THE EFFECT OF SUBMICRON AMMONIUM-SULFATE PARTICLES ON THE CORROSION OF COPPER

The effect of submicron-sized (NH4)2SO4 particles on the corrosion of copper has been investigated in air-H2O mixtures at 373 K and relative humidities (RH) of 65, 75, and 88%. At 65% RH, (MH4)2SO4 particles do not affect the oxidation of copper. At 75% RH, the ''critical relativ e humidity'' of (NH4)2SO4, localized formation of Cu2O and a basic cop per sulfate, brochantite [Cu4(SO4)(OH)6] or antlerite [Cu3(SO4)(OH)4], is observed, depending on the amount of particles deposited. At 88 % RH, sufficient water is absorbed by the particles to form a solution t hat spreads over a large surface area. A continuous thick layer of CU2 O forms rapidly and becomes overgrown by antlerite crystals. Beneath t he oxide scale, the copper substrate is locally corroded. The present work clearly-demonstrates that ammonium sulfate particles, which are a major constituent of urban atmospheric dust, are an important factor in the formation of patina on copper.