Acidic environments accelerate corrosion in non-passivating metals

Explain that acidic environments accelerate corrosion in non-passivating metals

  • 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)