Table Of Contentthe language of science
•••
Contents
Preface •••
Vlll
Symbol! •
XI
I F_.ame•tal c•c:epta I
1.1 Electron 8
transf~r
1.2 Mass transport 18
1.3 The'inte lay of electron transfer ;'and mass trans rt control 30
1.4 A sorption 32
l.S Electrocatalysis 38
1.6 Phue formation in electrode reactions 48
1. 7 Ghemical·i'eactions 50
1.8 The properties of electrolyte solutions Sl
1.9 The assessment of cell voltage S4
1.10 ElectrOchemistry at surfaces on open circuit SS
reading 58
Furthet~
2.1 General considerations 60
2.2 Costing an electrolytic process 64
2.3 Performance and figures of merit 70
2.4 Electrolysis earameters 91
2.S Principles of cell design 9S
2.6 The additional technology or electrolytic processes 109
2. 7 T~J:CII designs 141
2.8 Laboratory. data and scale•up 166
Further reading 171.
3 The dtlor. .l kali illdl8try 173
3.1 General concepts of brine electrolysis 175
3.2 Modem technological developments 177
3.3 Chlorine cell technologies 184
• Contents
VI
3.4 The production of potassium hydroxide 208
Further reading 209
4 The extraedoa. refinl111 and pro4actloa or metal 210
4.1 Electrowinning 211
4,2 Cementation 228
231
4.3 Electrorefining
245
4.4 Electrodeposition of metal powders
247
Further reading
249
5 Otller IIIOIPnic electrolytic proceas
249
5.1 Fluorine
256
5.2 Water electrolisis
269
5.3 Sodium ~;hlorate and sodium bromate
274
5.4 Peracids and their salts
275
5.5 Potassium permanganate
278
5.6 Potassium dichromate and chromic acid
279
5.7 Hydrogen peroxide
282
5.8 Ozone
288
5.9 Manganese dioxide
5.10 Cuprous oxide 290
5.11 Synthesis of metal salts via anodic dissolution 291
292
Further reading
6 Orpnic eleetrosyathesis 194
298
6.1 The hydrodimeri.zatioo of acrylonitrile
6.2 Other commercial electrosynthetic processes 311
326
6.3 Indirect electrosynthesis
329
6.4 The fut·ure of electrosyothesis
330
Further reading
7 Water ,...iftcation, treatment •• reeyeHna of
Wwtrial proce• streams 331
7.1 Metal ion removal and metal recovery 333
7.2 Hypochlorite and low-tonnage chlorine electrolysers 353
7.3 Electrodialysis 358
7.4 The treatment of liquors containing dissolved chromium 364
7.5 Electrolytic methods of phase separation 374
7.6 Flue-gas desulphurization 379
7.7 Other electrochemical processes 382
Further reading 384
8 Metal ftnillhlaa 385
8.1 Electroplating 386
8.2 Electroless plating 424
Contents VI•I•
8.3 Conversion coatings 434
8.4 Electrophoretic painting 441
8.5 . Other related surface-finishing techniques 447
Further reading
448
9
Electrochemical machining 457
Electrochemical etching 468
Further reading
479
10
10.1 Fundamentals of corrosion
483
10.2 ~ thermodynamics of corrosion 489
10.3 The kinetics of corrosion reactions 498
10.4 Corrosion problems in practice
S09
10.5 Corrosion prevention and control 518
10.6 Corrosion problems in electrolytic processing 536
10.7 Corrosion measurement and monitoring 538
Further reading
541
11 Batterkl .... , .. cella
~]
11.1 Battery characteristics
546
11.2 Battery specifications 551
11.3 Evaluation of battery performance 554
11.4 Battery components 5S5
11.5 Present battery systems 559
11.6 Batteries under development 584
11.7 Fuel. cells S90
Further reading S9S
••
11
~·;--•••••on monitorfaa t"""aM~aes S96
.1 ectrochemical procedures S96
12.2 Polarography to anodic stripping voltammetry 596
12.3 lon-teleCtive electrodes
603
12.4 Portable and on-line devices
609
12.5 Electroc:hemical biosensors 6)8
12.6 Elec,trochemical detector cells for high-performance
liquid chromatography {HPLC)
624
12.7 Miscellaneous
634
Further reading
636
Irukx
639
Preface
--- -------- ------ - ------
The objective of this second edition remains the discussion of the many diverse
roles of electrochemical technology in industry. Throughout the book, the
intention is to emphasize that the applications, though extremely diverse, all are
based on the same principles of electrochemistry and electrochemical engineer
ing. Those familiar with the first edition will note a significant increase in the
number of pages. The most obvious addition is the separate chapter on
electrochemical sensors but, in fact, al.l chapters have been reviewed thoroughly
and many have been altered substantially. These changes to the book partly
reflect the dift'erent view of a second author as well as comments from students
and friends. Also, they arise inevitably from the vitality and strength of
electrochemical technology; in addition to important improvements in tech
nology, new electrolytic processes and electrochemical devices continue to be
reported.
In the preface to the first edition it was stated:
... the future for electrochemical technology is bright and there is a general
expectation that new application.s of electrochemistry will become economic as
the world responds to the challenge of more expensive energy, of the need to
develop new materials and to exploit different chemical feedstocks and of the
necessity to protect the environment.
The preparation of this second edition, seven years after these words were
written, provided an occasion to review the progress of industrial electro
chemistry. To our great pleasure, the conclusion is that despite the fact that
energy has not become more expensive, the progress in terms of both improved
technology and completely new processes and devices is very substantial.
Improved membrane cell technology for the cblor- alkali industry, new processes
for the manufacture of low-tonnage organic and inorganic chemicals, the
appearance on the market of new lithium batteries and a variety of sensors, the
coming of age of cathodic electropainting, many electrolytic processes for
effluent treatment, the commercial availability of several families of electro
chemical tells, etc. are all symptoms of a healthy technology.
Matenal chron1ony prawem autorskun
Preface •
lX
Less satisfactory are the status of electrochemistry and electrochemical
engineering as academic disciplines. They remain insufficiently taught at both
undergraduate and postgraduate levels. Moreover, even when they appear
within the syllabus, aU too frequently one aspect of the subjects is covered to the
exclusion of aU others. It is a prime hope of both authors that this book will
encourage many more teachers to take up the challenge of teaching an integrated
applied electrochemistry course.
Following the two introductory chapters, we have tried to use a similar
approach for the discussion of the various groups of applications. We have
sought to relate the technology to the underlying principles and to discuss
current thinking and practice within the industries as well as to comment on
likely future trends. We would wish to emphasize, however, that it is never our
purpose to compare the technologies, cells or devices available from competing
companies; the examples selected are based on our personal experiences and are
in the text for illustration. We have also sought to describe only technology
which has already reached industrial usage. Hence, we have always tried to avoid
the temptation to outline the many other processes which have only been
demonstrated in the laboratory or on a small pilot scale (otherwise the book
would be in many volumes). We have attempted thereby, to produce a readable
account of real industrial electrochemistry, useful to both students and those
already engaged in the investigation of some aspect of the subject.
In writing this book, many compromises bad to be made. There have been
many lively (but friendly) debates between the two authors and topics discussed
have included the depth of treatment, the balance between fundamental and
applied aspects and the choice of illustrative material. By far the most vexed
topics were, however, those relating to signs, symbols and other conventions;
throughout we were aware that the established practices of electrochemists,
electroplaters, corrosion engineers, materials technologists and chemical en
gineers were quite different and they also depended on the country of origin. ln
these very unfortunate circumstances, authors are bound to offend most readers.
In some desperation we decided to follow a system which will be most readily
acceptable to electrocbemists since we expect them to be our largest group of
io
readers. Most of all, we have endeavoured achieve uniformity.
Finally, it is a pleasure to thank the many who have helped us in the
preparation of this book. The most obvious are those who have kindly
persuaded their organizations to release the photographs which illustrate the
text. There are, however, many other industrialists and academics who have
provided source material. We also feel that we owe much gratitude to the many
who have stimulated our interest in applied electrochemistry. In the case of one
of us (D.P.) special mention should be made of Professor Martin Fleischmann
(University of Southampton) and Dr Gordon Lewis (associate and guide
during a survey of industrial electrochemistry carried out in 1979). The other
(F.C. W.) would wish to single out Dr Des Barker (Portsmouth Polytechnic),
'v1 atenal chron1ony prawern autorsk1m
x Preface
Dr David Gabc (University of Loughborough) and Professor Martin Fleisch
mann. u particularly strong influences in his training. We are both also aware
of our debt to .everal companies who have given us practical training in the most
acceptable way - they have paid us as consultants! Thanks are due to Susan
Neale and David Jackson of the Frewen Library, Portsmouth Polytechnic who
checked the lists off urther reading at the end ofe ach chapter. Our typists are also
remembered with many thanks. Lutly, we wish to acknowledge the debt to our
families, especially our wives who have suffered extra duties to aUow the
completion or this book, but also our parents and children for their contributions
to our contented writing.
Derek Pletcher
Frank Walsh
Malena! chroniony prawer- autorsk1m
Symbols
Symbol Definition Typical units
a. Activity of cation Dimensionless
a_ Activity of anion Dimensionless
Mean ionic activity Dimensionless
a±
A Electrode area mz
m- 1
Electroactive area per unit reactor volume
As
m-1
Electroactive area per unit electrode volume
AE
£W- I s- 1
b Cost of a unit of electrical power
B Width of ftow channel m
c, Concentration of species i molm- 3
cj" Concentration of species i in the bulk solution molm- 3
cj Concentration of species i at the electrode molm- 3
surface
c,o, Initial concentration of reactant molm- 3
clll Concentration of reactant at time t molm- 3
coNI Concentration of reactant at inlet to reactor morm-3
Concentration of reactant at outlet of reactor molm - 3
C(OUT)
c
Capital invested £
c
C:..pacitance Fm- 2
c
Capacity of a battery electrode As
CE Electrolysis power cost £
Cp Fixed capital £
c,
Variable reactor investment cost £
CL Land capital £
c,
Cost of electrolyte agitation £
Cw Working capital £
Total scrap value of plant £
CaaAP
c,
Heat capacity at constant pressure Jkg- t K - '
d. Equivalent diameter of a ftow channel m
1
D Depreciation £year-
Maknal chromony prawel" autorskrm
xii Symbols
Symbol Definition Typical units
D, Diffusion ooefficient or species i m2 s- 1
v
E Measured or applied electrode potential
v
E Equilibrium electrode potential
I v
£•
Standard electrode potential
I
v
Equilibrium cathode potential
~
E:
v
Equilibrium anode potential
v
£C Cathode potential
E" Anode potential v
v
Equilibrium cell
potential(~-£:)
£'CELL
v
Cell potential (f:C-E")
EceLL
v
E. . Membrane potential
v
Ecoaa Corrosion potential
v
Potential at which transpassivity first occurs
~
v
Point or zero charge potential
EP·•·•·
v
Eta Tbermoneutral cell potential
F faraday constant A smol-1
g Acceleration due to gravity ms- 2
G, Total Gibbs rree energy for species i Jmot- •
Gj Gibbs free ene.rgy for species i in the absence Jmol-1
of a potential field
.1G Gibbs free energy cliange Jmol- 1
Standard Gibbs free energy of adsorption Jmol- 1
.1G~D&
JG:t
Gibbs free energy of activation for the Jmol- 1
forward process
wm-
h Heat transfer coefficient 1 K - 1
H Enthalpy Jmol- 1
i Current A
fo Exchange current for the cathodic process A
Exchange current for the metal dissolution A
~
reaction
Critical current for the onset of passivation
Current in the passive range
Mass transport controlled limiting current
i/
Current density; I= A
Exchange current density
Exchange current density for the hydrogen
evolution reaction
Exchange current density for the metal
dissolution reaction
Reduction (cathodic) partial current density
Oxidation (anodic) partial current density
Limiting current density (under mass transport
control due to diffusion or convective diffusion)
rvlatenal hroniony prawer- autorsk1m
...
Symbols
XJU
Symbol Definition Typical units
Am_,
Optimum current density
Ion
1,. Current density at a distance x along the Am-2
electrode
s- 1
k Rate constant for first order chemical process
1
l Rate constant for the forward (cathodic) process ms-
1
~ Rate constant for the reverse (anodic) process ms-
1
Rate constant for an electron transfer process at ms-
ko
E • 0 V vs. the reference electrode
1
k• Standard rate constant for an electrode process ms-
1
Mass transport coefficient ms-
kL
m: - 1
Averaged, overall heat transfer coefficient
kll 1
K' ohm- 1m '',mol_,,,
Kohlrausch constant
K• Selectivity constant for species i Dimensionless
1 Characteristic length m
L Length of a plate electrode m
m+ Molality of cation molkg- 1
m_ Molality of anion molkg- 1
Number of moles of electroactive species mol
'"
me Initial molar amount of reactant mol
rn, Molar amount of reactant at time t mol
Molar amount of reactant at the inlet to a mol
.
'"(IN)
reactor
'"toun Mcflar amount of reactant at the outlet of a mol
reactor
m, Molar amount of product mol
1
M Molar mass kgmol-
n Number of electrons Dimensionless
n, Number of moles of product Dimensionless
N Projected lifetime of plant years
Nc Chromatographic plate number Dimensionless
1
N,. Mass flow kgs-
q Electrical charge As
Q Volumetric flow rate mls- 1
Q Charge density Asm-2
w
Q. Heat flow
r Radius of disc or cylinder electrode m
1 1
R Gas constant JK- mol-
R Electrical resistance ohm
Rcm_L Cell resistance ohm
Raacurr Resistance of electrical circuit, including busbars ohm
R, Linear polarization resietance ohm
s Space-velocity s- 1
- 1
s. Normalized space-velocity s
vl1.enal chromony prawern autorsk1m
