Alkali and alkaline earth metals cation effects on the formation of akageneite in corrosion products of steel artifacts embedded in soil: a study under simulated laboratory conditions

X-ray diffraction (XRD), electrochemical tests, scanning electron microscopy and energy-dispersive X-ray analysis (SEM-EDXA) techniques were used to study the kinetics and growth of akageneite in corrosion products of steel exposed in moist soil added with chloride salts of sodium, potassium calcium, magnesium, and barium. The cations significantly affected the kinetics of corrosion and nucleation and growth of the akageneite. Divalent cations catalyze the corrosion and akageneite formation. The volume fraction of akageneite determined by XRD for monovalent cations (Na+ and K+) is observed in the range of 10-12% and that for divalent is in the range of 16-19%. This increase in akageneite leads to a decrease in the charge transfer resistance (Rct) for monovalent (Na+) and divalent cations (Ca++ and Mg++) (0.9 k Omega<middle dot>cm2 and 0.4 k Omega<middle dot>cm2, respectively). The mechanism of acceleration of corrosion by akageneite is discussed in light of disruption effects of added cations on electrical double layer formed at the steel-moist soil interface.