The potentiodynamic behaviour of iron in alkaline solutions under carefully controlled perturbation conditions reveals that the overall electrochemical process is more involved than was thought earlier. The electrochemical characteristics of the systems are explained through a series of successive conjugated redox coupks principally involving Fe(&), Fe(OH), gnd FeOOH as limiting stoichiometric species. The yield of soluble species such as either FeO:-or HFeO; increases with the pH. Ageing effects of reactants and products are also distinguished through the potentiodyoamic E/I records.

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The electrochemical and ellipwxnetric responses of iron electrodes in 0.04 M NaOH and in saturated Ca(OH), are investigated at 25"C, in the potential range where the passivating layer in the absence of oxygen under potential controlled and non-equilibrium conditions is formed. From the correlation of results a composite structure of the passivating layer is envisaged involving an inner layer which is difficult to electroreduce, probably related to FesO,, and an outer gelatinous iron hydroxide layer where a relatively fast, Fe(II)/Fe(III) redox process can be voltammetrically followed. The inhibitive properties of saturated Ca(OH), as compared to 0.04 M NaOH are explained through the absorption of Car' ions at the outer plane of the inner part of the passivating film and the corresponding transport of water into the gelatinous part of the passivating film.

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Rotating ring-disc electrode studies on the anodic dissolution and passivation of iron in potassium carbonate/bicarbonate buffers at 25°C show that in the active anodic dissolution potential range Fe(II) soluble species are generated. This reaction is favoured by the presence of bicarbonate ions in solution and it is explained through the formation of an unstable soluble complex containing Fe(lI) and HCO3 ions. This suggests that the anodic layer at a certain stage of its formation contains some amount of carbonate species. XPS data of surface layers produced at different anodic potentials confirm the presence of the carbonate species in thick anodic layers grown in the prepassive potential region in still solutions, whereas the opposite result is found for the thin passive layers formed at high positive potentials.

The electrochemical behaviour of nickel in alkaline aqueous solutions within the anodic potential range yielding Ni(OHh and under different potentiodynamic perturbations profiles has been investigated. The formation of Ni(OHh is characterized by an irreversible anodic current peak which is quantitatively interpreted in terms of a complex reaction pathway involving different hydroxoadsorbed slx.~cies.

The potentiodynamic response of the Ni/alkaline aqueous solution interface in the region of the hydrated normalNifalse(OH)2 to β‐normalNiOOH electrochemical reaction reveals that both species undergo phase transformations. The anodic product from the normalNifalse(OH)2 species involves the formation of three species energetically different which are detected during the electroreduction process. Under well‐defined perturbation conditions, a reasonable set of kinetic parameters pertaining to the anodic process is obtained which is formally interpreted through a consecutive three‐step mechanism of reaction involving a charge transfer, a chemical reaction, and a charge transfer and a proton transfer process. Side reactions involving water take into account the various aging processes of the reaction products.