What really controls the atmospheric corrosion of zinc? Effect of marine aerosols on atmospheric corrosion of zinc

This paper reviews the processes that control the production, transportation and deposition of aerosols and examines how these parameters affect the atmospheric corrosion of zinc on which the aerosols have deposited. The factors that influence the size and chemistry of aerosols are summarised. It is shown that marine aerosols may be acidified through the absorption of gases and strong acids, and that they may attain very low pH values. Aerosol transportation and deposition are size dependent, with aerosol deposition increasing with aerosol size and decreasing with transportation distance. Acidified marine aerosols may be transported to considerable distances from the sources of the acid precursor gases. The review examines the differences in the electrochemical phenomena on zinc surfaces under fine acidified marine or industrial aerosols and under large near neutral aqueous droplets, and shows that the low pH, fine size and high dissolved ionic salt content of the acidified marine aerosols leads to significant oxide dissolution and higher corrosion rates. Acidified marine aerosols disrupt protective oxide films and establish electrochemical cells in which anodic corrosion separation and resistance through the solution are small and oxygen depletion is unlikely. The authors' analysis shows that the susceptibility of zinc to chloride containing environments may in part be associated with the effect of acidified marine aerosols.