1. Influence of static magnetic fields in nickel electrodeposition
Adriana Ispas, Andreas Bund, Waldfried Plieth
SFB 609

2. Nickel sulphamate electrolyte (pH= 4) :
Outline
Fundamentals
electrodeposition
Electrochemical Quartz Crystal Microbalance (EQCM)
Results
current efficiency
hydrogen evolution
morphology aspects
magnetic properties
Nickel sulphamate electrolyte (pH= 4) :
1.26 M Ni(SO3NH2)2*4H2O ; 0.32 M H3BO3
0.04M NiCl2*6 H2O; 5.2*10-4 M Sodium Dodecyl Sulphate (surfactant)

3. Electrodeposition
After introducing a metal electrode in an aqueous solution of its ions, will be established a thermodynamic equilibrium, manifesting itself as a potential difference (ΔΦ0) between the electrode and the electrolyte. ΔΦ0 depends on the type of metal electrode and also on the concentration of metal ions.
Faraday showed that the electrodeposited mass is equivalent to the electrical charge that passes the interface electrolyte/electrode. The current is maintained by the following equation
Furthermore the following two equations can be relevant for electroplating:

4. Electrodeposition
Conway and Bockris made fundamental research about the
manner in which the hydration sheath is stripped from the metal ion
ion is incorporated in the lattice
Ni2+ (hydrated in solution). It diffuses to the electrode.
Ni+ (hydrated, at electrode). It is transferred to the electrode surface
Ni+ (partially hydrated, attached to the electrode surface as an “adion”). It diffuses across the electrode surface to a crystal building site.
Ni+ (adion at crystal building site). It becomes a part of the lattice.
Ni++e-Ni. The nickel becomes incorporated in the lattice
„adion“the entity that results from transfer from the solution side of the double layer to the electrode. The ion retains part of its chargetherefore it is an adsorbed ion

5. H.W. Pickering et al., J. Electrochem. Soc. 144 (1997) L58
Cathodic behavior of Nickel
Cathodic reactions: Ni2+ +2e– Ni
2(H++ e–) H2
Ni e–  Ni+ads
Ni+ads e–  Ni
Ni+ads H e–  Ni+ads + H*ads
2H *ads  H2
4‘ Ni+ads H*ads +H+ +e–  Ni H2
Ni–HadsNi(Hads)
H.W. Pickering et al., J. Electrochem. Soc. 144 (1997) L58

6. Electrochemical Quartz Crystal Microbalance
gold electrodes
film
shear motion
Sauerbrey equation:
10 MHz polished quartzes, AT-cut
(μq = shear modulus [g/cm s2]; ρq = density of the quartz [g/cm3]; A =piezoelectrically active area)

7. Equivalent circuit of a quartz crystal
M= mass
Cm= compliance (equivalent to 1/k; k: Hooke‘s constant )
r= coefficient of friction of a piston
The mechanical model of an
electroacoustical system
Lm=inertial component, related to the displaced mass (m) during oscillation
Cm=compliance of the quartz element representing the energy stored during oscillation
Rm =the energy dissipation during oscillation due to internal friction, mechanical loses and acoustical loses
ZM,L =mechanical impedance
Butterworth-van Dyke model

8. What predicts the theory?
Force acting on moving ions in the solution :
Magnetic field causes stirring:
Disk electrode ΔV
μ  10-8 m2 v-1s-1
B  1 T
q= electric charge
E=electric field
v= velocity
B= magnetic field
μ= mobility of ions in solution
C=concentration of anions/ cations

9. P- gradient of the pressure
Theoretical approach
Cauchy‘s equation:
P- gradient of the pressure
Dj – diffusion coefficient
Cj –concentration coefficient
Nernst-Planck equation

10. Theoretical approach
Paramagnetic force (in electrolytic solutions with paramagnetic ions):
m -the molar susceptibility,
C –concentration
 -the vacuum permeability, 4•10-7 H.m-1
Force due to the gradient of the magnetic field
Navier-Stokes equation:
Magnetic field effects in electrodeposition are non negligible just in the case when they are combined with the convective movements in the solution
J.M.D. Coey, and G. Hinds, Journal of Alloys and Compounds, 326 (2001)

11. Experimental set-up N S Reference Electrode Hg/ Hg2Cl2 Counter
Cell
Quartz
Working electrode
Computer
Potentiostat RE CE WE N S
Network analyser

12. Mechanical vs. magnetical stirring

13. Current efficiency
Calculation of the mass deposited given by Faraday’s law
M= atomic mass (58.69 g/mol for Ni)
F= Faraday constant (96485 C/mol)
z =valence of species (2)
A=active aria of the electrode
i=electric current
Side reaction occurs  current efficiency of Ni electrodeposition goes down

14. Hydrogen evolution

15. Damping of the quartz during Ni deposition

16. Morphology- preliminary results
B= 0 mT, i=-5 A dm2
i(H2)=-1.29 A dm-2
Small damping change
B= 740 mT, i=-5 A dm2
i(H2)=-0.78 A dm-2
Large damping change
AFM type PicoSPM, version 2.4
The tip of the cantilevers were pyramidal shape, made of silicon nitride

17. Roughness
Rq is the standard deviation of the Z values within the given area, calculated from the topography image (the height)
Zi is the current Z value
Zave- the average of Z values within the given area
N- number of points from the given area
Ra is the mean roughness
Lx, Ly are the dimension of the surface
f(x,y) give the relative surface to the central plane
B (mT)
530
740
Ra (nm)
5.14
23.26
26.93
standard error
1.18
2.44
2.48
Rq (nm)
6.55
29.66
34.05
1.51
2.39
2.29

18. Magnetic properties of deposited Ni layers
B= 0 mT
B=700 mT

19. Summary
EQCM is a useful tool for the in situ investigation of the deposited mass and of the current efficiency
Changes in morphology of the deposited layer in the presence of a B field parallel with working electrode
Magnetic field influence the roughness of the deposited layer and the lateral reactions of electrodeposition process

20. Acknowledgments
Special thanks to Dr. Stefan Roth for the VSM measurements
Thanks for the moral support to AK Plieth
Many thanks to DFG for the financial support