A Compatible and Efficient Fabrication of Bi-Continuous Nanoporous Copper Films

To cater to the application in various micro/nano devices, this paper reports a compatible and efficient approach combining electrodeposition and dealloying to fabricate bi-continuous nanoporous copper films. In the electrodeposition step, effect of concentration ratio of different ions, pH of the solution and cathode current density on the elementary composition and microscopic morphology of the deposited alloy are systematically investigated, obtaining an optimum condition with good stability and process compatibility. A uniform copper-zinc alloy with its zinc content improved to ~67 at.% is prepared under this condition. A uniform nanoporous copper with an average pore size of 150 nm is fabricated by ultrasonic assisted dealloying whose efficiency is significantly improved compared to free dealloying. This method is promising to be used in the mass production of nanoporous copper films, benefiting researches on various practical applications in micro/nano devices.

Efficiency definition of the deposition process of electrochromic Ni(OH)2-PVA films formed on a metal substrate from concentrated solutions

Electrochemical devices based on nickel hydroxide electrodes are used in different areas. The main ones are chemical current sources, variable transparency “smart” windows, devices for carrying out electrocatalytic reactions, sensors for determining various substances. In this regard, methods of nickel hydroxide synthesis are of great interest, especially those that allow forming nickel hydroxide directly on the surface of electrodes. One of these methods is electrochemical deposition with cathodic current polarization. The available information on nickel hydroxide synthesis from nickel solutions was considered. It was shown that the available data mainly covered information on dilute solutions from 0.01 to 0.25 mol/L Ni(NO3)2. In addition, no comparison was found in the literature for the efficiency of the cathodic formation of Ni(OH)2 at different concentrations of nickel nitrate. To eliminate the lack of information, the dependence of the current efficiency on the concentration of nickel nitrate in the electrodeposition solution was determined at a constant cathode current density of 0.625 mA/cm2. The resulting dependence decreased nonlinearly with increasing concentration. The nickel hydroxide deposit formed in this case had an X-ray amorphous structure, and it depended little on the Ni(NO3)2 concentration. In addition, the current efficiency reached zero at concentrations of 1.5 mol/L Ni(NO3)2 and higher. However, with polyvinyl alcohol in the solution and at Ni(NO3)2 concentrations of 1.5 and 2 mol/L, electrochemically and electrochromically active Ni(OH)2 films were deposited. The current efficiency calculated indirectly for 1.5 and 2 mol/L Ni(NO3)2 solutions was 3.2 and 2.3 %, respectively. Thus, it was concluded that polyvinyl alcohol affected the mechanism of nickel hydroxide electrodeposition from aqueous solutions of nickel nitrate.

Mechanism of Dy3+ and Nd3+ Ions Electrochemical Coreduction with Ni2+, Co2+, and Fe3+ Ions in Chloride Melts

The present paper is devoted to the study of the processes of the mechanism of electrochemical coreduction of Dy3+ and Nd3+ ions with Ni2+, Co2+, and Fe3+ ions in the equimolar NaCl-KCl melt at 973 K and characterization of the synthesized samples. The performed voltammetry analysis of the electrochemical coreduction processes elucidated a significant difference in the values of the extraction potentials of the studied metals. This melt testifies that intermetallic compounds of Dy and Nd with Ni, Co, and Fe may be synthesized in the kinetic regime. The intermetallic phases of Dy and Nd with Ni, Co, and Fe are found to be formed along with the phases of metallic Ni, Co, and Fe either during electrolysis at the cathode current densities exceeding the limiting diffusion current of Ni2+, Co2+, and Fe3+ ions or in the potentiostatic regime at the potentials of the corresponding voltammetry curves. Therefore, the following interrelated key parameters affecting the electrochemical synthesis of Dy and Nd intermetallic compounds with Ni, Co, and Fe were determined: (i) composition of the electrolyte, i.e., concentrations of FeCl3, CoCl2, NiCl2, DyCl3, and NdCl3; (ii) cathode current density or electrolysis potential and (iii) electrolysis time. The obtained samples were characterized by micro-X-ray diffraction analysis, cyclic voltammetry, and scanning electron microscopy methods.

Functional composite electrochemical coating Ni-Co-Al2O3 -an alternative to chromium plating

The physico-mechanical properties of composite electrochemical coatings (CEC) nickel-cobalt-aluminum oxide were investigated depending on the electrolyte parameters and electrolysis conditions. The previously developed low-concentration chloride electrolyte for nickel plating was used as an electrolyte to replace environmentally hazardous chromium plating electrolytes containing hexavalent chromium, which is prohibited by the laws of many countries. The wear resistance of the obtained CEC was determined on a three-ball friction machine. This made it possible to establish that the wear resistance of the CEC exceeds the wear of chrome coatings in dry friction mode by 2-2,5 times and is comparable to chromium in the friction mode with lubrication. In the dry friction mode, the higher wear resistance of the nickel-cobalt-alumina coating is explained only by the higher hardness of the latter. Probably, upon destruction of the coating, the particles of the alloying addition act as a solid lubricant, which causes an increase in the resistance of the CEC during wear. The microhardness of the CEC was determined using a PMT-3 microhardness tester and amounted to 6-25 GPa. The microhardness value was influenced by the concentration and properties of the dispersed phase, as well as the electrolysis conditions - the temperature and pH of the electrolyte, and the cathode current density. “Corrodcote” test was used in the study of corrosion. According to its data, the corrosion resistance of CEC is 2-3 times higher than the corrosion resistance of chromium deposits. The results obtained make it possible to recommend the developed functional CEC of nickel-cobalt-alumina instead of chromium coatings as corrosion- and wear-resistant.

On hybrid type of cathode attachment in high current vacuum arcs

This paper discusses the issues of a possible change of the type of cathode attachment of high-current vacuum arcs (HCVA) with an average cathode current density of more than 105 A/cm2. This type of HCVA is used as pumping plasma gun in experiments with plasma puff z-pinches. These experiments showed that the measured linear mass of the HCVA plasma jet is much higher (by a factor of 10 or more) than the expected mass, which can be obtained from the assumption that cathode attachment occurs only through a multitude of cathode spots emitting supersonic plasma jets. It is shown that in HCVA of the type under consideration, at some time instant there are two types of cathode attachments - cathode spots and thermionic erosion attachment (TEA). It can be said that HCVA of this type have a hybrid cathodic attachment. Unlike cathode spots, TEA produces a subsonic plasma flow, which contributes to an increase in the linear mass of the HCVA plasma jet.

Fabrication of Multi-Layered Zn-Fe Alloy Coatings for Better Corrosion Performance

Zn-Fe compositionally modulated multilayer alloy (CMMA) coatings were developed onto low carbon steel from acid sulphate bath; and their corrosion resistance was calculated using Tafel polarization and impedance methods. The deposit layers were formed galvanostatically by single bath technique (SBT), using square current pulses. An optimal configuration for the growth of most corrosion resistant Zn-Fe coating was proposed and discussed. At maximum switching cathode current density (SCCD) (2.0–5.0 A dm−2), the deposit with 300 layers showed ~43 times superior corrosion resistance than the same thickness of monolayer coating. The improved corrosion resistance of multilayered coatings is due to small change in iron content, leading to change the phase structure of the alternate-layers of the alloy coatings. The surface morphology and structure of film and roughness of the deposit were assessed using Scanning Electron Microscopy and Atomic Force Microscopy. Thus, superior corrosion resistance of Zn-Fe multilayer coatings was used for industrial applications including defense, machinery and automobile etc.

Definition of the influence of pulsed deposition modes on the electrochromic properties of Ni(OH)2-polyvinyl alcohol films

In this work, the influence of some types of the pulsed deposition mode of electrochromic films from aqueous solutions of nickel nitrate with the addition of polyvinyl alcohol was investigated. Glass coated with a fluorine-doped tin oxide film was used as the basis for deposition. The deposition of nickel (II) hydroxide – polyvinyl alcohol electrochromic films was carried out in three pulsed modes: –0.2 mA/cm2×5 s, 0 mA/cm2×5 s (10 minutes); –0.5 mA/cm2×2 s, 0 mA/cm2×8 s (10 minutes); –1 mA/cm2×1 s, 0 mA/cm2×9 s. In this case, the amount of electricity used for the formation of thin-film electrodes was the same for all samples. The resulting films showed dramatic differences in electrochemical, optical, and quality characteristics. The sample obtained in the mode of the highest cathode current density and the duration of the no-current condition (1 mA/cm2×1 s, 0 mA/cm2×9 s) had the worst specific capacity and optical characteristics. This sample was characterized by the highest number of coating defects and color non-uniformity as well. The sample, which was obtained at average current densities (–0.5 mA/cm2×2 s, 0 mA/cm2×8 s), had the highest specific characteristics among the electrodes in the series. The coating was uniform and solid. Also, this sample had the greatest stability of the coloration depth value, which varied from 79.1 to 78.1 % (first to fifth cycles). The sample obtained in the mode –0.2 mA/cm2×5 s, 0 mA/cm2×5 s showed moderate specific indicators, however, there were some coating defects. According to the results obtained, a mechanism was proposed that explained the differences in the characteristics of thin-film electrodes formed in different modes. This mechanism consists of changing the time of non-stationary processes and the distribution of the current density with a change in the value of the deposition current density, the duration of the cathode period, and the no-current condition.

ELECTROCHEMICAL DEPOSITION OF TIN–ZINC ALLOY FROM CITRATE–AMMONIA ELECTROLYTE

The cathodic processes of electrochemical deposition of a tin–zinc alloy in citrate–ammonia electrolytes have been investigated. The content of the main components of the investigated electrolyte (g/dm3): SnCl2·2H2O – 44, ZnO – 4, NH4Cl – 100, Na3C6H5O7 – 100. Wood glue (1.5 g/dm3) and neonol (4 ml/dm3) were added to the electrolyte as surfactants. It was found that high–quality coatings are deposited without heating and stirring only in the pH range from 6,0 to 7,0. The addition of these substances to the electrolyte is predicted to lead to inhibition of the reduction of metals, an improvement in the crystal structure of the deposit, but decreases the cathodic current efficiency. Hull cell studies showed that an electrolyte containing neonol as a surfactant showed better throwing power compared to other solutions. The dependence of the current efficiency of the alloy on the cathode current density showed that in the range of current densities from 0.5 A/dm2 to 4 A/dm2, the current efficiency decreases nonlinearly from 82 % to 52 %. The experimentally obtained dependence of the zinc content in the alloy on the cathodic current density showed the possibility of obtaining alloys with a zinc content of 8 % to 33 %. The obtained results allowed us to determine that for the deposition of an alloy with a zinc content of 20–25 %, which provides the best anti–corrosion properties of the coating, it is necessary to carry out the process at a cathodic current density of 1,5–2,0 A/dm2, while the current efficiency is about 70 %, and the deposition rate alloy is 0,44–0,54 μm/min. The received coatings have a semi–bright appearance, a fine–grained structure, light gray color, they are strongly adhered to the substrate.

ELECTROCHEMICAL SYNTHESIS OF TUNGSTEN OXIDE BRONZE POWDERS

Химическим анализом установлено, что при электрохимическом восстановлении в расплавах MWO -WO (M - Li, Na, K, Cs,Tl) образуются оксидные вольфрамовые бронзы различного состава и структуры. Изучена зависимость изменения равновесных потенциалов катодных продуктов от температуры и состава расплава. Установлено, что с увеличением содержания щелочного металла в вольфраматных расплавах число зародышей кристаллов уменьшается. Снижение температуры расплава и увеличение катодной плотности тока также приводит к уменьшению размеров зерен катодных осадков, что позволяет получать порошки оксидных вольфрамовых бронз контролируемой дисперсности. Методами рентгеноэлектронной спектроскопии и каналирования были исследованы структура конденсированных в среднем вакууме тонких пленок, а также монокристаллы натрийвольфрамовых бронз электрохимически циклированных в анодном и катодном режимах для получения информации о толщине окрашивающего слоя. Chemical analysis established that during electrochemical reduction in MWO - WO (M - Li, Na, K, Cs,Tl) melts, tungsten oxide bronzes of various compositions and structures are formed. The dependence of the change in the equilibrium potentials of cathode products on the temperature and composition of the melt has been studied. It was found that with an increase in the content of alkali metal in tungsten melts, the number of crystal nuclei decreases. A decrease in the melt temperature and an increase in the cathode current density also lead to a decrease in the grain size of the cathode deposits, which makes it possible to obtain powders of tungsten oxide bronzes of controlled dispersion.

RESTORATION OF MACHINE PARTS WITH GALVANIZED ZINC COATINGS

The article shows the role of electroplating in the restoration of parts, indicates the advantages of restoring parts with electroplating over other methods, and gives the characteristics and properties of coatings obtained by electroplating. (Research purpose) The research purpose is in increasing the speed of application of zinc electroplating when restoring parts. (Materials and methods) The cathode current density has a decisive influence on the coating speed. The main reason for limiting the cathode current density during galvanizing from sulfuric acid electrolytes is the chemical polarization of the cathode. The article presents a study on the designed installation for the application of galvanic coatings. When applying coatings to the internal surfaces of parts, there was used a device with activating elements having an electromechanical rotation drive. This device prevents depletion of the near-cathode layer of the electrolyte and reduces the chemical polarization of the cathode. Elements made of moisture-resistant skin were used as activators. (Results and discussion) The article presents the results of experiments as a dependence of the coating speed on the speed of the activator relative to the restoring surface. It also presents the relationship between the size of the abrasive grains of the activating elements, the force of their pressing against the cathode surface, the speed of movement of the activator and the speed of applying the zinc coating, as well as its quality. By activating the cathode surface, it was possible to raise the operating current density to 100-150 amperes per square decimeter. The speed of application of zinc coatings is 16-25 micrometers per minute. (Conclusions) In the course of research, authors determined the conditions of electrolysis during galvanizing, which provide a significant increase in the cathode current density and the rate of application of these coatings during the restoration of parts.