CHEMICAL MECHANISMS FOR THE ATMOSPHERIC CORROSION OF LEAD

The physical and chemical phenomena responsible for the atmospheric corrosion of lead are presented. Corrosion layer formation, morphology, and chemical makeup are discussed in the context of lead containing minerals and other crystalline structures that thermodynamics and kinetics suggest are likely to be present. Formation pathways for the minerals most often reported to be present in lead corrosion layers are shown in schematic diagrams. Lead is quite reactive to common atmospheric gases, outdoor exposures typically producing anglesite (PbSO4) and/or cerussite (PbCO3) and indoor exposures often producing lead carboxylates. The presence of these species is shown to be a natural consequence of the thin aqueous layer chemistry that obtains on lead in humid environments. The primary atmospheric agents responsible for degradation of lead are SO2, CO2, and carboxylic acids. Comprehensive kinetic simulations of the corrosion process are desirable, but await more extensive laboratory determinations of the rates of dissolution, precipitation, and transformation of lead containing chemical species.