Industrial Electrochemistry

335 Pages·1984·9.27 MB·English

by  Derek Pletcher (auth.)

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
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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