Popov K.I., Djokic S.S., Grgur B.N. Fundamental Aspects of Electrometallurgy
Подождите немного. Документ загружается.
x
Preface
example the text related to the morphology of electrodeposited metals is separated into
three levels: the mathematical approach, the physical model and, finally, a realistic
system. The current distribution in electrochemical cells is described in a new way.
Using this approach, classical complicated mathematical methods are not only
avoided, but also calculations of typical examples for electrochemical cell are per-
formed using simple relations of electrochemical kinetics (described in Chapter 2).
The reader is also introduced to the effects of additives and periodically changing rate
at a level which allows an understanding of metal deposition under these conditions. In
addition, in the third part (Chapters 6–12), theoretical aspects of the electrowinning
and electrorefining of metals, as well as electro- and electroless deposition of thin films
used in electronics, automotive and aerospace applications are discussed. Electro-
deposition of thin films of metals, alloys or composite coatings under direct or
periodically changing current conditions from aqueous or non-aqueous solutions, as
well as molten salts is described. Attempts have been made to up-to-date the current
knowledge with kinetics and mechanisms of electroless deposition and to critically
evaluate the similarities and differences of deposition processes with and without an
external current source.
In the next stage of technological development, we hope, this book will initiate
efforts for the advancement of theoretical fundamentals of electrometallurgy at a level,
which will permit the planning of technological processes without or with a minimum
of experimental data. This is in a way similar to challenge of Bockris and Razumney, a
half-century ago, which led to the appearance of this book.
ACKNOWLEDGMENTS
Chapters 1–8 of this book are based on a few classical studies and on research in
the field of metal electrodeposition performed in the Department of Physical Chemis-
try and Electrochemistry at the Faculty of Technology and Metallurgy, the University
of Belgrade, Yugoslavia. K. I. Popov and B. N. Grgur would like to acknowledge
Professor who initiated this research, and colleagues Professors
and
as well as numerous other colleagues and students who participate
in
it.
Chapters 9 to 12 represent a discussion of various aspects of electrodeposition of
alloys, composite coatings, electroforming, electrochemical oxidation of metals, elec-
troless deposition and electrodeposition from molten salts, found in the open literature.
acknowledges the cooperation of numerous colleagues and coworkers from
Sherritt Inc., The Westaim Corporation, and Dr. B. E. Conway at the University of
Ottawa. For the help in the literature search and manuscript preparation, is
thankful to and Mrs. C. Lepard.
Finally, we wish to express our thanks to Mr. Ken Howell for helpful advice and
to for the preparation of the camera-ready manuscript.
xi
This page intentionally left blank
CONTENTS
1.
WHAT IS ELECTROMETALLURGY
1
3
5
5
5
6
7
7
1.1
Further Readings
2.
DEFINITIONS, PRINCIPLES AND CONCEPTS
2.1
Basic Facts
2.1.1
Electrodes and electrochemical reactions, cell and circuit
2.1.2
The electrochemical double layer and possible
electrochemical reactions
2.2
Self Driving Cells
2.2.1
The Nernst equation and energy producing cells
2.2.2
Cementation
2.3
Electrolysis
2.3.1
Decomposition voltage
2.3.2
A cell with an insoluble anode
2.3.3
A cell with a soluble anode
2.3.4
Current efficiency
2.3.5
Faraday’s law
2.3.6
The current density—overpotential relationships
2.3.8
2.3.6.1
Basic equations
2.3.6.2
Some approximations
2.3.7
The cell voltage
2.4
Some Aspects of Electrocrystallization
3.
SURFACE MORPHOLOGY OF METAL ELECTRODEPOSITS
2.5
Conclusions
3.1
2.6
Further Readings
3.1.1
Specific energy consumption
Thin Compact Surface Metal Films
Crystallization overpotential
xiii
10
10
10
11
13
14
14
14
14
17
19
20
20
26
26
29
30
31
xiv
Contents
3.1.2
The nucleation exclusion zones
3.1.2.1
3.1.2.2
Basic definitions
Physical simulation
3.1.3
3.1.4
3.1.5
3.1.6
Nucleation rate and deposition overpotential
Deposition from simple salt solutions
Deposition from complex salt solutions
Deposition in the presence of adsorbed additives
3.1.6.1
3.1.6.2
Inorganic compounds
Organic compounds
3.1.7 Conclusions
3.2
Thick Compact Metal Electrodeposits
3.2.1 Coarse surfaces
3.2.1.1
3.2.1.2
3.2.1.3
Mathematical models
Physical simulation
Real systems
3.2.1.3.1
Optimum current density for compact metal
deposition
3.2.1.3.2
3.2.1.3.3
Cauliflower like forms
Carrot like forms
3.2.2 Smooth surfaces
3.2.2.1
3.2.2.2
3.2.2.3
Basic facts
Model of leveling
Quantitative treatment
3.2.3
Bright surfaces
3.2.3.1
3.2.3.2
3.2.3.3
3.2.3.4
Silver mirror
Electropolished surfaces
Electrodeposited surfaces
Conclusions
3.3
Disperse Deposits
3.3.1 Spongy deposits
3.3.1.1
3.3.1.2
3.3.1.3
Mathematical model
Physical model
Real systems
3.3.2 Dendritic deposits
3.3.2.1
3.3.2.2
3.3.2.3
Mathematical model
Physical simulation
Real systems
3.3.3
3.3.4
3.3.5
3.3.6
Powdered deposits
Granular deposits
Whisker deposits
Conclusions
3.4
Further Readings
34
34
36
38
41
43
44
44
45
47
49
49
49
54
56
56
57
59
61
61
63
65
66
66
67
71
72
72
72
72
74
76
78
78
82
83
89
92
93
95
95
Contents
xv
4.
THE CURRENT DISTRIBUTION IN ELECTROCHEMICAL
CELLS
4.1
Two Equal Plane Parallel Electrodes Arrangement
4.1.1
4.1.2
4.1.3
4.1.4
Ohmic resistance of the cell
The very edge ohmic resistance
The edge effect
The depth of the penetration of a current line between
the electrode edges and the cell side walls
4.1.4.1
4.1.4.2
4.1.4.3
Mathematical model
Cell voltage-current density dependencies
Determination of the current density distribution
4.1.5 Quantitative treatment
4.1.5.1
Calculation of the cell voltage-current density
distribution dependences
4.1.5.2
The critical current density for dendritic growth
initiation at the edges
4.2
Cells with Low Anode Polarisation
4.2.1 The dependence of the current density at the tip of a
stationary wire electrode on the current density in the middle
of the electrode
4.2.2 Experimental evidence
4.2.2.1
4.2.2.2
The effect of ohmic resistance
Deposition in the presence of strongly adsorbed
organic additives (effect of increased cathodic Tafel
slope)
4.2.2.3
Deposition from a complex salt solution (effect of
exchange current density)
4.3
Corner Weakness Phenomena in Electroforming
4.3.1
4.3.2
4.3.3
Ohmic controlled deposition
Mixed activation - diffusion - ohmic controlled deposition
Activation - diffusion controlled deposition
4.4
4.5
Conclusions
Further Readings
5.
ELECTRODEPOSITION AT A PERIODICALLY CHANGING
RATE
5.1
Basic Definitions
5.1.1
5.1.2
5.1.3
Reversing current
Pulsating current
Alternating current superimposed on direct current
101
103
103
106
108
109
109
111
115
118
119
122
124
124
127
127
129
131
133
133
136
140
141
142
145
145
145
146
148
xvi
Contents
5.1.4
Pulsating overpotential
5.2
Surface Concentration of Depositing Ions in the Periodic
Condition
5.2.1
Electrodeposition with periodically changing rate in the
millisecond range
5.2.2
5.2.3
Capacitance effects
Reversing current in the second range
5.3
Prevention of the Formation of Spongy Deposits and the Effect on
Dendritic Particles
5.4
Compact Deposits
5.4.1
5.4.2
Surface film
Electrode surface coarsening
5.5
5.6
5.7
Current Density and Morphology Distribution on a Macroprofile
Conclusions
Further Readings
6.
ELECTROWINNING
6.1
6.2
Theoretical Aspects of Electrowinning
Theoretical Aspects of Zinc Electrowinning
6.2.1
Technological scheme of zinc electrowinning
6.3
Further Readings
7.
ELECTROREFINING
7.1
Theoretical Aspects of Electrorefining
7.1.1
Selectivity of metal dissolution and deposition
7.2
Theoretical Aspect of Copper Electrorefining
7.2.1 Technological scheme of copper electrorefining
7.2.1.1
7.2.1.2
Refining of the electrolyte
Processing of the anodic slime
7.3
Further Readings
8.
OPTIMUM CONDITIONS FOR ELECTROPLATING
8.1
8.2
8.3
Cementation and Deposition from the Complex Salt Solutions
The Porosity of Metal Electrodeposits
The Condition for the Deposition of a Coating with a Minimum
Porosity
8.4
Further Readings
148
149
149
154
156
158
161
161
163
169
172
172
175
175
176
177
180
181
181
182
183
186
188
188
189
191
191
192
195
196
Contents
xvii
9.
ELECTROPLATING AND SURFACE FINISHING
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
Electrodeposition of Alloys
Electrodeposition of Composite Materials
Electroforming
Electroplating from Non-Aqueous Electrolytes
Electroplating from Room Temperature Molten Salts
Electropolishing
Electromachining
Electrochemical Oxidation of Metals
Further Readings
10.
METAL DEPOSITION WITHOUT AN EXTERNAL
CURRENT
10.1
Basic Definitions
10.1.1
10.1.2
10.1.3
Displacement deposition
Contact deposition
Autocatalytic deposition
10.2
10.3
Solutions for Electroless Deposition
Mechanistic Aspects of Electroless Deposition
10.3.1
10.3.2
10.3.3
10.3.4
10.3.5
The atomic hydrogen mechanism
The hydride ion mechanism
The electrochemical mechanism
Metal hydroxide mechanism
The universal mechanism
10.4
Applications and Properties of Electroless Deposited Films
10.4.1
10.4.2
10.4.3
10.4.4
Metallization of non-conductive surfaces
Electroless deposition of composite coatings
Electroless deposition of gold
Electroless deposition of other metals
10.5
Further Readings
11.
ELECTRODEPOSITION OF METALS FROM MOLTEN SALTS
11.1
11.2
Ionically Conducting Melts
Electrochemical Studies in Electrodeposition from Molten Salts
11.2.1
Electrolysis of alumina-cryolite melts
11.3
11.4
The Anode Effect
Nonconsumable Anode Materials in Molten Salts
Electrodeposition
11.5
Further Readings
197
197
210
216
219
223
226
233
236
243
249
250
250
251
251
252
259
259
260
261
263
265
266
267
267
268
269
270
271
273
275
276
286
287
289
xviii
Contents
12.
ENVIRONMENTAL ISSUES
12.1
Environmental Concerns in the Electrowinning and Electrorefining
from Aqueous Solutions
12.2
12.3
12.4
Environmental Concerns in the Molten Salts Electrolysis
Environmental Concerns in the Electroplating Technologies
Further Readings
291
292
293
294
299
INDEX
301
Chapter 1
WHAT IS ELECTROMETALLURGY
Electrometallurgy deals with technical aspect of metal electrodeposition.
The electrometallurgical processes can be categorized into four main groups:
1.
2.
3.
4.
Electrowinning,
Electrorefining,
Electroplating,
Electroforming.
The schematic representation of electrometallurgical processes is shown
in
Fig. 1.1.
1