Vladimir S. Egorkin

Charge transfer at the antiscale composite layer-electrolyte interface

Properties of composite coatings based on oxide layers formed on a titanium surface using the plasmic electrolytic oxidation method and processed using Forum® superdispersed polytetrafluorinethylene were investigated. A combination of electrochemical impedance spectroscopy, differential thermal analysis, and thermal gravimetry methods allowed one to establish the change of the surface state as a result of heating that determines the charge transfer mechanism at the heterostructure-electrolyte phase interface and the difference in the thermodynamic stability of the temperature fractions of the employed polymer.

Plasma Electrolytic Oxidation Coatings on Titanium Formed with Microsecond Current Pulses

The effects of shape and duration of the current pulses on the physico-chemical properties of the oxide layers on titanium formed by plasma electrolytic oxidation were examined. It was shown that in the investigated conditions transistor power source possess an advantage in comparison with thyristor one. Electrochemical properties of the heterooxide structures were examined by electrochemical impedance spectroscopy and potentiodynamic polarization methods.

Composite polymer-containing protective layers on titanium

The influence of treating the coatings obtained by plasma electrolytic oxidation (PEO) and various fractions of polytetrafluoroethylene on the state of the surface of formed composite layers has been studied by electrochemical impedance spectroscopy, differential thermal analysis, and thermogravimetry. Differences in the resistance to charge transfer at the oxide heterostructure/electrolyte interface for various composite layers have been found. The obtained data significantly enlarge and complement the possibilities of directly forming protective coatings, including antiscale ones, on the surface of titanium alloys operating in aggressive media at high temperatures.

Properties of coatings formed on titanium by plasma electrolytic oxidation in a phosphate-borate electrolyte

Effect of the component concentration of an orthophosphate-tetraborate aqueous electrolyte on the thickness, composition, surface structure, and protective properties of coatings deposited from this electrolyte was studied.

Features of the occurrence of electrochemical processes in contact of sodium chloride solutions with the surface of superhydrophobic coatings on titanium

A joint analysis of the results of electrochemical studies and the evolution of the parameters of a sodium chloride solution droplet in contact with the coating under test reveals the pattern of changes in the surface state which result from the electrochemical reactions and adsorption-desorption processes at the coating/electrolyte interface. Features of the corrosion process are studied on titanium samples with different protective layers on the surface: (1) a natural oxide, (2) a coating prepared via plasma electrolytic oxidation (PEO coating), (3) a PEO coating with a hydrophobic layer, and (4) a PEO coating with a superhydrophobic nanocomposite layer. The best protective properties in a chloride-containing electrolyte are exhibited by the superhydrophobic nanocomposite coating. The mechanism of corrosion protection of this coating is formulated.

Formation and properties of composite coatings on aluminum alloys

A study was made into the morphology, composition, and electrochemical and mechanical properties of protective composite coatings on various aluminum alloys, including those doped with Sc, Cu, and Ni. It was established that protective coatings significantly increase the corrosion resistance of the alloys in a 3% NaCl solution. Composite coatings produced by triple dip coating in an superdispersed polytetrafluoroethylene suspension have unique corrosion-resistance properties, reducing the corrosion current density for all the protected alloys to 3.1 × 10–11–4.0 × 10–12 A/cm2, which is more than three orders of magnitude lower than that for coatings formed by plasma electrolytic oxidation and five orders of magnitude lower than that for alloys without coating.

Formation of bioactive anticorrosion coatings on resorbable implants by plasma electrolytic oxidation

Calcium phosphate coatings (Ca/P = 1.61) containing magnesium oxide MgO and hydroxyapatite Ca10(PO4)6(OH)2 accelerating the growth of bone tissue have been prepared by the method of plasma electrolytic oxidation (PEO) on MA8 magnesium alloy. The phase and element compositions, morphology, and anticorrosion properties of coatings were investigated. Such PEO layers were found to essentially reduce the corrosion rate of magnesium alloy (polarization resistance being increased by two orders). This makes it possible to consider the formed PEO coatings as likely anticorrosion layers for medical bioresorbable implants.

Effect of polarizing signal duty cycle on the composition, morphology, and protective properties of PEO coatings on AMg3 aluminum alloy

This paper presents a study aimed at assessing the effect of polarizing signal duty cycle D in the plasma electrolytic oxidation (PEO) process on the composition, morphology, and protective properties of coatings produced on AMg3 aluminum alloy in a tartrate-containing electrolyte. It is shown that increasing the duty cycle of a short-pulse (τ = 5 μs) polarizing signal leads to a decrease in the porosity of the growing PEO layers. This, in turn, improves the protective properties and surface strength of the alloy. The pulse duty cycle influences the chemical composition and thickness of the growing oxide coatings.

Protective Properties of the Nanocomposite Coatings on Mg Alloy

Nanocomposite coatings were obtained by aggregation of nanoparticles from dispersion in decane on the surface of oxide coatings. Oxide coatings on magnesium alloy were formed by plasma electrolytic oxidation in silicate containing electrolyte in bipolar mode. Electrochemical properties and stability of nanocomposite coatings under conditions of prolonged exposure to chloride containing environment were studied by means of electrochemical impedance spectroscopy, potentiodynamic polarization and measurements of contact angles. The coatings possess superhydrophobic properties with the contact angle of 166o ± 3o and the rolling angle of 5o ± 3o. It was found that these nanocomposite coatings reduce the corrosion current of magnesium alloy by more than three orders of magnitude. High stability during immersion in aggressive media is due to a small contact area of the coatings with electrolyte and high adhesion of the hydrophobic agent molecules with the coating.

Morphological Features and Electrochemical Properties of the Hydrophobized Sealed PEO-Coatings on Al Alloy

The developed methods of formation and results of the study of the hydrophobic layers on aluminum alloy, previously subjected to plasma electrolytic oxidation (PEO), boiling in bidistilled water, and additional treatment (either in ethanol solution or under UV-radiation in the presence of ozone plasma) with subsequent deposition of the hydrophobic agent (methoxy-{3-[(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl) oxy] propyl}-silane solution in decane) have been described. It was found, that the formed composite layers possess hydrophobicity (contact angle higher 155o) and high anticorrosion properties (the impedance modulus (|Z|f = 0.01 Hz) ranges from 1.5·108 to 1.7·108 Оhm·cm2 depending on treatment procedure).