Corrosion Behaviour of lead in salt solutions: II. Lead - steel couple

Abstract

Galvanic currents flowing through electrically connected Pb and Fe sheets and the correspondmg corrosion rates in 1–10⁻⁶ M NaCl, 0·1–10⁻⁶ M Na₂SO₄ and sea water and in cement extracts have been measured. In neutral solutions Pb is initially anodic to Fe and its corrosion rate is enhanced. Reversal of polarity takes place after 2–20 min according to the salt concentration, and the corrosion rate of Pb decreases markedly with time. After reversal Fe becomes anodically polarised so that its corrosion rate becomes much higher in the coupled than in the uncoupled state. The corrosion rate of coupled Pb in sea water becomes vanishingly small after one month. Coupling results in a great increase in the corrosion rate of Pb in cement extract, but Cl⁻ and SO₄²⁻ ions counteract this effect. The influence of salt concentration on the galvanic current and the role played by Cl⁻ and SO₄²⁻ ions have been interpreted in the light of the electrode behaviour of the separate metals.