The Influence of CO 2 and NaCl on the Atmospheric Corrosion of Zinc: A Laboratory Study

Abstract

We report on a laboratory study of the atmospheric corrosion of NaCl‐treated zinc in air containing different concentrations of carbon dioxide (<l, 100, 350, 1000, and 40,000 ppm). Each sample was exposed individually to synthetic atmospheres with careful control of concentration and flow conditions. The relative humidity was 95%. The protective properties of carbonate‐containing corrosion products were investigated in 225 ppb . Mass gain and metal loss results are reported. The corrosion products were analyzed quantitatively and qualitatively by a combination of X‐ray diffraction, scanning electron microscopy, gravimetry, and quantitative analysis for carbonate. The corrosion of zinc in the presence of NaCl resulted in heavy pitting of the metal. Carbon dioxide slowed down the corrosion rate by a factor of three to six. This is explained by the neutralization of the surface electrolyte resulting in the precipitation of chloride in the form of insoluble . In the presence of NaCl large amounts of hydroxy carbonates formed. There is no indication that hydroxy carbonates are protective in a environment.