Vol 54, No 6 (2018)

Three compounds of azole derivatives were investigated as inhibitors for the dissolution of aluminum (Al) in 0.5 M HCl solution using electrochemical techniques, e.g., potentiodynamic polarization, electrochemical impedance spectroscopy electrochemical frequency modulation (EFM). The surface of Al was examined in the absence and presence of the some azole derivatives using scanning electron microscopy (SEM). The potentiodynamic polarization suggests that these compounds act as mixed type inhibitors because they enhance both the anodic and cathodic Tafel slopes. The inhibition efficiency (%IE), increased with increasing the concentration of inhibitors. SEM proved the surface of Al is improved due to the adsorption of the azole compounds on the surface of Al. The adsorption of the azole compounds on the Al surface is obeyed Frumkin isotherm. The sequence of the %IE increases in the following order 1,2,3-benztriazole > methyl imidazole > imidazole. The extent of inhibition depends on the molecular size of the molecule and the electron density of the substituent groups.

The corrosion behavior of mild steel (MS) in 5% NH₂SO₃H solution in the nonexistence and existence of aqueous extract of Juniperus was investigated using mass loss (ML), potentiostatic polarization (PP), AC electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM) techniques. It was found that, the inhibition efficiency (P%) of this plant extract depends on its concentration and temperature. Polarization studies revealed that this extract behaved as mixed-type inhibitor. The adsorption process was found to follow Langmuir adsorption isotherm. The effect of temperature on the rate of corrosion in the nonexistence and existence of this extract was also, studied and some activation and adsorption thermodynamic parameters were computed and discussed. The inhibitive action of the investigated extract was discussed in terms of blocking the electrode surface by adsorption of its active molecules through the active centers contained in their structures.

The kinetics of water vapor permeability of insulating tapes of the Polyen, Poliken, Nitto, and Furukawa series was studied by the gravimetric method in the temperature range from 20 to 70°С. It is shown that for all the investigated tapes, in spite of their two-layer construction, normal Fikov kinetics of permeability is observed. Diffusion coefficients that vary in the range from 2.5 to 3.1 × 10^–9 cm²/s are determined, the coefficients of vapor permeability vary in the range from 0.32 to 0.37 g/m² s. Data on the kinetics of permeability, diffusion coefficients and solubility are of practical importance for predicting the barrier properties of insulating tapes during their operation.

WNbN composite films with different Ag content were deposited by reactive multi-target magnetron sputtering. The microstructure, mechanical and tribological properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), high resolution transmission electron microscopy (HRTEM), nano-indentation and ball-on-disc tribo-mter analysis. The results indicated that WNbN-Ag film consists of face-centered cubic (fcc) WNbN, face-centered cubic (fcc) NbN, hexagonal close-packed (hcp) NbN and face-centered cubic (fcc) Ag. The hardness and elastic modulus of WNbN-Ag composite film decreases gradually as Ag content increases from 0 to 25.23 at %. At room temperature, the friction coefficient of the film firstly increases and then decreases, while the wear rate gradually increases with the increasing Ag content. As the temperature increases from room temperature to 700°C, the friction coefficient firstly increases and then decreases, while the wear rate gradually increases. The tribological properties of the film depended on the testing temperatures significantly because the testing temperatures influenced the hardness, the tribo-films and wear mechanism of the film.

ZrB₂, ZrSiB single-layer coatings, and ZrSiB/SiBC multilayer coatings have been fabricated by magnetron sputtering. The coating structure is studied by X-ray powder diffraction analysis, scanning electron microscopy, and glow-discharge optical emission spectroscopy. The mechanical properties of the coatings are identified by nanoindentation. The oxidation resistance and thermal stability of the coatings are studied in the temperature range of 600–1200°C. Doping the ZrB₂ single-layer coatings with silicon reduces the grain size of the hexagonal ZrB₂ phase from 8 to 2 nm. Application of silicon-containing layers results in complete amorphization of the structure of ZrSiB/SiBC multilayer coatings. The ZrB₂ coatings are found to possess the best mechanical properties: hardness of 37 GPa, Young’s modulus of 400 GPa, and elastic recovery of 73%. The ZrSiB coatings are characterized by the highest oxidation resistance: they resist oxidation at temperatures up to 1500°C due to the formation of a protective SiO₂-based film on their surface.

In this paper, we studied the modifying effect of montmorillonite modified with polyfluorinated telomeric alcohols and of antimony(III) polyfluoroalkoxide on the structure and properties of polymer composites based on polyamide 6. The nature of the effect of the modifier on the state of amorphous and crystalline phases in the supramolecular structure of this heterochain polymer was determined by X-ray diffraction analysis and microscopy. The effect of reducing combustibility due to the introduction of a fluorine-containing modifier is considered.

To improve the corrosion resistance of Mg alloys, an excellent anti-corrosive composite coating containing iron oxide was prepared on AZ31B Mg alloy by dipping method. Micro-arc oxidation (MAO) treated Mg alloys were modified by phytic acid/3-aminopropyltrimethoxysilane hybrid and ferrous sulfate heptahydrate/stearic acid solution in sequence. The surface morphology feature, composition and structure, and functional groups were examined by SEM, EDX, XPS, and FT-IR, respectively. Corrosion resistance of the composite coating was evaluated by electrochemical tests in 3.5% NaCl solution. The results confirmed that the as-fabricated composite coating improves corrosion resistance by about two or four orders of magnitude, compared with the single MAO coating and Mg alloy substrate. The surface of the composite coating, which is containing iron oxide with a flower-like network structure in nanoscale, represents an excellent sealing effect for micro-defects of the MAO coating, effectively restricting the penetration of a corrosive medium into the Mg substrate.

Nowadays, zirconia based ceramic coatings are extensively used in various industries thanks to their favorable corrosion and wear resistance behavior. In this study, zirconia and zirconia-Benzotriazole nanostructured coatings were deposited on the surface of Al2024 to improve corrosion protection properties by using sol-gel method. Phases and morphology analyses were performed, and chemical bonds were investigated, using GIXRD, FTIR, AFM, FESEM and ellipsometry. In addition, corrosion properties were evaluated by electrochemical methods including polarization and electrochemical impedance techniques using a 3.5% NaCl solution. Results indicated a homogeneous and crack-free zirconia-Benzotriazole hybrid nanostructured coating which exhibited a good corrosion resistance at a corrosion current density reduced by a factor of 47683.

The effect of the deposition conditions from colloid electrolytes on the chemical and phase composition, texture and electrocatalytic activity of PbO₂–TiO₂ composite materials was studied. The composition of the composites depends on the electrolysis regimes, the charge of the dispersed phase particles and the electrode, as well as the precipitation rate of lead dioxide, and the concentration of the components in the solution. By varying the electrolysis regimes and the composition of the electrolyte, composites with a TiO₂ content of up to 27 wt % can be obtained. The phase composition and texture of the resulting composites are determined by the electrolysis regimes and the composition of the electrolytes used. In addition, the presence of TiO₂ particles in the electrolyte leads, as a rule, to a decrease in crystal size and an increase in the content of α-phase of lead dioxide in the precipitate. Introduction of valve metal oxide particles into the lead dioxide materials generally results in an increase in OER overvoltage and in the rate of p-nitroaniline oxidative degradation due increasing the number of oxygen-bound particles firmly bound to the electrode surface and the parallel flow of photocatalytic processes at TiO₂ centers, providing additional quantity of oxygen-containing oxidants of radical and peroxide nature. The use of composite materials as an active and transition layer of low-wearing anodes makes it possible to obtain electrodes with a long service lifetime.

The problem of the absolute electrode potentials of metals is considered as a problem that encompasses both the thermodynamics of electrode reactions on metals and the surface state of a metal. Within the framework of the physical chemistry of the surface, an adsorption model of the surface layer (SL) of a metal is developed, differing by using the value of the excessive Gibbs surface energy \(\Delta {{G}_{{\text{S}}}}.\) For the low-index facet (hkl) of the metal, the magnitude of the absolute surface potential is introduced as E_s = \({{\Delta {{G}_{{\text{S}}}}} \mathord{\left/ {\vphantom {{\Delta {{G}_{{\text{S}}}}} {zF}}} \right. \kern-0em} {zF}}\) (z is the valence of metal), which, like the magnitude, depends on the electrode potential. On the other hand, a statistical model is used that relates the autoadsorption of point defects, the surface atomic vacancies V_(S) in SL, and adatoms with the surface energy as \(\Delta {{G}_{{\text{S}}}}\) = –RTlnN_V(S)= –RTlnN_ad. For an uncharged metal, the uncharged metal value \(\Delta G_{{_{{\text{S}}}}}^{0}\) is maximum, which gives a minimum of the mole fraction of N_ad = N_V(S) and leads to a zero charge potential formula as \(E_{N}^{0}\) = –\({{\Delta G_{{\text{S}}}^{0}} \mathord{\left/ {\vphantom {{\Delta G_{{\text{S}}}^{0}} {zF}}} \right. \kern-0em} {zF}}\). The ideal polarization of the electrode relative to E_N values of \(\Delta G_{{\text{S}}}^{{}}\) and G_adsto zero that corresponds to the maximum of N_V(S) or N_ad. These extreme points of the surface activity of atoms determine the scale of absolute values of E_s calculated using known table values \(\Delta {{G}_{{\text{S}}}}\)(hkl) at T = 0 K obtained by the DFT method. When assessing the effect of temperature or potential, the change in the ΔG_S and N_V(S) (or N_ad) values in thermal and electrochemical processes is considered. In Part 2, an application of this scale to the processes of evolution of hydrogen and passivation of metals is considered.

Carbon sorbents modified with poly(N-vinylpyrrolidone), betulin, and poly(N-vinylpyrrolidone) together with betulin have been synthesized. The synthesized samples have been studied by a complex of physicochemical methods (low-temperature nitrogen adsorption, thermal analysis, elemental analysis). Under model conditions, the antioxidant properties of the modified sorbents with respect to their ability to deactivate hydrogen peroxide have been studied. The effect of the carbon sorbents on the hydrogen peroxide decomposition rate has been determined by the gasometric method; the reaction rate constants have been calculated. Dependences of the hydrogen peroxide concentration on the time of contact with the test sorbents have been studied by the optical method using an LIR-2 interferometer.

Using the chemical, electrochemical, and X-ray phase analysis, it has been shown that intermetallic compounds in Zn–Sb, Cd–Sb, Mg–Sb, and Al–Sb systems dissolve mainly with metal ionization, partial ionization of antimony, and parallel processes such as “intermetallic compound–Sb” phase rearrangement and reverse reduction of the Sb³⁺ cations. It is postulated that the phase transformation process proceeds with the formation of a defective crystal lattice and appearance of reactive nanoclusters that interact to produce nuclei of a new phase and then a crystal structure. This process proceeds on the background of a partial uniform dissolution of the studied intermetallic compounds with reverse electrochemical reduction of Sb(III) cations in successive independent processes, as well as the parallel formation of the Sb-based few-atomic reactive clusters and further polyatomic nuclei of a similar phase. Chemical and electrochemical processes occur independently, but their relative rate depends on the magnitude of the potential determined by the level of cathodic and anodic polarization.

The effect of additives of sensitizing Zn(II) and Co(II) complexes with 5,15-(diethoxyphosphoryl)-10,20-diphenylporphyrin on the mobility of holes in thin poly3-hexylthiophene films is studied. The charge carrier mobility is measured using the CELIV and photo-CELIV methods. It is found that the sensitizing additive does not affect the mobility of the equilibrium charge carriers, but causes a decrease in the mobility of the nonequilibrium charge carriers.

New meso-tetra(benzo-12-crown-4)-substituted magnesium(II), aluminum(III), and gallium(III) porphinates are obtained. The structure of complexes is established using the data of electron absorption spectroscopy and MALDI TOF mass spectrometry. Comparative analysis of luminescent properties (energies of fluorescent transitions and fluorescence quantum efficiency) of metal porphyrinates and free meso-tetra(benzo-12-crown-4)-substituted porphyrin in a dimethylformamide solution at 25°C. It is found that the obtained metal porphyrinates are characterized by rather intense fluorescent radiation, as well as solubility in organic media of very different polarities, which allows considering new complexes as potential luminescent sensors for metal cations and as luminescent agents of metal cation interphase transfer.

This work deals with the creation of an enzyme biosensor based on electrochemical impedance spectroscopy (EIS) and the possibility of applying EIS in the quantitative determination of glucose using the screen-printed electrodes modified by glucose oxidase.