Influence of static magnetic fields
in nickel electrodeposition
Adriana Ispas, Andreas Bund, Waldfried Plieth
SFB 609
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)
SFB 609
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
M z   ze   M
(1)
Furthermore the following two equations can be relevant for electroplating:
(2)
H   e   1/2H 2
(3)
O 2  H 2 O  2e   2OH 
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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
1.
2.
3.
4.
5.
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
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Cathodic behavior of Nickel
Ni2+ +2e– Ni
Cathodic reactions:
2(H++ e–) H2
1.
2.
3.
4.
4‘.
Ni2+
Ni+ads
Ni+ads
2H *ads
Ni+ads
 Ni+ads
 Ni
e–  Ni+ads + H*ads
 H2
+ H*ads +H+ +e–  Ni + H2
+
e–
+
e–
+ H+ +
Ni–HadsNi(Hads)
H.W. Pickering et al., J. Electrochem. Soc. 144 (1997) L58
SFB 609
Electrochemical Quartz Crystal
Microbalance
film
gold electrodes
Sauerbrey equation:
f  2 f 0
2
m
A q  q 
10 MHz polished quartzes, AT-cut
1/ 2
shear motion
quartz
(μq = shear modulus [g/cm s2]; ρq = density of the quartz
[g/cm3]; A =piezoelectrically active area)
SFB 609
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
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What predicts the theory?
Force acting on moving ions in
the solution :




F  q  E  v B 







FL  j  B



j  Cq  v  Cq  v 
E=electric field
v= velocity
B= magnetic field
μ= mobility of ions in solution
C=concentration of anions/
cations
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
Disk
electrode
μ  10-8 m2 v-1s-1
q= electric charge
B1T
v  μE

Magnetic field causes stirring:
F

ΔV
B

I
Theoretical approach
Cauchy‘s equation:
 
 
  v   
ρ
 ρ v   v  P  τ  i  B

 t  



P- gradient of the pressure


i  B Lorentz force
τ - frictional forces,
 - the stress tensor
Nernst-Planck equation
i j  D jC j 
z jF
RT

D j CjΦ  C j v
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Dj – diffusion coefficient
Cj –concentration coefficient
Theoretical approach
Paramagnetic force (in electrolytic solutions with paramagnetic ions):

Fp
χ m B2 

C
2μ 0
m -the molar susceptibility,
C –concentration
 -the vacuum permeability, 4•10-7 H.m-1
Force due to the gradient of the magnetic field

F

χ m B B
 C
μ0
Navier-Stokes equation:
 
   

  v   
2
ρ
 ρ v   v  P  η v  i  B F B  F C

 t  



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) 238-245
SFB 609
Experimental set-up
Reference
Electrode
Hg/ Hg2Cl2
RE
CE
WE
Counter
electrode
N
Computer
Potentiostat
S
Cell
Working electrode
Quartz
Network
analyser
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Mechanical vs. magnetical
stirring
96
92
90
i=-0.5A.dm
88
94.5
-2
86
84
82
80
0
100
200
300
rot/min
400
500
600
current efficiency / %
current efficiency / %
94
-2
i=-0.5A.dm
94.0
93.5
93.0
92.5
-100
0
100 200 300 400 500 600 700
B / mT
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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
1 dm
Mi

A dt
nF
η
current efficiency / %
Side reaction occurs  current efficiency of Ni
electrodeposition goes down
98
dm/dt meas
dm/dt calc
-2
i=-0.01 A.dm
96
94
92
90
88
0
100
200
300
B / mT
SFB 609
400
500
600
Hydrogen evolution
dQ

i


 total
dt

Fz dm
i

Ni

M dt

i total  i Ni  i H 2
-2
i total = -0.05 A.dm
0.011
itotal= -5A.dm
1.0
-2
0.010
nichel sulfamate bath
( with surfactants)
-2
itotal= -0.01A.dm
4
iH2 (B)/ iH2(B=0T)
2
0.7
iH2 (B)/ iH2(B=0T)
0.8
iH2 / A.dm
-2
0.009
0.9
0.007
0.006
0.005
0.004
0.6
0
0
-100
nichel sulfamate bath
( without surfactants)
0.008
0
100
200
300
400
500
600
700
800
100
200
300
400
B / mT
B / mT
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500
600
700
Damping of the quartz
during Ni deposition
-2
0 mT
206 mT
740 mT
4
3
2
itotal= -0.01A.dm
0 mT
206 mT
410 mT
530 mT
20
1
0
-1
-50
2
25
0
50 100 150 200 250 300 350 400
time / s
Damping Rm / W
Damping w / kHz
5
itotal = -5A.dm
15
10
5
0
0
500 1000 1500 2000 2500 3000 3500
time / s
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Morphology- preliminary results
B= 0 mT, i=-5 A dm2
i(H2)=-1.29 A dm-2
Small damping change
AFM type PicoSPM, version 2.4
The tip of the cantilevers were pyramidal
shape, made of silicon nitride
SFB 609
B= 740 mT, i=-5 A dm2
i(H2)=-0.78 A dm-2
Large damping change
Roughness
Rq 
Ra 
2


Z

Z
 i ave
N
1
LxLy
Ly Lx
  f x, y dxdy
0 0
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)
0
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
standard error
1.51
2.39
2.29
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Magnetic properties of
deposited Ni layers
20 degr
40 degr
60 degr
80 degr
100 degr
120 degr
140 degr
160 degr
M/Ms
0.5
0.0
-0.5
-1.0
0 degr
20 degr
40 degr
60 degr
80 degr
100 degr
120 degr
140 degr
160 degr
1.0
0.5
M/Ms
1.0
0.0
-0.5
-1.0
-10000
-5000
0
5000
10000
-10000
H (G)
-5000
0
5000
H (G)
B= 0 mT
B=700 mT
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10000
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
SFB 609
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
SFB 609