FUNDAMENTAL ASPECTS OF ELECTROMETALLURGY This page intentionally left blank FUNDAMENTAL ASPECTS OF ELECTROMETALLURGY Konstantin I. Popov University of Belgrade Belgrade, Yugoslavia Westaim Corporation Fort Saskatchewan, Alberta, Canada Branimir N. Grgur University of Belgrade Belgrade, Yugoslavia KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW eBookISBN: 0-306-47564-2 Print ISBN: 0-306-47269-4 ©2002 Kluwer Academic Publishers NewYork, Boston, Dordrecht, London, Moscow Print ©2002 Kluwer Academic/Plenum Publishers New York All rights reserved No part of this eBook maybe reproducedor transmitted inanyform or byanymeans,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 CONTRIBUTORS Konstantin I. Popov Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Yugoslavia The Westaim Corporation, Fort Saskatchewan, Alberta, T8L 3W4, Canada Branimir N. Grgur Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Yugoslavia v This page intentionally left blank FOREWORD Electrometallurgy is a broad field but it is not a new one. It was the great Faraday in the 1830s who discovered laws covering the electrodeposition of metals and its relation to the current passed and equivalent weight of the metal undergoing deposi- tion. Since that time, applications and developments of his discoveries have spread to many areas of technology. Electrowinning is the most well known, partly because it embraces the process by which aluminum is extracted from its ores. In electrorefining, the impure metal is made into anode and the pure metal dissolved therefrom is deposited on a cathode. Electroplating is exemplified by its use in the manufacture of car bumpers. Finally, in electroreforming, objects may be metallized, often with a very thin layer of the coating desired. The numerous technologies vary greatly in the degree to which they are intellec- tualized. Until the work of Popov et al., electrometallurgy has been regarded as largely empirical, an activity in which there was much art and little science. This will all change with the publication of this book. Several aspects of the background of its senior author, Konstantin Popov, make him uniquely suited to the job of intellectualiz- ing electrometallurgy. First, he had as his mentor the great surely the leading electrochemist in Eastern Europe since the death of Frumkin. Second, he has had ample experience with the leading electrochemical engineer in America, Ralph White. And third, he has an admirable track record of a series of publications aimed at showing the remarkable variety of forms which may be made to arise in electrodeposition. Dr. Popov’s contributions are characterized by a comprehensive mathematical treatment of the phenomena he has discovered. Co-author too, has had much relevant experience in applying the ideas so extensively developed in Belgrade at Canadian companies. The contents of the present volume illustrate how certain fields of science become settled in certain countries. Industrial organic chemistry grew up in Germany, and developed predominantly there until World War II. In electrometallurgy, the intellec- tual development has been largely in Serbia, with the most fundamental studies in nucleation being carried out in the neighboring country of Bulgaria (Kaischev, Busev- ski). This is not to imply that there have been few American contributors (one recalls Brenner, Kardos, Lowenheim), but that the contributions made here in this field have vii viii Foreword come from commercial laboratories and have been near the commercialization stage. University or research institute work on electrometallurgical topics in the United States has been nonexistent since the 1950s. There are many figures in this splendid book of Popov et al. which impress me. The first is the strong, broad contents of its arrangement. There is a fine first chapter on the principles of application to electrochemical kinetics—the equations being written in a form modified for use in electrometallurgical situations (e.g., deposition on the tips of growing crystals of minimal radius of curvature and on corners and edges). Here, it is encouraging to find authors applying the electrochemical version of Kelvin’s equa- tion relating vapor pressure as a function of the radius of drops to the phenomena during the electrogrowth of dendrites. I personally find the treatments of the effects of current varying regimes (e.g., pulse, reverse pulse, square wave, sinusoidal, etc.) the most exciting for I have long thought that instead of the use of chemical additives to the solution, the type of surface finally produced—even the crystal shape—could be achieved by electrical variations only. This book contains much toward the realization of this approach. In the second half of the book, one finds the mathematical treatments of practical situations in electrowinning, electrorefining, electroplating, and electroreforming. What is the difference all this will make? It should enable to engineer to set up regimes to achieve what he wants with a minimum of prefatory experiments. This book has no competitor. There are certainly books on electroplating, but they are largely recipes for what to do which eschew the important question of why. Getting the intellectual side over to the practical engineer, of course, requires great lucidity, for he will not puzzle over material delivered over his head. I think the required clarity has been attained herewith, particularly in the early chapters where the concepts of exchange currents and overpotential are being added to the weary thermodynamics which covers most of what engineers are likely to know about electrochemistry. A great strength is in the photographs of electrodeposited crystals in all their variety. Such photographs can be found in the usual journals, but I have not previously seen such a collection accompanied by textual rationalization. Lastly, I was impressed by the application of the theory to areas which normally receive little more than a definition. I would cite electropolishing, where theory is seldom presented; electromachining; and electroless plating. This book is a feast simply to read, but I believe its main importance is that it gives for the first time an educational tool. It will surely lead to translations and its use will feed back upon the economics of electrometallurgical processes—with a reduction in cost many orders of magnitude greater than the total in purchases of the books. John O’M. Bockris Texas A&M University PREFACE In their preface to the book Fundamental Aspects of Electrocrystallization, Bockris and Razumney in 1966 wrote: “Electroplating, the electrochemical extraction of metals from ores and mixtures, and electrodeposition from nonaqueous solutions, together make up a large area in technology. It is relevant to distinguish two classes of technologies: those in which, the fundamentals and theory were understood first and the applications followed, and those in which the applied side began as a kind of art and the theory limped behind the art, sometimes dragged back by it and occasionally given a little push. Of course, the atomic energy and electronic industry are ideal example of the first two. The electrodeposition and electroextraction industry is a fair example of the second. It is clear enough that the rate of development of the first type of industry was much greater than that of the second, as the possibilities could be estimated or at least the direction in which to push defined, whereas the second type relied in the past on what might be called “inspired groping.” It is hoped that this small monograph may provide a basis for the training of research workers who can then perform the conver- sion of what remains an art in technological electrocrystallization into a technology with a largely rational basis.” In the meantime, although the electrochemistry of metals has significantly advanced, the message of Bockris and Razumney, especially in the light of education professionals, is practically the same. The bridge between high level theory and highly developed practice is still necessary, probably even more than previously. The purpose of this book is to enable this. It is written in order to explain the principles of electrometallurgical technologies, not to give their technical details. It should be easy to follow by a reader with a graduate or an undergraduate degree in either engineering or science. It assumes the knowledge of the basic facts required on the level of Modern Electrochemistry by Bockris and Reddy. The book comprises twelve chapters, which can tentatively be divided into three parts: Chapters 1,2,6, and 7 are written by Grgur and Popov, Chapters 3–5 and 8 by Popov and Grgur and Chapters 9–12 by In the first part (Chapters 1 and 2) the significance of electrometallurgy in science and technology is discussed. The fundamentals of electrochemistry necessary for an understanding of electrometallurgical processes are also given. In the second part (Chapters 3–6) the mechanisms of metal deposition are discussed at a high scientific level although efforts were made to simplify them in an approachable way. For ix