The Empirical and Adsorptive Description of Passivity of Iron

Issue 1(67) 2013
Pages 65-71
Podobayev A.N., Reformatskaya I.I., Artamonov O.Yu., Ashcheulova I.I., Afonkin A.E.
Keywords: iron, passivity phenomenon, essence, processes

In the modern theory of electrochemical corrosion of metals and alloys all terminology concerning the phenomenon of passivity is based on its empirical description. In this work the description of the phenomenon of passivity based on scientific representations about a nature of processes resulting in passivation of metals is given. The following definition of passivity is offered: «the Essence of the passivity phenomenon consists in that as a result of adsorptive interaction of metal with water molecules (or others oxygen-containing components of aggressive media) adsorbed oxygen atoms are formed on a surface and then the decrease of dissolution rate of metal occurs». In a case of iron, from these positions, potential of a beginning of passivation is a minimum value of potential, at which it is possible thermodynamically the interaction mentioned above. The complete passivation potential corresponds to limiting coverage of iron surface by adsorbed atoms of oxygen, and critical passivation potential is the value of potential adequate to conditions of a maximum on the stationary current - potential curve, dependent on constants of dissolution rate of metal and formation of adsorbed oxygen and also pH of environment.