Effects of NaCl and SO2 on the initial atmospheric corrosion of zinc

The influence of NaCl deposition on the corrosion of zinc in atmospheres with and without SO2 was studied via quartz crystal microbalance. Regularity of the initial corrosion of zinc under these conditions was analyzed. The results show that NaCl can accelerate the corrosion of zinc. Mass gain of zinc increases with the exposure time, which can be correlated by using exponential decay function. The relationship between mass gain and amount of NaCl deposition is well linear at any time in air containing 1 ppm SO2, but follows quadratic function in air without SO2. More amount of NaCl deposition will slow down the corrosion to some extent after exposure for certain time in the presence of SO2. The combined effect of NaCl and SO2 on the corrosion of zinc is greater than that caused by each single component. Fourier transform infrared spectroscopy and X-ray diffraction were used to characterize the corrosion products of zinc. In the absence of SO2, simonkolleite, Zn5(OH)8Cl2·H2O and zincite, ZnO are the dominant corrosion products, while zinc hydroxysulfate (Zn4SO4(OH)6·3H2O), zinc chloride sulfate hydroxide hydrate (Zn12(SO4)3Cl3·(OH)15·5H2O) and simonkolleite dominate in the presence of SO2. Brief discussion on the mechanisms of atmospheric corrosion under these conditions was introduced.