself toxic to marine life. Its effect is amplified, however, by the solubilization of metals and hydrolysis of other chemical compounds. 

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