Evidence for an Unusual Temperature Dependence of the Atmospheric Corrosion of Zinc

The atmospheric corrosion behavior of zinc in the presence of NaCl has been investigated using well-controlled laboratory exposures in 95% RH air at ten different temperatures in the range -4 to 22°C. Results show that a critical temperature (? -0.5°C) exists in zinc corrosion above which the rate of corrosion is constant/independent of temperature, and, below which there is a positive correlation between temperature and corrosion rate. The corrosion products formed above and below -0.5°C are also entirely different. While simonkolleite, hydrozincite and zinc carbonate hydroxide are the main corrosion products at T ?-0.5°C, the same compounds are absent at T < -0.5°C. Instead, sodium zinc carbonate (Na2Zn3(CO3)4.3H2O) is the dominant corrosion product at low temperature, together with Na2ZnCl4 · 3H2O and sweetite (Zn(OH)2). The results are interpreted in terms of two distinct corrosion modes prevailing at "high" and "low" temperature, respectively.