Influence of static magnetic fields in nickel electrodeposition

1
Influence of static magnetic fields in nickel
electrodeposition

• Adriana Ispas, Andreas Bund, Waldfried Plieth

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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)24H2O 0.32 M H3BO3 0.04M NiCl26
H2O 5.210-4 M Sodium Dodecyl Sulphate
(surfactant)
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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 (?F0) between the
electrode and the electrolyte. ?F0 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
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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

• 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.
• Nie-?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

• Cathodic reactions Ni2
  2e? Ni
• 2(H e) ?H2
• Ni2 e ?
  Niads
• Niads e ? Ni
  
• Niads H e ? Niads
  Hads
• 2H ads ? H2
• 4. Niads Hads H e ? Ni
  H2?
• NiHads?Ni(Hads)

H.W. Pickering et al., J. Electrochem. Soc. 144
(1997) L58
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Electrochemical Quartz Crystal Microbalance
Sauerbrey equation
10 MHz polished quartzes, AT-cut
(µq shear modulus g/cm s2 ?q density of
the quartz g/cm3 A piezoelectrically active
area)
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Equivalent circuit of a quartz crystal
M mass Cm compliance (equivalent to 1/k
k Hookes constant ) r coefficient of friction
of a piston
The mechanical model of an electroacoustical
system
Lminertial component, related to the displaced
mass (m) during oscillation Cmcompliance 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
Magnetic field causes stirring
q electric charge Eelectric field v
velocity B magnetic field µ mobility of ions in
solution C?concentration of anions/ cations
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Theoretical approach
Cauchys equation
Nernst-Planck equation
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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) 238-245
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Experimental set-up
Network analyser
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Mechanical vs. magnetical stirring
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Current efficiency
Calculation of the mass deposited given by
Faradays law
M atomic mass (58.69 g/mol for Ni) F Faraday
constant (96485 C/mol) z valence of species (2)
Aactive aria of the electrode ielectric current
Side reaction occurs ? current efficiency of Ni
electrodeposition goes down
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Hydrogen evolution
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Damping of the quartz during Ni deposition
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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
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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
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Magnetic properties of deposited Ni layers
B 0 mT
B700 mT
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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

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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