Abstract
The mechanism of the corrosion of lead in sea water has been investigated in stationary and laminar flow conditions (from 0·3 to 3 m/min). Some experiments were carried out in NaCl and Na2SO4 solutions in order to discriminate more efficiently between the action of certain ions (Cl−, SO4 2−) that might affect the corrosion kinetics, while using the same environmental parameters (temperature, dissolved oxygen, fluid flow rate).
These solutions all had the same anionic concentration and the same pH value as sea water. The primary lead passivation film consists of basic salts resulting from the simultaneous precipitation of various anions (OH−, Cl−, sO4 2−) together with Pb2+ ions. In particular, the non-conductive corrosion products forming the primary film leading to ‘mechanical’ passivation in sea water are Pb(OH)Cl and Pb3(OH)2(CO3)2 and, after 360 h immersion, they were found to be: Pb(OH)Cl, Pb3(OH)2(CO3)2, PbCO3, PbCl2, PbO, Pb2O3, and PbCl2. SOO4 2− ions do not inteifere with the lead passivation mechanism in sea water. In stagnant solutions, CO3 2− ions do, however, contribute to the formation of a compact and adherent film of basic carbonates and double salts inhibiting lead corrosion. But in moving solutions, lead corrosion is solely linked to the activity of Cl− ions and the anodic dissolution mechanism is the same as for NaCl-containing solutions.
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