Vol 54, No 3 (2018)

The Dubinin theory of volume filling of micropores (TVFM) was used to study the structure–energy characteristics of metal-organic frameworks based on salts of copper (C300), aluminum (A520), and zinc (Z205) produced by BASF. Isotherms of absolute adsorption of methane were measured on these adsorbents at the temperatures of 303, 313, 323, and 333 K and pressures up to 40 MPa. Dependences of differential molar isosteric heats of methane adsorption on the adsorption value and the dependence of the specific volume capacity of methane accumulation on pressure are calculated. In the technically significant range of pressures up to 10 MPa, adsorbents with high values of specific surface area cannot guarantee high specific capacities of methane accumulation. The thermodynamic Р,Т-parameters of adsorption systems of methane accumulation determine the optimum structural and energy characteristics of adsorbents suitable for high-performance methane accumulation.

The properties of metallic titanium nanoparticles as dependent on the number of atoms in the shells—namely, ionization potentials, electronic affinity, melting point and energy characteristics—are studied on the basis of the shell theory of nanoparticles.

The processes of electrodeposition of Ge and Ge–In from ammonia-tartrate solutions have been studied. The nature of interactions in thin-film systems obtained by germanium and indium codeposition has been investigated by means of potentiodynamic voltammetry in the inversion mode. The role of electrodesurface modification has been emphasized for deposition of a germanium film of a preset thickness from aqueous solutions. As was shown by the atomic force microscopy study, glossy films with a nanocrystalline structure had been formed. It has been established that, to develop silicon–germanium technologies, deposition of thin films must be performed from ionic liquids.

A technique for plasma spraying of a magnesium-substituted tricalcium phosphate powder has been developed; optimum modes of the plasma-jet arc current and the particle size of the sprayed powder have been determined. It has been found that the structure of the resulting coating contains microparticles and nanoparticles with a size of up to 90 μm and up to 100 nm, respectively. The adhesion of the substituted coatings is 13 MPa; on average, it is 20% higher than the adhesion of coatings based on unmodified powders.

Conditions for the formation of metal-catalyst nanoparticles in an aqueous medium by the hydrosol method in the presence of surfactant are studied. Based on the study of the colloidal chemical properties of the preparation TWEEN-20, which is a polyoxyethylene sorbitan monolaurate containing, in addition to TWEEN-20 itself, impurities of other fatty alkyl esters and fatty acids, the possibility of its use in the synthesis of an electrocatalyst, including platinum, as a dispersion stabilizer of freshly formed particles is shown. The formation of platinum nanoparticles and their uniform distribution over the surface of the carbon carrier is confirmed by transmission electron microscopy, small-angle X-ray scattering, and X-ray-diffraction analysis.

The present paper has aimed at studying heat resistance, electrochemical behavior, and tribological characteristics at high temperatures of superhard (~48 ± 2 GPa), multilayered with a modulation period of 17–18 nm, and nanostructured (nc)AlN-(am)Si₃N₄/(nc)TiN coatings obtained with an ion-plasma vacuum arc. The heat resistance of the coatings studied in the temperature range of up to 800°C inclusive was mainly determined by the oxidation of their surface layers without the substrate intrusion. Having a high coefficient of friction from 0.6 at 20°C to 0.8–0.85 at elevated temperatures, the coatings are characterized by virtually no wear, which was confirmed by profilometry measurements of friction zones. The obtained results concerning electrochemical behavior indicate that the Ti–Al–Si–N coatings are highly efficient in the protection of a cutting tool from corrosion in both acidic and alkaline media.

Data on the composition of the external polymer part of the composite polytetrafluoroethylene (PTFE) oxide coatings obtained on an aluminum substrate by plasma electrolytic oxidation (PEO) within a single stage are presented. The coatings were formed in an aqueous silicate electrolyte with addition of PTFE dispersed powder in a siloxane–acrylate emulsion. It has been established that the external polymer-like layer of the PTFE/PEO coatings does not represent a physical mixture of the siloxane–acrylate copolymer and PTFE particles, but is composed of fragments of them. A partial substitution of fluorine by hydrogen in fluorocarbons contained in the coatings has been revealed. The obtained data are crucial for expanding knowledge on the formation, structure, composition, and properties of the composite polymer-containing oxide coatings formed within a single stage by means of plasma electrolytic oxidation on the valve metal surface.

Composite electrochemical coatings (CECs) based on zinc–nickel alloy and modified by carbon nanotubes (CNTs) are obtained by pulsed electrolysis. The microstructure and tribological properties of these CECs are studied. It is found that addition of dispersed CNTs into the electrolyte for zinc–nickel alloy deposition results in a 1.35- to 1.65-fold decrease in the friction coefficient of the formed coatings. The electrochemical corrosion behavior of the zinc–nickel–CNT CECs is studied in 0.5 M H₂SO₄ solution.

In this study, NiCrAlY coating as a bond coat and 8YSZ coating as a top coat were applied on Inconel 718 super alloy substrates by APS method. The plasma power parameter has changed from 24.75 to 34.8 kW. The results show that with increasing the plasma power, the hardness and bond strength increase from 682 to 818 HV and 12.48 to 22.49 MPa, respectively. Also the image analysis shows that the porosity in coatings, decrease from 22.59 percent to 18 percent by increasing the plasma power.

The structural state under varied conditions of thermal and thermomechanical treatment, the possibility of realization of a reversible martensitic transformation, and electrochemical behavior and corrosion resistance of iron and its bioresorbable alloys Fe–(23–30)–Mn–5Si in the solution simulating the liquid fraction of bone tissue of the human body have been investigated by means of electron-microprobe X-ray analysis, X-ray diffraction and metallographic analysis, differential scanning calorimetry, chronopotentiometry, potentiodynamic voltammetry, and gravimetry. It has been shown that the manganese content increase from 23 to 30 wt % results in the significant decrease of the temperatures of the start of the direct and the finish of the reverse martensitic transformation and the acceleration of the electrochemical corrosion. A dual role of silicon in formation of corrosion-electrochemical properties of the alloys has been grounded.

Regularities of corrosion damage in the case of pitting and gap corrosion are studied on samples of austenitic stainless steel (AINSI 316L) produced using the powder selective laser-melting (SLM) technique. It is found that the corrosion rate and the appearance of corrosion damage considerably depend on the surface state and heat treatment. Heat treatment (austenitization) results in a decrease in the local corrosion rate by 20–25%, a decrease in the number of pittings, and smoothing of the crevice corrosion profile as compared to the initial SLM state. The opening of the subsurface pores in the course of machining somewhat decreases corrosion resistance. It is shown that the initiation and development of pitting and crevice corrosion are related to the presence of surface and subsurface pores in the SLM material.

The effect of dew point on the selective oxidation behavior, microstructure and mechanical properties of a high-Al low-Si dual phase steel is elucidated. The results showed that as dew point is increased from–30°C to +5°C, internal oxidation of alloying elements occurs, and consequently the mass of external oxides decreases, which improves the galvanisability of steel sheets. It was also observed that the dew point had an impact on the microstructure and mechanical properties of the experimental steel. With the increase of dew point, the decarburization layer on the surface was increased, leading to inferior mechanical properties. Compared with the industrial steel, the high-Al-low-Si DP steel exhibited excellent galvanisability under identical annealing conditions.

The inhibition capability of (2-(phenylthio)phenyl)-1-(2-(trifluoromethyl)phenyl) methanimine (PFM) on corrosion of low carbon steel (LCS) in 1.0 M HCl solution was investigated at various potentials and temperatures using electrochemical and microscopic techniques. The electrochemical results showed that the inhibition efficiency increases with increasing PFM concentration. Besides this electrochemical studies at open circuit and different potentiostatic potentials showed that electrostatic effects have an important role on the adsorption of PFM on the metal surface. Time dependent stability of the inhibitor was also investigated by Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The results confirmed that PFM has reduced the corrosive effect of HCl on low carbon steel even 120 h later.

Dynamic Electrochemical Impedance Spectroscopy (DEIS) has been used as an effective method for determining information about corrosion and inhibitor systems. Thus, it has been successfully applied to investigate the formation mechanism of pitting corrosion, the damage mechanism occurring over time in organic coatings, the cavitation caused by corrosion detection and the monitoring of the battery discharging process. This method has been suggested as an effective and useful tool for establishing the time of the best inhibition activity. In this study, benzotriazole (BTA) was used as a corrosion inhibitor for St37 steel in a 0.1MHCl environment. Consequently, the advantage of using DEIS to determine the electrochemical changes occurring over time with the addition of an inhibitor was demonstrated.

Constant phase elements (CPE) are widely used in fitting of electrochemical impedance spectra instead of ideal capacitances. The present work begins with a discussion of two commonly used models for conversion of the CPE parameters to an effective capacitance, i.e. Hsu and Mansfeld’s and Brug et al.’s; and then continues with presenting alternative geometric assumptions to derive some other formulae. Afterward, it provides a comparison between the results of the formulae together with comments on their applications. Through discussing the relation between the models, this work offers a better understanding of the mathematics of impedance exhibiting frequency dispersion.