The Effect of Submicron Ammonium Sulfate Particles on the Corrosion of Copper

The effect of submicron‐sized particles on the corrosion of copper has been investigated in mixtures at 373 K and relative humidities (RH) of 65, 75, and 88%. At 65% RH, particles do not affect the oxidation of copper. At 75% RH, the "critical relative humidity" of , localized formation of and a basic copper sulfate, brochantite or antlerite , is observed, depending on the amount of particles deposited. At 88% RH, sufficient water is absorbed by the particles to form a solution that spreads over a large surface area. A continuous thick layer of forms rapidly and becomes overgrown by antlerite crystals. Beneath the 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.