Vol 54, No 2 (2018)

This work considers the electronic mechanism of specific interactions between a neutral surfactant and an uncharged metal surface during an elementary adsorption event. Special attention was paid to a role of the residual electronic interactions upon the exchange of electron density between the valence adsorbate orbital and the Fermi sea of metal electrons during adsorption. This interaction was simulated by the Coulomb electron–hole interactions through a potential barrier separating the surfactant and metal-electron systems. As this task concerns the problems associated with the Fermi edge singularities, the Nozières–de Dominicis theory, which enables one to study an electron’s contribution to the energetics and kinetics of adsorption event, was used to interpret the donor–acceptor effects. The expressions of spectral characteristics of the localized electron density and tunneling time were analyzed in the context of the problem. There is a positive correlation between the surfactant adsorption parameters and the scattering phases of conductivity electrons screened in the metal by a potential field created by a hole at the valence surfactant orbital.

The photochemical activity of the anionic form of two-decker ytterbium and lutetium pthalocyaninates (LnPc₂, Ln = Yb, Lu) is observed in the process of electron transfer to 2-methyl-1,4-naphthoquinone (MNQ). Under illumination of solutions of LnPc₂ (1 × 10^–5 mol/L) and MNQ (5 × 10^–5 mol/L) in dimethyl formamide by light with wavelength λ_ph > 630 nm, the anionic form of the two-decker phthalocyaninate [(Pc^2–)Ln³⁺(Pc^2–)]^– passes into the neutral monoradical form [(Pc^2–)Ln³⁺(Pc^–)]^0•. The photochemical redox process is accompanied by accumulation of the reduced form of MNQ. The observed effect is the first example of electron phototransfer with the participation of two-decker lanthanide phthalocyaninates.

A new method was developed for preparation of hybrid functional nanostructures through interaction between terbium complex with tetra-15-crown-5-phthalocyanine Tb[(15C₅)₄Pc]₂ and the surface of highly porous nanostructured aluminum oxyhydroxids (NAOs). It was shown that immobilization of phthalocyaninate on an NAO surface may be reversible upon a sorption from the solution in chloroform, and irreversable, when the adsorption occurred on the NAO surface that was chemically modified using methyltrimethoxysilane and annealed at the temperature ranging from 500 to 1100°С (NAOM). Nanostructure and chemical properties of the obtained hybrid nanomaterials were studied with the use of different methods: scanning electron microscopy, XRD, IR and diffuse reflectance spectroscopy. The sensor properties of the obtained Tb[(15C₅)₄Pc]₂//NAO and Tb[(15C₅)₄Pc]₂//NAOM hybrid nanostructures were studied when they interacted with ammonia and iodine vapors. It was shown that the phthalocyaninate complex on the NAO surface was liable to reduction, while the phthalocyaninate complex on the modified NAOM surface was liable to oxidation.

Nowadays, powder coating can be used for many application, especially for protection against corrosive environments. Powder coating is usually done with using an electrostatic device and spraying gun. With using this method, a thin film layer is created on the surface which can play decorative or protective role. In this paper, the effect of some factors such as size of powder, charging, voltage, air flow, gun distance, charge–to-mass ratio, feed rate, coating functionality, glass transition temperature (T_g), viscosity, catalyst, temperature and curing time on the coating properties and their influence on the coating were mentioned. In recent years, nano composite polymers have been considered severely. Coating properties are improved by adding nanoparticles such as clay, SiO₂, TiO₂ and Al₂O₃ to the polymer composition. These coatings are used for reducing the gas permeability, thermal stability, optical clarity and increasing the mechanical and corrosion properties of coatings also these coatings have high mechanical properties that can be pointed to its high abrasion resistance. In this paper, the corrosion properties and the effect of adding nanoparticles on the corrosion resistance properties of powder coatings have been investigated, also the mechanical properties of powder coatings were reviwed.

This work deals with encapsulation of corrosion inhibitor in inorganic nanocontainer and the investigation of the corrosion inhibition rate from the nanocontainer. Halloysite nanotubes were used as inorganic nanocontainer for encapsulating the active corrosion inhibitor. These cylindrical shaped halloysite nanotubes are a natural aluminosilicate, which possesses similar chemical composition as that of pure kaolin clay. The structural morphology and functional organic attachments to the halloysite nanocontainers were determined by using TEM and FTIR analysis. It is found that, halloysite nanocontainers are having external and internal lumen is in nanosize (diameter) and length up to several micrometers. A maximum benzotriazole loading up to 10% (by weight) was achieved in inorganic nanotube of 50 nm external diameters and lumen of 15 nm. The release of corrosion inhibitor was carried out for 18 h at different pH ranging from 3 to 10. The weight percent of the benzotriazole encapsulated halloysite nanocontainer was varied from 2 to 10 and then dispersed in 2K clear coat epoxy-polyamide. The self-healing anticorrosion performance of these nanocomposites coating was tested with help of electrochemical impendence spectroscopy (EIS) and Tafel plot. From Tafel plots it is found that the I_corr value decreases to 1.018E^–7A/cm² from 0.018 A/cm², when coating was applied with 2 wt % nanocontainer.

A comparative analysis of the structural features and tribological properties of multilayer coatings based on refractory metal compounds has been conducted in this review. Features of formation of the electronic structure of the synthesized coatings have been discussed, and the effect of methods and conditions of deposition on changes in the physicomechanical characteristics of nanocrystalline structures based on transition metal nitrides has been shown. Dependences of antifriction properties, corrosion resistance, and thermal stability on the modulation period (Λ) and the number of bilayers in the studied multilayer coatings have been determined. A decrease in the modulation period of individual layers in a coating positively affects the oxidation resistance of the coating, while an increase in the number of interfaces between the layers slows down the diffusion of oxygen atoms deep into the coating and, thereby, increases the protective properties of the multilayer system as a whole. The effect of the droplet component in cathodic-arc coatings on corrosion development mechanisms in corrosive media has been shown. A class of multifunctional multilayer coatings with an adaptive friction mechanism, which is characterized by a change in the properties and structure during tribological tests, has been discussed separately.

Sol–gel method was used for applying of alumina coating on carbon steel substrate. Alumina sol was prepared with Al-isopropoxide as a precursor material. Specimens were coated with prepared alumina sol by dip coating technique. Either a film of Ni–P or phosphated intermediate layer has been pre-deposited on the carbon steel substrate by electroless plating to improve the adherence of alumina coating. The corrosion resistance of coatings in the presence of intermediate layers was evaluated by electrochemical measurement in 3.5% NaCl solution by open-circuit potential measurement at room temperature. The abrasive wear behavior of sol–gel coated specimens was measured in high stress conditions. The results indicate that, after applying an intermediate layer of phosphate or Ni–P by electroless plating technique, the wear and corrosion resistance of alumina coating have been improved. Moreover, the phosphate intermediate layer has been associated with a higher corrosion resistance, while the intermediate layer of Ni–P is more effective to improve the hardness and wear resistance of alumina coating.

In this work, a diffusion model was proposed to estimate the boron activation energies for FeB and Fe₂B layers during the pack-boriding of AISI D2 steel at temperatures of 1223, 1253 and 1273 K for a treatment time varying between 2 and 10 h. This model considers the effect of boride incubation times during the formation of the FeB and Fe₂B phases. To study the influence of diffusion annealing process on the boriding kinetics of AISI D2 steel, the mass balance equations were modified in order to follow the evolution of boride layers as a function of annealing time for the specified boriding parameters. Finally, the kinetic model was validated by a comparison of the experimental thicknesses of boride layers with the predicted ones at a temperature of 1243 K for 2, 4 and 6 h. A simple equation was then obtained for estimating the total time necessary to get a single boride layer (Fe₂B) that depends on the boriding parameters and on the thickness of each boride layer prior to the diffusion annealing process.

Corrosion of AD31 (AA6063) alloy in neutral 0.05 M NaCl solutions is investigated via scanningprobe microscopy, linear-sweep voltammetry, and electrochemical-impedance spectroscopy. Al−Fe−Si−Mg intermetallic particles are determined to prevail in the structure of alloy and act as local cathodes. Intermodulation electrostatic-force-microscopy imaging shows that their Volta potential differs by 570 mV from that of the host aluminum matrix, making the alloy prone to localized corrosion. We show that the corrosion of alloy in the studied electrolyte mainly develops locally and results in pitting, with charge transfer being the limiting stage of the process. A mechanism of corrosion of the AD31 (AA6063) alloy in neutral chloride-containing solutions is proposed.

A numerical model of nitriding of an isotropic gadolinium specimen and its states during further storage under normal conditions (room temperature and atmospheric pressure) is developed. The model is implemented on the basis of the principles of thermoelasticity and mass transfer. The dynamics of distribution of nitrogen (N) and gadolinium nitride (GdN) in the specimen, which represents an additional phase formed during nitriding of the specimen, is considered. An algorithm of numerical solution of model equations is given.

This article intends to study corrosion of 316 L stainless steel alloy in simulated concrete environments. A composition of 0.1 M sodium hydroxide plus 0.1M potassium hydroxide with different pH (9, 11 and 13) and 0, 3 and 10 wt % sodium chloride concentration has been utilized for this manner. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to study electrochemical behavior. The results of potentiodynamic polarization indicate that the formed passive layer becomes more stable and its failure takes place later as increasing pH. Electrochemical impedance test also has confirmed the obtained results and also showed that the corrosion resistance of the sample assessed over dilution time. At a solution with high alkalinity (pH 13) results showed increase in total impedance after 24 h of dilution related to passive film stabilization which did not observed in samples with lower pH. In this work, electrochemical behavior of 316 L stainless steel in alkaline environments of simulated concrete is studied with chlorine ion addition and pH adjustment.

Some critical issues when applying electrochemical noise (EN) in field corrosion detection of nuclear materials are solved. In this work, a portable EN measurement system for field test is established by using Compact RIO modular instrument and zero resistance ammeter (ZRA) module. The electrode system for EN measurement is built by using platinum wire or stainless steels coated with thermal sprayed ceramic coatings as counter electrode. Two EN sensors are developed based on the electrode system mentioned above, and field corrosion detection is successfully achieved. The corrosion of stainless steel pipeline surface in nuclear power plant and internal-surface corrosion of continuous blowdown piping are successfully evaluated by the established new EN measurement system.