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.

Electrolytic superconducting niobium coatings for a cryogyroscope rotor: creation and properties

Electrodeposition of niobium coatings on spherical substrates for a cryogyroscope rotor made of carbopyroceram was considered. A special design of the installation for obtaining coatings on spherical samples was created. The coatings were applied at a temperature of 750°C with the cathodic current density of 5·10−3 - 2–10−2 A·cm−2 and the electrolysis time of 8-12 h. It was found that the use of a cathodic current density of 2·10−2 A·cm−2 and higher is impractical, because there is a roughening of the coatings surface. The composition of electrolytic coatings was identified by XRD analysis. The macrostructure of niobium coatings was studied using electron microscopy. The concentration of metallic impurities in the niobium coatings was defined by spectral quantitative analysis. The content of gas impurities was determined by gas chromatography. The roughness, nonsphericity, and superconductive properties of niobium coatings were investigated.

Hybrid Zinc-Based Multilayer Systems with Improved Protective Ability against Localized Corrosion Incorporating Polymer-Modified ZnO or CuO Particles

Localized corrosion and biofouling cause very serious problems in the marine industries, often related to financial losses and environmental accidents. Aiming to minimize the abovementioned, two types of hybrid Zn-based protective coatings have been composed. They consist of a very thin underlayer of polymer-modified ZnO or CuO nanoparticles and toplayer of galvanic zinc with a thickness of ~14 µm. In order to stabilize the suspensions of CuO or ZnO, respectively, a cationic polyelectrolyte polyethylenimine (PEI) is used. The polymer-modified nanoparticles are electrodeposited on the steel (cathode) surface at very low cathodic current density and following pH values: 1/CuO at pH 9.0, aiming to minimize the effect of aggregation in the suspension and dissolution of the CuO nanoparticles; 2/ZnO at pH 7.5 due to the dissolution of ZnO. Thereafter, ordinary zinc coating is electrodeposited on the CuO or ZnO coated low-carbon steel substrate from a zinc electrolyte at pH 4.5–5.0. The two-step approach described herein can be used for the preparation of hybrid coatings where preservation of particles functionality is required. The distribution of the nanoparticles on the steel surface and morphology of the hybrid coatings are studied by scanning electron microscopy. The thickness of the coatings is evaluated by a straight optical microscope and cross-sections. The protective properties of both systems are investigated in a model corrosive medium of 5% NaCl solution by application of potentiodynamic polarization (PDP) curves, open circuit potential (OCP), cyclic voltammetry (CVA), and polarization resistance (Rp) measurements. The results obtained allow us to conclude that both hybrid coatings with embedded polymer-modified CuO or ZnO nanoparticles ensure enhanced corrosion resistance and protective ability compared to the ordinary zinc.

The Influence of Sodium Tungstate Concentration on the Electrode Reactions at Iron–Tungsten Alloy Electrodeposition

The investigation of Fe-W alloys is growing in comparison to other W alloys with iron group metals due to the environmental and health issues linked to Ni and Co materials. The influence of Na2WO4 concentration in the range 0 to 0.5 M on bath chemistry and electrode reactions on Pt in Fe-W alloys’ electrodeposition from citrate electrolyte was investigated by means of rotating disk electrode (RDE) and cyclic voltammetry (CV) synchronized with electrochemical quartz crystal microbalance (EQCM). Depending on species distribution, the formation of Fe-W alloys becomes thermodynamically possible at potentials less than −0.87 V to −0.82 V (vs. Ag/AgCl). The decrease in electrode mass during cathodic current pass in the course of CV recording was detected by EQCM and explained. The overall electrode process involving Fe-W alloy formation may be described using formalities of mixed kinetics. The apparent values of kinetic and diffusion currents linearly depend on the concentration of Na2WO4. Based on the values of partial currents for Fe and W, it was concluded that codeposition of Fe-W alloy is occurring due to an autocatalytic reaction, likely via the formation of mixed adsorbed species containing Fe and W compounds or nucleation clusters containing both metals on the electrode surface.

Effect of Cathodic Polarisation Switch-Off on the Passivity and Stability to Crevice Corrosion of AISI 304L Stainless Steel

The effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset.

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.

Investigation of IG-SCC growth kinetics in Al-Mg alloys in thin film environments

The effect of thin film environments on the intergranular stress corrosion cracking (IG-SCC) behavior of AA5083-H131 was investigated using fracture mechanics-based testing, high-fidelity monitoring of crack growth, and electrochemical potential measurements. A protocol for conducting thin film IG-SCC fracture mechanics experiments with anodized aluminum oxide (AAO) membranes is developed and the ability to maintain films of specific thicknesses without impeding oxygen diffusion during testing is validated via EIS testing and computational modelling. The IG-SCC susceptibility was found to increase once a critical thin film thickness of 82 µm was achieved; above this thickness a duality in IG-SCC susceptibility behavior was observed. These results are analyzed in the context of a coupled anodic dissolution and hydrogen (H) embrittlement mechanism, where susceptibility is found to scale with the cathodic limitation of the governing IG-SCC mechanism. Specifically, thinner film thicknesses led to limitations on the amount of cathodic current availability, which caused a decrease in the dissolution at the crack tip, a less aggressive crack chemistry development, and thus lower levels of H production. A close correlation between the open circuit potential of the bulk surface and the crack growth kinetics was also observed, consistent with trends reported in previous IG-SCC studies on this alloy.

Electrodeposition of Graphene Oxide Modified Composite Coatings Based on Nickel-Chromium Alloy

Composite electrochemical coatings (CECs) based on nickel-chromium alloy and modified with multilayer graphene oxide (GO) were obtained. The electrodeposition process of these coatings was studied in the potentiodynamic mode. The structure and the composition of nickel–chromium–GO CECs were studied by scanning electron microscopy and laser microspectral analysis. Nickel–chromium–GO CECs are dense and uniform. The carbon content in them increases when moving from the substrate to the surface. It was established that the addition of GO particles into the composition of electrolytic coatings with a nickel-chromium alloy results in the increase in their microhardness from 4423–5480 MPa to 6120–7320 MPa depending on the cathodic current density.

Electrodeposition of Copper and Brass Coatings with Olive-Like Structure

One method of creating a brass coating is through electrodeposition, which is most often completed in cyanide galvanic baths. Due to their toxicity, many investigations focused on the development of more environmentally friendly alternatives. The purpose of the study was to explore a new generation of non-aqueous cyanide-free baths based on 1-ethyl-3-methylimidazolium acetate ionic liquids. The study involved the formation of copper, zinc, and brass coatings. The influence of the bath composition, cathodic current density, and temperature was determined. The obtained coatings were characterized in terms of their morphology, chemical composition, phase composition, roughness, and corrosion resistance. It was found that the structure of the obtained coatings is strongly dependent on the process parameters. The three main structure types observed were as follows: fine-grained, porous, and olive-like. To the best knowledge of the authors, it is the first time the olive-like structure was observed in the case of an electrodeposited coating. The Cu-Zn coatings consisted of 19–96 at. % copper and exhibited relatively good corrosion resistance. A significant improvement of corrosion properties was found in the case of copper and brass coatings with the olive-like structure.