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

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)

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:

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

H.W. Pickering et al., J. Electrochem. Soc. 144 (1997) L58 Cathodic behavior of Nickel Cathodic reactions: Ni2+ +2e– Ni 2(H++ e–) H2 Ni2+ + 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

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)

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

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

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

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

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

Mechanical vs. magnetical stirring

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

Hydrogen evolution

Damping of the quartz during Ni deposition

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

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

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

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

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