Electrodeposition of quaternary alloys in the presence of magnetic field
© Ebadi et al 2009
Received: 11 March 2010
Accepted: 6 July 2010
Published: 6 July 2010
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© Ebadi et al 2009
Received: 11 March 2010
Accepted: 6 July 2010
Published: 6 July 2010
Electrodeposition of Ni-Co-Fe-Zn alloys was done in a chloride ion solution with the presence and absence of a Permanent Parallel Magnetic Field (PPMF). The PPMF was applied parallel to the cathode surface. The deposition profile was monitored chronoamperometrically. It was found that the electrodeposition current was enhanced in the presence of PPMF (9 T) compared to without PPMF. The percentage of current enhancement (Γ%) was increased in the presence of PPMF, with results of Γ% = 11.9%, 16.7% and 18.5% at -1.1, -1.2 and -1.3 V respectively for a 2400 sec duration. In chronoamperometry, the Composition Reference Line (CRL) for Ni was around 57%, although the nobler metals (i.e. Ni, Co) showed anomalous behaviour in the presence of Zn and Fe. The anomalous behaviour of the Ni-Co-Fe-Zn electrodeposition was shown by the Energy Dispersive X-Ray (EDX) results. From Atomic Force Microscopy (AFM) measurements, it was found that the surface roughness of the Ni-Co-Fe-Zn alloy films decreased in the presence of a PPMF.
Alloy electrodeposition of two or more metals has been investigated to examine properties such as grain size, hardness, and corrosion resistance in relation to the parent metals. For example, the electrodeposition of Zn with iron group elements (i.e. Fe, Ni, Co) is applied mostly as finishing layers.
Brenner  has classified the alloy electrodeposition of Zn with the iron group elements. The main problem with alloy electrodeposition is the anomalous behavior exhibited during the electrodeposition process. For instance, the Zn-iron group alloys face the problem of anomalous behavior where the less noble metal (i. e. Zn) is preferentially deposited compared to the more noble metals in the order Ni > Co > Fe. Several theories have been developed [2–4] to explain this anomalous behavior. Dahm and Caroll  attribute the anomalous behavior to the Hydroxide Suppression Mechanism (HSM). Their theory suggests that the more noble ions are hindered from electrodeposition by formation of hydroxides of the less noble ions. This theory is further based on the solubility constant (Ksp) of M (OH)2 that the Ksp of Zn < Fe < Co < Ni.
Some investigators [6, 7] have found that the pH value in the vicinity of the cathode was increased during alloy electrodeposition, while others [8–10] have disagreed with those results. Several investigators [7, 8, 11, 12] have examined and explored this anomalous behavior by studying the pH, current density, potential range and temperature and its relevance to the anion concentration in the electrolyte. According to some, the electrodeposition rate of the more noble ions rise with the increase of pH of the electrolyte [6, 13]. This anomalous behavior during electrodeposition diminishes with rising temperature . In addition to the use HSM theory to explanation above, some authors [8–10, 14, 15] found that the Under Potential Deposition (UPD) of less noble ions can also lead to the above anomalous electrodeposition. At low potential, normal co-deposition takes place, whereas with increasing potential, anomalous co-deposition occurs . The anions present also affect the pattern of UPD. For instance increasing the concentration of Γ in the zinc electrolyte the peak of the Zn electrodeposition curve shifts to a more negative value in the voltammogram, whereas with increasing PO4 3- shifts the peak in the positive direction along the potential axis .
Mass transport in the electrodeposition of ions on the electrode surface can be controlled through diffusion, ionic migration and convection (natural and forced). When a Permanent Parallel Magnetic Field (PPMF) is applied parallel to the cathode surface, additional forces such as the Paramagnetic Force ( ), Field Gradient Force ( ), Lorentz Force ( ), Electrokinetic Force ( ) and the Magnetic Damping Force ( ) increase of rate of transport of ions to the electrode surface, thus increasing the mass transport current of the electrode reaction. This effect is also known as the Magneto-Hydrodynamic (MHD) which is largely the result of the Lorentz force .
It is observed that the normal diffusion layer thickness δ 0 could be diminished to a narrow layer of δ D, when the magnetic flux B was aligned parallel to the cathode surface.
Therefore the MHD effect, (largely caused by the Lorentz Force) reduces the diffusion layer thickness, thus increasing the mass transport to the electrode surface. This work examines and characterizes the electrodeposition of Ni-Co-Fe-Zn alloys with the presence and absence of a PPMF to the cathode surface.
All experiments were carried out in aqueous electrolyte. Copper plates (0.01 × 1 × 1 cm) were used as working electrodes. Each was electrochemically polished and activated by immersion into mixed acids (HCl 30% - H2SO4 10% - HNO3 5% - CrO3 3%) for a few seconds and then rinsed with double distilled water. The chloride plating solution for the Ni-Co-Fe-Zn alloys electrodeposition via chronoamperometry contained: NiCl2.6H2O 1 M, CoCl2.6H2O 0.25 M, FeCl2.4H2O 0.25 M, ZnCl2 0.25 M, and H3BO3 0.5 M in the Teflon (4 × 8 × 12 cm). The electrolyte was free from additives such as levellers and brighteners. The electrolyte was kept at room temperature and the pH was adjusted to 4 ± 0.1 with hydrochloric acid. In addition, solutions for cyclic-voltammetery experiments were prepared from 0.01 M each of Ni2+, Co2+, Fe2+, Zn2+ ions. The CV and electrodeposition via chronoamperometry was done using Princeton Applied Research (PAR) Versa-Stat3 instrument in the absence and presence of the Permanent Parallel Magnetic Field (PPMF) of 9 Tesla. All experiments were conducted at temperature 30-32°C. The Saturated Calomel Electrode (SCE) and platinum wire were the reference and counter electrodes respectively. The topography of the deposited layers was investigated via Atomic Force Microscopy (AFM PS 3000-NS3a). The mass of electrodeposition was determined by the mass difference of the bare and coated Cu plates. Scanning Electron Microscopy (SEM-FEI Quanta 200F) was used to capture images of the surface morphology of the electrodeposited samples and it included the Energy Dispersive X-Ray (EDX) analysis using Energy Dispersive System INCA energy 400.
Figures 2C and 2F and Figures 2D and 2H confirms the theory of UPD where the electrodeposition of a less noble element shifts to more positive potentials for alloy electrodeposition compared to the electrodeposition of pure elements (i.e. Zn, Fe). Figure 2C shows the electro-reduction of Fe2+ occurring at a peak of -1.10 V, and Fig. 2F shows a peak at -1.00 V for the Ni-Co-Fe alloy electrodeposition. Fig. 2D also shows the peak for Zn2+ electro-reduction occurring at -1.30 V, while Fig. 2H shows a wave at -1.20 V for the Ni-Co-Fe-Zn electrodeposition. This confirms Eq. 1, where an increase of the electro-reduction current in the voltammograms for the Ni-Co-Fe-Zn alloy has taken place in the presence of a PPMF compared to without the PPMF.
Fig. 4 depicts the mass electrodeposition under various current densities in the presence and absence of the PPMF, which also can be confirmed by Eq. 3. The mass of the Ni-Co-Fe-Zn alloy electrodeposited layers were calculated from difference in mass before and after electrodeposition on the copper plates. Our previous results [24, 25] have also shown that the mass of the electrodeposited layers was greater with the PPMF than without. Furthermore as given in a previous section, the difference between of mass of electrodeposition in the presence and absence of the PPMF increases with the increase in the current. As the current increases, the Magneto-Hydrodynamic (MHD) effect becomes more pronounced due to the increase of Lorentz Force, where Δ m = 0.03 to 0.107 mg cm min-1 from Fig. 4.
Notably, the lowest elemental content of the alloys belonged to Fe, where the chemical oxidation of Fe2+ to the more stable Fe3+ takes place in the solution. Some authors reported  that the co-electrodeposition of alloys with Fe2+ can take place by using citric acid or iron powder in the solution to avoid the precipitation of Fe (OH)3. In this work, the solution was free of any chelating reagent to prevent the oxidation of Fe2+ to Fe3+ leading to the lowest elemental content being Fe for the deposited layers. It is also noteworthy that the %wt Co increases due to the increase of the applied potential and the applied PPMF compared to Ni because of the anomalous behaviour in Co electrodeposition.
in the presence of the magnetic field,
where Ueff and Uc are effective and applied cathodic potentials, respectively, I is the deposition current and R is the resistance of dendrites (filaments) with l height. Subsequently, effective potential at the end of the dendrites was reduced with increasing magnetic flux (B). Eventually, the valley space of the electrodepositing surface will be filled with the depositing charged particles, and therefore a smoother surface results from the magneto-electrodeposition process.
The influence of the magnetic field (9 T) oriented parallel to the cathode surface for the electrodeposition of Ni-Co-Fe-Zn alloys was studied at room temperature. The PPMF influence the electrochemical reaction by decreasing the double layer thickness and thus the current density and the mass deposition were increased. The increase of current was shown in the voltammograms in the presence of the PPMF (9T). The electrodeposition using chronoamperometry occurred at potentials -1.1, -1.2 and -1.3 V for duration 2400 sec with and without PPMF (9T). The increase in electrodeposition potential to more negative values correlated with the increase of the percentage of current enhancement (Γ%) with values 11.9%, 16.7% and 18.5% at -1.10, -1.20 and -1.30 V respectively, for 2400 sec, with the presence of PPMF. The surface roughness of the electrodeposited alloys was reduced with the presence of PPMF from 48.5 nm (Fig. 7A; without PPMF) to 23 nm (Fig. 7C; with PPMF) at -1.1 V depositional potential. Furthermore, for deposition at potential -1.3 V, the roughness factor was reduced from 112 nm (7B; without PPMF) to 39 nm (7D; with PPMF).
Atomic force microscopy
Composition Reference Line
Energy Dispersive X-Ray
Hydroxide Suppression Mechanism
solubility constant : Paramagnetic Force; : Field Gradient Force; : Lorentz Force; : Magnetic Damping Force; : Electrokinetic Force;
Permanent Parallel Magnetic Field;
Scanning Electron Microscopy
Under Potential Deposition.
We would like to thank the University of Malaya for the financial support provided by university research grant PS 388/2008C, UMCiL grant (TA009/2008A) and (TA007/2009A). One of the authors (M. Ebadi) acknowledges the University of Malaya for his fellowship. Discussion with C. G. Jesudason is also acknowledged.