Electrochemistry and Corrosion Science PDF
Preview Electrochemistry and Corrosion Science
ELECTROCHEMISTRY AND CORROSION SCIENCE ELECTROCHEMISTRY AND CORROSION SCIENCE by Nestor Perez Department of Mechanical Engineering University of Puerto Rico KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW eBook ISBN: 1-4020-7860-9 Print ISBN: 1-4020-7744-0 ©2004 Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print ©2004 Kluwer Academic Publishers Boston All rights reserved No part of this eBook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: http://kluweronline.com and Kluwer's eBookstore at: http://ebooks.kluweronline.com Contents ix Preface xiii Dedication CHAPTERS: 1 FORMS OF CORROSION 1 1.1 INTRODUCTION 1 1.2 CLASSIFICATION OF CORROSION 3 1.2.1 GENERAL CORROSION 3 1.2.2 LOCALIZED CORROSION 3 1.3 ATMOSPHERIC CORROSION 4 1.4 GALVANIC CORROSION 7 1.4.1 MICROSTRUCTURAL EFFECTS 12 1.5 PITTING CORROSION 16 1.6 CREVICE CORROSION 18 1.7 CORROSION-INDUCED SPALLING 19 1.8 STRESS CORROSION CRACKING 20 1.9 NONMETALLIC MATERIALS 24 1.10 SUMMARY 25 1.11 REFERENCES 25 2 ELECTROCHEMISTRY 27 2.1 INTRODUCTION 27 2.2 ELECTRICAL POLES 28 2.3 ELECTROCHEMICAL CELLS 31 2.3.1 OPEN-CIRCUIT CONDITION 38 2.3.2 CLOSED-CIRCUIT CONDITION 39 2.3.3 APPLICATION OF GALVANIC CELLS 40 2.4 THERMODYNAMICS 41 2.5 STANDARD ELECTRIC POTENTIAL 53 2.6 POURBAIX DIAGRAMS 56 2.6.1 DIAGRAM FOR WATER AND OXYGEN 56 2.6.2 POURBAIX DIAGRAM FOR A METAL M 59 vi CONTENTS 2.7 ELECTRICAL DOUBLE LAYER 61 2.8 DEGREE OF DISSOCIATION 64 2.9 SUMMARY 67 2.10 PROBLEMS/QUESTIONS 68 2.11 REFERENCES 70 3 KINETICS OF ACTIVATION POLARIZATION 71 3.1 INTRODUCTION 71 3.2 ENERGY DISTRIBUTION 72 3.3 POLARIZATION 80 3.4 ACTIVATION POLARIZATION 81 3.5 POLARIZATION METHODS 83 3.5.1 LINEAR POLARIZATION 83 3.5.2 TAFEL EXTRAPOLATION 85 3.6 CORROSION RATE 90 3.7 IMPEDANCE SPECTROSCOPY 97 3.8 CHARACTERIZATION OF ELECTROLYTES 105 3.9 ELECTROLYTE CONDUCTIVITY 109 3.10 SUMMARY 113 3.11 PROBLEMS/QUESTIONS 113 3.12 REFERENCES 118 4 KINETICS OF CONCENTRATION POLARIZATION 121 4.1 INTRODUCTION 121 4.2 MASS TRANSFER MODES 121 4.3 MIGRATION MOLAR FLUX 125 4.4 FICK’S LAWS OF DIFFUSION 126 4.4.1 DIFFUSION IN A RECTANGULAR ELEMENT 127 4.4.2 DIFFUSION IN A CYLINDRICAL ELEMENT 129 4.4.3 SOLUTION OF FICK’S SECOND LAW EQUATION 129 4.4.4 STATIONARY BOUNDARIES 138 4.5 DIFFUSION AND MIGRATION 140 4.6 REVERSIBLE CONCENTRATION CELL 141 4.7 LIMITING CURRENT DENSITY 142 4.8 GALVANOSTATIC POLARIZATION 147 4.9 A.C. POLARIZATION 148 4.10 SUMMARY 149 4.11 PROBLEMS/QUESTIONS 149 4.12 REFERENCES 153 5 MIXED POTENTIAL THEORY 155 5.1 INTRODUCTION 155 5.2 MIXED-ELECTRODE POTENTIAL 155 5.3 INTERPRETATION OF POLARIZATION 159 5.4 PREDETERMINED CORROSION RATE 161 5.5 POLARIZATION OF A GALVANIC CELL 163 CONTENTS vii 5.6 EFFECT OF SURFACE AREA 165 5.7 SUMMARY 165 5.8 REFERENCES 165 6 CORROSIVITY AND PASSIVITY 167 6.1 INTRODUCTION 167 6.2 INSTRUMENTATION 167 6.2.1 TREE-ELECTRODE SYSTEM 170 6.3 POLARIZATION CURVES 172 6.4 CYCLIC POLARIZATION CURVES 177 6.5 PASSIVE OXIDE FILM 178 6.6 KINETICS OF PASSIVATION 179 6.7 MECHANISM OF PASSIVATION 184 6.8 SUMMARY 185 6.9 PROBLEMS 186 6.10 REFERENCES 187 7 ELECTROMETALLURGY 189 7.1 INTRODUCTION 189 7.2 ELECTROWINNING 192 7.3 MATHEMATICS OF ELECTROWINNING 198 7.3.1 FARADAY’S LAW OF ELECTROLYSIS 198 7.3.2 PRODUCTION RATE 200 7.3.3 ECONOMY 205 7.3.4 ELECTROWINNING OF ZINC 206 7.4 ELECTROREFINING 208 7.5 ELECTROPLATING 209 7.6 MOLTEN SALT ELECTROLYSIS 211 7.6.1 CURRENT EFFICIENCY MODEL 213 7.6.2 MAGNETOHYDRODYNAMIC FLOW 215 7.7 MOVING BOUNDARY DIFFUSION 219 7.8 DIFFUSION AND MIGRATION 222 7.9 MASS TRANSFER BY CONVECTION 223 7.9.1 STATIONARY PLANAR ELECTRODES 223 7.9.2 ROTATING-DISK ELECTRODE 231 7.10 LIMITING CURRENT DENSITY 233 7.11 SUMMARY 237 7.12 PROBLEMS 238 7.13 REFERENCES 243 8 CATHODIC PROTECTION 247 8.1 INTRODUCTION 247 8.2 ELECTROCHEMICAL PRINCIPLES 248 8.3 CATHODIC PROTECTION CRITERIA 252 8.4 IMPRESSED CURRENT TECHNIQUE 255 8.5 STRAY CURRENT TECHNIQUE 260 viii CONTENTS 8.6 POTENTIAL ATTENUATION 262 8.7 EQUIVALENT CIRCUIT 270 8.8 MASS TRANSFER IN A CREVICE 272 8.9 CREVICE GROWTH RATE 275 8.10 DESIGN FORMULAE 276 8.11 DESIGNING PRESSURE VESSELS 283 8.12 SUMMARY 290 8.13 PROBLEMS/QUESTIONS 291 8.14 REFERENCES 292 9 ANODIC PROTECTION 295 9.1 INTRODUCTION 295 9.2 DESIGN CRITERIA 295 9.3 RELEVANT DATA 298 9.4 SUMMARY 300 9.5 REFERENCES 300 10 HIGH-TEMPERATURE CORROSION 301 10.1 INTRODUCTION 301 10.2 THERMODYNAMICS OF OXIDES 302 10.3 POINT DEFECTS IN OXIDES 312 10.4 KINETICS OF CORROSION IN GASES 315 10.4.1 PILLING-BEDWORTH RATIO 316 10.4.2 MATHEMATICS OF OXIDATION 318 10.5 IONIC CONDUCTIVITY 322 10.6 WAGNER THEORY OF OXIDATION 327 10.7 EXPERIMENTAL DATA 331 10.8 SUMMARY 336 10.9 PROBLEMS 337 10.10REFERENCES 338 A SOLUTION OF FICK’S SECOND LAW 339 A.1 FIRST BOUNDARY CONDITIONS 340 A.2 SECOND BOUNDARY CONDITIONS 341 A.3 THIRD BOUNDARY CONDITIONS 341 B CRYSTAL STRUCTURES 343 C CONVERSION TABLES 345 D GLOSSARY 349 INDEX 353 Preface The purpose of this book is to introduce mathematical and engineering ap- proximation schemes for describing the thermodynamics and kinetics of elec- trochemical systems, which are the essence of corrosion science. The text in each chapter is easy to follow by giving clear definitions and explanations of theoretical concepts, and full detail of derivation of formulae. Mathematics is kept simple so that the student does not have a stumbling block for under- standing the physical meaning of electrochemical processes, as related to the complex subject of corrosion. Hence, understanding and learning the corrosion behavior and metal recovery can be achieved when the principles or theoretical background is succinctly described with the aid of pictures, figures, graphs and schematic models, followed by derivation of equations to quantify relevant para- meters. Eventually, the reader’s learning process may be enhanced by deriving mathematical models from principles of physical events followed by concrete examples containing clear concepts and ideas. Example problems are included to illustrate the ease application of electro- chemical concepts and mathematics for solving complex corrosion problems in an easy and succinct manner. The book has been written to suit the needs of Metallurgical and Mechani- cal Engineering senior/graduate students, and professional engineers for under- standing Corrosion Science and Corrosion Engineering. Some Mechanical Engi- neering students comply with their particular curriculum requirement without taking a corrosion course, which is essential in their professional careers. Chapter 1 includes definitions of different corrosion mechanisms that are classified as general corrosion and localized corrosion. A full description and detailed scientific approach of each corrosion mechanism under the above classi- fication is not included since books on this topic are available in the literature. Chapter 2 is devoted to concepts and principles of thermodynamics of elec- trochemical systems. An overview of thermodynamics of phases in solution and the concept of charged particles are succinctly described as they relate toe elec- trical potential (voltage) difference between the solution and a metal surface. Chapter 3 and 4 deal with the kinetics of activation and concentration po- larization of electrochemical systems, respectively. The electrochemical reaction kinetics is essential for determining the rate of corrosion (rate of dissolution) of a metal M or an alloy X immersed in a aggressive and destructive chemical so- lution, containing positively and negatively charged ions (atoms that have last or gained electrons). Chapter 5 is concentrated on a mixed activation polarization and concen- tration polarization theory. Entire polarization curves are analyzed in order to determine the change in potential of a metal immersed in an electrolyte during oxidation and reduction. Chapter 6 deals with the degree of corrosivity of electrolytes for dissolving metals and the ability of metals immersed in these electrolytes to passivate or protect from further dissolution. Thus, passivity due to a current flow by external or natural means is studied in this chapter. x PREFACE Chapter 7 is devoted to Electrometallurgy of Production of Metals. This topic includes principles electrochemical which are essential in recovering metals and precious metals (gold, silver, platinum) for metal oxides (minerals) in acid solutions. Chapter 8 and 9 provide schemes for designing against corrosion through cathode protection and anodic protection, respectively. These chapters include procedures for protecting large engineering structures using current flow and coating (phenolic paints). Chapter 10 deals with high temperature corrosion, in which the thermo- dynamics and kinetics of metal oxidation are included. The Pilling Bedworth Ratio and Wagner’s parabolic rate constant theories are defined as related to formation of metal oxide scales, which are classified as protective or nonprotec- tive. The content in this book can be summarized as shown in the flowchart given below. A solution manual is available for educators or teachers upon the consent of the book publisher.
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