Vol 54, No 5 (2018)

The possibility of describing isotherms of gas adsorption on flat carbon surfaces by means of lattice model equations and equations of the theory of micropore volume filling has been demonstrated. The obtained results have been compared to data on the adsorption in micropores of active carbon.

The Dubinin theory of volume filling of micropores and the linearity of adsorption isosteres were used to calculate the adsorption of hydrogen on model microporous adsorbents with slitlike pores. In calculating, the model adsorbents were considered the micropores of which were formed through a progressive removal of one, two, and so on to seven layers of hexagonal carbon in a graphite crystalline structure, while the micropore sizes varied within a range from 0.5 to 2.5 nm. The integral energy of adsorption was evaluated for the model structures and most of industrial carbon adsorbents. The obtained results were compared with experimental data. Dependences of the gravimetric density of hydrogen on temperature and pressure were analyzed.

This paper continues a study of the magnitude of thermodynamic estimation of the Rehbinder effect as a function of volume concentration in a liquid solution of a surface-active substance (surfactant) in the case of an S-shaped adsorption isotherm on an undeformed and uncharged surface. A generally piecewise linear approximation of the isotherm is used. The conditions of existence of a bounded concentration action area of the Rehbinder effect, such that the area does not fall outside the bounds of defining data from the adsorption isotherm, are derived analytically in terms of theory parameters. The width of this area is compared to the data in the literature on the Rehbinder effect for quartz and granite obtained during dodecyltrimethylammonium bromide adsorption.

The aim of this work was to study changes in the state of a nanosystem surface, adsorption forms, and their transformations at a transition from room temperature to elevated temperatures using the example of carbon oxide chemisorption.

For the development of a composite of nickel highly porous permeable cellular material with an applied secondary layer of alumina, transformation of the surface of the highly porous permeable cellular material is investigated at the stages of electrochemical synthesis and stages of alumina application on its surface. Etching of foamed-polyurethane bondings with 20% potassium hydroxide solution is accompanied by destruction of their surface and the formation of defective areas in the form of hillocks, hollows, and other imperfections acting as tin-hydroxide crystallization nuclei. Application of tin chloride with its subsequent hydrolysis leads to the formation of hemispherical tin-hydroxide grains with a mean size of about 80 nm uniformly distributed over the surface. The optimum values of temperature (50°C), solution pH (9–10), and electroless-nickel-plating duration (20–30 min), providing the formation of a conductive sublayer of chemically reduced nickel, are established. Nickel electroplating for 30 to 35 h at a current density of 0.1 A/dm2 yields high uniformity of a metal coating of foamed-polyurethane bondings across the thickness both in the bulk and at the outer periphery of a sample of 30 μm. A composite of nickel highly porous permeable cellular material with an applied alumina secondary layer is synthesized. The latter shows a high degree of uniformity and uniform thickness over the whole surface of bondings of the obtained composite.

Conformational transformations in the structure of the surface layer and the substrate of initial and working nanofiltration films have been investigated in this work using large-angle X-ray scattering. It has been determined that the mechanical load caused by excess pressure corresponding to 1.5 MPa in the case of OFAM-K porous-composition film has resulted in conformational changes of Phenylon C-4 macromolecules in crystal and amorphous intercrystallite phases; in this case, the calculated degrees of crystallinity have decreased from 49 to 36%. It has been noted that there is the polymorphous rearrangement of the crystal phase with the change of the sizes of crystal cell toward the crystal axis (c) and an increase in the crystallinity from 44 to 55% in the working specimen of the OPMN-P-composition nanofiltration film; in this case, the amorphous phase opens. A full calculation of the radial-distribution function of the atoms of initial and working films has been carried out, which confirms that there is rearrangement of lattice cells due to the increase in atomic distance.

A new tetrafluorene-substituted copper(II) porphyrinate (CuTFP) with intense phosphorescent glow in the red spectral region is obtained. It is found that the phosphorescence lifetime of CuTFP in a polystyrene matrix changes significantly when the sample is cooled (5 μs at 25°C and 344 μs at–196°C), while the intensity of phosphorescence in the same temperature range changes only 8.1-fold. The dependence of variation of the CuTFP lifetime in polystyrene on the temperature is analyzed. It is found that the lifetime changes little at positive temperatures centigrade, while lifetime variation in the negative temperature range is very significant, which allows considering the new material as a promising phosphorescent sensor for measurement of low temperatures, e.g., under Arctic conditions.

Fe-containing oxide coatings fabricated by the plasma-electrolytic oxidation (PEO) method have been studied by means of scanning electron and magnetic force microscopy. The data comparison has demonstrated that ferromagnetic properties of the coatings are mainly associated with concentrating of iron in specific pores. A scheme has been suggested that would explain iron distribution in the course of the coating growth.

Coatings formed by plasma spraying of electrocorundum on VT6 titanium alloy and subsequent microarc oxidation at different current densities were examined. The parameters of structure and hardness of metal-oxide layers were studied. The effect of current density on them was also found. During microarc oxidation, the open porosity (from 50.3 ± 4.5 to 10.3 ± 1.5%), the thickness (from 47.4 ± 3.3 to 30.2 ± 5.3 μm), and the average size of structural elements of presprayed coating were decreased, while its hardness was increased from 760 ± 486 to 875 ± 238 HV₂. The magnitude of changes in the structure of the plasma coatings depended on the current density during modification. Microarc oxidation makes it possible to form structural elements in the form of pores and crystals with a size from 15 to 150 μm on the surface of sprayed aluminumoxide coatings.

Mixtures of benzoic acid with various organic compounds are subjected to plastic deformation in Bridgman anvils under a pressure of 1 GPa at room temperature. The influence of high-pressure plastic deformation on the calorimetric behavior of the deformed layer of benzoic acid in mixtures with various organic components is studied under conditions of thermal treatment (programmed heating at a constant rate). The parameters for the process of melting of deformed layers of benzoic acid mixtures depending on the chemical composition are studied by differential scanning calorimetry (DSC). In all cases, the melting point T_m decreased by 5–8 deg. The melting enthalpy both can increase by 1.7 times and decrease by 2.3 times. In mixtures with organic indicators, the melting enthalpy of the acid depends on the pH of the indicator and reaches 750 J g^–1 in a mixture with Congo red.

The passivation behavior of Ni electrode in NaOH solutions is studied by cyclic voltammetry technique. Different experimental factors, such as, electrolyte concentration, voltage scanning rate and the sweeping potential range are examined. The cyclic voltammgrams data, Cvs, indicated a correlation between two well–defined anodic oxidation peaks and only cathodic peak. The first anodic peak was attributed to the oxidation of Ni to Ni(OH)₂, followed by a passive region corresponding to the transformation of Ni(OH)₂ to β-NiOOH. The second anodic peak was suggested to correspond to the oxidation of Ni(OH)₂ or NiO to some higher oxides of nickel. The cathodic branch of the cyclic voltammogram was characterized by only one cathodic peak, which was splitted into two sub peaks on increasing the concentration of NaOH. These peaks are thought to correspond to the reduction of (or part of) the products formed during the second anodic peak.

In this work we investigated the mechanical and corrosion behavior of aluminum can bodies. The results obtained show homogeneous distribution of intermetallic particles. The magnesium presence, in the surface of the can bodies, causes instabilities in the tensile curves and provokes localized corrosion surrounding the split up, fissured, sheared and non sheared intermetallic particles by dissolution of magnesium, in the Keller reactant and chloride solution, in the discontinuities of varnish in the inside of can bodies. It is also seen that the localized corrosion observed is caused by a lateral propagation mode. The heterogeneity of thickness of the can body surface, due to the deep drawing, causes an increase corrosion sensitivity of the can body surface and cancel the sheet anisotropy. The Lankford coefficient is very low in the three directions and the planar coefficient in some area takes negative values. It is also seen that all the observations showed an increase on the global strain inducing a premature beginning of diffuse necking. The zones where the diffuse necking appears are sensitive to localized corrosion.

Methyl hydroxyethyl cellulose was tested as a green inhibitor for corrosion of copper in 1M HCl solution, because it is nonpoisonous, natural polymer, eco-friendly and minimal cost material. The inhibition behavior of methyl hydroxyethyl cellulose was studied utilizing cyclic voltammetry, potentiodynamic polarization and weight loss techniques. The inhibition efficiency increment with incrementing the concentration of methyl hydroxyethyl cellulose and with incrementing the immersion time. The morphology of the surface and the adsorption isotherm were studied. The values of activation energy (E_a) and heat of adsorption (Q_ads) were computed and expounded. The inhibition action was explicated on the basis of adsorption of methyl hydroxyethyl cellulose on the surface of copper constitutes obstruction of mass and charge transfer leading to safeguard the copper surface from the offensive ions.

Superhydrophobic and self-cleaning glass slides were fabricated using a facile and low-cost method through spray-coating of four types of blends consisting of stearic acid, the mixture of stearic acid and SiO₂ nanoparticles, the mixture of stearic acid and SiO₂ nanoparticles modified with oleic acid, and the mixture of stearic acid and SiO₂ aerogel onto the surface. The nanocoated surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and water contact angle (WCA) measurements. The results have shown that the mixture of stearic acid and SiO₂ nanoparticles modified with oleic acid coating possessed the highest contact angle of about 158.6° and a low sliding angle while the mixture of stearic acid and SiO₂ aerogel had an almost similar WCA but with a more satisfactory durability. In contrast, the stearic acid coating alone had a hydrophobic property and the mixture of stearic acid and unmodified SiO₂ nanoparticles showed superhydrophobic properties without any self-cleaning and durability features.

The objective of this study was to characterize the surfaces of the steel products produced locally during their exposure to the industrial and marine atmosphere of the Arabian Gulf region after being treated by sodium dihydrogen orthophosphate. Corrosion rates were determined by weight loss measurements. Sodium dihydrogen orthophosphate performed well throughout the test period. At the end of the exposure duration of 180 days, the corrosion rates of 10 mM sodium dihydrogen orthophosphate treated specimens were 71% of the corrosion rates of the untreated specimens. At certain periods of atmospheric exposure, the (disc shape) specimens were retrieved and studied by SEM and EDS surface analysis techniques. Analysis of the specimens by SEM and EDS at different exposure periods showed that sodium dihydrogen orthophosphate treated surfaces had much lower number of corrosion blisters than those on untreated surfaces at the same period of exposure. They were also smaller in size.

The synthesis of di-cationic surfactants were occurred by the reaction of three straight-chain amide derivatives with (2-bromoethyl)trimethylammonium bromide. After characterization of these di-cationic surfactants using FT-IR and NMR, the corrosion inhibition tests were performed at room temperature (25°C) in 1.0, 2.0 and 4.0 M of HCl solutions for different immersion times. Over 92% of corrosion inhibition efficiencies were obtained from the weight loss measurements. As evidence for the preventing of the oxidation on carbon steel, very small amount of corrosion rates were measured from the weight loss values. To establish the inhibition efficiency results in 1.0, 2.0 and 4.0 M of HCl solutions, SEM analysis of the metal coupons used were performed.

Comparative analysis of sclerometry and micro-, and nanoindentation methods is performed for evaluation of hardness of thin multicomponent nanostructured coatings.

The cyclic potentiodynamic polarization technique is a method for evaluating the susceptibility of a metal to localized corrosion such as pitting and crevice corrosion. This paper provides the information to conduct the cyclic polarization test correctly and to help performing the interpretation of the polarization scan properly. The effect of critical parameters including solution resistivity, scan rate, point of scan reversal, aggressive ions, corrosion inhibitors, metastable pits, metallurgical variables, temperature, dissolution gases, pH, immersion duration and surface roughness on the cyclic polarization curve and results interpretation are discussed. Then a number of cyclic potentiodynamic polarization curves for common metals and alloys in prevalent environments are given.