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

This research focused on the development and use of a novel methodology to study corrosion under aqueous electrolyte drops ranging in diameter from 20–1000 μm, the most common deposited aerosol size range found in coastal marine environments. A drop-on-demand inkjet printer was custom built by coupling a commercial jetting device with a programmable two-axis stage. Singular droplets of sodium chloride solution were deposited onto steel and pure iron substrates with various surface finishes, followed by an isohumidity exposure for 24 hours. The volume loss increased with drop diameter according to a power law with an exponent of approximately 2 for highly polished steel and iron, increasing to 3 for iron with higher surface roughness. Attack was primarily filiform-like for the smallest drops, whereas deep, separate pits formed under the largest drops. Corrosion was not consistently observed under all drop sizes. The fraction of drops that showed no corrosion increased with decreasing drop size for all substrates. This behavior appears to have a strong dependency on the microstructure and surface finish. Corrosion initiation on 1010 steel was dominated by manganese sulphide inclusions when a mirror surface finish was maintained. For high purity iron, initiation was dominated by surface roughness.