Vol 52, No 5 (2016)

The well-known model of a plasmaron was applied to describe the states of quantum charges on a metallic surface. A theory of a surface self-localized axial plasmaron was suggested. The theory considers the plasmaron as a structure that results from interactions between both axial plasmon and an electron adjacent to the inner side of a metal surface with an energy close to the Fermi level. The proposed model is very important for physicochemical and electrochemical applications, since it determines adequately the role of the attractor factor of a metal surface (a Fermi sea) determining the affinity of metal to quantum charge. It is suggested that the phenomena of self-localization of an electron (hole) by a plasmon attractor is behind the physics of chemisorption processes on metals and plays an important role in understanding the nature of electrochemical effects on metal electrodes.

Electrolytic hydrogen absorption in 5 М KОН solution by double- or triple-walled carbon nanotubes (CNТs), which are applied onto a steel membrane and capsulated by an electrolytic nickel layer with a thickness of 10 nm, is studied. CNТs are produced by catalytic pyrolysis of methane and characterized by an inner diameter of 2–4 nm, length of up to 10 μm or more, and a specific surface of 600–800 m² g^–1. Investigations are carried out using the electrochemical diffusion technique, cyclic voltamperometry, and electrochemical impedance spectroscopy. Data on the accumulation of electrolytic hydrogen by double- or triple-walled CNТs agree with previously obtained results for multiwalled carbon nanotubes and are in a range of 5–14%. However, the observed scatter of experimental results is probably caused by bifurcation characteristic for nanoobjects.

The kinetic parameters of liquid-phase adsorption of a model organic dye, such as methyl orange, from aqueous solution on carbon sorbents were determined under static conditions. Activated carbon and carbon modified with carbon nanotubes synthesized by chemical vapor deposition on metal oxide catalysts were used as experimental materials. It was found that the presence of carbon nanomaterial in the structure of activated carbon intensifies the sorption process and increases the equilibrium adsorption in 2.1 times. The calculated values of the adsorption rate constants showed a 1.5 times higher rate of the extraction process on modified carbons than on standard materials. In addition, the sorption of organic dye was adequately described by the pseudosecond order model, thus, implying a significant contribution of the chemical interaction between adsorbate and adsorbent to the sorption process.

The effect of the treatment of solid skeletal electrolytes, such as double zirconium phosphates Me_0.5Zr₂(PO₄)₃ (Me = Ni and Co), with high-frequency H₂ and Ar plasma on the adsorption and desorption of CO₂ was examined. It was found that the treatment of cobalt zirconium phosphate with high-frequency H₂ plasma increases its specific surface area, while the pore size is reduced approximately tenfold (from 6.2 to 0.56 nm). Treatment with H₂ and Ar plasma influences the adsorption characteristics of CO₂ in various ways. The activated character of CO₂ adsorption on the initial NiZr and CoZr phosphates remains after their treatment with high-frequency H₂ plasma, while the strength of binding between adsorbate molecules and the surface increases. Treatment with Ar plasma leads to a reduction of CO₂ adsorption with increasing temperature, and the isosteric heats do not depend on the nature of the conductive ion (Co²⁺ or Ni²⁺).

Composites with photoelectrical, nonlinear optical, and photorefractive properties have been prepared. The composites consist of polyvinyl alcohol, single-wall carbon nanotubes, and fullerene C₆₀. Addition of C₆₀ with a long wavelength boundary near 630 nm resulted in an eight- to tenfold increase in both the quantum efficiency of generation of mobile hole charges and the photorefractive two beam gain coefficient measured at wavelengths exceeding 1000 nm (over an area of optical absorption of nanotubes). This is attributed to electron trapping by acceptor fullerene, which limits the regeneration of photogenerated charges and provides an increase in mobile hole charges.

In this work we investigate influence of the composition and specific surface of a precursor on the porous structure of tantalum powders obtained via magnesium vapor reduction of the Та₂О₅, MgТа₂O₆ and Mg₄Та₂O₉. Sorption and nitrogen capillary condensation have allowed an increase in the specific powder surface to be established due to the increasing amount and specific surface of mesopores with a size below 10 nm.

Methods of scanning electron microscopy with an X-ray probe, Raman spectroscopy, and thermogravimetry are used to study the morphology and composition of metal–oxide nanostructures obtained by thermal oxidation of spherical microparticles of iron powder with a diameter of 1–3 μm. It is shown that unidimensional hematite nanoflakes and fibers grow under atmospheric annealing at 300°C and above in the radial direction from powder microparticles, which is accompanied by depassivation and acceleration of corrosion layer growth. An increase in temperature and oxidation time results in transformation of microparticles into urchinlike multilayer nanoparticles consisting of elongated crystalline α-Fe₂O₃ nanowhiskers growing normally to the surface of the particle consisting of an iron core and shells of the magnetite and hematite phases. Growth of hematite nanowhiskers continues until the metallic core is completely oxidized.

The method of layer-by-layer (LbL) deposition from aqueous solutions was used to obtain electrostatic self–organized composites consisting of cationic fragments of octa-[(4′-benzo-15-crown-5)oxy]phthalocyaninates of metals (Mcr8Pc)/K⁺ and anionic fragments of sodium polystyrenesulfonate or 4,4′,4″,4‴-[cobalt phthalocyaninate-2,(3),9,(10),16,(17),23,(24)-tetrayl-tetrakis(oxy)]-tetrabenzoic acid. The electronic absorption spectra of composite coatings indicate preservation of structures formed in aqueous solutions of Mcr₈Pc: coaxial associates, noncoaxial associates, and high-order aggregates. An increase in the content of noncoaxial associates and the possible presence of suspension particles in the composite are observed.

In this study, the Ni–B–Al₂O₃ composite was successfully coated on the surface of Ck45 steel by elecroless method. X-Ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were utilized in order to investigate and identify the coating properties. Wear behavior of the coating was studied by the pinon- disk test. Corrosion behavior of the Ni–B and Ni–B–Al₂O₃ coatings was investigated by using Tafel polarization diagrams in the 3.5% NaCl solution at room temperature. The obtained data demonstrate that the addition of Al₂O₃ nanoparticles to the coating has resulted in improving the tribological behavior of the coating due to the presence of the composite nanoparticles. Also, the results of electrochemical testing show that corrosion resistance of the electroless Ni–B coating with Al₂O₃ nanoparticles has dramatically increased.

The characteristics of surface feature and microstructure of the near-surface of nickel were investigated after high current pulsed electron beam (HCPEB) irradiation. Based on a physical model, the temperature profile was simulated. The depth of heat-affected zone, the initial melting position, heating rate and quenching rate were computed. The initial coarse-grained structure on the surface was refined, of which the size is about 70 nm. The TEM observations indicate that dislocation wall, sub-dislocation wall, twin and twin boundary steps were achieved on the surface of material after HCPEB irradiation. Furthermore, huge numbers of vacancy defect clusters including dislocation loops, stacking fault tetrahedras (SFT) and voids were also formed within the sublayer of the irradiated surface. The fact that supersaturation vacancies migrated towards the surface along grain boundaries and/or various dislocation configurations led to the formation of microporous feature on the irradiated surface.

Mixtures of cyanuric acid with different polymers are subjected to plastic deformation under pressure of 1 GPa, and the DSC method is used to establish that endothermal processes with enthalpies that can reach 50 J g^-1 occur in deformed mixtures under heating in the range of 50–250°C. The occurrence of endothermal processes is related to the destruction of intermolecular bonds formed at the acid–polymer interface and due to formation of double electric layers and appearance of interphase electrostatic attraction.

The study on the corrosion behavior of the composite and evaluation of surface modification technique are of importance since the addition of reinforcement particles affects the continuity of inherent oxide layer on the matrix and hence its corrosion resistance. The present study deals with the investigations of effect of ceramic coating on the corrosion behavior of 6061 Al/SiC_P (20 volume % reinforcement) composite in 3.5 M NaCl solution at high temperatures namely 30 and 40°C using potentiodynamic polarization technique and cyclic polarization plots. Aluminum coating by magnetron sputtering technique is employed on the composite and it is subjected to heat treatment at 200°C for duration of 2 h for the alumina formation. The alumina coating formed on the composite surface acts as corrosion protective coating. The potentiodynamic polarization technique is used to determine the corrosion rate of the composite specimen with and without ceramic coating in the corrosion media. The cyclic polarization technique is used to study the pitting behavior of the composite with and without ceramic coating. The microstructural analysis is carried out using scanning electron microscopy (SEM). X-RD analysis shows the amorphous nature of Alumina coating obtained on the composite. The results show that the peak aged composite is more prone to corrosion among the aged group of composites but when coated with alumina shows a vast improvement in pitting nucleation resistance even at high temperatures.

Three new microarc (MAO) ceramic coatings were fabricated in the Ca-P electrolyte with three eco-friendly easily degradable complexing agent GA, TEA and EDTMPS and compared to that fabricated with the current common agent EDTA–2Na. A 3-Dimensional video microscope and scanning electro microscope were utilized to observe surface and cross-sectional morphology; the statistics of the coating surface were measured by the image software Image J × 2.0. Compositions of elements and phases were detected by the energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively; X-ray photoelectron spectroscopy was further applied to provide more information about the components of the four complexing agents for MAO coatings surfaces. The surface morphologies show difference, which is a result of different quantity of melting metal during the treatment. The EDS results indicate that the elements compositions of the four MAO ceramic coatings are similar. The phases show little difference which is a result of the crystal transformation of TiO₂ in different physical characteristic electrolytes. The biocative tests of four complexing agent MAO coatings shows good bioactive performance. The surface morphology of MAO coatings could meet the demand of biological implanting. Corrosion resistance properties are improved effectively in simulated body fluid (SBF). The wetting angles are less than 90 degrees, which indicates better solid-liquid affinity. After 28 days of sedimentation experiments in SBF, the white substance-carboxyl apatite (HA) generate on the surface of the coatings. The biological activities of the four MAO coating samples are demonstrated.

Glucose is an organic molecule whose characteristics are corrosion inhibitors. The adsorption and inhibitory effect of glucose on copper surfaces in alkaline (pH 8.0) Chloride solutions were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The data obtained indicate that glucose behaves as a mixed-type inhibitor by physically adsorbing onto copper surfaces according to the Langmuir isotherm. The inhibition activity of glucose increases with increasing the concentration of glucose.

Inhibition effect of some hydroxytriazenes on copper in nitric acid medium has been studied using weight loss technique at temperature range between 303 to 343 K. The used hydroxytriazene compounds are 3-Hydroxy-3-phenyl-1-(4-sulphonato(sodium salt) phenyl) triazene(HPST), 3-Hydroxy-3-(3-methylphenyl)- 1-(4-sulphonato(sodium salt) phenyl) triazene(HMMPST), 3-Hydroxy-3-(4-methylphenyl)-1-(4-sulphonato (sodium salt) phenyl) triazene (HPMPST), 3-Hydroxy-3-(3-chloroplenyl-(4-sulphonato (sodiumsalt) phenyl) triazene (HMCPST), 3-Hydroxy-3-(4-chloroplenyl-(4-sulphonato (sodiumsalt)phenyl) triazene (HPCPST). Results reveal that inhibition efficiency increases with increasing concentration of hydroxytriazenes from 0.0005 to 0.002 M in following order HPMPST > HPST > HMMPST > HPCPST > HMCPST. HPMPST compound in 0.002M concentration show maximum inhibition efficiency of ~90 at % 303 K temperature. Effect of temperature on inhibition efficiency and thermodynamic parameters have also been reported. The adsorption of hydroxytriazenes obeyed Langmuir Adsorption Isotherm.

The initial period of growth of a passive film of iron in borate solutions (pH 7.4 and 6.7) is studied using the quartz crystal resonator technique (EQSN) and pulsed chronoamperometry. Dependences of the surface layer thickness on time are obtained at the metal passivation and prepassivation potentials. Regions corresponding to different stages of passive layer formation are found in anodic current transients, which allowed the ambiguous effect of atomic hydrogen on kinetics of hydrogenated iron dissolution to be explained. It is shown that the iron hydrogenation promoter prevents formation of a primary passive film by accelerating iron dissolution at prepassivation potentials.