Sulfidation of Zinc by Traces of Hydrogen Sulfide in Air

Abstract

The effect of in the sub‐parts per million range on the atmospheric corrosion of zinc has been investigated in the laboratory. Each sample was exposed individually to air with careful control of pollutant concentration, relative humidity, and flow conditions. Monitoring of concentration at the outlet of the corrosion chamber was used to study the reaction of with zinc metal during the first 24 h. Four‐week exposures were also performed to study the corrosion rate and the corrosion products. The deposition of on zinc strongly depended on the relative humidity. In dry air deposition was limited to an uptake on the order of a monolayer. At 70 to 99% RH the initial deposition rate of was faster, and the deposition reached a steady state after 15 to 20 h of exposure. Analysis of the evolved from the samples when treated with acid showed of the deposited on zinc to be present in sulfide form. X‐ray photoelectron spectroscopy and ion chromatographic analysis supported this finding, small amounts of sulfate being detected besides sulfide. After a 4 week exposure to at 95% RH, zinc blende (sphalerite) was identified by grazing angle x‐ray diffraction. It was concluded that the zinc sulfide film grows by bulk diffusion of ions. The rate of zinc sulfidation was independent of concentration between 25 and 780 ppb.