| Metals in Passive State |
| 15.12.2008 г. | |
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Yu. A. Popov
Karpov Institute of Physical Chemistry, ul. Vorontsovo Pole 10, Moscow, 103064 Russia Received November 17, 2003
Abstract — A theoretical model [1–4] of the passive state of metals is discussed. This model considers hopping migration of ionic components in the passive layer (PL) lattice, which delivers reactants to take part in interphase processes at PL boundaries with metal and electrolyte, thus binding the latter kinetically and structurally, and defines the dependence of lattice point defectiveness on the potential. The defectiveness results in the transpassivity transition, i.e., the finiteness of the passivity range. A theoretical model of passivity should involve (predict) the transpassivity transition. This serves as a criterion of its consistence. Nonlinear equations of hopping migration in a strong electric field that violates the Ohm law are generalized. Their solution provides a more precise expression for PL point defectiveness and its dependences on the anodic potential, current density, and other parameters. An expression for transpassivity potential that was shown to linearly depend on the defec-tiveness is derived. A model describing formation of new PL elementary oxide cells at PL–metal interface, i.e., the “processing” of metal to give passivating oxide is generalized. This process compensates the electrochemical dissolution of PL at the solution boundary. The process of PL origination is also considered, namely, its crystallization in the prepassive range by the mechanism of two-dimensional nucleation of oxide.
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