Zinc-cobalt Alloy Research Articles

Construction of zinc-cobalt alloy film by supercritical-CO2 electrodeposition pathway: Evaluation of electrochemical robustness

• Zn-Co alloy film was prepared by supercritical-CO 2 electrodeposition pathway. • The higher incorporation of cobalt significantly improves the corrosion resistance. • Cobalt act as an inhibitor in the alloy coating. • The inhibition of coating is 27.6 % increase in the supercritical-CO 2 process. Supercritical-CO 2 (SC-CO 2 ) approach to the electrodeposition process has received significant attention due to its advantages, such as low surface tension, high diffusivity, and permeability. These properties can even replace the role of toxic additives and surfactants. Here in, we demonstrated the green fabrication of zinc-cobalt (Zn-Co) alloy film by SC-CO 2 electrodeposition process and explored its electrochemical performance. The prepared films were characterized by various micro-and spectroscopic analyses. Based on the results, the SC-CO 2 method prepared films show a compact structure with reduced crystallite size and 27.6 % improved corrosion resistance than the conventional method.

Formation and Cathodic Reduction of Taurine Complexes with Zinc and Cobalt(II)

Stability constants of zinc and cobalt(II) complexes with Taurine were determined at 25°C and ionic strengths of 0.5, 1.0, and 1.5 (KNO3). The thermodynamic stability constants were calculated. The processes in which zinc-cobalt alloys are electrodeposited onto 08kp steel from electrolytes with addition of Taurine and the physicochemical properties of the coatings were examined. It was shown that the ratio between the alloy components affect the chemical composition and microstructure of the coatings. The most homogeneous and finely crystalline structure is observed for zinc-cobalt alloy coatings obtained at a cathode current density of 1 A dm−2 from an electrolyte with zinc concentration twice that of cobalt. At these concentration conditions, zinc-cobalt alloy coatings with 15.1 at % Co were obtained. The kinetic patterns of deposition of zinc-cobalt alloys at temperatures of 25 and 50°C were demonstrated. A relationship between the chemical composition, microstructure, and corrosion rate of the zinc-cobalt coatings obtained was determined.

Corrosion properties of mild steel surface modified by bright Zn-Co alloy electrodeposit from acetate electrolytic bath

The zinc-cobalt (Zn-Co) alloy coatings were electrodeposited on mild steel using acetate electrolytic bath at various current densities. The corrosion behaviour of the Zn-Co alloys was determined in a 3.5% sodium chloride solution. Highest corrosion protection efficiency with corrosion rate of 7.33 mpy was obtained at Current density 4.0 A.dm−2. The effect of current density with temperature, throwing power, corrosion behaviour and surface morphology of the deposits were discussed. The surface texture and hardness of the deposit were investigated by scanning electron microscopy (SEM) and Vickers hardness tester. The surface morphology of an alloy deposit depends mostly on the presence of cobalt in the alloy deposit. The XRD pattern has shown the η-phase orientation of (110) plane and the peak intensity were hugely increased with Co content in the deposit.

THE INFLUENCE OF CO2+ CONCENTRATION ON THE PROPERTIES OF THE ELECTRODEPOSITED ZINC–COBALT ALLOY COATINGS

The effects the concentration of cobalt on zinc-cobalt alloys obtained from sulphate baths under continuous current deposition are described. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. Protection against corrosion properties studied in a solution of 3 % wt NaCl in the potentiodynamic polarization measurements (Tafel), electrochemical impedance spectroscopy (EIS) to the potential of corrosion free. The parameters that characterize the corrosion behavior can be determined from the plots and Nyquist plots. It has been observed that the Zn–Co alloy is characterized by enhanced the resistance of corrosion compared to the Zn alloys and the addition of Co in the Zn-Co increases the micro-hardness, XRD and SEM results an identify any coatings Zn-Co alloy composition reveals that. zinc - rich ( η- phase) , cubic Co5Zn21 .

Magnetic field effect on Zn-Co alloy electroplating

Zinc-cobalt (Zn-Co) alloys were electrodeposited under a magnetic field parallel to the electrode from a sulfate bath. These alloys were investigated using chronopotentiometric measurement as one of the well-known galvanostatic techniques. The magnetic field was found to shift the potential of electrodeposition of alloys toward anodic values. The Zn-Co electrochemical impedance spectroscopy studies clearly showed the effects of the magnetic field on the electrodeposition process. The crystallographic structures of the deposits examined by X-ray diffraction (XRD) revealed the existence of CoZn13 phase, pure zinc phase, and η phase. The presence and absence of each of the phases were found to be greatly dependent on both the electrolyte composition and on the magnetic field amplitude and the latter of which also affected the lattice cell parameters. Indeed, an increase in the magnetic field amplitude decreases the size of the grains. These results were confirmed by morphological study using scanning electron microscopy (SEM).

Electroplating of zinc–cobalt alloys from oxalate electrolytes

The processes of electroplating of zinc–cobalt alloys from oxalate electrolytes and the physicochemical properties of these coatings are investigated. The effect of the proportion between the alloy components on the corrosion resistance, structure, and microhardness of the coatings is revealed.

Agar templated electrodeposition of binary zinc-cobalt alloy and formation of zinc-cobalt-carbon nanocomposite for application in secondary lithium batteries

Thin layer electrodeposition of binary Zn-Co alloy on Cu substrate is carried out using different concentrations of agar, namely, 0.0029 M, 0.0074 M, and 0.0148 M as a template for application in lithium-ion battery anodes. The concentration of agar highly influences the morphology of the deposited films and the formation of nanoflake structures over their surfaces. The optimal agar templated electrode shows good morphological characteristics with a well-defined nanoflake structure, as confirmed by texture coefficient (Tc) values calculated from X-ray diffraction (XRD) results and by field emission scanning electron microscopy (FE-SEM) images. Zn-Co-C nanocomposite electrodes are prepared by subjecting the electrodeposited materials to a calcination step to decompose the agar into C; the resulting electrode shows the initial specific capacity of 827 mAh g−1 and 92% capacity retention after 100 cycles (vs. 20th discharge capacity) whereas Zn-Co alloy electrode shows 829 mAh g−1, with 62% capacity retention after 100 cycles. The chemical compositions of the electrodeposited films are further confirmed by X-ray photoelectron spectroscopy (XPS). Electrochemical studies including charge–discharge cycles and electrochemical impedance spectroscopy (EIS) provide information regarding the lithiation and delithiation processes, and electrode/electrolyte interactions before and after cycling in the prepared electrodes.

Zinc-Cobalt Alloy Deposited on the Titanium Surface as Electrocatalysts for Borohydride Oxidation

The present work is focused on the investigation of the oxidation of BH4− ions in an alkaline solution on a low-cost ZnCo alloy deposited on the Ti surface. The Co and ZnCo alloy coatings were deposited on the Ti surface via electrodeposition. The morphology, structure and composition of the prepared catalysts were examined by FESEM and EDX. The activity of the fabricated catalysts was investigated toward the oxidation of BH4− ions by means of cyclic voltammetry and chronoamperometry. It has been determined that Co/Ti and ZnCo/Ti catalyze the oxidation of H2 generated by the catalytic hydrolysis of BH4− and direct oxidation of BH4− ions. The H2 oxidation current densities measured on both the catalysts are rather close and reach up to 60 mA cm−2, whereas the borohydride oxidation current densities are ∼3–4 times higher at −0.2 V on ZnCo/Ti than those obtained on Co/Ti and Zn/Ti.

Zinc-Cobalt Alloy Deposited on the Titanium Surface as Electrocatalysts for Borohydride Oxidation

The present work is focused on the investigation of the electrochemical oxidation of BH4 – ions in an alkaline solution on a low-cost ZnCo alloy deposited on the titanium surface. The Co and ZnCo alloy coatings were deposited on the titanium surface via electrodeposition. The morphology, structure and composition of the prepared catalysts were examined by Field Emission Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy. The activity of the fabricated catalysts was investigated towards the oxidation of BH4 – ions by means of cyclic voltammetry. It has been determined that Co/Ti and ZnCo/Ti catalyze the oxidation of H2 generated by the catalytic hydrolysis of BH4 – and direct oxidation of BH4 – ions. The H2 oxidation current densities measured on both the catalysts are rather close and reach up to 60 mA cm–2, whereas, the borohydride oxidation current densities are ~3 times higher at -0.2 V on the ZnCo/Ti catalyst than those obtained on the Co/Ti catalyst.

Zinc-Cobalt Alloy Deposited on the Titanium Surface As Electrocatalysts for Borohydride Oxidation

The present work is focused on the investigation of the electrochemical oxidation of borohydride in alkaline solution on low-cost ZnCo alloy deposited on the titanium surface (denoted as ZnCo/Ti). The ZnCo alloy coatings with the thickness of ~5 µm were deposited on the titanium surface (1 x1 cm) via electrodeposition from the electrolyte described in Ref. [1]. Prior to ZnCo alloy deposition, the titanium plates were degreased with acetone and then pretreated in diluted H2SO4 (1:1 vol) at 90 oC for 10 s. Cobalt coatings with the thickness of ~3 µm were deposited from the same electrolyte [1] with only difference that zinc ions were excluded from the plating bath.The morphology, structure and composition of the prepared catalysts were examined by FESEM, EDS and ICP-OES. Activity of the fabricated catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry.It was found that the ZnCo alloy coating, electrodeposited on the titanium surface, consists of ~81.3 at. % of Zn and ~16.1 at. % of Co.It has been determined that the Co/Ti and ZnCo/Ti catalysts catalyzes oxidation of H2 generated by catalytic hydrolysis of BH4 – and direct BH4 – ions oxidation. Notably, the H2 oxidation current densities measured on both catalysts are similar and reach up to 60 mA cm–2, whereas, the borohydride oxidation current densities are ~3-6 times higher on the ZnCo/Ti catalysts than those obtained on the Co/Ti catalyst. The chronoamperometry and chronopotentiometry studies also confirmed a high electrocatalytic activity of the ZnCo/Ti catalyst for the direct electro-oxidation of BH4 – ions as compared to that of Co/Ti electrode.The ZnCo/Ti catalysts are promising low-cost anode material for direct borohydride fuel cells.

Electrochemical synthesis of polyaniline films on zinc-cobalt alloy deposited carbon steel surface in sodium oxalate

Polyaniline (PANI) coatings were electropolymerized on zinc-cobalt alloy deposited carbon steel (CS/ZnCo) electrode from an aqueous sodium oxalate solution using three different scan rates in cyclic voltammetric technique. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the polymer film. The SEM images showed that the increase in scan rate induced an increase in grain size of the PANI film. The corrosion behavior of CS/ZnCo electrodes with and without PANI film in 3.5% NaCl solution were investigated through electrochemical impedance spectroscopy (EIS) and anodic polarization studies. The results of the study showed that the PANI coatings provided significant and effective protection for the CS/ZnCo electrode, in preventing corrosion. In addition, the PANI film that was synthesized at a high scan rate, exhibited the best anti-corrosive performance due to the formation of protective oxide layers through its catalytic efficiency.

Electrodeposition of zinc-cobalt alloys from choline chloride–urea ionic liquid

The electrodeposition behavior of zinc-cobalt (Zn-Co) alloy was investigated in choline chloride/urea (1:2 molar ratio) deep eutectic solvent containing 0.11M ZnCl2 and 0.01M CoCl2. Cyclic voltammetry revealed that Co reduced preferably with respect to Zn and anomalous codeposition of Zn-Co did not occur in this solvent. Chronoamperometric investigations combined with field emission scanning electron microscopy (FE-SEM) indicated that the electrodeposition of Zn-Co alloys followed the mechanism of instantaneous nucleation. Energy dispersive spectroscopy (EDS), grazing incidence X-ray diffraction (GI-XRD) and SEM results showed that the deposition potential influenced the compositions, phase structure and surface morphology of the Zn-Co alloys.

The influence of polyaniline (PANI) coating on corrosion behaviour of zinc–cobalt coated carbon steel electrode

Zinc–cobalt alloy plating (ZnCo) was successfully deposited on carbon steel (CS) applying current of 2mA with galvanostatic technique. Polyaniline film (PANI) was synthesized with cyclic voltammetry technique from 0.20M aniline containing 0.20M sodium tartrate solution on zinc–cobalt plated carbon steel (CS/ZnCo) electrode. PANI film characterized by scanning electron microscopy (SEM), was covered with a dark green-brown homopolymer film of strongly adherent homogeneous characteristic while the other one was plated with a porous light ZnCo one. The corrosion behaviour of zinc–cobalt deposited carbon steel electrodes with and without polyaniline (PANI) film in 3.5% NaCl solution was investigated with AC impedance spectroscopy (EIS) technique and anodic polarization curves. The results showed that PANI coating led to decrease of the permeability of metallic plating. The PANI homopolymer film provided an effective barrier property on zinc–cobalt coating and a remarkable anodic protection to substrate for longer exposure time.

Effect of aromatic aldehydes on the electrodeposition of ZnCo alloy from cyanide-free alkaline-gluconate electrolytes

The effects of vanillin and anisaldehyde on electrodeposition of zinc–cobalt alloys onto AISI 1018 carbon steel were studied in an alkaline gluconate zincate electrolyte. The influence of an additive on the metal discharge depends on the structure of the added molecule and on the nature of the substrate. The composition of the deposit varies during the electrodeposition process. Maximum cobalt content is observed close to the steel–ZnCo interface for ZnCo formed with or without vanillin, but the composition profile becomes more uniform when anisaldehyde is added to the bath. The morphology of Zn-rich Co-alloy coatings was evaluated: Cobalt ions produce porous ZnCo alloys; vanillin induces slightly porous deposits, whereas uniform and more compact deposits were observed with anisaldehyde. Furthermore, a crystallographic study showed that the orientation of the lattice planes changes, with highly oriented deposits produced in the presence of anisaldehyde.

Electrochemical studies of zinc–cobalt alloy coatings deposited from alkaline baths containing glycine as complexing agent

Co-deposition of Zn–Co alloy coatings that were electrodeposited from weakly alkaline glycine solutions has been studied by cyclic voltammetry. Scanning electron microscopy (SEM), energy depressive spectroscopy (EDS), and X-ray diffraction (XRD) analyses were used to study surface morphology, chemical composition, and phase structure of the coatings. Corrosion behavior of the coatings was also studied using potentiodynamic polarization tests in 3.5 wt% NaCl solution. Cyclic voltammetry results showed that in Zn–Co deposition from an alkaline bath in the presence of glycine, cobalt deposited at a potential near to that of zinc together with successful co-deposition of Co and Zn. It was also shown that reduction–oxidation (redox) reactions of Zn–Co alloy deposits were quasi-reversible and resulted in deviation of electrodeposited alloys from the equilibrium phase diagrams. The corrosion resistance of the deposits was also highly influenced by the composition and morphology of the coatings. Overall, Zn–Co deposit containing 0.89 wt% Co showed that the highest corrosion resistance among the coatings that was due to its single phase structure and fine morphology.

Morphology and texture of pulse plated zinc–cobalt alloy

Pulse electrodeposition was used to produce zinc–cobalt (Zn–Co) alloy deposits from an alkaline non-cyanide electrolyte with and without additives. The influence of additives’ concentration and pulse parameters, such as ON-time ( T ON), OFF-time ( T OFF), and pulse peak current density ( I P) on the surface morphology, grain size, composition and crystal orientation were investigated using scanning electron microscope (SEM), atomic forced microscope (AFM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF), X-ray diffraction (XRD), respectively. At constant T OFF and I P, cobalt content in the deposits decreases with T ON and cluster size increases. Increase in T OFF at constant T ON and I P, decreases the cluster growth with increase in cobalt content. The same trend was observed with increasing I P (without additives) at constant T ON and T OFF. The presence of additives at 7 Adm −2 drastically decreases the cobalt content in the deposits from 2.5 to 0.7 wt.%. Co and the preferred crystallographic orientation was [10.1] at 69.1% as confirmed by XRD.

Kinetics of electrodeposition of Zn–Co alloy using mild steel rotating disc electrode

The rotating disc electrode technique was used to investigate the electro deposition of Zn–Co alloys onto mild steel from both acid and alkaline solutions. Measurements made under controlled hydrodynamic conditions show that zinc–cobalt alloy deposition from alkaline electrolytes is charge transfer controlled over a range of rotation speeds. This was true up to a limiting current at which the deposition became mass transport controlled. Deposition from the acid electrolyte was verified to be charge transfer controlled at very low over potential. Scanning electron microscopy and energy dispersive spectroscopy were used to reveal the influence of the electrode rotation speed on the morphology and chemical composition of the deposit.

Effects of thiourea and urea on zinc–cobalt electrodeposition under continuous current

The effect of thiourea and urea on zinc-cobalt alloys obtained from chloride baths under continuous current deposition are described and discussed. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The use of additives does not refine the grain size of the Zn–Co alloy and an especially porous alloy was produced in the presence of urea. The preferred crystallographic orientations of zinc–cobalt alloys do not change in the presence additives. Zinc–cobalt alloys were without texture in the presence and absence of additives. Also, in the absence of additive and in the presence of urea, the XRD lines of the Zn–Co alloys are slightly shifted with respect to the pure zinc XRD lines, whereas, in the presence of thiourea, the XRD lines are not shifted. The alloy composition was examined using Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases slightly from 1.04 to 0.91 wt.% in the presence of urea and in the presence of thiourea it increases from 1.04 to 7.70 wt.%. Voltammetric studies show that thiourea increases the reduction rate of cobalt. This explains the increase in cobalt percentage in the alloy in the presence of thiourea.

Electrodeposition and characterization of zinc–cobalt alloy from chloride bath; influence of coumarin as additive

Zinc–cobalt alloys were electrodeposited from chloride bath under continuous current and in the presence and absence of coumarin. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. Zinc–cobalt alloys was without texture in the absence of coumarin whereas, the preferred crystallographic orientations was (103) at 65% in the presence of coumarin. The presence of coumarin yields deposits with a finer grain size. The alloy composition was examined using the Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases from 1.04 wt.% to 0.69 wt.% in the presence of coumarin. Voltammetric studies show that coumarin affects the reduction of zinc but it was without effect on cobalt reduction. That explains the decrease of cobalt percentage in the alloy in the presence of coumarin.

Corrosion performance of zinc and zinc-cobalt alloy compositionally modulated multilayer (CMM) coatings

Varieties of zinc and Zn−Co alloy compositionally modulated multilayer (CMM) coatings were electrodeposited onto steel substrates using dual bath technique. The surface and cross-sectional morphologies of coated samples were examined using scanning electron microscopy (SEM). The existence of internal stress in Zn−Co alloy deposits was confirmed by the cross-sectional morphologies for the occurrence of micro-cracks in the thick Zn−Co alloy deposit alone. The corrosion performance was evaluated using neutral salt spray testing, corrosion potential measurement and anodic polarization methods. The experimental results show that the zinc and Zn−Co alloy CMM coatings were more corrosion-resistant than the monolithic coatings of zinc or Zn−Co alloy alone with a similar thickness. The analysis on the micrographic features of zinc and Zn−Co alloy CMM coating, using field emission gun scanning electron microscopy (FEGSEM) after corrosion testing, explains the probable reasons why the Zn−Co/Zn CMM coating system has a better protective performance.