Effect of NO<sub>2</sub> on the Atmospheric Corrosion of Metals

Abstract

NO2 is an air pollutant which accelerates the atmospheric corrosion of metals, since it transforms into corrosive nitrous and nitric acids, when dissolved in thin water-films on metals. The concentration of SO2 in the atmosphere, which is also a common air pollutant, has been decreasing recently, whereas the concentration of NO2 has not been decreasing, and its effect on metals has become relatively serious.In this study, corrosion behaviours of common metals, Zinc, Aluminum, Iron, nickel, and copper in NO2-containing atmospheres are investigated.The results are as follows:(1) NO2 does accelarate the corrosion of metals, but its effect is not so serious as SO2. (2) The corrosion rate of each metal in NO2-containing atmosphere is nearly equal value. (3) The corrosion rate of metals in NO2-containg atmosphere depends on relative humidity, as well as SO2-containing atmosphere. (4) Nitrate is formed as a corrosion product on the metal surface exposed to NO2-containing atmosphere. (5) NO2 added to SO2-containing atmosphere has the effect of decreasing the corrosion rate of metals. (6) The corrrosion product formed on Zinc, Iron, and Nickel surface in NO2-containing atmosphere does not accelarate the corrosion of each metal.