Secondary spreading of acidified aerosols on the surface of Zn

Secondary spreading of acidified sodium chloride (NaCl) aerosol droplets on the surface of zinc have been studied. The in-situ observation of the secondary spreading, corrosion morphology, corrosion products under different position and volume loss are used to understand the secondary spreading of the acidified aerosol. The results reveal that the secondary spreading effect of NaCl aerosol droplet is more pronounced compared to the acidified aerosol droplets which are mainly embodied in larger spreading region and faster spreading rate. The difference of the secondary spreading effect is associated with acidification which inhibits the increase in the pH at the periphery. Furthermore, lower corrosion rate was observed for the acidified aerosol droplets due to smaller secondary spreading area (cathodic region). The main corrosion product in the center of NaCl aerosol droplet and the aerosol droplet acidified by HCl is Simonkolleite, while for the aerosol droplet acidified by H2SO4 which shows several different corrosion morphologies in the center, the main corrosion products are Gordaite, Simonkolleite and Zn4Cl2(OH)4SO4 ∙ 5H2O. The formation of protective corrosion products Gordaite that can inhibit the anodic reaction leads to the smallest spreading area and the lowest corrosion rate for the aerosol droplet acidified by H2SO4.