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Future Trends in Electrochemistry
1701. 18, No. 10
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By Willia m Blum NATIONAL BUREAUOF STAN] I A R D S , WASHINGTON, D. C.
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HE task of a prophet would be a dangerous one, were it not for the fact that no one takes him seriously. His predictions are almost certain to be forgotten, regardless of whether they prove correct, when he may secure some small comfort by saying, “I told you so,” or whether they are wrong, in which case he is careful not to recall them. Dr. Slosson, in his “Sermons of a Chemist,” has suggested that the study of history is like a chauffeur’s mirror, in which he sees what is behind in order to know what is coming. The only safe basis for prediction is the study of the past. Even in such a study we are concerned not so much with what has been accomplished as with the failures. The ingenuity and pertinacity of modern science and industry are such that one is fairly safe in assuming that if a recognized and clearly defined need exists in any field it will be met, directly or indirectly, with a t least some measure of success. In the following remarks, therefore, an effort will be made to point out some of the needs of the electrochemical industries, with confidence that if such needs really exist they can and will be met in the not distant future. To some extent these predictions represent the attitude that “the wish is father to the thought,” and are necessarily colored by the personal views of the author. Such criticisms as are made or implied regarding existing conditions are intended to be constructive, and are made with a realization of the fact that present methods may be fully justified by existing conditions, but perhaps not by future developments. Scope of Electrochemistry Recently, in an address of welcome to the American Electrochemical Society, Dr. Stieglitz remarked that modern scientific theories point so strongly to the electrical nature of matter and of chemical changes that we might properly consider that all chemistry is electrochemistry. I do not believe, however, that even with so convincing an argument the American Electrochemical Society is seriously considering the absorption of the AMERICAN CHEMICAL SOCIETY! Actually, as usually defined, electrochemistry is not a distinct science, but rather a field of applied science, in which inorganic, organic, analytical, and physical chemistry, as well as physics and metallurgy, all play an important part. It is difficult, therefore, to define the field of electrochemistry. In a narrow sense it may be said to include all those processes in which chemical changes cause, or are caused by, a flow of electric current. This dehition clearly includes all types of electric batteries and all processes in which electrolysis is conducted. The inclusion in electrochemistry of such subjects as corrosion on the ground that corrosion is now generally supposed to be electrochemical in its nature, is justified only if we assume that in corrosion there are definite and specially separated anodic and cathodic areas. Practically, it has been found expedient also to include in texts and courses in electrochemistry, the subject of electrothermics, upon which now rest many important industries. Electrical discharge in gases, which was formerly considered entirely as a part of physics, has assumed new interest to chemists and is frequently listed as a branch of electrochemistry, in view of its important applications to such processes as the fixation of nitrogen and the production of ozone. General Predictions With such a wide scope and with such varied processes and products as are normally included in electrochemistry it is
obviously difficult for anyone, and especially for one whose direct interest has been in a rather narrow field of electrochemistry, to make helpful or significant suggestions or predictions regarding the various specific processes. It may he possible, however, to outline a few factors which may apply in some degree to the whole field. The very fact that electrochemistry represents an applied science emphasizes its relation to the fundamental principles of chemistry and physics, and its great dependence, not only upon more complete and satisfying theories of the constitution of matter and the nature of chemical changes, but also upon their interpretation. The last few decades have revolutionized scientific thought and, as indicated above, have shown clearly the electrical nature of matter and of chemical changes. At first glance we might therefore assume that, electrochemistry would be in the forefront of the application of the new theories of matter and energy. Actually, as one of my colleagues has expressed it, the theories of electrochemistry are in an eddy of the stream of scientific thought. We still depend upon theories of conductivity that we know do not even describe correctly the behavior of dilute solutions, much less the concentrated solutions universally employed in commercial electrolysis. Our reasoning regarding electrolytic potentials is usually based on static or equilibrium conditions, which throw little light on the actual mechanism of the electrolytic processes. Until we know more of the atomic structure of the materials used for electrodes, and the nature of the reactions by which electron exchange takes place, we will be unable to get any clear understanding of such processes as polarization and overvoltage. The future of electrochemistry therefore depends very directly on the progress that will be made in the study of atomic physics, and especially upon the extent to which discoveries in that field are interpreted and made applicable to the specific problems of electrochemistry. Vnless those engaged in electrochemical industries encourage and, where possible, furnish financial support to fundamental researches in physics and chemistry. the electrochemistry of the future will not even be in an eddy of the scientific stream; it will be left high and dry on the shores of empiricism ! In the course of the future progress in this field, the teachers, especially of electrochemistry, have a great opportunity and responsibility to serve as interpreters of the latest developments in physics and physical chemistry. Teachers of physical chemistry have usually and naturally been interested in electrochemistry chiefly to the extent that electrochemical properties, such as the conductivity and standard potentials, throw light upon the constitution and properties of matter. The electrochemists have an equal right and duty, however, to consider how the facts and theories of physical chemistry may aid in the development and perfection of electrochemical processes. There is today too great a distance mentally, if not geographically, between the departments of physical and electrochemistry in many of our universities. If the future teacher of electrochemistry will show the student how to apply to this industry a sound knowledge of physics and physical chemistry, the student will be able to acquire after graduation that detailed knowledge of existing processes and their technic that is necessary in industry. To the industrial laboratories we must look for much of the development work or “industrial research” that is necessary for the successful commercial application of scientific facts and
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principles, While the progress in this field in the last twentyfive years is a monument to the efforts of the scientists and technologists engaged in these industries, many companies might t o advantage still further expand their technical staff, especially to include more investigators with broad education and experience, I n some cases at least, it appears probable that a detailed study of existing processes and the possibilities for their improvement might yield greater returns than an equal investment upon new processes or products. Some one has suggested that if a process has been in operation for twenty years or more, and is apparently standardized, it is safe to assume that in the light of modern knowledge and methods it is highly inefficient. I n some cases at least, the most promising fields for such research are those in which electrochemistry plays only an incidental, even though essential, part and has hence been overlooked or neglected. With a sound basis of fundamental science, interpreted to meet the requirements of this field, and taught to both graduate and undergraduate students in our colleges, and with increased opportunities for such graduates in the electrochemical industries, the development and application of new methods and processes are inevitable. It is safe to say that much of the progress of recent decades has been due to mechanical ingenuity in the design of equipment for special purposes. Such ability is essential to industrial success, and should in no sense be depreciated; but we should bear in mind that no apparatus can be successful unless it rests upon, or utilizes, sound scientific principles, even though these may at a given time be but poorly understood. Trend of Progress in Electrodeposition of Metals 111 order that the foregoing suggestions may not be entirely yeiled in generalities, I will attempt to point out some of the most probable, or at least the most necessary, directions for progress in the field of electrodeposition, and will leave t o others the application of these same principles, in so far as they may be applied, t o other phases of electrochemistry. For convenience, the field of commercial metal deposition may be divided into electrorefining, electrowinning, electroplating, and electroforming; which are named in the order of their present industrial magnitudes, a t least in America. Electrowinning refers to the deposition by the use of insoluble anodes of nietals from solutions obtained by extracting ores, while electroforming is the production or reproduction of articles such as sheets and tubes, and electrotypes. While essentially the same principles are involved in Ihese yarious applications, the conditions of operation are so clifferent as to warrant separate consideration.
Electrorefinzng The electrolytic refining of metals, especially of copper, is one of the oldest and most important applications of electrochemistry. Large laboratories have been maintained by these refineries, but apparently most of the work conducted has been on analytical chemistry, including the development and routine application of exact methods of analysis that are so essential to the production of highly purified metals. If one may judge from the literature, no great amount of research has been devoted to the actual electrochemical problems, such as the analysis of the voltage and power consumption, the effects of solution composition upon the polarization and conductivity, and the influence of these properties upon the purity and structure of the cathode deposits. I n short, it appears as if the processes have been considered more largely from a purely chemical than an electrochemical standpoint. It seems safe to predict that in the future the chemist in an electrolytic refinery will be as familiar with a potentiometer as with a balance, and will learn to predict and control largely
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by electrical measurements both the cost and purity of the refined metals. The operation of copper-refining is an illustration of the great difference between static and dynamic relations in electrolysis. Under reversible conditions, which of course prevail only when infinitesimal current densities are used, i t requires, theoretically, no voltage except that needed to overcome the resistance, to transfer copper from the anode to the cathode. With commercial current densities, however, owing to polarization a t both the anode and cathode, an appreciable voltage is required, which represents a large part of the energy required for the operation. Even though the process of copper-refining is so highly developed that there is practically no possibility of appreciably improving the purity of the refined copper, it is at least probable that through a study of potential relations, such as is now being made by some of the copper companies. the conditions for producing satisfactory copper deposits of the required purity nith the minimum expenditure of electrical energy will be better defined than is at present possible. I n electrolytic nickel-refining conditions are decidedly different, as indicated by the fact that, although cathode copper as deposited usually contains from 99.98 to 99.99 per cent copper, it is difficult to obtain consistently electrolytic nickel with a purity better than 99.80 per cent, and some lots are appreciably less pure. This failure to produce more nearly pure deposits is undoubtedly due in large part to the fact that there has been no such demand for very pure nickel as there has been for pure copper. There is no obvious benefit in reducing to, say, 0.01 per cent, the copper content of refined nickel which is to be subsequently alloyed with copper. There are indications, however, of increasing demands for nickel of higher purity-e. g., for making malleable nickel and nickel-chromium alloys, and for anodes in electroplating and electroforming. Such requirements are being met in part today by the use of imported nickel, produced by the llond (carbonyl) process. No doubt nickel of equal purity can and will be produced by electrolytic refining if there is sufficient demand for it. It is probable, however, that to attain such purity great stress must be laid upon chemical methods for the purification of the electrolyte, as it does not appear feasible to deposit nickel of the highest purity from a solution containing appreciable amounts of such impurities as iron and copper. In any case it would appear promising to develop the possibilities of nickel chloride electrolytes, instead of the sulfate solutions now generally used. The use of chloride solutions, if practicable, will lead to a saving i n power. on account of their lower resistivity and polarization; and chloride baths will probably also facilitate the retention of copper or other relatively noble metals by the anodes, as nickel is much less inclined to passivity in the chloride solution. An obvious disadvantage of chloride solutions-i. e., their tendency to attack lead linings and pipes-could probably be overcome. if conditions warrant their use, by the substitution of materials of construction other than lead, as has been done in the electrowinning of copper from solutions containing nitrates and chlorides. The electrolytic refining of tin, though shown to be feasible on a commercial scale, has been discontinued in this country for economic reasons. For similar causes, the electrolytic refining of lead has been confined to a few plants, working on lead containing bismuth. The future of these two processes depends upon the development of methods which, under economic conditions a t a given time, will be able to compete with the nonelectrolytic methods. There is no question about being able to produce pure tin and lead electrolytically; it is simply a matter of cost. The time that may elapse till the market prices of lead and tin invite the extension of
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electrolytic refining is the right period for conducting researches on these processes, which are in all probability subject to substantial improvements. Those interested in such projects will find no time or opportunity for research when the demand for more or purer lead and tin becomes pressing; and will then be in the position of Mark Twain’s character, who saw no use to mend the roof when it .was clear and could not mend it when it was raining!
Electrowinning The electrowinning of metals is confined chiefly to copper and zinc, for both of which large plants are now in operation. Such processes furnish metal of a purity equal to that of electrolytically refined metals. Their success under any given conditions therefore depends largely on economic factors, among the most important of which is the relative energy cost of this and any competing process. The occasional reference to electrowinning as “electrolytic smelting” is a recognition of the fact that the extraction and deposition operations of winning replace the smelting and electrorefining of the older processes. I n comparing the energy requirements of these two methods of recovering metals from their ores, we should recall that in any electrolysis the total voltage required for a given current density is equal to the sum of ( a ) the decomposition potential-i. e., the minimum potential a t which the process can be conducted reversibly-@) the I R drop through the solution, ( c ) the anode polarization, and (d) the cathode polarization. For practical purposes we may assume that of these, the I R drop (b) and the cathode polarization (d) are the same in both the winning and refining processes. In the latter, however, with soluble anodes, the decomposition potential is zero, while in winning it has a definite and usually appreciable value, which can be computed from the free energy of the process. In electrowinning, the anode polarization, equal in this case to the oxygen overvoltage on the anode used, is usually much greater than the anode polarization with a soluble anode. The excess voltage required in electrowinning above that in refining is therefore equal to the decomposition potential plus the difference in anode polarization upon a soluble and an insoluble anode. If, for simplicity, we assume that the cost of leaching, purifying, and handling the solutions used in electrowinning is about equal to the cost of handling the materials in the smelting processes, including the casting of the anodes, it is the excess electrical energy used in the electrowinning process that must be compared in cost with the fuel used in smelting. I n other words, the energy efficiency and commercial feasibility of an electrowinning process may depend upon such an apparently academic factor as oxygen overvoltage; and not simply upon selecting an anode that is insoluble in the electrolyte. While in the future as in the past, the electrowinning of zinc and copper will involve careful study and vigilant control of the purity of the solutions, marked economies will probably depend upon a more complete knowledge of the potential relations, as determined by the anodes used and the type of electrolyte employed.
Electroplating I n the electroplating industry conditions are quite different from those in the refining and winning of metals. The latter industries are conducted in large plants in which are employed numerous chemists and engineers, by whom the equipment is designed and the details of the process are rigidly controlled. Electroplating, on the other hand, is not an end in itself but a single and sometimes minor step in the production of manufactured articles of the most diverse character. In consequence, most plating is carried on in relatively small depart-
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ments, either connected directly with industrial establishments, or conducted as “job shops,” for custom plating. These plants are usually supervised by foremen platers, few of whom have had any systematic scientific education, though many of them have in recent years acquired a working knowledge of simple chemical principles-. g., by attending classes conducted under the auspices of the American Electroplaters’ Society. In addition, many large firms that maintain chemical laboratories, such as the manufacturers of automobiles and electrical and optical equipment, have detailed chemists to give all or part of their time to the study and improvement of plating processes. A still smaller number have conducted laboratory researches on electroplating, while a few have also engaged the services of consulting chemists in this field. I n considering the future of the electroplating industry, we are faced with the fact that, in spite of a greatly increased interest during the past ten years, all too many manufacturers still consider their plating plant as a purely incidental, even though necessary, part of their plant, and are content to blame the plater for any failure of their products, but unwilling to expend time or money to improve their equipment or processes. The increased use of specifications for the quality of the plating on finished products and the introduction of new methods and processes of plating point inevitably to the fact that in the not distant future every plating plant of any size will require the consistent application of chemistry, a t least for control of the solutions and products. According to the size of the plant, and the abilities and personalities of the platers and chemists that may be connected with it, such chemical service may be rendered either by a plater who has acquired a sufficient knowledge of analytical chemistry to make the usually simple tests required, or by a chemist working in cooperation with the plater. The importance of cooperation cannot be too strongly emphasized. The plater has through long years of experience acquired a fund of usually reliable information that it is often difficult for a scientifically trained man to grasp or apply. I n addition he is able t o route and check work through numerous operations, often conducted by ignorant and unskilled laborers. The plating foreman who shows the executive ability necessary to manage his department, and is progressive enough to acquire such a knowledge of chemistry that he can at least interpret and utilize the reports of the chemist, need not fear for his position, certainly not in this generation. The works chemist usually has not the desire, and often not the temperament, to direct the details of a plating department. He should, however, win the confidence of the plater, instruct him as much as possible in chemical principles, and give serious consideration to the methods used by the plater, even when such methods at first appear to have no scientific basis. In addition to employing platers and chemists to maintain the existing conditions and quality, the progressive larger concerns will no doubt conduct more actual research work on their own electroplating problems. Smaller concerns (as well as the larger) will find it advantageous to cooperate in joint research projects, such as that fostered by the American Electroplaters’ Society. Even such joint researches will leave ample room for the initiative and ingenuity of individual concerns to adapt the results to meet their own needs. Among the specific applications of plating the only one that bids fair to bring about marked developments in the near future is chromium plating, which is now so prominently before the public. Although chromium plating is not very expensive, it is not so cheap as nickel plating. Chromium does, however, have a much greater hardness and resistance t o tarnish than nickel or other common metals, and deserves consideration where such properties are desirable or essential. Because of its hardness it has been successfully
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applied on printing plates, including electrotypes for long editions-e. g., of cartons, labels, and wrappers, and intaglio plates for printing paper currency. It is safe to predict that in the printing industry alone there are a large number of plants which might to advantage install chromium plating, though their total consumption of chromium (as chromic acid) would not be large. Other uses resting especially upon the hardness of chromium include its application to dies, gages, gears, shafts, and other steel parts which are now usually casehardened. The extensive adoption of chromium plating on these or other articles of very irregular shapes will depend upon improving its “throwing power,” which is usually rery poor in the present type of baths. Blthough the reflecting power of chromium is only about 65 per cent as compared with 90 per cent for silver, its resistance to tarnish makes it especially suitable for outdoor reflectors, such as in headlights and flood lights, for which its use will no doubt soon become commercial. I n connection with the more general application of chromium plating, it is necessary to recall that chromium does not protect exposed iron against corrosion. I n order, therefore, for chromium to exert a protective action superior to a nickel coating, it is necessary that the chromium plating be more nearly impervious than the nickel plating. Whether this can be accomplished practically remains to be seen. From present indications, however, it seems safe to predict that chromium plating will be used largely as a supplement to nickel plating, to increase the resistance to tarnish and abrasion, rather than as a substitute for nickel plating. Thus it is sigdicant that one motor firm that has adopted chromium plating for radiator shells and other parts is applying the’ chromium over a substantial coat of nickel.
Electroforming In electroforming we include electrotyping, a well-established industry, and the production of tubes and sheets, which latter process is still in its infancy. In electrotyping, which like electroplating has in past years been conducted largely on an empirical basis, there has been recently a new interest in applications of science. From present indications this interest is more likely to manifest itself in the standardization of existing processes than in the development of radically
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new procedures. There is good reason to believe, however, that by careful study it might well be possible to bring about marked improvements in this industry, which has not changed greatly in recent years. The manufacture of sheets and tubes by electrodeposition has always been a fascinating dream of the inventor. Its attraction lies in the fact that it is apparently simple to make by electrodeposition very complicated shapes, and, unlike rolling or drawing processes, it is cheaper to make article5 with thin walls than thick ones. In spite of these apparent advantages electroforming has been, a t least until recently, a will-of-the-wisp that has attracted large investments and yielded few returns. During the past few years copper sheets and iron tubes have been successfully made on a commercial scale in this country, but it is still too early to tell whether these processes will survive competition. The chief obstacles to success are the difficulty of producing impervious deposits and of getting uniform distribution of metal of suitable structure and physical properties. While there is no reason to believe that such obstacles are insuperable, it is a t least safe to say that they will never be overcome except by careful research, involving the application of all germane principles, and by scrupulous control of operating conditions, such as freedom of the solutions from suspended matter and other impurities. In short, the successful electroforming of sheets and tubes will be a scientific and not an empirical process. Conclusion
In making the foregoing suggestions and predictions, it is fully realized that industrial success in any project depends jointly upon sound scientific principles, sound engineering, and sound economics. In emphasizing the importance of scientific research in this field, I hare in no way intended to belittle the significance of the other two essentials, either of which may in a given problem be the determining factor for success. The importance of engineering and economics is often more obvious, especially to executives, than is the need for basic scientific studies. As chemists it is therefore our right and duty to emphasize the scientific aspects, and thus help to build a sound and broad foundation for the future of the electrochemical industries.
The Future Trend of Cellulose Chemistry By Gustavus J. Esselen, Jr. SKISNER, SHERDlAS
8r ESSELEX, INC.,
EVERAL years ago, before the method of x-ray crystal analysis had been discovered, a small group of chemists was discussing informally what might be the next great step forward in the science of chemistry. -4younger member of the group expressed the thought that perhaps the simple formula NaCl or Cas04 might not tell the whole story and that the next great advance might be some sort of constitutional formula for our simple inorganic salts. Since this \vas an entirely revolutionary idea so far as inorganic chemistry was concerned, it was rather frowned on by the older members of the group. Yet in a few years the discovery of the new research tool showed that our young friend’s idea was almost prophetic. It must, therefore, be recognized that similar new and revolutionary developments, which may suddenly change the trend of progress, may arise at any time. Such discoveries may make or break any prophecy, yet such speculation is not entirely futile and may be justified
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on the ground that it does no harm and may even be a stimulus in pointing out needs and thereby stimulating research. K e can at least consider what the tendency appears to be and whether this is what we would like to have it. I n the last analysis the trend of progress in any branch of science is going to be governed largely, if not entirely, by the demand. The word “demand” is used here neither in the economic sense nor in the sense of a need of industry, but rather to denote the securing of information necessary for further progress, be it in pure science or in industry. Of course, it will be remarked that this is obvious in industrial research, but is it not also true in the field of pure science? Many researches are undertaken for the prime purpose of securing data required for the solution of other problems, and in almost all researches many points arise which in themselves would be interesting t o investigate further but which must be put aside in concentrating on those phases of the problem
