Atmospheric corrosion is a costly problem. Accelerated laboratory tests, such as the salt fog chamber, have been created to predict corrosion of materials without the need to expose them over long periods of time outdoors. However, these accelerated tests often do not accurately reproduce the types and rates of corrosion found in field exposures. Silver exhibits this discrepancy and has been used in recent years in an attempt to correct the shortcomings of these accelerated tests. X-ray photoelectron spectroscopy (XPS) was used to identify the corrosion products on field-exposed silver samples.  This study identifies Ag2SO3 and Ag2SO4 on field-exposed silver coupons. The presence of these species on field-exposed silver has been contested in the literature. Evidence suggests that Ag2SO3 is an intermediate step in the formation of Ag2SO4. Furthermore, the presence of alkali cations, such as Na+, determines the final oxidation state of the sulfur species on silver. If Na+ is present, Ag2SO4 is the final state, whereas Ag2SO3 is not found in the presence of cations. The identification of sulfite and/or sulfate on field-exposed samples suggests the need for further improvement of salt fog tests which do not currently include a sulfur source. Furthermore, the identification of these species indicates that surface-sensitive techniques, such as XPS, are necessary in the identification of corrosion products.

Influence of the atmosphere on the corrosion of Ag

245th National Meeting (2013)

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