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Theory and Practice of Metal Electrodeposition

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Theory and Practice of Metal Electrodeposition

Page 2: Theory and Practice of Metal Electrodeposition978-1-4419-9669-5/1.pdf · Theory and Practice of Metal Electrodeposition. ... Theory and Practice of Metal Electrodeposition 1 3. ISBN

Yuliy D. Gamburg • Giovanni Zangari

Theory and Practice of Metal Electrodeposition

1  3

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ISBN 978-1-4419-9668-8 e-ISBN 978-1-4419-9669-5DOI 10.1007/978-1-4419-9669-5Springer New York Dordrecht Heidelberg London

Library of Congress Control Number: 2011930260

© Springer Science+Business Media, LLC 2011All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connec-tion with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden.The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

Dr. Yuliy D. GamburgRussian Academy of SciencesA.N. Frumkin Institute of Physical Chemistry and ElectrochemistryMoscow [email protected]

Dr. Giovanni ZangariUniversity of VirginiaDepartment of Materials Science and EngineeringCharlottesville VA [email protected]

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Preface

The book reflects in a concise form the modern state of both theoretical and ap-plied aspects of metal electrodeposition. The theoretical part concerns the electro-chemistry of metals and includes a discussion of electrochemical thermodynamics and kinetics, the structure at the metal/electrolyte interface, nucleation, growth and morphology of metals and alloys, and current distribution. The applied part con-tains general information on the applications of metallic coatings, their selection, electrochemical basics and technology of deposition of selected metals and alloys, including individual peculiarities, properties and structure of coatings, testing and characterization. The book includes, where possible at an elementary level, a quan-titative discussion of phenomena of relevance, providing formulas for the calcula-tion of important quantities. Additionally, it contains information on surface level-ing, hydrogenation, inclusion of impurities, physical properties of deposits, that is rarely available in textbooks on electrodeposition. The section on electrodeposition technology includes the most important processes and chemistries; information on any definite material system is provided using a unified scheme, namely: properties of the coating, advantages and disadvantages, solution chemistries and methods of preparation, peculiarities, anodes, and additives.

The essential concepts in theoretical electrochemistry necessary for the investi-gation of metal deposition processes is provided here, including data that are com-monly absent in specialized academic courses. These topics are important for the reader aiming to achieve a thorough understanding of the latest scientific publica-tions in this field. Information on different aspects of the process of electrolytic crystallization is gathered here from a large body of publications and is considered from a unified point of view.

The book is suitable for professional electrochemists, advanced undergraduate and postgraduate students and also for electrodeposition specialists with a physical, technical or chemical education. It can also be useful for engineers and specialists engaged in research on new electrodeposition technologies related to metallic lay-ers, crystals and other metallic objects.

One of the authors (Yu. Gamburg) is hugely grateful to his colleagues from the Laboratory of the surface layers structure (A. N. Frumkin Institute, Russian Acad-emy of Sciences) and particularly indebted to Maria R. Ehrenburg who translated the chapters 10 and 11 written originally in Russian.

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Contents

1   Introduction to Electrodeposition: Basic Terms and Fundamental Concepts  ................................................................................. 11.1 Electrodeposition of Metals ................................................................... 11.2 Examples of Electrocrystallization ........................................................ 21.3 Electrode Processes. Faraday’s Law ...................................................... 21.4 Current Density ...................................................................................... 31.5 Electrodes and Electrode Potential ......................................................... 51.6 Equilibrium Potential and Overpotential ............................................... 71.7 Mixed Potential ...................................................................................... 91.8 Potential–Current Curves (Voltammograms) ....................................... 101.9 Current Efficiency ................................................................................ 121.10 The Various Steps Occurring in Electrode Processes. Fast

and Slow Steps ..................................................................................... 131.11 Electrolytes Used for Electrodeposition ............................................... 151.12 The Influence of Deposition Parameters on

Electrodeposition Processes ................................................................. 171.13 Electric Conductivity of Solutions ....................................................... 181.14 Composition, Structure and Properties of Deposits ............................. 201.15 Current and Metal Distribution ............................................................ 231.16 Anodic Processes .................................................................................. 24References ..................................................................................................... 25

2  The Structure of the Metal-Solution Interface ......................................... 272.1 Introduction: Spatial Separation of Electric Charge ............................ 272.2 Compact Part of the Double Layer: Helmholtz Layer ......................... 302.3 Diffuse Layer: Gouy-Chapman Layer .................................................. 312.4 Adsorption at Electrodes ...................................................................... 36

2.4.1 Model Adsorption Isotherms .................................................... 372.5 Specific Adsorption .............................................................................. 432.6 Adsorption of Uncharged Organic Species .......................................... 452.7 Double Layer on Polycrystalline Solid Surfaces ................................. 46

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2.8 Some Calculations of Double Layer Parameters ............................... 48References ................................................................................................... 51

3  Electrochemical Thermodynamics and Electrochemical Kinetics  ....... 533.1 Electrochemical Potential ................................................................... 533.2 Equilibrium at Electrolyte-Solid Interfaces ....................................... 543.3 Electrode Potential. Nernst Equation ................................................. 553.4 Measurements of Electrode Potential ................................................. 563.5 Theory of Charge Transfer ................................................................. 573.6 Exchange Current Density. Overpotential. Polarization Curves ........ 623.7 Multistep Electrochemical Processes ................................................. 663.8 Chemical Steps ................................................................................... 683.9 Ion Discharge Kinetics in Presence of Surface-Active Agents .......... 703.10 Peculiarities of the Discharge of Complexes ..................................... 73References ................................................................................................... 75

4  Influence of Diffusion on the Rate of Electrochemical Process  ............ 774.1 Ion Transport and Current .................................................................. 774.2 Diffusion ............................................................................................. 804.3 Limiting Current ................................................................................. 824.4 Diffusion Overpotential ...................................................................... 844.5 Mixed Kinetics ................................................................................... 854.6 The Influence of the Electric Field on the Limiting Current .............. 874.7 Role of Diffusion in the Discharge of Complex Species ................... 904.8 Diffusion Layer on the Rotating Disc Electrode ................................ 91References ................................................................................................... 96

5  Thermodynamics and Kinetics of Nucleation  ........................................ 975.1 Introduction ........................................................................................ 975.2 Homogeneous Nucleation .................................................................. 985.3 Heterogeneous Nucleation ................................................................. 100

5.3.1 Three-Dimensional Nucleation .............................................. 1005.3.2 Two-Dimensional Nucleation ................................................ 102

5.4 Nucleation Mechanisms ..................................................................... 1035.5 The Peculiarities Of Electrocrystallization ........................................ 1045.6 The Partition Function For the Nuclei Size Distribution ................... 1055.7 The Steady State Nucleation Kinetics ................................................ 106

5.7.1 Fokker–Planck Equation ........................................................ 1065.7.2 The Non-Equilibrium Flux ..................................................... 1075.7.3 An Estimate of the Steady State Flux ..................................... 1085.7.4 Peculiarities of the Steady State Flux Result ......................... 109

5.8 Non-Steady State Nucleation ............................................................. 1105.9 Experimental Methods ....................................................................... 1125.10 Kinetics of Mass Crystallization ........................................................ 113

Contents

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5.11 The Growth of an Individual Hemispheric Oluster Under Mixed Control .................................................................................. 115

5.12 The Nucleation and Growth With Overlap ...................................... 118References ................................................................................................... 122

6  Morphology of the Growing Metal Surface  ............................................ 1236.1 Steps and Kinks .................................................................................. 1236.2 Adatoms and Adions .......................................................................... 1256.3 Normal Growth and Layer-by-Layer Growth .................................... 1266.4 The Rate of Normal Growth ............................................................... 1276.5 Rate of Step Propagation During Layer-by-Layer Growth ................ 1286.6 Nucleation Rate Distribution Between Growth Steps ........................ 1306.7 Influence of Adsorption on the Rate of Crystallization ..................... 1326.8 Ohmic Drop Near a Growing Step ..................................................... 1336.9 Grain Size of Deposits as a Function of Overpotential ...................... 1346.10 Morphological Features of Compact Electrodeposits ........................ 136

6.10.1 The Morphological Types of the Deposit Surface ................ 1366.10.2 Pyramids and Spirals ............................................................ 1376.10.3 Layered or Lamellar Morphology, and Other

Morphological Types ............................................................ 1386.10.4 On the Nature of Macrosteps ............................................... 139

6.11 Crystalline, Irregular Roughness ........................................................ 140References ................................................................................................... 141

7   Potential Distribution in the Electrolyte and Current Distribution on the Electrode Surface  ..................................................... 1437.1 Statement of the Problem ................................................................... 1437.2 Primary, Secondary and Limiting Field Distributions.

Polarization Fields .............................................................................. 1447.3 Basic Principles of Calculation of Electric Fields in the

Electrochemical Cells ......................................................................... 1497.4 Typical Examples of Primary and Secondary Current Distribution ... 151

7.4.1 The Strip-Shaped Cathode; Primary Current Distribution (PCD) ................................................................. 151

7.4.2 The Disc Electrode; PCD ....................................................... 1527.4.3 Gap Cells and Angular Cells with Linear Cathodes; PCD ..... 1537.4.4 The Cylindrical Cathode ........................................................ 1547.4.5 The Sinusoidal Profile; PCD .................................................. 1547.4.6 Arbitrary Case; PCD .............................................................. 1557.4.7 Arbitrary Case; Secondary Current Distribution (SCD) ........ 1567.4.8 The General Case ................................................................... 158

7.5 Throwing Power of Electrolytes and Polarizability of Electrodes. Standard Definition of Throwing Power ......................... 158

7.6 Throwing Power and Cathodic Polarization. Methods for Improvement of Current Distribution ................................................ 161

Contents

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7.7 Current Distribution on Microstructured and Nanostructured Electrodes: Through-Mask Electrodeposition .......... 1637.7.1 Current Distribution at the Workpiece Scale .......................... 1657.7.2 Current Distribution at the Pattern Scale ............................... 1657.7.3 Current Distribution at the Feature Scale ............................... 166

References ................................................................................................... 167

8  Current Distribution at Rough Electrodes  ............................................. 1698.1 Introduction ........................................................................................ 1698.2 Coefficient of Current Distribution and the Basic Problem

of Microdistribution ........................................................................... 1718.3 Geometric Leveling ............................................................................ 1728.4 Microprofile Evolution as Result of a Non-Uniform

Primary Current Distribution ............................................................. 1738.5 Roughness Evolution Under Secondary and Tertiary

Current Microdistribution .................................................................. 1778.6 True Leveling ..................................................................................... 1808.7 Stability of the Growth Front During Electrocrystallization .............. 1838.8 Bright Deposits ................................................................................... 186References ................................................................................................... 187

9   Non-steady State Electrodeposition Processes and Electrochemical Methods  ......................................................................... 1899.1 Non-steady State Diffusion ................................................................ 1899.2 On–Off Switching of the Current or Overpotential ........................... 1919.3 Superposition of a Sinusoidal Current ............................................... 1939.4 Steady State and Pulsating Diffusion Layers ..................................... 1969.5 Rectangular Pulses ............................................................................. 1979.6 Role of the Pause and of the Anodic Period ....................................... 1999.7 Current Distribution, Current Efficiency and Inclusions of

Impurities During Non-steady State Processes .................................. 1999.8 Linear Current or Potential Scans; the Optimum Sweep

Rate for the Acquisition of Polarization Curves ................................ 201References ................................................................................................... 204

10  Electrodeposition of Alloys  ....................................................................... 20510.1 Introduction ........................................................................................ 20510.2 Applications of Electrodeposited Alloys ............................................ 20510.3 Partial Polarization Curves for Alloy Components ............................ 206

10.3.1 Construction of Partial Curves ............................................. 20610.3.2 Depolarization and Overpolarization ................................... 207

10.4 Conditions for Alloy Formation ......................................................... 20810.5 Structure Types of Electrodeposited Alloys ....................................... 21110.6 Phase Diagrams of Alloys .................................................................. 214

Contents

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10.7 Alloys of the Mechanical Mixture Type ......................................... 21610.8 Alloys of the Solid Solution Type .................................................. 217

10.8.1 Underpotential Metal Deposition and Cathodic Metal Intercalation into a Foreign Substrate .................... 217

10.8.2 Formation of Solid Solutions ........................................... 21910.9 Intermetallic Compounds and Amorphous Alloys ......................... 22010.10 Equilibrium and Steady-State Potentials of Alloys ........................ 22110.11 Accounting for the Energy of Alloy Formation in

Calculations of Potentials of Alloy Deposition .............................. 22310.12 Nucleation and Growth of Metal Clusters on a Foreign

Substrate upon Electrodeposition of an Alloy of the Mechanical Mixture Type .................................................... 225

10.13 Effect of Various Factors on Alloy Composition ........................... 22610.14 Electrodeposition of Multilayer and Surface Alloys ...................... 228

10.14.1 Multilayer Alloys ........................................................... 22810.14.2 Surface Alloys ................................................................ 231

References ................................................................................................... 232

11  Codeposition of Impurities ....................................................................... 23311.1 Sources of Impurities in Electrodeposits ........................................ 23311.2 Theoretical Analysis of the Codeposition Kinetics ........................ 234

11.2.1 Adsorption Equilibrium .................................................... 23511.2.2 Capture of Adsorbed Species ........................................... 23611.2.3 Mass Transport of Impurities to the Cathode ................... 23911.2.4 Derivation of the Main Equation ...................................... 23911.2.5 Limiting and Intermediate Cases ...................................... 24111.2.6 Adsorption Control of Codeposition ................................ 24111.2.7 Diffusion Control of Incorporation .................................. 24211.2.8 The Case of Mixed Control .............................................. 242

11.3 Dependence of the Concentration of Impurities on Electrodeposition Conditions ......................................................... 24311.3.1 Dependence on the Current Density ................................. 24311.3.2 Dependence on the Impurity Concentration in Solution .. 24411.3.3 Dependence on Temperature ............................................ 244

11.4 Factors Complicating the Codeposition Kinetics ........................... 24511.5 Chemical State of Codeposited Impurities ..................................... 24611.6 The Incorporation of Inhibitors Into the Deposit and

Inhibition of the Electrodeposition Process .................................... 24711.7 Hydrogenation of Deposits ............................................................. 24811.8 Mechanisms of Substrate Hydrogenation ...................................... 24911.9 Hydrogen Permeability of Membranes .......................................... 25111.10 Conclusion ...................................................................................... 252References ................................................................................................... 252

Contents

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12   Technologies for the Electrodeposition of Metals and Alloys: Materials and Electrolyte Selection, Substrate Preparation ................. 25312.1 Materials Selection ........................................................................... 253

12.1.1 Decorative Properties: Au, Ag, Rh, Pt, Ni, Cr, Ni–Sn ....... 253 12.1.2 Enhancing Solderability and Welding: Sn Alloys,

Ni, Cu, Au, Pd .................................................................... 254 12.1.3 Antifriction Properties: Pb or Sn Alloys, In, Au ................. 254 12.1.4 Corrosion Protection: Zn, Sn, Cd, Ni, Zn–Ni, Pd,

Ag, Ag–Pd, Au ................................................................... 255 12.1.5 Electrical Contacts and Conductivity: Cu, Ag and

Its Alloys, Au and Its Alloys, Pd, Ni, Sn, Sn–Pb ................ 255 12.1.6 Hardness and Wear-Resistance: Cr, Ni, Ni–W,

Ni–B, Rh, Sn Alloys ........................................................... 256 12.1.7 Miscellaneous Properties ................................................... 256

12.2 Deposit Thickness ............................................................................ 25712.3 Selection of the Electrolyte .............................................................. 25812.4 Chemical and Electrochemical Degreasing ..................................... 25912.5 Pickling ............................................................................................ 26012.6 Additional Treatments ...................................................................... 262References ................................................................................................... 263

13   Technologies for the Electrodeposition of Metals and Alloys: Electrolytes and Processes  ........................................................................ 26513.1 Deposition of Copper and Its Alloys ................................................ 265

13.1.1 Properties and Fields of Application of Copper Deposits .. 265 13.1.2 Solutions for Copper Deposition ........................................ 266 13.1.3 Copper Plating for Semiconductor Interconnects .............. 268 13.1.4 Solutions Make Up and Purification .................................. 269 13.1.5 Mechanism and Kinetics of Deposition ............................. 270 13.1.6 Peculiarities, Anodes, and Additives. Removing

Deposits of Poor Quality .................................................... 270 13.1.7 Brass, Bronze and Copper–Nickel Alloys Plating ............. 271

13.2 Silver and Its Alloys with Sb, Cu and Pd ......................................... 273 13.2.1 Properties and Applications of Silver Deposits .................. 273 13.2.2 Solutions for Silver Deposition .......................................... 274 13.2.3 Solutions Make Up and Purification .................................. 275 13.2.4 The Mechanism of Silver Deposition ................................ 276 13.2.5 Peculiarities; Anodes; Additives ........................................ 277 13.2.6 The Silver Alloys with Antimony, Copper or Palladium ... 278

13.3 Electrodeposition of Gold and Its Alloys ......................................... 278 13.3.1 Properties and Applications for Gold Coatings .................. 278 13.3.2 Solution Chemistries, Compositions and

Operating Conditions ......................................................... 279 13.3.3 Solutions Make Up ............................................................. 281 13.3.4 Peculiarities; Anodes; Impurities; Correction .................... 282 13.3.5 Electrolytes for Gold Alloys Deposition ............................ 283

Contents

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13.4 Electrodeposition of Zinc and Its Alloys .......................................... 284 13.4.1 Properties and Applications ................................................ 284 13.4.2 Electrolyte Formulations and Operating Conditions .......... 285 13.4.3 Electrolyte Preparation ....................................................... 286 13.4.4 The Peculiarities; Anodes; Removal of Zinc Coatings ...... 288 13.4.5 Electrolyte Corrections ....................................................... 288 13.4.6 The Additives for Zinc Deposition ..................................... 289 13.4.7 Zinc Alloys Plating ............................................................. 289

13.5 Electrodeposition of Nickel and Its Alloys ...................................... 290 13.5.1 Properties, Applications and Peculiarities .......................... 290 13.5.2 Electrolyte Formulations .................................................... 292 13.5.3 Solutions Make Up and Purification .................................. 293 13.5.4 Anodes ................................................................................ 294 13.5.5 Correction and Elimination of Harmful Impurities ............ 295 13.5.6 Electrodeposition of Nickel Alloys .................................... 295

13.6 Chromium Electrodeposition ........................................................... 296 13.6.1 Properties and Applications ................................................ 296 13.6.2 Bath Compositions ............................................................. 298 13.6.3 Preparation of the Electrolytes ........................................... 299 13.6.4 Peculiarities ........................................................................ 299 13.6.5 Anodes ................................................................................ 300 13.6.6 Electrolyte Correction ........................................................ 301 13.6.7 Trivalent Electrolytes ......................................................... 301

13.7 Iron and Its Alloys ............................................................................ 301 13.7.1 Electrodeposition of Soft Magnetic Materials ................... 302

13.8 Low-Melting Metals: Bi, Cd, In, Pb, Sb, Sn. The Alloy Sn–Pb ...... 304 13.8.1 Bismuth .............................................................................. 304 13.8.2 Cadmium ............................................................................ 304 13.8.3 Indium ................................................................................ 305 13.8.4 Lead .................................................................................... 305 13.8.5 Antimony ............................................................................ 307 13.8.6 Tin ...................................................................................... 307 13.8.7 Tin–Lead, Tin–Bismuth, and Tin–Zinc Alloys ................... 309

13.9 Platinum Metals: Pd, Pt, Rh ............................................................. 310 13.9.1 Palladium ............................................................................ 310 13.9.2 Platinum ............................................................................. 311 13.9.3 Rhodium ............................................................................. 313

13.10 Troubleshooting Electroplating Operations: Some Possible Reasons for Poor Deposit Quality .................................... 314

References ................................................................................................... 316

14   Structure and Microstructure of Electrodeposited Metals  and Alloys  ................................................................................................... 31714.1 Formation of the Polycrystalline Metal ............................................ 31714.2 Grain Boundaries ............................................................................. 318

Contents

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14.3 Stacking Faults and Twin Boundaries .............................................. 32214.4 Dislocations and Disclinations ......................................................... 32514.5 Point Defects .................................................................................... 32614.6 Post-Electrolysis Structure Relaxation ............................................. 32714.7 Techniques for Structural Investigations .......................................... 330References ................................................................................................... 333

15   Physical Properties of Electrodeposited Metals and Alloys. Quality Control and Testing Methods ..................................................... 33515.1 Introduction ...................................................................................... 33515.2 Specific Electrical Resistance .......................................................... 33615.3 Measurements of the Specific Electrical Resistance ........................ 33915.4 Thermoelectric Force and Contact Resistance ................................. 34115.5 Magnetic Properties ......................................................................... 34515.6 Ductility ............................................................................................ 34615.7 Tensile Strength ................................................................................ 34815.8 Methods of Measurements of Strength and Ductility ...................... 35015.9 Microhardness .................................................................................. 35215.10 Internal Stresses (IS) ...................................................................... 35515.11 Methods of IS Measurement .......................................................... 35815.12 Adhesion of the Deposit to a Substrate .......................................... 36015.13 Methods to Provide Strong Adhesion ............................................ 36015.14 Methods of Adhesion Measurement ............................................... 36215.15 Porosity .......................................................................................... 36515.16 Corrosion Resistance ...................................................................... 36715.17 Solderability ................................................................................... 36815.18 Control of the deposit thickness ..................................................... 36815.19 The Peculiarities of the Properties of the Electrodeposited Alloys 371References ................................................................................................... 373

Index ................................................................................................................. 375

Contents

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List of Symbols

A atomic weightA different constantsA the more electropositive metala thermodynamic activitya first Tafel coefficienta attraction constant in Frumkin equationB the more electronegative metalB adsorption constantb second Tafel coefficientС electric capacitance (per unit area)C, с concentrationCE current (cathodic) efficiencyD grain sizeD diffusion coefficientd densityd distanceE Young’s modulusE potentialE0 standard potentialEeq equilibrium potentiale electrone electronic chargeF Faraday constantf F/RTf frequencyf different functionsG Gibbs energyg gravity factorg number of atoms in the clusterh height, thicknessH hardnessH root-mean-square roughness

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I electric currenti current densityi0 exchange current densityid diffusion current densityilim limiting current densityIS internal stressJ fluxK, k different constantsK electrochemical equivalent of the metalKm mass transfer coefficientkr roughness coefficientkB Bolzmann constantL ligandl length, distanceM metalM molar massMz+ ion of metalm massN number of speciesNA Avogadro numbern net amount of transferred electronsP leveling power of the electrolyteQ net charge passed through the circuitq electric chargeqm electric charge at the metal surfaceR molar gas constantR Ohmic resistanceRc contact resistanceR radiusr distance along the radiusω angular rotation rateRDE rotating disc electrodeS areaSAS surface active substanceT absolute temperatureTP throwing powert timeU voltage (between cathode and anode)V volumev volume per one speciesVm molar volume of the metalW Wagner numberw velocity (of a flux)x distancey distance

List of Symbols

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z electric charge of the species in electron unitsZ number of clustersα transfer coefficientβ polarizability ∂η/∂iγ interface energyГ adsorptionГ∞ limiting adsorptionδ thickness of the reaction layerδN Nernst diffusion layerδпр Prandtl layerε relative permittivityε roughness amplitudeη overpotentialηc cathodic overpotentialηa anodic overpotentialθ coverageκ conductivityl distance of propagationλD Debye lengthμ chemical potentialμ electrochemical potentialνi stoichiometric coefficientsν viscosity (kinematic)ρ volume charge densityρ resistivityσ surface tension (specific surface energy)σ stressσB breaking stressτ duration of the processФ electric potentialФ form factorφ Galvani potentialω angular rotation rate (RDE)ω frequencyω fraction (mass, molar)

List of Symbols