Influence of pH on the electrolytic deposition of Ni–Co films

Journal of Superconductivity and Novel Magnetism, 2013

The effect of electrolyte pH on structural, magnetic, and magnetoresistive properties of Co-Ni films was studied. The films were deposited on a titanium substrate from the electrolytes with 4.10 ± 0.05, 3.14 ± 0.05, and 2.14 ± 0.05 pH values. The Co-Ni system exhibited anomalous codeposition. Structural analysis indicated that the films had (220) preferential oriented face-centered cubic structure and their surface became smoother as the electrolyte pH decreased. The compositional and magnetic analysis revealed that an increase of the Co content in the films resulted in an increase in saturation magnetization and coercivity. Magnetoresistance curves indicated that the films show anisotropic magnetoresistance. Longitudinal and transversal magnetoresistances were found to be the highest values of 8 % and 7 %, respectively, for the film deposited at a low electrolyte pH. The variation of the Co:Ni ratio in deposits caused by the change of the electrolyte pH has a considerable effect on the properties of the films.

2016

The changes in the phase composition (through X-Ray analysis) and the corrosion behaviors (through potentiodynamic polarization studies in 4 % NaCl) of Ni-Co alloys, electrodeposited from a citrate electrolyte by changing the Ni/Со ratio, content of organic additive (saccharine) and the content of sodium citrate in the solution, are studied. It is found that the increase of Ni/Со ratio from 1 to 5 increases the content of Ni in the Ni-Co alloy to 48 mass %. The proportion between the phases of Co and Ni with cubic face-centered crystal lattice is in approximate compliance with the proportion of the two metals in the alloy. The peaks in the difractograms are weak and stretched, which corresponds to the nano-sized structure of the alloy. The Ni-Co alloys with highest content of Ni have a higher corrosion resistance compared to those containing a higher percentage of Co. It is also shown that the Ni-Co coatings obtained in the presence of addition of saccharine show a much higher corro...

2015

The kinetics of independent and joined deposition of Ni and Co in citrate electrolyte in the presence of three types of additives: saccharine (SCH), urotropine (URT) and gelatine (GLT), is examined. Comparison is made between the chemical composition, the current cathodic efficiency (CCE) and the morphology of Ni-Co alloys depending on the type of the additive, both in constant potential mode (CPM) and in pulse potental mode (PPM). The study specifies the effect of GLT and SCH for formation of smooth, shiny, nanostructured Ni-Co coatings with average crystallite size less than 100 nm with a high CCE (about 80 % for SCH, and over 90 % for GLT), in both potential modes. The presence of SCH in the electrolyte with simultaneous application of PPM increases the content of Ni in the alloy to 25-30 mass % Ni. The optimum additive of SCH containing 0.5-1.0 g dm-3 is specified, wherein the electrolyte remains stable during continuous operation.

Journal of Solid State Electrochemistry, 2006

In this paper, the morphology and phase structure of Ni-Co powders electrodeposited from ammoniacal electrolyte are investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni 2+ /Co 2+ concentration is found to influence both, the phase structure and the morphology of Ni-Co alloy powders. It is shown that the current density practically does not influence the morphology of Ni-Co alloy powders as well as alloy powder composition. At the highest ratio of the Ni 2+ /Co 2+ ions typical spongy particles were obtained. With the decrease of the Ni 2+ /Co 2+ ions ratio agglomerates of the size of about 100 lm, composed of a large number of fern-like dendrites on their surface were obtained. At the lowest Ni 2+ /Co 2+ concentration ratio, among more dendritic particles, agglomerates typical for pure Co powder deposition were detected. It is also shown that depending on the Ni 2+ /Co 2+ ratio different types of Ni and Co codeposition could be detected: anomalous and irregular. At the Ni 2+ /Co 2+ ions ratio higher than 1 only b-Ni phase was detected, while at concentration ratios Ni 2+ /Co 2+ <1 h.c.p. a-Co phase together with b-Ni phase was detected in the alloy powder deposit.

Surface and Coatings Technology, 2019

NieCo alloy electrodeposits have been widely employed in industry due to their good corrosion and wear resistance, high mechanical strength, moderate thermal conductivity and outstanding electrocatalytic and magnetic properties. This review aims to provide an insight into the mechanism of electrodeposition and effect of operational parameters and deposit microstructure, together with the mechanical, electrochemical and tribological characteristics of NieCo alloys and included particle, composite deposits. Potential applications of the coatings have also been considered in applications as diverse as additive manufacturing, micro-tools, microsensors, electronic imaging and electrochemical energy conversion. 1. A clarification of the role of tribofilms and wear debris on the tribological behavior of NieCo deposits. 2. Developing techniques, such as compositionally graded coatings and application of pulsed current have limitations including complex equipment and high cost. 3. The deposit microhardness needs to be increased further and direct nanostructured alloy deposition needs to be achieved by optimizing bath additives and plating conditions. 4. Despite many studies on coarse-grained deposits, there have been relatively few investigations of nanocrystalline NieCo coatings.

Ionics, 2011

Ni thin films were electrodeposited on gold substrate from chloride solution with different pH at room temperature. The effect of electrolyte pH on Ni coatings was studied by using the cyclic voltammetry, the scanning electron microscopy (SEM), x-ray diffraction, and alternating gradient force magnetometer measurements. From electrochemical measurements, the onset potential for reduction of Ni was gradually shifted towards more cathodic scan with increase in pH; this is due to the protons in the case of low pH values and to the hydroxide ions in the case of higher pH values. The SEM study showed that a granular and compact structure of the electrodeposited Ni layers and the variation of film morphology with bath pH are established. The x-ray diffraction spectra revealed the formation of fcc structure Ni thin films with a preferential orientation along the Ni(111). The size of the deposited crystals in both the cases has been found to be in the range of 49-153 nm. Magnetic properties such as coercivity and saturation magnetization showed strong dependence on the electrolyte solution pH and consequently the crystallite size. Coercivity higher than 130-160 Oe was achieved for a pH value of 4 to 5. The differences observed in the magnetic properties were attributed to the structural changes caused by the electrolyte pH.

Transactions of the IMF, 2013

The electrocrystallisation of Co, Ni and Co-Ni alloys on ruthenium surface from chloride baths has been studied by cyclic voltammetry and chronoamperometry measurements. The structural and magnetic properties were studied by X-ray diffraction and alternating gradient force magnetometer techniques respectively. The Co-Ni alloys were deposited from solution with molar ratios (Co/Ni) of 5 : 1, 1 : 1 and 1 : 5. From cyclic voltammetry measurements, for all molar ratios for electrodeposited Co-Ni, preferential deposition of Co occurs and anomalous codeposition takes place. Therefore, variation in the composition of thin films alloy is possible depending on the deposition potential. The Scharifker and Hills model was employed to analyse the current transients. For both Co and Co-Ni alloys, the nucleation was a good agreement with the instantaneous model followed by threedimensional diffusion limited growth. However, for Ni after t max , the nucleation process changes from progressive to instantaneous model. It is evident that the compositions of the electrolyte do not have influence on the type of nucleation for Co-Ni alloys. X-ray diffraction measurements indicate a small crystallite size with the presence of a mixture of hcp and fcc Co-Ni structures. The hysteresis loops with a magnetic field in the parallel and perpendicular directions showed that the easy magnetisation axis of Co-Ni thin film is in the film plane.

2015

The kinetics of deposition of Co, Ni, and Ni-Co from low-acid citrate electrolyte on Cu and on chemically oxidized Al is compared. It is found that the formation of Ni-Co alloy on the Al cathode is hampered to a greater extent in comparison with the Cu electrode. In both cases (Cu and Al electrodes) &quot;anomalous&quot; co-deposition of Co and Ni is registered especially in an electrolyte with higher content of Ni. In case of deposition on Al cathode in stationary potentiostatic mode (cpm), the content of Co in the Ni-Co alloy is by 10 wt% higher than that in case of deposition of Ni-Co on Cu cathode. The Ni-Co alloy deposited on Al may be characterized as island-style coating, with spheroidal shape of the crystals (10-17 µm). The application of pulse potential mode (ppm) of deposition on the Al cathode leads to increased structural homogeneity and higher extent of filling the surface with crystals of Ni-Co alloy. The effect of the application of pulse potential mode, however, is s...

Journal of Solid State Electrochemistry, 2023

Alloy electroplating using deep eutectic solvents (DES), compared to aqueous electrolytes, has essential benefits in a wide potential range, the high solubility of metal salts (including chlorides and oxides), and an environmentally friendly alternative. This research aimed to compare the coatings obtained by electrolysis of the Ni-Co alloy conventionally from an aqueous solution against the electroplating obtained in 2:1 ethylene glycol-choline chloride. The electrochemical behavior was studied through potentiodynamic polarization kinetic analysis carried out complying with Abner's rules for alloy deposits; hydrodynamic conditions were modified, keeping the temperature at 60 °C and the salt concentration in both baths constant. As a result, nickel electrolysis has been carried out successfully by taking advantage of the benefits of using DES in energy consumption with 80% efficiency compared to water as a solvent under the same conditions. The composition and morphology of Ni-Co alloy coatings were characterized by scanning electron microscopy (SEM/EDS), and corrosion resistance was investigated by potentiodynamic polarization and electrochemical impedance (EIS). Coatings were obtained for both electrolytic baths with a chemical composition within the range of the alloy but with a higher cobalt content in the deposits obtained in water; in contrast, the distribution of the Ni-Co alloy was more homogeneous with changes in morphology and crystallization in the deposits obtained from the DES bath. The coatings' anti-corrosion performance showed that the Co content difference increases the corrosion resistance of the Ni-Co alloy obtained from aqueous electrolytes compared to deposits obtained from DES.

2015

In the paper the results from the study of the kinetic of joint electrodeposition of Ni and Co in Ni-Co alloy system are reported. It is found that the co-deposition of Ni and Co in Ni-Co alloy system in slightly acidic citrate electrolyte occurs under combined diffusion-kinetic control with a typical mechanism of nucleation similar to those in the case of Co. The application of the method of chronoammetry proved that the mechanism of nucleation for Ni-Co alloy is spontaneous with three-dimensional nucleation and nuclei growth. The difference in the independent deposition mechanisms of the two metals is a possible explanation for their anomalous co-deposition in the electrolyte examined. The anomalous codeposition is more clearly noticeable in electrolytes with higher content of cobalt than nickel. The SEM-analysis proves that the alloys enriched in cobalt have crystallites with more even and rounded shape, which is expected in the case of spontaneous nucleation.