- The corrosion of non-passivating metals is accelerated in acidic environments when compared to basic or neutral environments.
- The reduction of oxygen proceeds more rapidly at pH below 7:
pH ≥ 7: O2 + H2O + 4e– → 4OH– (0.4 V)
pH < 7: O2 + H+ + 4e– → 4OH– (1.23 V)
- The second half-equation is more rapid due to its higher reduction potential.
- The reduction of sulfate to sulfide is also accelerated in acidic environments.
- Generally, seawater is slightly alkaline.
- Acidic microclimates can form within seawater due to the activities of microorganisms and other chemical processes.
- Around shipwrecks where there is an abundance of organic material for bacteria to feed upon, such acidic microclimates can form.
- This would accelerate the corrosion of the shipwreck.
- When pH is less than 3, hydrogen ions can directly oxidise passivating metals, such as iron:
Fe (s) + 2H+ → Fe2+ + H2 (g)