THE EFFECTS OF SULFIDES ON THE PASSIVITY OF CARBON-STEEL IN ORGANIC SOLUTIONS

Corrosion is known to initiate at sulfide inclusion in aqueous solutio ns. The effects of sulfides on the passivity and the breakdown of pass ivity of 99.999% iron and 1018 carbon steel was investigated in two ap rotic nonaqueous solvents: (1) propylene carbonate (PC) with LiClO4 or LiAsF6 as supporting electrolytes and (2) dimethoxyethane (DME) with LiAsF6 electrolyte. Carbon steel was also examined in PC-DME/LiAsF6 mi xtures. Sulfides do not appear to interfere with passivation when it i s provided by solvent adsorption in either nonaqueous solvent. Sulfide s may lower the solvent oxidation potential and decrease the anodic po tential at which breakdown initially occurs in either pure solvent. Su lfides also influence the kinetics of repassivation above the solvent oxidation potential of either solvent when passivation is provided by salt film formation or electropolymerization. The bleeding of sulfur o r sulfide from inclusion sites where electropolymerization has occurre d in PC/DME mixtures undermines attempts at passivation and promotes i nstability leading to anodic current increases with time and further c orrosion of carbon steel. Published by Elsevier Science Ltd