Vol 53, No 3 (2017)

The paper shows the efficiency of electrospark alloying (ESA), based on the studies of the formation of a doped layer (DL) under different processing conditions, and the properties of the surface layer and the roughness parameters. The article proposes the kinetic and functional criteria for evaluating the effectiveness of the spark alloying process, allowing us to select the material for a doping electrode and processing modes for the maximum thickness of the DL and its continuities, as well as taking into account the changes in its physicochemical, strength, and performance properties and parameters of the surface relief.

The process of recombining oxygen atoms on the surface of an aluminum foil and thin film is investigated in the positive column of the DC glow discharge in oxygen at a gas pressure of 200 Pa, a discharge current of 50 mA, and surface temperatures of 350–530 K. It is shown that an increase in the average surface roughness leads to a decrease of the probability of the heterogeneous recombination of O(³P) atoms. The values of the apparent activation energy for the process of heterogenic recombination of oxygen atoms are calculated.

The paper describes the electret properties of low-density polyethylene and the effect of gamma irradiation on them. It is shown that the thicker polyethylene film the more stable the surface potential, electric field strength, and effective surface charge density values. The negative impact of gamma-radiation on the electret properties of the films that is caused by the release of the injected charge carriers from the traps due to clearing the energy barrier thanks to radiation energy is revealed. Irradiated polyethylene films, in turn, are polarized badly in a corona discharge because of the oxygen-containing groups on the surface formed during gamma-irradiation that act as charge carrier traps with low capture energy. It was found that the formation of cross bonds in the bulk of the polymer and carbonyl groups on its surface slightly raises the degree of crystallinity and the specific volume resistivity and decreases the specific surface resistivity.

This paper presents a quantum-mechanical model to describe the electron localization dynamics in a tetrameric cluster under an external low-frequency electric field, taking into account the electron-vibrational interaction. A system of differential equations concerning the time-dependent amplitudes of the electron localization probability at each of the tetramer centers has been developed. The proposed model is used to describe the tetramers of the linear and cyclic (square-planar) configurations. For both types of tetramer configuration, the numerical calculations are performed at various values of the model parameters. At the same time, this study is focused on the tetramer in which the centers are weakly tunnel-connected and the electron-vibrational interaction with the ligand environment at each of the centers is significant. The control role of the electric field has been found, the variation of the amplitude and frequency of which allows us to implement different electron localization regimes in a cluster by adjusting the duration of the full localization of an electron on the cluster centers and switching a cluster between states with a localized and delocalized electron.

Protection against corrosion using Sinapis alba was studied for the corrosion control of stainless steel in 0.5 M HCl. The electrochemical techniques such as potentiodynamic polarization measurements and electrochemical impedance spectroscopy were used for the stainless steel protection studies. Surface morphology studies were done using scanning electron microscopy/energy dispersive X-ray analysis. Kinetic and thermodynamic parameters were evaluated and discussed. The mechanism for the corrosion inhibition was proposed. The obtained results showed that Sinapis alba acted as a mixed-type inhibitor, with the maximum inhibition efficiency of 88% for the concentration of 0.1 g L^–1 at 323K. It was chemically adsorbed on stainless steel and obeyed the Langmuir adsorption isotherm. Sinapis alba emerged as an effective eco-friendly corrosion inhibitor for the corrosion control of stainless steel in the HCl acid medium. Surface morphology studies confirmed the adsorption of this inhibitor onto the surface of the metal. The results obtained via potentiodynamic polarisation and electrochemical impedance spectroscopy was in agreement with each other.

It is found that the use of transition layers of copper, coated by the electric-spark method in a protective argon atmosphere, improves the heat removal from the contact area and increases the steel bases’ adhesion strength with an antifriction babbitt layer as compared with the traditional technology by 35%. Electric-spark alloying babbitt B83 by indium and stannum allowed us to form running-in coatings without hard inclusions with a thickness of 130 and 100 microns, respectively. New technological solutions allow decreasing the temperature in the friction zone, increasing the thickness of the oil layer, and, as a result, creating a bearing with a better load carrying capability and reliability.

The mineralogical and chemical compositions and the physical properties are determined for three representative clay samples from the Sidi Bouzid area in Tunisia in order to evaluate their industrial aptitude for ceramic applications. The semi-quantitative mineralogical analysis shows that illite and kaolinite are the major clay phases associated with crystalline phases as quartz, K-feldspar and calcite. In addition, some quantities of smectite, interstratified illite–smectite, dolomite and gypsum are also detected. The chemical analysis reveals that the silica phase is relatively high. The CaO rate is approved by the mineralogical analysis. The classification of the selected clays by the Holtz and Kovacs diagram suggests their possible use in the manufacturing of the red bricks in ceramic industry. For the Geotechnical test, ceramic products were prepared by mixing the three clays with different weight proportions (40, 40, and 20% respectively for green clay, red clay and red silty clay samples).