Complexity at a humid interface: throwing fresh light on atmospheric corrosion

Atmospheric corrosion of metals arising from exposure to water vapor is a pervasive problem across a wide range of practical scenarios, including nuclear material storage and historical artifact conservation. Frequently, it is hypothesized that this phenomenon becomes an issue once the number of monolayers of water growing atop a substrate is sufficient to facilitate corrosion chemistry, but supporting evidence remains scarce. We apply both near ambient pressure X-ray photoelectron spectroscopy and vibrational sum frequency spectroscopy to further elucidate the interaction of water vapor with zinc, a common engineering substrate for corrosion protection applications. Data acquired as a function of relative humidity indicate that water sorption is much more complex than expected, involving micropore filling and capillary condensation in the adventitious carbon layer covering the zinc surface. These results suggest that current mechanistic models for atmospheric corrosion, as well as other interfacial phenomena occurring in humid environments, require extensive revision and should embrace explicit consideration of the role of surface carbon contamination.