Mechanism of the protective PEO-layers formation and the corrosion process at the heterooxide structure/electrolyte interface

摘要

Composite protective layers formation and corrosion process taken place at their surface in the corrosion active media have being considered in the relationship with charge transfer mechanism realized at the heterooxide /electrolyte interface. The multifunctional composite coatings which possess the practically important properties (anticorrosive, antiscale, bioinert/bioactive and etc.) were obtained on titanium, aluminium, magnesium alloys as well on the steel and nitinol surfaces by means of the unipolar or bipolar modes of the plasma electrolytic oxidation (PEO) in different water electrolytes. The application of the nanosizable polymer and inorganic compounds in the coatings composition allows increasing their stability in corrosion active media. The chemical composition of the heterooxide coatings, their morphology, electrochemical properties and protection against scale formation in the sea water were investigated by different modern physical-chemical methods. The study of the PEO-coatings and composite layers with using the impedance spectroscopy method allowed determining their morphology structure, homogeneity and to research the charge transfer mechanism which is realized at the oxide heterostructure/electrolyte interface. Application of the local electrochemical impedance spectroscopy (LEIS) method enable one to research the kinetics of the development of the defect zones in the PEO-coating obtaining on the surface of the magnesium alloy during the sample exposure in the corrosion-active solution. The developmental stages of the corrosion-active process have been established. The Randies equivalent electrical circuit which adequately describes the mechanism of the corrosion process in the defect of the protective PEO-coatings has been suggested.