Anodic Behavior of Iron in Ammoniacal Carbonate Solution: I. Steady-State Polarization and Cyclic Voltammetry

Two distinct Tafel regions are observed in the active region of the anodic polarization curve of iron in ammoniacal carbonate solution. A prepassive layer may form in the Tafel region at the higher overpotentials. A hydrogen oxidation peak is proposed to occur in the lower overpotential Tafel region. Anodic dissolution of iron in both Tafel regions is under mixed surface and diffusion control. The passivation of iron in ammoniacal solution involves charge transfer followed by a rate controlling chemical step. The stability and/or thickness of the passive layer and the Fe(III)/Fe(II) ratio increase with more noble potentials in the passive region.