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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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This feature discusses measuring the levels of equipment damage caused by airborne substances and determining the effect of ionic particles on the corrosion mechanism.

The atmospheric corrosion of zinc in the presence of (NH4),504 particles has been investigated at 300 and 373 K in air-water vapor mixtures. The development of corrosion products was followed by several in situ techniques, including Fourier transform infrared spectroscopy, x-ray diffraction, pH measurements, and scanning Kelvin probe measurements. Unlike earlier work on copper and aluminum, zinc reacts with the particles below the critical relative humidity (CRH) of (NH4),504. At 300 K reaction was observed at 65% relative humidity (RH), but not at 60% RH. This is attributed to the presence of basic zinc carbonate on the surface, which absorbs sufficient water at this low RH to make electrochemical reactions possible. At and above the CRH of (NHJ2504, zinc reacts with (NH4)2504 forming mixed ammonium zinc sulfate and later on basic zinc sulfate, and at 373 K additionally zincite (ZnO). Above the CRH of (NH4),504, the corrosion potential decreases directly after formation of droplets surrounding the particles and zinc becomes active. Corrosion mechanisms are proposed to explain the observations. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-06-18 to IP

The effect of (NH4)2S04 particles on the atmospheric corrosion of aluminum has been investigated at 300 and 373 K at various relative humidity (RH) levels. Aluminum reacts with (NH4)2S04 particles only at or above the critical relative humidity (CRH) of (NH4)2S04 at either temperature. The corrosion rate increases with increasing RH and temperature. Above the CRH of (NH4)2S04, droplets are formed on the particles at both temperatures, making electrochemical reactions possible. The (NH4)2504 decomposes and ammonia evaporates from the droplets. At 373 K mixed ammonium-metal-sulfates are formed, followed by basic metal sulfates; oxide formation is enhanced at 373 K compared to 300 K. At 300 K no solid corrosion products containing Al are found, but it was shown that Al dissolves in the droplets. A corrosion mechanism has been proposed that explains the experimental observations, including pH and corrosion potential changes with time. InfroductionCompared to other metals, aluminum corrodes rather slowly under atmospheric conditions, because it forms an insulating, amorphous oxide film of low solubility in air and aqueous solutions over the pH range from 4 to 8.6. However, enhanced corrosion occurs in marine environments and in some urban areas.' Common corrosion prod ucts found under these conditions are basic aluminum sul-. fates and amorphous aluminum sulfate hydrate.1'2 Indoors, sulfate is the most abundant anion found on aluminum surfaces.3 The presence of SO42 on these surfaces may be due to SO2 induced corrosion or sulfates associated with particle deposition, The accumulation of inorganic ionic substances is primarily due to particle deposition.4Because of their high ionic content and high indoor coneentration, fine particles (<2 m) play a major role in the corrosion of electronic materials.45 Ammonium and sulfate ions are the most abundant ions in fine dust particles commonly found in urban environments, and may, therefore, play. a dominant role in the corrosion process. The effect of (NH4)2S04 on copper, another metal common1y used in the electronic industry, has been reported previously.6-9 * Electrochemical Society Active Member. * *Electrochemical Society Fellow.start to absorb water vapor from the atmosphere, cannot be simulated.Patterson and Wilkinson10 investigated the effect of NaC1 and NH4C1 particles on the corrosion of aluminum at 293 K and 80% relative humidity (RH). The weight increase due to NaC1 particles was linear with time and was small compared to the weight increase due to NH4C1 particles. With NH4C1, Al showed an initial phase of slow weight increase, and after 5 days, a sudden rapid weight gain. Also the appearance of the specimen changed after

The effect of the surface concentration of submicrometer ammonium sulfate (NH 4 ) 2 SO 4 dust particles on the mechanism of atmospheric corrosion of copper has been investigated at 298 K and 93% relative humidity ͑RH͒. For surface concentrations from 1 g/cm 2 to 10 mg/cm 2 , the same corrosion products are formed at relative humidities well above the critical relative humidity of (NH 4 ) 2 SO 4 . Initially, a Cu(NH 3 ) 2ϩ complex is formed. The basic copper sulfate posnjakite precipitates when its solubility product is exceeded while NH 3 evaporates. Posnjakite may be converted to antlerite or brochantite if higher amounts of (NH 4 )SO 4 particles were deposited. The basic copper sulfates then decompose at the inner interface to form Cu 2 O. With low amounts of (NH 4 ) 2 SO 4 particles, the conversion is 100%. With high amounts of particle deposits, residual copper sulfate remains on top of a Cu 2 O-layer. With increasing amounts of deposited (NH 4 ) 2 SO 4 particles on copper, the sequence of corrosion products that are formed takes more time. The mechanism proposed in earlier work for the corrosion of copper with (NH 4 ) 2 SO 4 particles in humid air is improved to explain the new experimental findings.Before 1995, essentially all laboratory studies on the atmospheric corrosion of metals were conducted using corrosive gases in concentrations that were excessively high relative to those found in the troposphere. The corrosion product films that were produced were frequently unrealistic. For example, for copper it was not possible to produce a surface layer similar to the naturally formed patina using gaseous pollutantes like SO 2 and NO 2 . [1][2][3][4][5][6][7][8][9] However, the 1930s, Vernon demonstrated that dust particles, especially dust particles consisting of ammonium sulfate, significantly influence the corrosion of copper and lead to higher corrosion rates. [10][11][12][13][14][15][16] The factors that determine the amount of ionic surface contamination relevant for atmospheric corrosion on metal surfaces was later studied by Sinclair et al. [17][18][19][20][21][22][23] The extent of ionic deposition on indoor surfaces is influenced by the concentration of dust particles in the outdoor air, the air exchange rate between indoors and outdoors, efficiency of air filtration systems, the velocity of the air, the surface area to volume ratio, the temperature of the surface, the distance between surfaces and source of particles, and the orientation of the surface. It was shown that most of the sulfur acquired by zinc and aluminum surfaces is supplied as dry deposition, and not, as previously assumed, in gaseous form from the reaction with SO 2 . It was also shown that fine particles ͑Ͻ1 m͒, produced from corrosive gases through chemical and physical processes that occur in the atmosphere, play the decisive role in the atmospheric corrosion of metals because of their higher concentration indoors ͑due to low filtration efficiencies for fine particles͒ and because of their greater content of soluble ions compare...