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The corrosion mechanism of copper at 373 and 300 K in the presence of submieron (NH~)2SO4 particle deposits has been investigated. Several in situ techniques have been used to monitor the corrosion process in real time. At and above the critical relative humidity of (NH4)2SO4, dissolution of Cu is followed by formation of Cu20, oxidation of Cu(I) ions to Cu (II) ions, and precipitation of antlerite [Cu3(SO4)(OH)4], broehantite [Cu4(SO4)(OH)6], or posnjakite [Cu4(SQ)(OH)~ -HzO]. The amount of corrosion product formed increases with amount of (NH4)2SQ particles, relative humidity (RH), and temperature. The in situ techniques allowed us to confirm and refine the individual steps in the multistep mechanism proposed in earlier work. ~ ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2015-06-18 to IP

The effect of submicron-sized (NH4)2SQ particles on the corrosion of copper has been investigated in air-H20 mixtures at 373 K and relative humidities (RH) of 65, 75, and 88%. At 65% RH, (NH~)2SO4 particles do not affect the oxidation of copper. At 75 % RH, the "critical relative humidity" of (NH4)2SO4, localized formation of Cu20 and a basic copper sulfate, brochantite [Cu4(SO4)(OH)6] or antlerite [Cu~(SO~)(OH)4], isobserved, 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 Cu20 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.

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