Protection of Metals and Physical Chemistry of Surfaces最新文献

The influence of the adsorption of monohydric alcohols with different hydrocarbon radical lengths (C2–C4) and with isomerism of the OH^– group position in the alcohol molecule (C3) on the electrochemical behavior of self-assembled monolayers (SAMs) of dodecanethiol (DDT) on the surface of mechanically renewable Au and Co electrodes was studied using voltammetry and potentiostatic chronoamperometry. An increase in the strength of alcohol binding to the Au surface in the ethanol–propanol–butanol series and to Co in the propanol–ethanol–butanol series was observed, which affected the adsorption of dodecanethiol and the properties of SAMs. It was shown that the OH^– group position affects the alcohol’s adsorption activity (using 1-propanol/2-propanol as an example) on the surface of Au and Co, while the stronger adsorption of 1-propanol to a greater extent prevents the adsorption of DDT and the formation of a dense SAMs film.

In this work, the influence of the physicochemical properties of the nonmetallic substrate on the physicomechanical properties of highly elastic carboxyl-containing polyacrylates was assessed. For this purpose, Raman spectroscopy and dynamic relaxation spectroscopy methods were used to study the structure and relaxation behavior of polyacrylate films of different elasticities deposited on a thermosetting polyimide film in the temperature ranges of the elastic properties of the polymer (from –150 to 100°C).

The PtMoO₃/carbon nanotube (CNT) catalyst was synthesized and its characteristics were investigated in the electrocatalytic oxidation of ethanol in an alkaline medium. It has been shown that PtMoO₃/CNTs is superior in activity to the commercial catalysts PtRu/C and Pt/C. Optimization has been performed of the architecture of the membrane-electrode assembly (MEA) of an ethanol–oxygen fuel cell (FC) with an anode based on PtMoO₃/CNT catalyst, including the selection of the optimal cathode catalyst. The nonplatinum catalyst CNT_N is active in the oxygen reduction reaction (ORR) in an alkaline environment and significantly outperforms the commercial catalyst 40% Pt/C for tolerance to the toxic effects of alcohol. When studying the influence of content of PtMoO₃/CNT catalyst as part of the anode active layer (AL), an increase has been established on the characteristics of the MEA maximum power density, expressed in mW/cm², with an increase in platinum loading in the range of 0.2–1.34 mg_Pt/cm². The obtained results indicate a high degree of accessibility of the active centers of the catalyst in the volume of the AL of the developed architecture. Based on the results of testing the optimized MEA at a temperature of 20°C excess pressure and humidification of the oxidizer, a maximum power density of 14.6 and 11 mW/cm² when the cathode operates in oxygen and air environments, respectively, was obtained. The achieved parameters correspond to the best results described in the literature for similar experimental conditions.

Nickel plating is one of the most complex processes in electroplating. The presented review provides a brief analysis of literary sources that examine the influence of process parameters and introduced organic additives on the formation and quality of the resulting coatings. Data are presented on relatively new areas in electrochemical nickel plating: obtaining nanocrystalline coatings, the use of nonaqueous electrolytes, and nontraditional approaches to the process and nonstationary electrolysis modes (pulsed and reverse current). The problems of developing new organic additives to electrolytes are discussed.

The pseudo-first and pseudo-second order equations used to describe the kinetics of adsorption in solutions are considered. It is shown that they are mainly empirical approximating equations. Based on the mathematical analogy with adsorption isotherms, new expressions for approximating kinetic adsorption curves are proposed. Molecular kinetic analysis of monomolecular adsorption in solutions was performed. A new model of this process has been obtained, taking into account the influence of temperature, hydrodynamics, and other factors on its kinetics. As a consequence, the proposed model yields the Langmuir equation and a number of expressions that allow one to calculate the value of equilibrium adsorption, as well as to estimate the parameters of the adsorption process based on data on its kinetics. It is shown that the integral form of the pseudo-second order equation is also a consequence of the proposed molecular kinetic model. A comparison was made with experimental data on the kinetics of adsorption in solutions published in the literature.

A new catalytic system based on manganese phthalocyanine and nitrogen-doped carbon nanotubes (CNTNs) was synthesized and studied as a platinum-free electrocatalyst in the oxygen reduction reaction (ORR) in an alkaline medium. The synthesized MnPc/CNTN electrocatalyst showed high activity in the ORR both under model conditions using a rotating disk electrode and as part of an alkaline fuel cell (AFC) with a membrane-electrode assembly (MEA) with an anion-exchange membrane. Results obtained were compared with a commercial monoplatinum catalyst’s characteristics under the same conditions. The maximum power density values were 30 and 51 mW/cm² for an MEA with 60Pt/C and MnPc/CNTN, respectively. It has been shown that the MnPc/CNTN system under the operating conditions of an AFC with an MEA is characterized by a higher tolerance to toxic agents (including the ionomer) than the platinum catalyst, which is an important advantage of an MEA based on MnPc/CNTs.

The results of studies of the effect of metals on the physicochemical and physicomechanical properties of polyacrylates based on the analysis of the energy characteristics of the polymer are generalized. For this purpose, the effect of introduced into a polymer composition highly dispersed metal/metal-containing inorganic fillers on the relaxation behavior of the polymers is studied. An analysis of the properties of polyacrylates with different elasticities in the presence of a metal was performed based on the internal friction spectra and temperature–frequency dependences of the oscillatory process of a composite that are obtained using dynamic relaxation spectroscopy based on the determination of the temperature regions of materialization of the elastic properties of a composite at –150 to 100°C. The results of studies of the effect of metal powders of iron and zinc and zinc oxide on the physicochemical and physicomechanical properties of acrylic elastomers are presented and generalized versus an unfilled polymer.

Thin films of tungsten oxide were obtained by cathodic electrodeposition from an electrolyte based on sodium tungstate at a potential of –0.45 V versus an Ag/AgCl reference electrode. WO₃ photoanode film consists of a monoclinic modification (ε-WO₃) with a crystallite size of 10–12 nm. The electrocatalytic activity of WO₃ photoanode in reactions of photoelectrochemical oxidation of mono-, di-, and trihydric alcohols was studied. It was shown that the photoelectrocatalytic activity of WO₃ photoanodes is explained by an increase in the photoelectrooxidation rate symbatically with the number of alcohol adsorption sites.

Ti/CrN/TiN coatings were deposited by cathodic arc deposition at substrate bias voltages ranging from 20 to 60 V. The study examined the effect of bias voltage on the topography and the mechanical and corrosion properties of the coatings using laser and scanning electron microscopy, X-ray diffraction, nanohardness testing equipment and electrochemical testing. The results show that bias voltage significantly affects the morphology of Ti/CrN/TiN coatings. With an increase in bias voltage from 20 to 60 V, the concentration of macroscopic defects decreased significantly, and average surface roughness R_a, measured by the contact method, decreased from 0.227 to 0.179 μm per 4 mm of length. Nanoindentation showed that coatings deposited at a bias voltage of 60 V have maximum hardness and elastic modulus. Corrosion tests in 3.5 wt % NaCl solution showed that coatings deposited at 20- and 40-V bias voltages had better corrosion resistance than coatings deposited at 60 V, probably due to a denser microstructure acting as a barrier to the diffusion of aggressive substances.

Data on the effect of a metal substrate on the physicochemical and physicomechanical properties of polyacrylate coatings are generalized taking into account the energy characteristics of the metal and relaxation behavior of the polymer. An analysis of the properties of polyacrylates with different elasticities in the presence of a metal is based on the experimental data on the internal friction spectra and temperature–frequency dependences of the oscillatory process obtained using dynamic relaxation spectroscopy based on the determination of the temperature regions of materialization of the elastic properties of the polymer at from −150 to 100°C. To confirm the effect of the characteristics of the metal surface on the physicomechanical properties of the film-forming polymer, this paper generalizes the data of the works of the authors, in which the characteristic features of the occurrence of dissipative processes in film-forming latex polyacrylates localized on metal substrates of different chemical natures are analyzed taking into account their surface energy.