Dmitry V. Mashtalyar

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.

Composite coatings formed by plasma electrolytic oxidation

The prospects of using organic and inorganic nanosized materials are shown in the process of the formation of surface multifunctional composite protective layers obtained using plasma electrolytic oxidation on metals and alloys.

Magnetic properties of surface layers formed on titanium by plasma electrolytic oxidation

The magnetic properties of the coatings formed by plasma electrolytic oxidation on titanium and modified by nanoparticles of cobalt were studied. The coercitivity of the obtained magnetoactive layer were equal to 514 Oe at room temperature and to 1024 Oe at 2 K. The high coercitivity is the result of the nanosize effects of particles embedded in the coating. The structure of the nanoparticles, which consist of a Co ferromagnetic core and a CoO antiferromagnetic shell, determines the magnetic properties of the coatings on the whole.

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.

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.

Fabrication of coatings on the surface of magnesium alloy by plasma electrolytic oxidation using ZrO 2 and SiO 2 nanoparticles

Reverse osmosis (RO) membranes modified with SnO2 nanoparticles of varied concentrations (0.001-0.1 wt.%) were developed via in situ interfacial polymerization (IP) of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) on nanoporous polysulfone supports. The nanoparticles dispersed in the dense nodular polyamide on the polysulfone side. The effects of IP reaction time and SnO2 loading on membrane separation performance were studied. The modified reverse osmosis membranes were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), contact angle measurement, and atomic force microscopy (AFM). The synthesized SnO2 nanoparticles size varies between 10 and 30 nm. The results exhibited a smooth membrane surface and average surface roughness from 31 to 68 nm. Moreover, hydrophilicity was enhanced and contact angle decreased. The outcomes showed that an IP reaction time was essential to form a denser SnO2-polyamide layer for higher salt rejection, the developed reverse osmosis membranes with the incorporation of the SnO2 nanoparticles were examined by measuring permeate fluxes and salt rejection, and the permeate flux increased from 26 to 43.4 L/m2ċh, while salt rejection was high at 98% (2000 ppm NaCl solution at 225 psi (1.55 MPa), 25°C).Structural modifications and their impact upon magnetic properties are studied in amorphous and nanocrystalline NANOPERM-type 57Fe75Mo8Cu1B16 alloy. They are introduced by irradiation with 130 keVN+ ions to the total fluencies of up to 2.5 × 1017 ions/cm2 under different cooling conditions. Increased temperature during the irradiation triggers formation of nanocrystallites of bcc-Fe in those subsurface regions that are affected by bombarding ions. No crystallization occurs when good thermal contact between the irradiated sample and a sample holder is assured. Instead, structural rearrangement which favours development of magnetically active regions was determined by the local probe methods of Mossbauer spectrometry. Dipole magnetic interactions dominate in subsurface regions on that side of the ribbons which was exposed to ion irradiation. Nevertheless, structural modifications demonstrate themselves also via macroscopic magnetic parameters such as temperature dependence of magnetization, Curie temperature, and hysteresis loops. Impact of only the temperature itself to the observed effects is assessed by the help of samples that were subjected just to heat treatment, that is, without ion irradiation.Results of investigation of the incorporation of zirconia and silica nanoparticles into the coatings formed on magnesium alloy by plasma electrolytic oxidation are presented. Comprehensive research of electrochemical and mechanical properties of obtained coatings was carried out. It was established that the polarization resistance of the samples with a coating containing zirconia nanoparticles is two times higher than that for the sample with base PEO layer. One of the important reasons for improving the protective properties of coatings formed in electrolytes containing nanoparticles consists in enhanced morphological characteristics, in particular, the porosity decrease and increase of thickness and resistivity (up to two orders of magnitude for ZrO2- containing coating) of porousless sublayer in comparison with base PEO layer. Incorporation of silica and zirconia particles into the coating increases the mechanical performances. The layers containing nanoparticles have greater hardness and are more wear resistant in comparison with the coatings formed in the base electrolyte.

Features of the Magnesium Alloys Corrosion in the Chloride-Containing Media

A greater corrosion stability of the MA8 (Mg-Mn-Се) alloy as compared to that of VMD10 (Mg-Zn-Zr-Y) magnesium alloy in the chloride-containing solution has been demonstrated using the scanning vibrating probe method (SVP) as well as the methods of optical microscopy, gravimetry and volumetry. It has been established that the crucial factor of the corrosion activity of the samples under study consists in the occurrence of the micro galvanic couples at the samples surface. MA8 alloy contains less amount of the secondary phases (cathodic parts) relative to VMD10. The corrosion rate of the samples with coatings formed by the plasma electrolytic oxidation (PEO) method and composite polymer-containing coatings at the surface of various magnesium alloys has been measured. It has established, that PEO-coating decrease the values of the corrosion rate in several times (more than one order of magnitude for MA8 and more than 2 times for VMD10) in comparison with bare alloys.

Effect of conditions of treatment with superdispersed polytetrafluoroethylene on properties of composite coatings

A purposeful selection of the number of layers and the treatment temperature depending on the used fraction of superdisperced polytetrafluoroethylene (SPTFE, the Forum trademark) provides a maximum penetration of the polymer into pores and the formation of a uniform and continuous film on the surface. This information is of crucial importance for obtaining composite, including multifunctional, protective (antiscale and anticorrosion) layers on titanium products that operate under different temperature conditions in aggressive chloride-containing environments.

Incorporation of Zirconia and Silica Nanoparticles into PEO-Coatings on Magnesium Alloys

The effect of dispersity and zeta-potential of the nanoscale materials (ZrO2 and SiO2) used as an electrolyte component for plasma electrolytic oxidation on the composition and properties of the coatings was investigated. In was established the improvement of the protective properties for coatings with the incorporated nanoparticles has been explained by the greater thickness of the protective layer, relatively low porosity and presence of narrow non-through pores. The layer with zirconia has a impedance modulus measured at low frequency (|Z|f=0.01 Hz = 5.9·105 Ω·cm2) on one order higher than the PEO-coating formed in the electrolyte without nanoparticles (|Z|f=0.01 Hz = 8.0104 Ω·cm2).