Atmospheric Corrosion of Zinc in the Presence of Ammonium Sulfate Particles

Abstract

The atmospheric corrosion of zinc in the presence of 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 . 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 , zinc reacts with forming mixed ammonium zinc sulfate and later on basic zinc sulfate, and at 373 K additionally zincite (ZnO). Above the CRH of , the corrosion potential decreases directly after formation of droplets surrounding the particles and zinc becomes active. Corrosion mechanisms are proposed to explain the observations.