Papers by Keyword: Electrolysis

Abstract: In this study, a single-cell, zero-gap, unipolar alkaline water electrolyzer which operates on a 30 wt.% KOH electrolyte solution was developed for production of hydrogen. Suitable material properties such as density, toughness, electrical conductivity, and corrosion resistivity were evaluated in Ansys Granta 2019 with the aid of material property charts; and thermal and stress simulations of the modelled components performed using Autodesk Inventor Nastran 2019. A DC power source supplied voltages below 3.0 V across the nickel electrodes, maintaining an operating temperature of 50 °C, and operating pressure at 0.1 MPa. The electrolytic process produced hydrogen and oxygen gases at the electrodes, and the membrane performed the gas separation. Polytetrafluoroethylene plastic was experimentally found to be a superior and more suitable material for the electrolyzer endplates and spacers to polypropylene plastic. Polypropylene nonwoven geotextile fabric was also found to be a low-cost and efficient membrane material, against Zirfon Perl UTP 500 membrane which is an efficient but expensive industrial membrane; polyester geotextile fabric got corroded after about 24 hours of good service. The optimal performance of the electrolyzer cell was obtained at a cell voltage of 2.2 V and a current of 1.30 A, while producing 14 ml of hydrogen gas per minute. This performance gave an electrolysis efficiency of 55.6%, an energy efficiency of 67.3%, and a hydrogen production efficiency of 75.4%. The produced hydrogen and oxygen gases generated electrical energy in a reversible PEM fuel cell device which powered a 0.2 W DC electric motor for a minute.

Abstract: An experimental method to calculate average charge of metal ions by electrolysis at different temperatures is proposed. Aluminium undergoes dissolution to the Al³⁺ ions at all temperatures. Iron undergoes dissolution to the Fe²⁺ or the Fe³⁺ ions and copper undergoes dissolution to the Cu⁺ or the Cu²⁺. It depends on temperature and electric current density. Direct electric current value and anode mass decreasing were measured during electrolysis into concentrated NaCl solution in water (5 mol/kg or 23.1%, freezing point equals -22°C, pH 6.5–7.5) at room temperature and 100°C. The average charges of copper, iron, and aluminium ions were calculated using Faraday’s law of electrolysis at electric current density 3,000 A/m² (or 30 A/dm²): +3 for aluminium; +2 for iron; and +1 for copper at room temperature, and +3 for aluminium; +2 for iron; and +1.5 for copper at temperature 100°C. The main condition was z_Al=3. We concluded that calculations of the average metal ions charges, z_Fe and z_Cu, were correct since z_Al=3. The result is as follows: the Al³⁺, the Fe²⁺, and the Cu⁺ ions dissolve into concentrated NaCl solution in water at room temperature; the Al³⁺, the Fe²⁺, the Cu⁺ and the Cu²⁺ ions (50%/50%) dissolve into the solution at temperature 100°C. We have obtained experimentally and by mathematical modelling that aluminium anodes (cylindrical or spherical) dissolve into the solution more rapidly with temperature increasing during electrolysis accordingly to the Arrhenius law, while copper anodes (cylindrical or spherical) dissolve more slowly with temperature increasing from room temperature to temperature 180°C like “inverse Arrhenius law”. Iron electrochemical corrosion rate practically does not depend on temperature below 100°C (and, obviously, up to 180°C) like “zeroth Arrhenius law”. The spherical anode effect is greater than the cylindrical anode effect in 1.5 times.

Abstract: In recent years, the EU policy identified the hydrogen as one of the main energy vectors to support the power production from renewable sources. Coherently, electrolysis is suitable to convert energy in hydrogen with no carbon emission and high purity level. Among the electrolysis technologies, the anion exchange membrane (AEM) seems to be promising for the performance and the development potential at relatively high cost. In the present work, AEM electrolysers, and their technological bottlenecks, have been investigated, in comparison with other electrolysers’ technology such as alkaline water electrolysis and proton exchange membranes. Major efforts and improvements are investigated about innovative materials design and the corresponding novel approach as main focus of the present review. In particular, this work evaluated new materials design studies, to enhance membrane resistance due to working cycles at temperatures close to 80 °C in alkaline environment, avoiding the employment of toxic and expensive compounds, such as fluorinated polymers. Different strategies have been explored, as tailored membranes could be designed as, for example, the inclusion of inorganic nanoparticles or the employment of not-fluorinated copolymers could improve membranes resistance and limit their environmental impact and cost. The comparison among materials’ membrane is actually limited by differences in the environmental conditions in which tests have been conducted, thereafter, this work aims to derive reliable information useful to improve the AEM cell efficiency among long-term working periods.

Abstract: Our investigations show that electrochemical corrosion of copper is faster than electrochemical corrosion of aluminium at temperatures below 100°C. Literature data analysis shows that the Al atoms diffuse faster than the Cu atoms at temperatures higher than 475°C, Al rich intermetallic compounds (IMCs) are formed faster in the Cu-Al system, and the Kirkendall plane shifts toward the Al side. Electrochemical corrosion occurs due to electric current and due to diffusion. An electronic devise working time, for example, depends on initial copper cover thickness on aluminium wire, connected to the electronic devise, temperature, and volume and dislocation pipe diffusion coefficients, so copper, iron, and aluminium electrochemical corrosion rates are investigated experimentally at room temperature and at temperature 100°C. Intrinsic diffusivities ratios of copper and aluminium at different temperatures and diffusion activation energies in the Cu-Al system are calculated by proposed here methods using literature experimental data. Dislocation pipe and volume diffusion activation energies of pure iron are calculated separately by earlier proposed method using literature experimental data. Aluminium dissolved into NaCl solution as the Al³⁺ ions at room temperature and at temperature 100°C, iron dissolved into NaCl solution as the Fe²⁺ (not Fe³⁺) ions at room temperature and at temperature 100°C, copper dissolved into NaCl solution as the Cu⁺ ions at room temperature and as the Cu⁺ and the Cu²⁺ ions at temperature 100°C. It is found experimentally that copper corrosion is higher than aluminium corrosion, and ratio of electrochemical corrosion rates, k_Cu/k_Al>1, decreases with temperature increasing, although iron electrochemical corrosion rate does not depend on temperature below 100°C. It is obvious, because the melting point of iron is more higher than the melting point of copper or aluminium. It is calculated that the copper electrochemical corrosion rate is approximately equal to aluminium electrochemical corrosion at temperature about 300°C, so copper can dissolve into NaCl solution mostly as the Cu²⁺ ions at temperature about 300°C. The ratio of intrinsic diffusivities, D_Cu/D_Al<1, increases with temperature increasing, and the intrinsic diffusivity of aluminium could be approximately equal to the intrinsic diffusivity of copper at temperature about 460oC. Intrinsic diffusivities ratios in the Cu-Zn system at temperature 400°C and in the Cu-Sn system at temperatures from 190°C to 250°C are analyzed theoretically using literature experimental data. Diffusion activation energies and pre-exponential coefficients for the Cu-Sn system are calculated combining literature experimental results.

Abstract: The article is devoted to the description of a method for producing electrolytic copper powder with an average particle size of 3 to 10 μm. In order to increase the proportion of the finely dispersed fraction during the electrolysis process, the composition of the electrolyte was changed. In particular, the content of chloride ions was increased from 6 to 53 mg/dm³. After the growth of the powder in industrial baths, its subsequent drying and sieving on vibrating screens, samples were obtained with a fraction of 5 μm content in the range from 3 to 38 %. Additionally, air classification of powders was carried out at various speeds of the classifier rotor from 800 to 2000 rpm. Based on the results of the study, the optimal ranges of the specific surface area and the size of the initial powder particles before classification, as well as the composition of the electrolyte and the operating modes of the classifier, were determined.

Abstract: The research data on the specific features of the formation of oxide films on the Ti6Al4V alloy in the ethylene glycol-water electrolytes have been given. The kinetic dependences obtained for the alloy allowed us to establish that the specific features of the formation of oxide films during the electrochemical oxidation of the alloy surface depend on the solution composition and the current density. For the water-to-alcohol ratio of 50:50 the kinetic dependences show the sections that correspond to the formation of the barrier oxide layer and also to the formation of the pores due to the desorption of fluoride ions and the growth of the porous portion of oxide. As the water-to- alcohol ratio is decreased the indicated peculiarities of kinetic dependences are met not so often and do not obey any regularity. The obtained data are explained by the fact that an increase in the portion of the organic component of the solution results in a decreased etching capacity of the electrolyte due to the controlled activity of fluoride ions. The anode current density value has a similar effect on the variation of kinetic dependences. Its effect is explained by that an increase in the alloy oxidation rate results in the fast formation of the surface oxide and the specific features of kinetic curves are concealed. The linear relationship between the formation time of oxide of a minimum thickness for given conditions and the current density is unavailable and it is conditioned by the chemical interaction of the oxide film with electrolyte components. The obtained research data can be used for the formation of the individual bioinert and bioactive coatings for the implants of a medical purpose or for the formation of the matrix used for the production of composite coatings.

Abstract: This work presents studies on the material composition and physico-mechanical characteristics of an alumina-containing estimate formed during the production of aluminum on electrolyzers with self-baking anodes during technological operations. The material is a mixture of fine powder 2.5 mm in size (62.78% on average mass) with the presence of pieces of material ranging in size from 0.5 to 6 cm (average 20.26% by weight). The samples contain pieces of hardened aluminum with sizes from 5 to 20 mm (16.96%). The largest content in the sample has the fineness classes-0.315 + 0.16 mm in the volume of 29.85% and the largest class +2.5 mm-37.22%. B It was established that aluminum is concentrated in the fractions-0.315 + 0.16 mm (45.7%) and 0.16 + 0 mm (48.8%), silicon in the fraction-0.63 + 0.315 mm (1.91%), iron at-1.25 + 0.63 mm (0.601%) and-0.63 + 0.315 mm (0.62%). The material consists of cryolite (Na₃AlF₆), chiolite (Al₃F₁₄Na₅), quartz, feldspar, carbonaceous matter and the technogenic phase of the composition (NaF) 1.5CaF₂ AlF₃. The material is characterized as non-abrasive (working index Ai - 0.0184) and very soft in relation to impact crushing (working index CWi - 3.64), the working index of ball grinding Bond (BWi - 6.47) characterizes a very low resistance to ball grinding. The implementation of the crushing operation of an alumina-containing estimate will allow the use of dry cascade-gravity and centrifugal classification to separate impurities in the form of SiO_2, and Fe₂O₃ for the use of alumina-containing material in primary aluminum technology. On the basis of laboratory tests, it is established that alumina-containing raw materials can be separated and photometric and gravitational separation methods can be used. A mathematical model of the motion of particles of primary and prepared alumina-containing raw materials in a cascade-gravity classifier was developed. The criteria and factors characterizing the alumina-containing material, as well as influencing and determining the maximum material enrichment, are established.

Abstract: The aim of this paper is to establish a regulatory change of zinc powders key physicochemical properties with varying electroextraction conditions. It was studied influence zinc concentration, alkali concentration and current density. Quantitative dependencies of zinc powders particle size and specific surface area from mentioned electroextraction parameters are shown. At increasing of zinc concentration, decreasing of NaOH concentration and decreasing of current density of powders particle size growth, correspondingly specific surface area is declined. It is indicated, that electrolytic zinc powders bulk density varies from 0.61 g/cm³ to 0.75 g/cm³ with a decrease of average particle size from 121 μm to 68 μm. In comparison, spherical powders bulk density used in various industries is currently 2.45-2.6 g/cm³. In all experiments, metal zinc content varied in the range of 91.1-92.5%, the rest - ZnO. To a greater extent, this indicator depends on powder washing quality from alkali and storage conditions.

Abstract: Electric corrosion of aluminium and copper is investigated experimentally. It is found that the electric corrosion of copper is higher than the electric corrosion of aluminium. It is also clarified that the intrinsic diffusion coefficient of Cu is higher than the intrinsic diffusion coefficient of Al in each phase, so inert markers move to Cu. Copper has a higher electric conductivity, higher thermal conduction, and lower material cost than gold, so it is possible to use Cu instead of Au for wire bonding in microelectronics packaging, because the thin Al pad (1.2 μm thickness) can prevent gold and copper corrosion. Intermetallics disappearance and Kirkendall shift rates calculation methods are proposed. Methods involve mass conservation law and concentration profiles change during mutual diffusion. Intermetallics disappearance and Kirkendall shift rates in Al-Cu (Al is thin layer on Cu), Cu-Al (Cu is thin layer on Al), Al-Au, Zn-Cu, and Cu-Sn systems are analyzed theoretically using literature experimental data. Diffusion activation energies and pre-exponential coefficients for Cu-Sn system were calculated combining literature experimental results.

Abstract: The paper presents experimental data on nickel oxidation during electrolysis under rectangular alternating current in alkaline solutions, when the cathode pulse (I_к ) is greater than the anode pulse ( I_а ). During the process, intense nickel destruction occurs forming bivalent oxide powder. Under prolonged electrolysis, this powder deposits at the bottom of the electrolyzer in the form of a sponge. The results obtained can be used to produce active mass in the porous nickel oxide electrode of a chemical current source.