Vol 55, No 1 (2019)

The concepts of the absolute surface potential (ASP) E_S of the (hkl) facet of a metal crystal with E_S = ΔG_s/zF directly related to the Gibbs surface energy ΔG_S and with an equilibrium between (auto) adsorption of its own atoms on this facet of N_ad and negative charged surface vacancies (NCSV). On this basis, the ASP scale is a scale of adsorption potentials with point defects—the NCSV and adatoms, which determine their surface statistics as a result of the action of surface and electrostatic forces on these quasiparticles. This dualism is aimed at overcoming differences in the understanding of the surface potential in Helmgholz theory and Gibbs theory. The adsorption scale of the singular metal face has a special point—the potential of the zero charge (PZC) of the electrode \(E_{{\text{N}}}^{0}{\text{ = }}-\Delta G_{{\text{S}}}^{0}{{(hkl)} \mathord{\left/ {\vphantom {{(hkl)} {zF}}} \right. \kern-0em} {zF}}\) with a minimum of adsorption of atoms and NCSV. Point of absolute adsorption devides the scale of cathodic and anodic polarization (Fig. 4.1, Part 1) with predominant adsorption of NCSV or adatoms, reaching the maximum degree at the potential of the second special point \(E_{{\text{S}}}^{0}\) in each area of the ideal electrode polarization. Part 2 discusses the transition from the ASP to hydrogen scale using the ratio between the standard and absolute values ​​of a hydrogen electrode adopted by the International Union of Physical and Applied Chemistry. Combining the ASP scale with the scale of the absolute potentials of electrode reactions made it possible to calculate the electrode potential of a chemisorption and electrocatalytic reaction of hydrogen evolution on various metals, as well as the potential for the formation of passivating oxide on metals (Ni, Cr), known as the “Flade potential.”

Cellulose was modified via impregnation of a polymer sample with a solution of C₆₀ nanocarbon particles in o-xylene. The sorption kinetics of Cu(II), Ni(II), and Cd(II) ions from an aqueous environment on cellulose and composite material is studied. There is an increase in extraction efficiency of metals with a fullerene-containing sorbent compared with that of initial polymer. Quantitative characteristics of sorption kinetics are found for metal ions in the framework of models of pseudo-first- and pseudo-second-order reactions. The equilibrium sorption of Cu(II) ions on cellulose and composite is described with different isotherms, which is due to different mechanisms of interaction of metal ions with initial cellulose and composite.

The present study deals with the application of activated carbon for the adsorptive removal of Cu(II) from its aqueous solutions. This paper incorporates the effects of pH, adsorbent dose, contact time, concentration and temperature. Equilibrium adsorption isotherms are usually used to determine the capacity of an adsorbent. The adsorption behavior of the Cu(II) has been studied using Langmuir and Freundlich adsorption isotherm models. The monolayer adsorption capacity determined from the Langmuir adsorption equation has been found as 13.7 mg g^–1. Adsorption of Cu(II) on adsorbent was found to increase on decreasing initial concentration, increasing pH up to 7 and increasing temperature. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. SPSS software was employed for prediction and investigation of factor importance in determining of reminded Cu(II) after adsorption. According to Beta-value the importance order of factors is: concentration, adsorbent dose, time, pH and temperature respectively. Also, the obtained results from this study show the good adaptation between experimental and prediction values of % Cu(II).

The Gibbs free energy and water vapor adsorption isotherms on the surface of a silver iodide nanoparticle at a temperature of 260 K have been calculated via the bicanonical statistic ensemble at the molecular level. The profiles of dependences reveal the capability of a surface to retain microdroplets in water vapors, as well as evidencing the condensation scenario of the formation of the contact between the dense phase and the solid surface as the most feasible way of heterogeneous nucleation under atmospheric conditions.

A method for the preparation of film coatings of titania doped with bismuth (Bi³⁺) and lead (Pb²⁺) ions, separately and simultaneously, has been developed based on sol–gel synthesis. According to X-ray phase analysis, the films represent a single-phase system of titania in anatase modification. It has been shown that doping of titania with bismuth and lead leads to a shift of the absorption maximum to the visible light region; in this case, the largest shift is observed in the sample containing 2.5 wt % bismuth and lead. The film coatings have been studied as catalysts of photoelectrooxidation of methanol, formic acid, and phenol. It has been shown that the highest catalytic effect is observed for the samples containing simultaneously bismuth and lead; however, doping of titania with bismuth has the greatest effect on the rate of organic substrates oxidation. It has been assumed that photoelectrochemical oxidation of the model systems with visible light is due to a decrease in the band gap of doped titania to 2.7 eV.

Corrosiveness of palm oil biodiesel blends was measured using surface plasmon resonance with polypyrrole chitosan cobalt ferrite nanoparticles sensing layers. Diesel fuel which is relatively corrosive and lower flash point is often mixed with biodiesel of low corrosiveness and higher flash point. Biodiesel blend fuels were prepared from the mixture of normal palm oil biodiesel and diesel fuel where the percentage of the mixture was in the range of 10–90%. The corrosiveness of all the samples was in the class 1a according to the standard copper strip test, but the concentrations of copper and iron ion that were released in biodiesel blend were distinctly different. In this article, the corrosiveness of biodiesel blend was investigated using surface plasmon resonance from the measurement the concentration of copper and iron ions. The corrosiveness of biodiesel blends consistently decreased with increasing the concentration of biodiesel. Moreover, the sensitivity of polypyrrole chitosan /cobalt ferrite and polypyrrole chitosan sensing layer was compared. Consequently, the polypyrrole chitosan cobalt ferrites have sensitivity higher than polypyrrole chitosan sensing layer.

A new composite adsorbent was obtained by hydrolytic polycondensation of N,N'-bis(3-triethoxysilyl propyl)thiocarbamide in the presence of poly-2-methyl-5-vinylpyridine. The sorption activity of the composite toward platinum(IV) ions was studied in hydrochloric acid solutions. The maximum extraction efficiency of Pt (IV) and the maximum values of sorptive capacity (218 mg g^–1) and coefficient of interphase distribution (7090 cm³ g^–1) of the studied adsorbent in 1 М solution of HCl were found at 338 K. The Langmuir, Freundlich, and Dubinin–Radushkevich models were used to describe adsorption nature.

This work is devoted to the deposition of coatings based on FeNiCrWMoCoCB metallic glasses on a surface made of 35 steel; the deposition is carried out by electrospark machining in a medium of granules of metals and alloys used as electrode materials. X-ray diffraction analysis showed that an amorphous phase is predominant in the composition of coatings. At a temperature of 1100°C, the amorphous phase crystallizes in borocarbide of the M₂₃(C,B)₆ type, an intermetallic of iron, nickel, and chromium, and αFe phase. Polarization tests of the coating in the NaCl solution (3.5%) demonstrate a lower corrosion current and a higher polarization resistance compared with the 35 steel. It is found during the study of a heat resistance at 600, 700, and 800°C that the use of the FeNiCrWMoCoCB coating on the 35 steel enhances a resistance of its surface to a high-temperature gas corrosion in 8.7, 6.3, and 3.0 times, respectively (the experiment time was 40 h). The wear resistance of the FeNiCrWMoCoCB coatings in a dry sliding wear mode at loadings of 10 and 25 N was 2.2 and 1.7 times higher than for the 35 steel. The samples with the coatings based on the FeNiCrWMoCoCB metallic glasses show a high catalytic activity for a decomposition of a methylene blue solution as at the presence of hydrogen peroxide, as well as without it.

The aim of this paper was to investigate the formation of an amorphous phase in the coating structure due to reduction in porosity and improvement in corrosion resistance of Ti6Al4V alloy during PEO process. The effect of crystallization on the electrochemical corrosion behavior and surface property of Ti6Al4V coating fabricated by plasma electrolytic oxidation (PEO) technique, was investigated in 5 wt %HCl solution. The coating compositions and electrochemical behaviors were examined by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) and polarization tests. The results showed that an increase in the ionic strength of electrolyte had a direct effect on the crystal size, the lattice strain and corrosion resistance. An increase in lattice strain due to Ti–O–Si led to a reduction in coating adhesion and corrosion resistance. A significant effect in phase transformation for Titania in the PEO process was not only led to an increase in polarization resistance but also reduced the number and size of porosity.

Pitting formation in carbon steel in saturated Ca(OH)₂ solutions containing different concentrations of added NaCl is studied experimentally using cyclic voltammetry and choronoamperometry. The dependences of corrosion, pitting, and repassivation potentials on the NaCl concentrations are established. The possibility of pitting corrosion of carbon steel in such solutions is evaluated. We discuss the limitations of the used electrochemical methods to long-term forecasting of pitting corrosion of metals.

The corrosion behaviour of 316L stainless steel (316L SS) in 10% H₂SO₄ solution (94°C) with various concentrations of NaCl (0–0.085 mol/L) was studied by immersion corrosion test and polarization methods, combined with SEM/EDS, XPS and XRD tests. The influence of NaCl on the corrosion of 316L SS was investigated. The results showed that at lower NaCl contents (0–0.0085 mol/L), the steel presented a general corrosion characteristic with a higher corrosion speed and the corrosion rate increased with the NaCl content. At higher NaCl contents (≥0.017 mol/L), the corrosion rate decreased remarkably due to the protective corrosion products precipitation which contained metallic sulphates and NaHSO₄. However, the higher concentration of chloride ions caused micron pitting-like local dissolution on the surface. The addition of Na₂SO₄ effectively inhibited general corrosion of the steel because of a dense and continuous products layer enriched with more NaHSO₄ and metallic sulphates formed.

The corrosion inhibitory effect of (1-benzyl-1H-1,2,3-triazol-4-yl) methanol (BTM) for mild steel in 1 M HCl at (298–328 K) was studied using electrochemical impedance spectroscopy (EIS), Tafel polarization curves and weight loss measurements. Polarization measurements revealed the mixed type inhibitor character. The inhibiting action of this molecule is discussed in terms of blocking the electrode surface by the adsorption of inhibitor molecules obeying Langmuir isotherm. Quantum chemical calculations using the Density Functional Theory (DFT) were performed to determine the relationship between molecular structure and its inhibition efficiency. Monte Carlo simulations were also applied to search for the most stable configuration and adsorption energies for the interaction of the inhibitor with Fe surface. The theoretical data obtained are, in most cases, in agreement with experimental results.

The corrosion of copper has been received much attention due to its high affected to everyday life and industry. Eugenol is abundant natural product and can be extracted from Cloves. This work eugenol was used as inhibitor for copper corrosion. The effect of eugenol concentration, immersion time and temperature has been studied. The results showed that eugenol can protect corrosion with inhibition efficiencies of 70% (1.2 M HCl environment at 303 K). The HPLC, FT-IR and SEM techniques have been employed to characterize and to study surface morphology. Furthermore, the sorption isotherms have been evaluated and revealed the adsorption mechanism is best described by the Frumkin isotherms with the free energy of –15.68 k J mol^–1 and consistent with the physical adsorption. Quantum chemical calculation has been also used and discussed relating to corrosion inhibition.

The formation regularities and quantitative porosity characteristics of nanofibrous electrospun composite materials based on polyacrylonitrile and its mixtures with polyvinylpyrrolidone and commercially available Vulcan^® XC72 or Ketjenblack^® EC-600 carbon blacks were studied by standard contact porosimetry. It was shown that a significant increase in the total specific surface area could be achieved due to an increase in the temperature of oxidative warming up of mats from 250 to 330°C followed by vacuum pyrolysis at 900–1000°C. Such carbon materials, after deposition of nanocrystalline platinum onto them, can be used as gas-diffusion electrodes in an intermediate temperature hydrogen–air fuel cell on a polybenzimidazole membrane.