Electronic materials and devices corrode in the same ways as automobiles, bridges, and pipelines, but their typically small dimensions make them orders of magnitude more susceptible to corrosion failure. As elsewhere, the corrosion involves interactions with the environment. Under control, these interactions can be put to use, as in the formation of protective and functional oxide films for superconducting devices. Otherwise, they cause damage, as in the electrolytic dissolution of conductors, even gold, in the presence of humidity and ionic contamination from atmospheric particles and gases. Preventing corrosion entails identifying the damaging interactions and excluding species that allow them to occur.

This paper explores the simple principle that a metal surface wets when the surface relative humidity ͑RH͒ exceeds the deliquescent RH ͑DRH͒ of any salts on the surface. Data from field exposures across 19 sites in China, the Philippines, Indonesia, and Australia is used to determine the conditions under which openly exposed surfaces wet. At each site, surface temperature ͑of a zinc plate͒, ambient RH, sensor wetness, airborne salinity, and gaseous SO x and NO x were determined over a one-year period. In conjunction with these microclimate measures, the chemistry of airborne and deposited aerosols, as well as rainwater, were measured. Complimentary data from an environmental scanning electron microscope are presented in which salts derived from the evaporation of sea salt are rewetted. Using all of this data, an assessment of the probable contaminants controlling sensor wetting at each site is made. It is found that sites with similar International Standard Organization, ͑ISO͒ 9223, classifications in terms of industrial and marine airborne pollutants show similar surface contaminants and wetting characteristics. It is proposed that dominant contaminates can be identified for each ISO classification that are consistent with the general principle that wetting occurs when surface RH exceeds the DRH of the salts making up the contaminates. These salts can change from day to day due to the continual change in the composition of the contaminates and the ongoing homogenization of previously deposited salts through chemical reaction between salts and with the surface. Rain events usually clean the surface and start the cycle over again. The application of these findings to process models of corrosion is discussed, while generalized rules for predicting surface wetting based on climate data are proposed. It is found that these generalized rules predict total time of wetness to a high degree of accuracy.The concept of time of wetness ͑TOW͒ has been a very useful one for atmospheric corrosion scientists. 1 Indeed, the principle that corrosion can only occur in the presence of an electrolyte is based on fundamental electrochemical considerations. 2 Since the TOW concept was first proposed, sensors to measure TOW, 3-5 dose functions to define metallic corrosion 6-8 as a function of TOW, and degradation maps 9 based on these dose functions have been developed. However, the approximation commonly used to estimate TOW and included in International Standard Organization ͑ISO͒ 9225 ͓that TOW is the time when temperature is above 0°C and relative humidity ͑RH͒ is above 80%͔ cannot be directly derived from an understanding of the processes of surface wetting. Further studies of hygroscopic salts and aerosols indicate that salts, and thus the surfaces that they are on, may wet over a range of RH, depending on the deliquescent RH ͑DRH͒ of the salt. [10][11][12] In recent years, a number of authors have proposed refinements to the TOW concept in order to either derive better statistical fit with their corrosion data, or to account for...

We have built a particle analyzer capable of real-time detection and characterization of individual particles. Particle analysis is accomplished by pulsed laser ablation of a particle followed by time-of-fiight mass spectrometry of the resulting atomic and molecular ions. The detected ions are characteristic of a particle's

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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