Vol 52, No 5 (2016)

The influence of pulse recurrence frequency on the accuracy of electrochemical machining of steel 08KP, nickel H1, and copper M1 is shown. Variation of the pulse recurrence frequency leads to similar changes in the tool electrode copying accuracy. This allows us to extend the scope of application of the pulsed mode of electrochemical machining. The correlation between the surface passivity and the effects of the pulse mode is demonstrated. A possible explanation of the observed effects using the existing theoretical background regarding the motion of charged particles in nonstationary inhomogeneous electric fields is discussed.

Study of the electrochemical activity of fractions of boron-gluconate electrolyte used for the manufacturing of nanocrystalline Co–W coatings (the fractioning is performed based on the different molecular weights of the solution components) shows that the electrodeposition results in the formation of an alloy with a very low concentration of tungsten (~1% at.) only from the fractions with a high molecular weight. Electrodeposition from the low-molecular fraction that contains chloride, boron-gluconate, and wolframate ions with cobalt inclusions is not observed. The obtained results are found to be described correctly by the Podlaha–Landolt model of the induced codeposition of iron-group metals with refractory metals.

Nanostructural materials exhibit different mechanical, physical, chemical, and electrochemical properties relative to conventional structures. For instance, nanostructural nickel shows enhanced properties compared to those of polycrystalline nickel, such as higher microhardness, increased wear resistance, higher brightness and lower roughness. In order to produce nanostructural materials, some additives are used as grain refiners. Saccharin is one of the additives that is usually added to the Watts bath in the electroplating process as a grain refiner. The aim of this study is to clarify the functional mechanism of saccharin as a grain refiner in order to realize which functional group of this molecule works as a grain refiner and causes enhancement of properties. To investigate the impact of a functional group of saccharin in the production of nanocrystalline nickel deposits, three different materials with the same functional groups as saccharin were chosen: benzene sulfonic acid, methyl sulfonamide, and benzothiazole. In the process of nickel electroplating these materials were added to the Watts bath as additives. The X-ray diffraction patterns were used to determine the average grain size of the nanocrystalline nickel coatings. The results indicate that the presence of a benzene ring in saccharin, benzene sulfonic acid and benzothiazole cause these molecules to move from the electrolyte to the electrode surface and, by blocking the electrode surface, enhance the grain size and produce nickel coatings with an average grain size below 50 nm. The results also showed that the presence of materials containing a benzene ring with a weak ionic group enhances adsorption on the electrode surface.

Montmorillonite (MMt) from Tunisia has been subjected to fine grinding and studied using FTIR spectroscopy, X-ray diffractograms, BET surface area, Brönsted and Lewis acidity analyse, and FTIR spectroscopy. As a result, significant changes in structural vibrations when MMt was mechanochemically treated were revealed. These changes include: a shift and a gradual decrease of structural OH, Si–O, and M–OH groups (M: octahedral cations; Al, Mg and Fe), which means that an imperfection was formed in the crystal mineral via a mechanochemical treatment. The grinding is associated with amelioration of the oxidative power of clay, which is manifested by the sharpening of the infrared absorption shoulder near 880 cm^–1. The thermo-FTIR adsorption of N-butylamine showed that acidity did not improve upon grinding. On the contrary, the mechanochemical treatment led to the creation of the basic sites which promote the adsorption of atmospheric dioxide carbon.

Copper oxide nanoparticles synthesized via hydrothermal method and used to modify a carbon paste electrode are reported. The structural characterization of nanopowder by XRD clearly shows the formation of monoclinic phase with high crystallinity. The morphological structure is characterized by field emission scanning electron microscope shows the formation of flake like structures. The modified electrode is used for the determination of dopamine and ascorbic acid separately using cyclic voltammetry. The voltammograms obtained during the oxidation studies revealed that nano CuO exhibits better catalytic function towards the oxidation of dopamine and ascorbic acid. The overlapping voltammetric response of both the biomolecules at the bare electrode gets resolved into well defined voltammetric peaks with enhanced oxidation currents.

The aqueous lithium–ion batteries using LiMn₂O₄ as cathode materials are considered to be one of the most promising stationary power sources for large-scale energy storage devices. In the present work, LiMn₂O₄ nanoparticles were successfully synthesized by using sol-gel method, and the morphology of particles was characterized by SEM. We made three electrodes of this active material with PVDF binder and different conductive agents and another electrode of this active material with PTFE binder and Vulcan as a conductor. Electrochemical performances were tested in 5 M LiNO₃ aqueous electrolyte, and comparisons between these electrodes were accomplished.

The electret state of high-density polyethylene subjected to an electric gas barrier of an AC discharge is studied. It is established that under the effect of the discharge a negative charge is formed on the film surface. Using thermally stimulated polarization, we study the space-charge processes in both the thermoand corono-electrets processed in the barrier discharge in the air gap between the dielectrics (glass–polyethylene). A comparison of the stability of the electret state in polyethylene films is carried out.