Industrial Electrochemistry PDF
Preview Industrial Electrochemistry
Industrial Electrochemistry Industrial Electrochemistry DEREK PLETCHER Department ofChemistry The University, Southampton, UK Springer-Science+Business Media, B.V. © 1982, 1984 D. Pletcher ISBN 978-0-412-26530-3 ISBN 978-94-017-1872-1 (e Book) DOI 10.1007/978-94-017-1872-1 This title is available in both hardbound and paperback editions. The paperback edition is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. All rights reserved. No part of this book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage and retrieval system, without permission in writing from the Publisher. To Gill, Linda and Ian Contents Preface ix Listofsymbols xi Fundamentalconcepts 1 1.1 Electron transfer 5 1.2 Mass transport 16 1.3 Adsorption 26 1.4 Electrocatalysis 32 1.5 Phaseformation inelectrode reactions 41 1.6 Electroanalytical techniques 48 2 Electrochemicalengineering 52 2.1 Costinganelectrolyticprocess 53 2.2 Figuresofmerit 56 2.3 Electrolysisparameters 62 2.4 Principlesofcelldesign 65 2.5 Typicalcelldesigns 78 3 Thechlor-alkaliindustry 88 3.1 Generalconcepts ofbrineelectrolysis 89 3.2 Moderntechnological developments 91 3.3 Chlorinecelltechnologies 95 3.4 The production of potassiumhydroxide 113 4 Metalextractionand refining 114 4.1 Electrowinning 115 4.2 Electrorefining 127 5 Other inorganicelectrolyticprocesses 132 5.1 Fluorine 132 5.2 Waterelectrolysis 134 5.3 Sodiumchlorate 143 5.4 Peracidsand their salts 144 viii Contents 5.5 Potassium permanganate 145 5.6 Potassium dichromate and chromic acid 149 5.7 Manganesedioxide 150 5.8 Cuprousoxide 151 6 Organicelectrosynthesis 152 6.1 Thehydrodimerizationofacrylonitrile 153 6.2 Other industrial processes 166 7 Metalfinishing 172 7.1 Electroplating 172 7.2 Anodizing 192 7.3 Other related surface finishing techniques 195 7.4 Electrophoreticpainting 196 8 Metalsprocessing 200 8.1 Electroforming 200 8.2 Electrochemical machining 204 8.3 Electrochemicaletching 214 :9 Corrosion control 217 9.1 The thermodynamicsof corrosion 218 9.2 The kinetics ofcorrosion reactions 219 9.3 Passivation 224 9.4 Corrosion problemsin practice 226 9.5 Electrochemical measuresagainstcorrosion 230 9.6 Acorrosion mechanism for chemicalreactions 237 10 Batteriesand fuel cells 239 10.1 Batterycharacteristics 242 10.2 Battery specifications 247 10.3 Evaluation of batteryperformance 249 10.4 Batterycomponents 250 10.5 Present batterysystems 254 10.6 Batteries under development 272 10.7 Fuel cells 277 11 Watertreatmentand environmentalprotection 281 11.1 Metalion removaland metal recovery 283 11.2 Hypochloriteand low-tonnage chlorine electrolysers 292 11.3 Electrodialysis 293 11.4 Electrolyticmethodsof phaseseparation 299 11.5 Other electrochemicalprocesses 301 11.6 Electroanalyticalprocedures 302 Index 320 Preface Electrochemistryisclearlyanimportant component of the technologyofmany quite diverseindustries.Moreover,the future for electrochemicaltechnologyis bright and there isageneralexpectation thatnew applicationsofelectrochemistry willbecome economicasthe world responds to the challengeof more expensive energy, ofthe need to developnew materials and to exploit differentchemical feedstocks and of the necessity to protectthe environment." Inthissituation,the present ratherfragmentary state ofelectrochemical technologyisdisappointing. Whilethere aremany similaritiesinthe underlying principles andeventhe practices of the electrochemicallybasedindustries, theyare oftennotfully appreciated.Certainly,the RandDprogrammes inmany industries areinthe hands ofthose with little formal training and whoseexperience ofand interestin other branches ofelectrochemistryisverylimited. Moreover,the academicworld hasdone little to help.Electrode processesare,too often,totally ignored in coursesto bothscientists and engineersand certainlyelectrochemical technologyisalmost nevertaughtasaunifiedsubject with anappropriate balance between fundamentals,engineeringand applications.Overall,it isnotsurprising thatthe variousstrands havenotinterwovenand thatscientists and engineersdo not haveaproperappreciation of the importance ofelectrochemicaltechnology. Inthe first halfof1979 Iconductedasurveyinto the research and development needs of the variousindustries in Britain usingelectrochemicaltechnology.The discussionsIheld with companies and academic institutionsre-emphasized the need to seekto unify the variousaspects ofelectrochemicaltechnologyintoasingle subject. The contacts developed alsogavemeaunique opportunityto assessthe present state ofthe variousindustriesand to collect the information onwhich this bookisbased. Certainly,Ibecame fascinated by the breadthand scope ofapplied electrochemistry,inparticularby the exciting advancesofrecent years,and felt promptedto write this book. Ihavesought to apply auniformapproachto each group ofindustrialapplication applicationsand throughout Ihaveattempted to emphasize and explain present attitudesand the currentstate ofthe varioustechnologies. Onthe otherhand,I should emphasize that Ihaveneverset out to discusspatentcellsor devicesor to compare the technologies of competingcompanies sinceit seemsto methatsuch a discussionisonly ofinterest to the potential customer.Also,Ihaveresisted the x Preface temptation to discussthe many potentialapplicationsofelectrochemistrywhereit isamatterofconjecturewhethertheywillbe economically orsociallyviable. HenceIhaveset out to produce areadable account ofrealindustrialelectrochemistry which Ihope might be useful to the studentwho isconsidering acareerin electrochemistryand interestingto those already engagedin Rand Din one branch of the subject and who would benefit from someknowledge ofothertopics within electrochemicaltechnology. Iwould liketo expressmy gratitude to the many whohavecontributed to the appearance ofthisbook.The most obviousarethose who havekindly persuaded their companies to releasephotographsto illustratethe text.There are,however, many otherfriends and colleagueswhohavehelped with specificinformation and references and evenmore, bothinside and outside the ElectrochemistryGroupin Southampton,who by discussionsoveralongperiodoftime havestimulatedmy interestinvarioustopics. Perhaps the many willforgivemeifImake special mention ofProfessor Martin Fleischmannand DrGordon Lewis.Itistraditionalto thankthe typistbutin my caselowe aparticular debt to MrsKate Welfarefor her improvementsmade during typing and her endless patience during the several revisions.Finally,I must thankmy family, particularlymy wifebut alsomy parents and children,for their continuoussupportand understanding during my many absencesfrom their lives. September 1981 Derek Pletcher List of Symbols Thefollowingisalist ofsymbols usedrepetitively throughout the text. C Capacitance;alsocapacity c Concentration ofspeciesi eu Concentration ofspeciesi at the electrode surface I C·"" Concentration ofspeciesiin the bulk solution I D Diffusion coefficient ofspeciesi j de Equivalent diameterofacell E Potentialapplied to or measured at anelectrode versusareference electrode Equilibrium potential(also termed the reversiblepotential) for an electrode process measured versusareference electrode Equilibrium potentialof the anode reaction versusareference electrode Equilibrium potentialofthe cathode reaction versusareference electrode E ~ Standardelectrode potential foranelectrode reaction versusareference e electrode ec ECELL Potentialofacell,i.e.EA - E Corrosion potential CORR E Potentialofzero chargeversusareference electrode pzc F The Faraday t:.G Free energy changeinareaction per mole 1 Measuredor applied current density h Limitingcurrent density (commonlythe mass-transport-limitedcurrent density) 1 Exchange current density 0 1r Partial cathodiccurrentdensity Partial anodic current density I Corrosion currentdensity CORR k Rate constant for achemical process k Rate constantfor acathodicprocess k Rate constant for an anodic process ko Rate constant foranelectron transfer reaction atE =0
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