Applications of magnetoelectrolysis Citation for published version (APA): Tacken, R. A., & Janssen, L. J. J. (1995). Applications of magnetoelectrolysis. Journal of Applied Electrochemistry, 25(1), 1-5. https://doi.org/10.1007/BF00251257 DOI: 10.1007/BF00251257 Document status and date: Published: 01/01/1995 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 03. Oct. 2021 JOURNAL OF APPLIED ELECTROCHEMISTRY 25 (1995) 1-5 REVIEWS OF APPLIED ELECTROCHEMISTRY 38 Applications of magnetoelectrolysis R. A. TACKEN, L. J. J. JANSSEN Department of Chemical Engineering, Laboratory of Instrumental Analysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 31 January 1994; revised 1 June 1994 A broad overview of research on the effects of imposed magnetic fields on electrolytic processes is given. As well as modelling of mass transfer in magnetoelectrolytic cells, the effect of magnetic fields on reaction kinetics is discussed. Interactions of an imposed magnetic field with cathodic crystalli- zation and anodic dissolution behaviour of metals are also treated. These topics are described from a practical point of view. Nomenclature ml, m2 regression parameters (-) n charge transfer number (-) al, a2 regression parameters (-) q charge on a particle (C) B magnetic field flux density vector (T) R gas constant (Jmo1-1 K -1) c concentration (molm -3) T temperature (K) Ccx~ bulk concentration (tool m -3) t time (s) D diffusion coefficient (m2 s -1) V electrostatic potential (V) de diameter of rotating disc electrode (m) ~3 particle velocity vector (m s -1) E electric field strength vector (Vm -1) Ei induced electric field strength vector (V m -1) Greek symbols Es electrostatic field strength vector (Vm -1) c~ transfer coefficient (-) F force vector (N) 7 velocity gradient (s -1) F Faraday constant (C tool -1) AMS potential difference between metal phase H magnetic field strength vector (Am -1) and point just inside electrolyte phase (OHP) i current density (Am -z) 01) iL limiting current density (A m -2) diffusion layer thickness (m) i o limiting current density without applied G0 hydrodynamic boundary layer thickness magnetic field (Am -z) I without applied magnetic field (m) I current (A) p density (kg m -3) /L limiting current (A) cr electrolyte conductivity (fU 1m -1) J current density vector (Am -2) # magnetic permeability (V s A -1 m -1) K reaction equilibrium constant u kinematic viscosity (m2 S-1) k reaction velocity constant w vorticity kb Boltzmann constant (J K -1) 1. Introduction 2. Mass transport effects The practical relevance of the application of magnetic 2.1. Magnetohydrodynamie phenomena fields in electrochemical processes is potentially large. Improved mass transfer in cells, better deposit quality Magnetohydrodynamic phenomena arise from the and control of corrosion are just some of the effects interaction of velocity fields with electromagnetic that can be promoted. In addition, magnetic fields fields. The total force on a charged particle (elec- are powerful scientific tools in, for instance, reaction tron, ion) moving in an electromagnetic field is the kinetics and metal deposition or dissolution studies. Lorentz force [2]: A review paper by Fahidy [1] appeared in 1983 and F= q(E + v x B) (1) since then research has continued and progressed in the field, while its scope is broadening. This review where E is the sum of the electric and electrostatic summarizes results obtained on magnetoelectrolytic fields E1 + Es. Since the Lorentz force is capable of processes and emphasizes practically relevant aspects producing movement of charged particles such as in four main areas of interest: mass transport, reac- ions, a magnetic field applied during electrolysis tion kinetics, cathodic metal deposition and anodic gives rise to convection of the electrolyte. This mag- metal dissolution. netohydrodynamic effect not only influences mass 0021-891X © 1995 Chapman & Hall 1 2 R.A. TACKEN AND L. J. J. JANSSEN transfer, but also reaction kinetics and deposit tive diffusion layer the magnetic field superposition quality. Orientating and attracting ions can only be may be represented as a 'MHD-perturbation' model, achieved by using large B-gradient fields, because where the conventional convective diffusion equa- these communicate a potential energy larger than tions are modified by small order contributions from the ionic thermal kinetic energy (kbT ,,~ 0.025eV at MHD phenomena [1]. For the specific case of a verti- room temperature) [3]. cal electrode in a weak or moderate (up to 1 tesla) In magnetohydrodynamics, the vector and scalar v magnetic field being horizontal and perpendicular to and B fields are the most important variables;j and E the electrode, the rate of mass transport is propor- can be deduced from these. Fundamental equations in tional (based on free convective diffusion theory) to magnetohydrodynamics are as follows [2]: 91/4 [9, 10]. j= ~r(E + v x B) (2) When the magnetic field is vertical and parallel to vertical plate electrodes, the strongly enhancing B curl - =j (3) effect of magnetic field superposition cannot be pre- # dicted by a simple 'MHD-perturbation' model [11]. Op For this case, and low and moderate fields (up to -- div (or) (4) Ot 0.685T), Fahidy [4] made an attempt to model the Ov magnetic field effect. Analysing experimental data p~- + (v- grad)v + gradp =j x B + pvV2v + pF on copper deposition, where limiting current density (5) increased from 20 to 25.6 A m -2 on increasing a mag- netic field from 0 to 0.685 T, he proposed the inter- j2 relationship between limiting current density, iL, and E.j = -- -j. (v x B) (6) o- magnetic field flux density, B, for electrodes consist- ing of nonmagnetic material and where B is parallel d (p)- ~. grad v = ~curl (~-~)(7) p to the cathode surface to be B B 2 iL = i ° + al Bin' (9) j x B = (B. grad) ~ - grad~-~ (8) where iL° is the limiting current density without Given sufficient boundary conditions, a rigorous appfied magnetic field. Using this equation, for magnetoelectrolytic mass transport model based on copper deposition: iL = 20Am -2, al = 10.916 and the above magnetohydrodynamic equations may in m I = 1.6435 was determined. By comparing the theory be solved. In practice, however, simplified experimental data on limiting current densities and models [1, 4] and empirical relations have been magnetic field strength with various mass transfer deduced. models, Fahidy estimated the magnitude of the corre- sponding diffusion layer thickness (5, and proposed the following equation: 2.2. Empirical results on magnetoelectrolytic mass (5 = (50 _ azBrn2 (10) transport where (5o is the hydrodynamic boundary layer thick- The effect of applying a magnetic field during electro- ness without applied magnetic field. lysis is strongest when mass transport is the control- Chopart et al. [12] showed for copper magneto- ling mode (limiting current conditions), because of electrolysis that a magnetic field induces a magneto- interactions of the field with the convective diffusion hydrodynamic velocity gradient, 7, at a rotating disc layer at the electrodes. Using laser interferometry electrode, which corresponds to techniques, this effect can be made visible [5]. The rela- tive strength of this effect is strongly dependent on the 11 = 0.678FDZ/3 coodV3 71/3 (11) mutual positions of the electrodes and the direction of Aaboubi et al. [13] showed that: the magnetic and gravity fields. In certain configu- rations (magnetic and electric fields parallel), mass 7 = kac~ (12) transport can even be retarded [6]. Thus, the limiting current IL is proportional to B1/3 4/3 Quraishi et al. [7] described the magnetic field coo • effects on natural convective mass transport with The beneficial effect of coupled electric/magnetic regards to the position (inclination) of circular disc fields is more manifest in multiple electrode cells electrodes. The magnetic field was directed parallel where enhancement in mass transport can be much to the gravity field. It was clear that mass transport larger relative to single pair electrode cells. In experi- was enhanced more when the electrodes were slightly ments in a multiple electrode cell by Mohanta et al. inclined to the horizontal, than to the vertical plane.