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)2*4H2O ; 0.32 M H3BO3

0.04M NiCl2*6 H2O; 5.2*10-4 M Sodium Dodecyl Sulphate (surfactant)

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Electrodeposition

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

(1) MzeM z

Furthermore the following two equations can be relevant for electroplating:

2OH2eOHO (3)

1/2HeH (2)

22

2

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.

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ElectrodepositionConway 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. Ni2+ (hydrated in solution). It diffuses to the electrode.

2. Ni+ (hydrated, at electrode). It is transferred to the electrode surface

3. Ni+ (partially hydrated, attached to the electrode surface as an “adion”). It diffuses across the electrode surface to a crystal building site.

4. Ni+ (adion at crystal building site). It becomes a part of the lattice.

5. 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 chargetherefore it is an adsorbed ion

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Cathodic behavior of Nickel

Cathodic reactions: Ni2+ +2e– Ni

2(H++ e–) H2

1. Ni2+ + e– Ni+ads

2. Ni+ads + e– Ni

3. Ni+ads + H+ + e– Ni+

ads + H*ads

4. 2H *ads H2

4‘. Ni+ads + H*

ads +H+ +e– Ni + H2

Ni–HadsNi(Hads)

H.W. Pickering et al., J. Electrochem. Soc. 144 (1997) L58

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Electrochemical Quartz Crystal Microbalance

Sauerbrey equation:

2/12

02qqAmff

(μq = shear modulus [g/cm s2]; ρq = density of the quartz [g/cm3]; A =piezoelectrically active area)

quartz

gold electrodes

film

shear motion

10 MHz polished quartzes, AT-cut

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Equivalent circuit of a quartz crystal

Lm=inertial component, related to the displaced mass (m) during oscillation Cm=compliance of the quartz element representing the energy stored during oscillationRm =the energy dissipation during oscillation due to internal friction, mechanical loses and acoustical loses ZM,L =mechanical impedance

The mechanical model of an electroacoustical system

Butterworth-van Dyke model

M= massCm= compliance (equivalent to 1/k; k: Hooke‘s constant ) r= coefficient of friction of a piston

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What predicts the theory?

Disk electrode

ΔV

B

I

F

Magnetic field causes stirring:

Force acting on moving ions in the solution :

BvEqF

q= electric chargeE=electric fieldv= velocityB= magnetic fieldμ= mobility of ions in solutionC=concentration of anions/ cations

Eμv μ 10-8 m2 v-1s-1

B 1 T

vqCvqCj

BjFL

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Theoretical approach

Cauchy‘s equation:

BiτPvvρ

tvρ

vCΦCjDRT

FzCDi jj

jjjj

Nernst-Planck equation

P- gradient of the pressure

force Lorentz Bi

tensorstress the-forces, frictional -τ

Dj – diffusion coefficient

Cj –concentration coefficient

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Theoretical approachParamagnetic force (in electrolytic solutions with paramagnetic ions):

C2μ

BχF

0

2m

pm -the molar susceptibility, C –concentration -the vacuum permeability, 4•10-7 H.m-1

0

m

μBBχ

CF

Force due to the gradient of the magnetic field

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

CB2 FFBivηPvvρ

tvρ

Navier-Stokes equation:

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Experimental set-up

Network analyser

Counterelectrode

ReferenceElectrode Hg/ Hg2Cl2

Cell

Quartz

Working electrode

ComputerPotentiostat

RECEWE

N S

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Mechanical vs. magnetical stirring

0 100 200 300 400 500 60080

82

84

86

88

90

92

94

96

curr

ent e

ffici

ency

/ %

rot/min

i=-0.5A.dm-2

-100 0 100 200 300 400 500 600 700

92.5

93.0

93.5

94.0

94.5

curr

ent e

ffici

ency

/ %

B / mT

i=-0.5A.dm-2

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Current efficiencyCalculation of the mass deposited given by Faraday’s law

nFMi

dtdm

A1

Side reaction occurs current efficiency of Ni electrodeposition goes down

calcdm/dt

measdm/dtη

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 electrodei=electric current

0 100 200 300 400 500 600

88

90

92

94

96

98

curr

ent e

ffici

ency

/ %

B / mT

i=-0.01 A.dm-2

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Hydrogen evolution

2HNitotal iii

dtdm

MFzi

dtdQi

Ni

total

-100 0 100 200 300 400 500 600 700 800

0.6

0.7

0.8

0.9

1.0 itotal

= -5A.dm-2

itotal= -0.01A.dm-2

B / mT

i H2 (B

)/ i H

2(B=0

T)

0

2

4

iH2 (B

)/ iH2 (B

=0T)

0 100 200 300 400 500 600 700

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0.011

nichel sulfamate bath( with surfactants)

i H2

/ A.d

m-2

B / mT

i total = -0.05 A.dm-2

nichel sulfamate bath( without surfactants)

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Damping of the quartz during Ni deposition

-50 0 50 100 150 200 250 300 350 400-1

0

1

2

3

4

5

Dam

ping

w

/ kH

z

time / s

0 mT 206 mT 740 mT

itotal

= -5A.dm-2

0 500 1000 1500 2000 2500 3000 3500

0

5

10

15

20

25

Dam

ping

R

m /

time / s

0 mT 206 mT 410 mT 530 mT

itotal

= -0.01A.dm2

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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 changeAFM type PicoSPM, version 2.4 The tip of the cantilevers were pyramidal shape, made of silicon nitride

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Roughness

B (mT) 0 530 740Ra (nm) 5.14 23.26 26.93

standard error 1.18 2.44 2.48Rq (nm) 6.55 29.66 34.05

standard error 1.51 2.39 2.29

N

ZZR

2avei

q

y xL

0

L

0yxa dxdyyx,f

LL1R

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 valueZave- the average of Z values within the given areaN- number of points from the given area Ra is the mean roughnessLx, Ly are the dimension of the surfacef(x,y) give the relative surface to the central plane

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Magnetic properties of deposited Ni layers

-10000 -5000 0 5000 10000

-1.0

-0.5

0.0

0.5

1.0

M/M

s

H (G)

20 degr 40 degr 60 degr 80 degr 100 degr 120 degr 140 degr 160 degr

-10000 -5000 0 5000 10000

-1.0

-0.5

0.0

0.5

1.0

M/M

sH (G)

0 degr 20 degr 40 degr 60 degr 80 degr 100 degr 120 degr 140 degr 160 degr

B= 0 mT B=700 mT

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• 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

Summary

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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