Vol 52, No 1 (2016)

The aim of this investigation was to reveal the processing differences in achieving nanoporous anodized aluminium from aluminium alloys and their application for cobalt nanowires electrodeposition. The following types of aluminium were tested: pure Al (99.99%), and commercial alloys: AA1050, 6082 and 6060. Because of the differences in the surface temperature and high voltages during the anodizing steps, some stresses can be built up in the material. Therefore a strict temperature control should be done to limit thermal stresses in materials. Alloying elements (Si, Mg) cause precipitates that are observed on the surface, especially for 6060 alloy. Nevertheless, a nanoporous structure can be obtained at the end of second anodization step on all aluminium alloys investigated. It was shown that the number density of pores on the surface is practically independent on the aluminium alloys used. However, the degree of hexagonal distribution of the pores depends on the type of anodized aluminium alloy. Also, a successful fabrication of Co nanowire arrays using nanoporous anodic alumina template produced on Al alloy has been demonstrated, and the uniform filling of the template by cobalt nanowires arrays is discussed.

The aim of this work is the development of technology for obtaining electrode materials from Colmonoy-WC alloys and hard alloys containing TiC, WC, Mo₂C, Tin, Co, Cr, Ni, and Al. The phase composition and structure are studied along with the kinetics of mass transfer, hardness, and wear resistance of electrospark coatings made of the manufactured alloys. The methods used were metallography and electron microscopy and X-ray phase and durometric analyses. It was shown that the alloys Colmonoy (Ni-Ni₃B–Si–Cu), Colmonoy-10% WC, and Colmonoy-25% WC have a eutectic structure. With an increase in the WC content in the alloys, the structure is found to be an aggregation of the phases of a hard solution based on nickel and tungsten carboborosilicide. At the pulse energy of 7.5 J, the thickness of the coatings formed was 3–4 mm. The wear resistance of the coatings increased with the growth of the WC content in the coatings from 64.5 μm/km for Colmonoy to 18.5 μm/km for the alloy with 70% WC, and the steel wear resistance under those conditions was 160 μm/km. It was established that the structure and composition of the manufactured electrode materials from the hard alloys based on TiC and WC carbides make it possible to produce electrospark coatings with a thickness up to 100 μm and hardness up to 20–24 GPa. The developed materials can be used to harden/recondition worn workpieces made of constructional steels by the electrospark method.

A new MAO ceramic coating was fabricated in Ca-P electrolyte with a eco-friendly easily degradable complexing agent EDTMPS instead of current common EDTA-2Na. A 3-Dimensional video microscope and SEM were utilized to observe surface and cross-section morphology, and statistics ofcoating surface were measured by image software ImageJx 2.0. Elements and phases compositions were detected by EDS and XRD respectively, and XPS was further undertaken to provide more information about the components of the two complexing agents MAO coatings surfaces. The results indicate that the elements and phases composition of the two MAO ceramic coatings are similar. The surface morphologies show the difference, which is a result of more melting metal during the treatment in EDTMPS electrolyte compared with EDTA-2Na. The results of recent studies of discharge and discharge plasma in low temperature liquid and thermodynamics were introduced into the establishment of MAO process models which was divided into three parts: cusp area, even area and sunk area. Active particles, O₂, free radical ^•OH, free radical H₂O₂, free radical ^•H brought by discharge and discharge plasma play a significant effect on the phase transformation, electrolyte elements diffusion from electrolyte to coating and substrate and chemical reactions. Crater shape of surface morphology is mainly attributed to the sharply increasing pressure with the decreasing of temperature. Finally, a interpretation of MAO process based on the theory of thermodynamics, and discharge plasma in low temperature liquid was developed.

The experience gathered from the use of plasma electrolytic methods in the context of improving the performance of valve group metals is summarized. Emphasis is placed on the formation of coatings by microarc oxidation (MAO) in slurry electrolytes containing powders with different degree of dispersion (a few nanometers to a few tens of microns) and nature (oxides, carbides, nitrides, borides, graphite, etc.). A phenomenological model of the mechanism of formation of MAO coatings in slurry electrolytes is proposed; characteristics of the electrolytes and the coatings are discussed. The results of our studies of the composition of MAO coatings carried out by nuclear backscattering (NBS) spectrum simulation are described. A significant improvement in the properties of MAO coatings formed in slurry electrolytes is registered. It is concluded that this modification can considerably extend the range of application of the MAO method not only in conventional fields of mechanical and instrument engineering but also in aerospace engineering, medicine, biology, and living systems technology.

The dependences of the parameters of corona discharge current–voltage characteristics on the gas temperature are considered in this work. It is shown that the corona discharge ignition voltage U_c(T) of helium and nitrogen decreases with the increase in temperature. The dependence of the parameter A(T) is complicated. It increases at the initial and final sections of the studied temperature range (20–369°C) and decreases at its central portion with two extrema. As the discharge in nitrogen is unstable, we failed to obtain any definite regularity. Generalized dependences that make assertions about the presence of a discharge different from a corona are presented. We made an assumption of an important role of two effects in the observed processes: the absorption of ions by the surface of electrodes and the continuous change in ion mobility due to the ion mass variation in the course of clustering and declustering of ions. It is supposed that there is a dynamic equilibrium between them in a steady state.

This paper reports the results of an experimental study of electronic topological transitions in bismuth glass-covered wires doped with acceptor (Sn) and donor (Te) impurities. The temperature dependences of the thermoelectric power and resistance are measured within the temperature range from 1.5 to 300 K and magnetic fields up to 14T. The position of the Fermi level ε_F and the concentration of charge carriers at doping are estimated from the Shubnikov de Haas (SdH) oscillations which are clearly visible from both L electrons and L and T holes in all crystallographic directions. We demonstrate anomalies in the temperature dependences of the thermopower in Bi wires doped with acceptor (Sn) and donor (Te) impurities in the form of a triple (doping by Sn) and double (doping by Te) change in the sign of the thermopower. The effect is interpreted with relation to the manifestation of impurity Lifshitz topological transitions. The SdH oscillation method was used to determine the energy position of the Σ band by doping Bi wires with the acceptor impurity Sn and the T band conduction by doping with Te. It is shown that the appearance of the Σ and T bands in Bi wires doped with the acceptor and donor impurities is responsible for the anomalies in the diffusive thermoelectric power, which gives a good conform with to the theoretical models and predictions.

This paper reviews opportunities for using electron microscopy in various gas atmospheres for the analysis and morpho-physiological modification of biological structures. The approaches that allow varying the gaseous phase content, as well as temperature, humidity, and pressure, are considered. The applicability of both kinetic and dynamic approaches to the tissue and bioinorganic structure manipulations is pointed out. The possibility of simulation of the beam-induced formation and disintegration of abiogenetic molecular structures is also mentioned as a particular case of the electron beam influence and treatment of the precursor medium in an artificial atmosphere.