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

Abstract

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.

Aerosol Salt Particle Deposition on Metals Exposed to Marine Environments: A Study Related to Marine Atmospheric Corrosion

“…9), with corrosion morphologies similar to those reported by Cole et al 35 The EDXA spectrum (Fig. 9f) of a corroded area (in Fig.…”

“…Notice that the severity of KI test site was mainly due to the acid rain in the volcanic environment (pH approximately equal to 3). However, it is assumed that the acid environment did not affect the corrosion of metals during the 30-minute exposure since the acidification of seawater droplets through the absorption of SO 2 only occur to droplets with diameters less than approximately 3 μm, 35 which are smaller than the majority of the seawater droplets in this study. The specimens were attached to the exposure racks (angled 30…”

Marine Aerosol Drop Size Effects on the Corrosion Behavior of Low Carbon Steel and High Purity Iron

“…One hypothesis is that as the drop size decreases, the oxygen delivery rate surpasses the consumption rate and the concentration gradient diminishes because the diffusion distance is no longer appreciable from any side of the drop; without the oxygen concentration gradient there is no driving force for Evans-type corrosion. 1,7,9 Despite growing research in this area, information to date is insufficient to establish a rigorous correlation between drop size and corrosion rate under drops in the size range of coarse mode aerosols. The cause of the inconsistent corrosion behavior is still uncertain, and it has yet to be determined if factors other than drop size affect this behavior.…”

“…Grain boundaries, inclusions and other metallurgical defects provide initiation sites for corrosion. 1 It is postulated that small drops will have a lower probability of covering an initiation site than large drops. [7][8][9] Exposure experiments have shown alternative corrosion attack morphologies to that of the classic Evans drop for small drop sizes.…”

“…In coastal marine locations (<2 km from the beach), the most common aerosols deposited are in the 'coarse-mode' size range: 1-100 μm in diameter. 1 Laboratory atmospheric corrosion studies and a number of accelerated tests, however, have traditionally focused on corrosion under large drops (several millimeters in diameter) or thin films.…”