INVESTIGATION ON PASSIVATING FILM FORMATION ON ALUMINUM AND STEEL BY SPECIAL CV AND MICROCALORIMETRIC TECHNIQUES

Passivating films formed on steel working electrodes were characterise d by the values and ratio of the rate constants (k(ox)(0) and k(red)(0 )) of the charge transfer of the Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox cou ple. k(0) values were determined by a special CV technique in the solu tions containing both the oxidised and reduced forms of the redox coup le. These values were influenced by the chemical composition of steel and the chemical conditions of the solutions where the passive layers formed. The small reaction enthalpies of the formation of the passivat ing film on aluminum and steel were determined with a reaction microca lorimeter. These reactions are exothermic for both metals. In the case of aluminum the number of oxide monolayers was calculated on the base of a model including the factors that control the passivation process .