Vol 52, No 4 (2016)

Temperature dependences of parameters n and E are calculated according to the adsorption equation of Dubinin–Astakhov for methane adsorption on eight active carbons in the range of supercritical temperatures of 170–340 K and pressures of 0–20 MPa. At temperatures above ~240 K, characteristic adsorption energy E of methane grows linearly at an increase in temperature. The temperature coefficients of characteristic energy of methane adsorption on active carbon tend to decrease at an increase in standard characteristic adsorption energy E₀. The average value of parameter <n> for the studied adsorbents tends to grow at an increase in standard characteristic adsorption energy E₀.

Surface properties of silica gels modified by trifunctional polyfluorosilanes n-C₆F₁₃(CH₂)₂SiCl₃ and iso-C₃F₇(CH₂)₂SiCl₃ are studied using the methods of adsorption and gas chromatography with respect to nitrogen, hydrocarbon, and water molecules. It is shown that the branched structure of the grafted group and high concentration of grafted groups (2.7 nm^–2) provide better screening of both residual silanols of the support and of additional hydroxyl groups formed in the course of synthesis as a result of hydrolysis. Comparison with the properties of silica gel with grafted monofunctional silane n-C₆F₁₃(CH₂)₂Si(CH₃)₂Cl shows that, in the case of an overall decrease in the adsorption values and considerable surface lyophobization, modification by trifunctional silanes irrespective of the modifier chain length allows obtaining adsorbents containing more polar centers than those in silica gel due to the possible participation in adsorption of additional silanols and a polar fragment of the grafted chain of–CH₂–CF₂–. A considerable difference in the course of isotherms of nitrogen and hexane adsorption–desorption is found in the range of capillary condensation hysteresis related to liophobicity of polyfluoroalkyl layers, a significant decrease in the pore wetting and the corresponding increase in wetting angle θ by hexane. Adsorption of water on fluorinated silicas is negligible and capillary condensation is not observed due to nonwettability of the pore surface by liquid adsorbate (θ > 90°).

A theoretical model of the dimensional dependence of a nanoscale object’s specific heat capacity has been constructed. The model is based on Hill’s nanothermodynamic method. A proprietary topological method for calculation of structural units and elements in a finite-dimensional object is applied.

The reactions of nanostructured TiB₂ films (mean grain size is 3.3 ± 1.1 nm) with mineral acids (HCl, H₂SO₄, H₃PO₄, and HNO₃) of different concentrations have been studied. It is found that the dissolution of the films is a congruent process showing linear kinetics for the time periods in the range from 300 to 1500 min. The corrosion depth parameters of nanostructured TiB₂ films in mineral acids are determined, and their corrosion resistance is graded on a ten-point scale. The studied films show the lowest corrosion resistance in their reaction with nitric acid solutions, and the highest resistance is observed in phosphoric acid solutions.

In the present work iron oxide nanoparticles have been prepared by microwave assisted synthesis with the influence of different precursor salts and synthesis of magnetite, hematite, Iron oxide hydroxide and maghemite nanoparticles. Synthesized iron oxide nanoparticles were characterized with Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Energy-dispersive X-ray Spectroscopy (EDX). XRD measurements show that the peaks of diffractogram are in agreement with the theoretical data of magnetite, hematite, FeO(OH) (Iron oxide hydroxide) and maghemite. Crystallite size of the particles was found to be 33, 45, 36 and 43.5 nm for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃. FESEM studies indicated that size of the particles is observed in the range of about 19.4 to 46.7 nm (Fig. 2a, average 32 nm), 29.1 to 67.6 nm (Fig. 2b average 45 nm), 29.1 to 40.8 (Fig. 2c average 36.6 nm), 29.1 to 80 nm (Fig. 2d average 43.5) for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃ respectively. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR graphs indicated absorption bands due to O–H stretching, C–O bending, C–H stretching and Fe–O stretching vibrations.

The mechanism of transport of saturating components from the electrolyte into the treated material during the anode nitrocarburizing of steel in an electrolyte containing glycerol, ammonium nitrate, and ammonium chloride has been described. The effect of the electrolyte component concentrations and treatment conditions on the pattern of formation and properties of the diffusion layers has been determined. The possibility of preparing a nitrocarburized layer with a thickness of up to 0.2 mm and a surface microhardness of up to 870 HV has been shown.

A set of aluminum–nickel alloys has been studied. The elemental composition of the samples has been determined by atomic emission and atomic absorption spectrometry. X-ray diffraction analysis has revealed that the alloying of the metals leads to the formation of Al₃Ni and Al₃Ni₂ intermetallic compounds, while a portion of Al remains in a metallic phase. The local chemical composition and surface morphology of the original alloys and the alloys activated with the liquid Ga–In eutectic have been studied by scanning electron microscopy and X-ray microanalysis. It has been shown that the original alloys are characterized by a pronounced morphological heterogeneity of interfacial regions in the near-surface layers. It has been found that the studied Al–Ni alloys are activated by the liquid Ga–In eutectic; however, one of the alloy components—the Al₃Ni intermetallic compound—does not undergo significant morphological and chemical changes in contact with the liquid eutectic.

Interaction between GO and the counterpart of the bone tissue, calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA), is modeled in the course of synthesis of nanosize composite materials (CMs) based on graphene oxide (GO) and biocompatible HA with a GO content of 0.1, 1.0, 2.0, and 5.0 wt % GO from aqueous solutions in the system of Ca(OH)₂–H₃PO₄–GO–H₂O under native conditions (37°C). The effect of CM composition on the size and morphology of HA nanocrystals (HA NCs) is determined using the methods of physico-chemical analysis (chemical, XRD, IRS, DTA, TDG, SEM, TEM). The solubility of HA NC CMs by Ca²⁺ ions in distilled water is determined under in vitro conditions, and the possible results of interaction between GO and native calcified tissues are analyzed.

The process of template-free DNA synthesis was detected in two ways: by measuring the pH of the solution by a semiconductor sensor and by measuring the conductivity in the recording of impedance spectra. Synthesis was carried out without using template DNA, with only two enzymes being involved in the reaction: DNA polymerase and nicking endonuclease (nickase) in the presence of deoxynucleotide triphosphates. Previously, Purushothaman et al., by applying the recording of the results of template-directed synthesis with a pH-sensitive field-effect transistor, showed that protons are released into solution in the incorporation of nucleotides [4]. Regarding this, it was important to establish that the same release of protons into solution occurred in the template-free synthesis as in the template-directed synthesis and to identify the changes by measuring the conductivity of the solution using impedance spectra. It was found that the template-free synthesis was accompanied by the generation of protons (ΔpH is ~1.5 pH at an initial concentration of deoxynucleotide triphosphates of 150 µM) and a decrease in the value of active impedance component by ~25% of the initial value. The effect of a decrease in the active impedance component was explained as being due to an increasing conductivity of medium due to a growth in the concentration of protons.

The biomimetic method is used to obtain hydroxyapatite (HAP) coatings on Ti6Al4V, Ti and AISI 316L SS substrates. These substrates with different pretreatment surface operations (HNO₃, anodic polarization, base-acid) were immersed in concentrated simulated body fluids (SBF) for different days at physiologic conditions of 37°C, initial pH of 7.4. Then the corrosion behaviours of substrates after immersion in concentrated SBF were examined by electrochemical methods in Ringer’s and 0.9 wt% NaCl solutions at a temperature of 37°C. Ions concentrations and pH analyses were carried out after incubation in concentrated SBF. After immersion in SBF for different days, the surface morphology remains almost unchanged and no apatite formation is observed. Corrosion currents of substrates increased after immersion. Ions concentrations and pH values were shown variability according to soaking time and pretreatment surface operations.

The protective action of biopolymer starch on 6061 Al-15%_(v) SiC_(P) composite in 0.25 M hydrochloric acid was studied by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques with temperature ranging from 303 to 323 K. The concentrations of starch used were in the range of 0.1 to 0.8 g L^–1. The surface morphology studies were carried out using Scanning Electron Microscope, Energy Dispersive X-ray analysis, Atomic Force Microscope and X-ray Diffraction analysis techniques. Suitable mechanism was proposed for the corrosion and inhibition process. Results indicated increase in the efficiency of the inhibitor with its increase in the concentration and with temperature. Maximum inhibition efficiency of 84% was observed at 323 K for 0.8 g L^–1. Starch acted as a mixed inhibitor. Kinetic and thermodynamic studies showed that starch underwent chemical adsorption and obeyed Langmuir adsorption isotherm. Surface morphology studies confirmed the adsorption of inhibitor on the surface of metal matrix composite. Results obtained by potentiodynamic polarization method and electrochemical impedance spectroscopy method were in good agreement with one another.

A new cationic surfactant was prepared and examined as an inhibitor for the corrosion of carbon steel in 1.0 M HCl solution using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The chemical structure of the prepared cationic surfactants has been proven by FTIR spectra. The inhibiting effect of the cationic surfactant as a result of the formation of the protective layer adsorbed on the carbon steel surface The adsorption of the inhibitor was discussed accordingly to the Langmuir isotherm. Polarization data indicated that the cationic surfactant is a mixed-type inhibitor.. The effect of temperature on the corrosion rate of carbon steel in1. 0 M HCl solution devoid of and containing the novel cationic surfactant was examined and thermodynamic parameters were computed. Some surface parameters were calculated and explained.

This paper investigates the effect of yttria (Y₂O₃) coating on high temperature oxidation behaviour of low alloy 9 Cr–1Mo steel. The superficial coating is Y₂O₃ was prepared for experimental investigation. The isothermal corrosion study of uncoated and coated specimens was carried out in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterized in SEM, EDS and XRD. The results clearly indicate that Y₂O₃ coated specimen improves the high temperature oxidation resistance than uncoated specimens. The improvement of oxidation resistance in presence of Y₂O₃ coating can be attributed to the changed mechanism of scale growth from outer cation migration to inner anion migration and enhancement of scale adhesion with the substrate. Further, enhancement of scale adhesion with the substrate in case of Y₂O₃ coating also improves the oxidation resistance. The detail mechanism of the oxidation of Y₂O₃ coated and uncoated specimen is further discussed in this paper.

In this work, clinoptilolite hydrogen forms are obtained from the Khonguruu zeolite locality (Republic of Sakha, Russia) using hydrochloric acid solutions of different concentrations. The chemical composition is identified via X-ray spectral microprobe analysis and thermogravimetry. IR vibrational spectra of the alumino–silico–oxygen framework are studied in its dealumination and decationization. The effect of the aluminum content in clinoptilolite hydrogen forms on the intensity change and frequencies of the principal vibrational bands of alumino–silico–oxygen framework is established as well.