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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering CHAPTER 3 MATERIALS SCIENCE AND ENGINEERING AS A MULTI DISC IP LINE* * This chapter draws heavily on the work of COSMAT Panel II, and of its chairman, Richard S.Claassen in particular, and also on the work of Daniel C.Drucker and N.Bruce Hannay of Panel V.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering This page in the original is blank.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering CHAPTER 3 MATERIALS SCIENCE AND ENGINEERING AS A MULTIDISCIPLINE MATERIALS, THE MATERIALS CYCLE, AND THE ROLE OF MATERIALS SCIENCE AND ENGINEERING Materials are ubiquitous, so pervasive we often take them for granted. Yet they play a central role in much of our daily lives, in practically all manufacturing industries, and in much research and development in the physical and engineering sciences. Materials have a generality comparable to that of energy and information, and the three together comprise nearly all technology. For COSMAT purposes, we define materials as substances having properties which make them useful in machines, structures, devices, and products. It is useful to depict a global materials cycle, shown in the Frontispiece. The earth is the source of all materials as well as the ultimate repository. Minerals and oils are taken from the earth, and trees and vegetable materials are harvested. Through beneficiation, purification, refining, pulping, and other processes these raw materials are converted into useful industrial materials—metals, chemicals, paper, for example. In subsequent processing, these bulk materials are modified to become engineering materials aimed at meeting performance requirements. The engineering materials are then fashioned by manufacturing processes into shapes and parts which are assembled to make a useful end-product. The product, once its useful life has finished, is eventually returned as waste to the earth, or it undergoes dismantling and material recovery to provide basic materials to feed into the materials cycle again. The materials cycle thus divides naturally into two sections: the left-hand (materials supply) side is primarily concerned with obtaining industrial materials, whether from the earth or by reclamation, and from a knowledge viewpoint is generally within the province of the mineral, earth, and forestry technologies; the right-hand (materials consumption) side is primarily concerned with the uses of industrial materials in the manufacture of structures, devices, and machines, and their subsequent performance. Again, from the knowledge viewpoint, this side of the cycle is the main arena for materials science and engineering, the subject of this report. However, as the diagram clearly brings out, there is intimate interdependence among all stages of the overall materials cycle. The diagram also portrays the role of recycling—any way which enables materials to keep circulating in the right-hand side of the diagram reduces the demand for new raw materials from the earth in the left-
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering hand side. Any step taken in any part of the materials cycle may have repercussions elsewhere in the cycle. New paths around the cycle are continually being opened up through researches which lead to new materials, new applications, and thereby new demand and consumption patterns for materials. Furthermore, the materials cycle is not an isolated entity: every stage of the cycle consumes energy and can affect the environment. Increasingly, therefore, it is necessary for the specialist in MSE to consider the effects of technological changes on the complete system of the total materials cycle, including energy consumption and environmental quality. INNOVATION IN MATERIALS SCIENCE AND ENGINEERING MSE has become a basic instrument in bringing about technological changes. Discoveries of new materials and improvements to old ones—all undergirded by deeper understanding of the intimate relations between the processing, composition, and structure of materials on the one hand, together with their properties and function on the other—lead repeatedly to higher performance and efficiency in existing technologies (e.g. improved process for extracting titanium) and to the creation of new ones (e.g. silicon and the solid-state electronic industry). By the same token, a breakthrough in understanding the physics and chemistry of biocompatibility of synthetic materials could have a dramatic effect on the prosthetics industry. MSE is both creative and responsive. New insights gained, often unexpectedly, through research on the properties and phenomena exhibited by materials can lead through development and engineering stages to new products and applications of benefit to mankind. But often it is the perception of some potential market or societal need for a product that stimulates the appropriate engineering and development and, in turn, the support of considerable applied and even basic research. Whether MSE is operating in a creative or a responsive mode, it is having a technological and social impact at a very basic level. Materials as such are usually not very visible to the public that is primarily concerned with end-products and tends to take materials for granted. Yet materials are the working substance of all hardware used in all technologies and are crucial to successful product performance. Between the introduction of materials and the final product, there are often numerous manufacturing stages where extra value is added. Thus, an improved or new material may be decisive in determining the success, usefulness, or social value of a product, even though the cost of the material or the improvement might be very modest compared with the total product or social value. In this sense, materials can frequently be said to exert high economic leverage. Color TV has been made possible by the development of special phosphors; synthetic fibers, such as nylon and dacron, have made drip-dry apparel possible. There are also instances of low leverage in which materials improvements, while useful, do not exert such an enormous change in the end-product or in social patterns; such an example might be the change in steel used for making cans. Materials, and industries devoted completely to them, may represent about one-fifth of the Gross National Product, but without them there would be no Gross National Product.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Materials are often looked upon as relatively unspecific media which may find their way into a great variety of end-products. New materials or improved ones may lead to a whole variety of end-products involving widely different industries. For example, fiberglass lends itself for use in pleasure boats, as housing construction material, and as automobile bodies. Hence, materials can be said to have a relatively high degree of proprietary neutrality. One consequence of this situation is that materials research often forms a more neutral, yet broadly applicable, base for governmental support and cooperative ventures among companies than does research in various end-product technologies. Besides the direct application of MSE to technology, innovation in the field can have important consequences for materials demand and consumption patterns, the consumption of energy, and the quality of the environment. MSE can play a vital role in meeting man’s needs for better transportation equipment, prosthetic devices, and the generation, transmission, and storage of energy. But by wreaking such technological changes, it can often change drastically the need or consumption patterns for materials and energy. New materials made from more abundant raw materials can often be developed as substitutes for old ones made from scarcer or ecologically less desirable raw materials; new ways can often be found for performing needed technological functions, e.g. transistors have replaced vacuum-tube triodes as basic amplifying elements in electronic circuits, and in more recent years integrated circuits replaced boxes of complex electronic equipment made up of many components. Looking ahead with another example, present work in certain forms of levitated ground transport, if successful, could lead to greatly increased demands for new magnetic or superconducting alloys. Or again, development of suitable catalysts based on relatively abundant materials could significantly reduce demand for platinum catalysts for treating automobile exhaust gases and for use in chemical processes. As regards energy-consumption patterns, MSE has much to contribute in all phases—making new forms of generation possible, e.g. by finding solutions to the problem of fuel swelling under radiation damage in nuclear reactors; enabling new forms of electrical power distribution, e.g. through superconducting or cryogenic transmission lines; finding more efficient ways to store energy, e.g. through solid electrolytic batteries or fuel cells; and through finding more efficient ways of using and conserving energy, e.g. in more efficient materials-processing and manufacturing operations, and in the development of better thermal insulation materials. Concerning environmental quality, MSE has much to contribute in finding, for example, cleaner materials processes, effective uses for waste materials, materials and designs more acceptable from the consumer viewpoint, and in developing instrumentation to monitor and control pollution. Thus, innovation in MSE can play a significant role in the economy, in raising the standard of living, in minimizing demands for energy, in improving environmental quality, and in reducing demands for imported materials with a consequent favorable impact on the U.S. international trade balance. In the remainder of this chapter, therefore, a detailed examination will be made of the nature and scope of MSE and the factors that influence its potency as a multidiscipline.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering CHANGING CHARACTER OF MATERIALS TECHNOLOGY Science-Intensive and Experience-Based Technologies Historically man has made use of materials more-or-less readily available from nature. In this century, however, he has repeatedly demonstrated an ability to synthesize radically new materials to meet increasingly complex and demanding requirements, an ability which so often depends on the latest in scientific knowledge. In fact, so successful has MSE been in recent years that designers and engineers have increasingly come to feel that somehow new materials can be devised, or old ones modified, to meet all manner of unusual requirements. In the past, remarkable progress has been made in utilizing materials based on empirical knowledge of their properties and behavior related to their source and subsequent treatment. Many of the important alloys and ceramics were initially developed in this way. This approach is still invaluable and widely practiced. Graphite is a recent example of a material which has solved important problems in missiles where it forms rocket nozzles and as structural components in nuclear-power reactors. Yet, the necessary development was achieved by an enlightened empirical approach in a company which was very much material-source oriented. Graphite is a most complex material whose physical properties depend on the nature and processing of raw materials, on the quality of the initial carbon-containing material, on binder pyrolysis, and on a variety of processing variables. The most practical approach to development of a special graphite to withstand high temperature and pressure was a systematic study, therefore, of the dependence of properties on processing parameters. The starting point was an initial observation that hot pressing of normal-density carbon yielded a body of high density and high strength. Science was able to provide only a very general framework for the planning and execution of this program. This important graphite development also illustrates a governing feature of the historical mode in materials development. Without a complete science framework and lacking a few broad unifying concepts, the practitioner in graphite development necessarily needed to know a very large collection of facts based on past experience in graphite. For that reason, he was material-source oriented and tended to be more affiliated with the material supplier than with the material consumer. In recent decades, the interest in materials properties has been broadened from that of the supplier to include that of the consumer. In some programs, such as space and the solid-state electronics industry, the material user cannot meet all his objectives with presently existing materials. This, in turn, has often caused the user to become interested in the discovery and development of completely new materials. It has also caused a closer working relationship to be established between the material developer and the material user. Further, the programs which have run into materials limitations of the kind that determine success or failure are, in general, those which are straining for the utmost out of sophisticated science and technology generally. It has, therefore, been natural for the people involved to expect materials development likewise to utilize scientific contributions when available.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering At the same time that the material users have been entering into materials development, the underlying knowledge and understanding in solid-state physics and chemistry has advanced tremendously. These two sciences have evolved several unifying concepts which reach across many materials and now provide common guidance to what seemed previously like disconnected problems in materials development. Advances of fundamental understanding and the ability to design materials properties to exacting specifications have been most marked in the case of electronic materials. In other areas, our level of fundamental understanding is a long way from enabling us to design materials to withstand new uses and environmental conditions without considerable trial and error. Far from nearing saturation, fundamental understanding of the properties of the vast majority of materials and the consequent ability to develop new materials to specifications has barely begun. The term science-intensive technology is used to designate those activities in which specific performance is at a premium and in which the generation of new fundamental understanding of materials is necessary before the desired performance can be achieved. Thus the descriptor, science-intensive technology or high technology, usually denotes an emerging area where knowledge and practice are changing rapidly and where there has not yet built up a widely based fund of experience and practical knowledge. A familiar example to illustrate high technology is the space program where it is mandatory that a component must function in the desired manner at the proper time. Because the entire success of an expensive mission may depend upon the proper functioning of this component it is natural to expend whatever R & D is required to assure success. The actual cost of the materials making up the component becomes a secondary consideration. Another example is found in nuclear-power reactors. Fuel cladding must be of sufficient integrity to guarantee against hazardous release of radioactive byproducts. In the design and fabrication of the fuel cladding, considerable effort at a sophisticated scientific and engineering level is justified to achieve safety goals. In the solid-state electronics industry, we find an example where highly sophisticated and costly effort on materials is justified in terms of the overall product value—both the processing of semiconductor material and the assembly into discrete devices or integrated circuits requires a degree of control which would be unbelievable in most industrial situations. The term experience-based technology, or low technology, is used to refer to programs which are not science intensive—in other words, which rely on more empirical approaches or which may be highly forgiving of manufacturing and processing variations. Typically, large material quantities are involved so that unit material costs are important. Examples are the manufacturing of dishes and structural steels; many tires are assembled in traditional ways involving much hard work; conventional approaches prevail in the construction of roads and highways where unit cost is of great importance; and the paper industry continues to use long-standing, empirically-derived processes.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Relative Pace of Innovation There is a familiar pattern in the growth, development, and diffusion of a technology. At the birth and in the early stages of a new technology, such as solid-state electronics or nuclear-power reactors, the pace of invention is high and the innovating company or nation may well achieve a commanding position in the market for its new technology. In this premarketing stage, cost is of secondary importance, or rather it is an administrative decision related to some perception of the eventual pay-off. Later, the inventive pace begins to slacken while, at the same time, other companies or nations with the necessary educational level and technical competence are acquiring the knowledge and skills to catch up. The formerly commanding position of the original innovator is gradually eroded as the relevant technological capability diffuses nationally and internationally. In this stage, where the technology is termed as becoming mature, commercial advantage is kept by, or passes to, that company or nation that can most effectively minimize production and marketing costs while safeguarding the integrity of the product. Process innovation can then assume more importance than further product innovation. The early stages of a technology, when the inventive pace is high, are often science-intensive, and are commonly referred to as “high technology.” It seems that high technologies in which the U.S. has been in the forefront, such as aerospace, computers, and nuclear reactors, have also been generally associated with international trade surpluses for the U.S. In the more mature stages, the science content of further developments in the technology can then be referred to as experience-intensive or “low technology.” Such technologies may be assimilated by developing countries, and are more likely to be associated with shifts in trade balance since the latter countries usually enjoy lower costs, primarily through lower labor rates. When a technology reaches this phase, the U.S. runs the risk of becoming quite dependent for further developments in that technology on foreign enterprise. This may be acceptable for some technologies but not for others critical to national economic and military security. The primary metals industries are prime examples of such experience-intensive technologies facing very severe foreign competition. Other industries in which technological leadership may have been lost by the U.S. are tires and various consumer goods such as shoes and bicycles. Still other technologies, some of which are regarded as high technologies, are moving in the same direction, e.g., automobiles, consumer electronics, and certain aircraft products. The implications for materials technology in the U.S. in order to meet foreign competition and maintain viable domestic industries are that high inventive pace must be created or maintained in certain fields so as to create new high technologies and safeguard existing ones, and that the technological level must be raised and production costs lowered in selected, critical, mature industries. This must be done within the structure of U.S. industry which can be roughly classified, for our purposes, into the materials-producing and the materials-consuming industries. The former tend to be experience-intensive, while high-technology industries tend to fall in the latter category. The high-technology industries, if their commercial bases are sufficiently large, are more accustomed to maintaining a balanced, although product-oriented, R & D effort than are the low-technology industries.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Disciplinarity, Interdisciplinarity, and Multidisciplinarity In the materials field, universities have evolved in the past along disciplinary lines—physics, chemistry, metallurgy, ceramics, and so on. Similar segmentation is apparent in the industrial sphere, some industries specializing in metals, others in ceramics, in glass, in chemicals, or in crystalline materials for electronics. In addition, there has tended to be segregation in another direction, between materials science on the one hand, embracing the traditional scientific disciplines, and materials engineering on the other, embracing those parts of the engineering disciplines concerned with developing processes and applications for materials. Such separations are practical only when the technical objectives, scientific or engineering, are relatively simple or straightforward. For example, metallurgists may have the requisite knowledge to cope with the problem of developing improved alloys for use as electrical conductors. In such cases, the traditional, disciplinary approach can be adequate for pursuing a problem from the research phase to the production phase. But nowadays the trend in technology is towards ever more complex performance requirements, product and device designs, and dependence on more sophisticated knowledge of the physical phenomena that characterize an increasing diversity of materials. The areas of knowledge required to develop, say, an integrated circuit or a biomedical material are not at all coincident with the traditional disciplinary boundaries. It is obvious that many complex technologies call for knowledge and skills that may cut across several disciplines, including science and engineering. Thus, we see an increasing need for interdisciplinary approaches in order to achieve technical objectives. But the interdisciplinary mode is by no means limited to applied research and development programs. This is also happening in basic materials research. The very core of materials science, the relation of properties to structure and composition, implies a need for the combined efforts of physicists, metallurgists and chemists, etc. In the past the physicist has too often made unrealistic assumptions about the composition, purity, and quality of the materials of his researches; the metallurgist has too often not understood sufficiently how the physical phenomena exhibited by a solid relate to its structure and composition. We believe that materials research provides a natural meeting-ground for specialists from the various scientific and engineering disciplines, from basic research to applied research, development and engineering, and that the pressure for such interdisciplinary collaboration will grow in the future. It is vital, therefore, to establish the factors that are conducive to effective interdisciplinary materials research. The field of MSE, broadly speaking, constitutes a multidisciplinary matrix of those disciplines which are related through the structure/property/processes/function/performance linkage of materials. At times, these disciplines are only loosely coupled and interact mainly through the diffusion of knowledge. But frequently, these disciplines are purposefully coupled together in various combinations in order to meet an objective; such groupings are defined as interdisciplinary. It will be shown that the multidiscipline of MSE has proved eminently effective as a medium for many clusters of interdisciplinary activity.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering DEFINITION OF MATERIALS SCIENCE AND ENGINEERING Many forces have served to shape the multidisciplinary field which has become known as materials science and engineering. In the first place, MSE has come to be regarded as central to the industrial materials used for machines, devices, and structures. Second, there is growing awareness of the integral role played by materials in the general fabric of society and of the increasingly sophisticated demands made on materials by complex technologies. Third, this increasing recognition of the importance of materials is coupled with a growing appreciation of the ways in which the societal demands for materials often have an adverse effect on environmental quality. Fourth, there is new concern that the rate at which the earth is being mined will lead to severe shortages for certain key materials in the near future, and that industrial processes for minerals and materials are significant consumers of energy. Fifth, in addition to these external pressures, there are important forces working within the field itself. There is growing realization that basic concepts and questions pervade throughout various classes of materials. These intellectual stimuli serve to draw together individuals from many different disciplines to achieve, by combining their knowledge and skills, that which none could achieve alone. Thus, through this combination of external and internal pressures, we see the multidisciplinary field of MSE evolving, forwarding the quest for deeper understanding of materials on the one hand and, on the other, bringing this scientific endeavor closer to the needs of technology and society generally. We are led, therefore, to propose the following definition: Materials science and engineering is concerned with the generation and application of knowledge relating the composition, structure, and processing of materials to their properties and uses. SOME ASPECTS OF MATERIALS SCIENCE AND ENGINEERING Materials What is meant by “materials” in MSE is clear to anyone until he is asked to define it. Are foods materials? Fuels? Drugs? Bones and muscle? In the broader sense, the answer is “Yes.” However, a tradition has built up in MSE which focuses on industrial or engineering materials. Thus food, fuels used in their natural state, and some other categories are usually excluded. Exclusion is often based on lack of modification of the original properties of the material prior to usage; little processing; substantial tolerance of the product to quality variations; or little durability in use. These boundaries have, of course, been changing with time. But for the purposes of this report, the principal classes of materials falling within the field of MSE are broadly covered by the typical labels: ceramics and glass, metals and alloys, plastics, single crystals,
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering and certain natural materials such as wood, stone, and sand. But new ways of categorizing materials are evolving. Because of the spill-over of knowledge and applications from one class of materials into another, the traditional boundaries between classes of materials are becoming increasingly blurred. Instead, it is becoming common and useful to consider and classify materials according to their function or application—for example, structural, electronic, biomedical, energy, etc. Disciplines The principal disciplines and subdisciplines involved in the multidisciplinary field of MSE are solid-state physics and chemistry, polymer physics and chemistry, ceramics, and metallurgy, and portions of most engineering disciplines. The field embraces parts of synthetic, structural, dynamic, and theoretical chemistry; and chemical, mechanical, electrical, electronic, civil, environmental, aeronautical, nuclear, and biomedical engineering. Many other disciplines and subdisciplines, such as economics and management, interface with these central activities. It is to be emphasized that the disciplinary or subdisciplinary boundaries to the field are indistinct and continually evolving. Activities and Style MSE. encompasses the entire spectrum of R & D relevant to materials, from basic or curiosity-motivated research done without much thought of its immediate application, to the engineering and design of devices, machines, and structures on the basis of available materials data. It can include such fundamental topics as the structure and properties of solidified gases at very low temperatures or the optimization of materials design for high-temperature gas turbines, the developing of an ability to predict the physical properties of plastics from a knowledge of their molecular configurations, or the exploration for suitable catalysts for treating automobile exhausts. MSE also interacts strongly with related activities: education and teaching, commerce and industrial economics, national security, and environmental quality. The multidisciplinary nature of the field undoubtedly aids its involvement in a wide range of human concerns and interests. MSE includes both the scientific, rigorous approach to acquiring and applying knowledge and the long-standing empirical method. Often the two go hand-in-hand, building on each other—empirical observations of the behavior of materials suggest phenomenological models for their explanation which, in turn, often get refined into predictive, analytical models. Both the phenomenological and more rigorous approaches suggest new ways to proceed, say, in endeavoring to optimize desired material properties. Examples of this mixture of the scientific method and empiricism are the continuing searches for superconductors with higher transition temperatures, for cheaper and more efficient catalysts, and for textured alloys with superior strength-to-weight ratios. But always, in its most ambitious reaches, MSE relates a fundamental understanding of the behavior of molecules, atoms, and electrons to the real
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering ways in which the energy levels can be varied by influences from neighboring atoms. This variation is found for well-defined positions in single crystals. The electron bond to an individual atom can have its energy level changed by a large variety of physical mechanisms, some of which are discussed briefly. The sum of these interactions leads to a statistical distribution of energy for the large number of atoms involved in any real sample, and the result is a broadening of the emission line. Crystalline field splitting is the term used to describe variation in energy level due to the interaction between the electric fields in the crystal and a specific electron state or orbit. If the electron state is not spherically symmetrical and if the crystalline field varies along major directions of the lattice, the energy level will depend on the relative orientation between the electron orbit and the crystal. A low-symmetry atomic site can be beneficial when the desired line is forbidden as is the case in the europium 4f shell. Y2O3 has two rare-earth acceptor sites, one of moderately high symmetry and one of very low symmetry. This was an important reason for choosing Y2O3. Lattice vibrations are a frequent source of line broadening. The lattice is not rigid but rather is in a continual state of vibration due to thermally-induced stationary mechanical waves. Solid-state physics has developed an elegant way of treating these vibrations in terms of phonons which can be much more readily manipulated theoretically. Phonons are a mechanical analogy to electromagnetic quanta. They represent a discrete energy of activation and may be thought of as particles in their interaction with other entities such as the electron bound to an atom or an electron in the conduction band of a solid. Phonons are created or destroyed depending on whether energy is added to or taken from the mechanical system. If a phonon interacts with an electron at the time of emission, the line may be of longer of shorter wavelength depending on whether a phonon is created or destroyed. Y2O3 was known from infrared spectroscopy to have a phonon spectrum which coupled weakly with photons in the visible region and therefore contributed little line broadening. Exchange forces which lead to exchange splitting are a purely quantum-mechanical effect which has no classical analog. Fundamental particles, such as the electron, are identical to the extent that there is no observation which can be made to distinguish whether the particles have exchanged places. If two electron orbits share some common space (wave functions overlap), it is possible for them to exchange positions. The effect on the energy level of each orbit will depend on the relative alignment of the electron spins. This phenomenon is called exchange coupling and is most important in solids when magnetic ions are involved. Magnetic fields can also change the energy of the electron state. Every electron has an intrinsic spin with which is associated a magnetic moment. The magnetic moment can interact with a magnetic field. In addition, some states of the electron can be thought of as having an associated electric current which interacts with the magnetic field. Magnetic interactions are of course particularly large in materials containing the transition metals such as iron and nickel with their large magnetic moments. Resonance broadening is an important concept to understand in studying line radiation from solids. If an electron state is weakly coupled to another of identical frequency, resonance will occur between the two and the electron
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering energy will be perturbed, leading to a broadened line. The GT&E group had done a considerable amount of work on ferrites and garnets where resonance is an important phenomena in line broadening in the radio-frequency spectrum. The work on garnets illustrates the close coupling between material preparation and its use; it set the stage for the phosphor development. Wickersheim and Lefever had earlier identified the presence of a silicon impurity in the yttrium-iron garnet at the tetrahedral oxygen site. The silicate ion is incorporated in a tetravalent state in contrast to the trivalent cations in the normal host material. The quadrivalent silicon provides a mechanism for incorporation of a compensating divalent ion to maintain charge neutrality. It has been hypothesized that ferrous iron is introduced from the melt to provide the divalent ion. White had recently provided some confirmation of a theory by Kittel, Portis, and de Genes on line broadening of the magnetic resonance which occurs at a few gigahertz. Fe++ is strongly coupled to the magnetic lattice and in turn is coupled to the rare earth ion by resonance. The result is an easy path for draining energy from the activated atom to the lattice. From this experience, these three investigators were well sensitized to the degree to which the nature of the host and impurities might need to be controlled to obtain narrow-line radiation from a rare-earth activator and consequently high efficiency. Research Environment The research environment was an important element in this example of MSE. This work was carried out in an industrial laboratory where there was considerable latitude available to the investigators to pursue directions which they believed to be most promising. At the same time, the program was being carried on for an applied purpose. Because of the close relationship between GT&E Laboratory and Sylvania, an operating Company, it was well known in the Laboratory that the TV industry had need for improved colored phosphors for the cathode ray tubes and the nature of the required improvements. As a result, a span of knowledge was achieved which extended from scientific investigation to commercial application. There was an extremely close working interaction between the three individuals of different background and training. In particular, there was a thorough understanding of just what material characteristics were desired and how they should be reflected in the physical properties of the material. This knowledge was not something which was established a priori and left fixed through the life of the project. Rather, the close interaction modified and refined the material characteristics and requirements as the project developed. With respect to the phosphor development, most of the close interaction required had already been accomplished in the garnet work. Yttrium oxide was chosen as a laser-host candidate for several reasons. First, the symmetry of the crystal sites for europium were known to be of low symmetry, that is, the local crystal fields vary with direction. Low symmetry is desirable because it removes the forbiddenness of some important 4f transitions in the rare earths. Second, Y2O3 has a phohon spectrum which couples weakly with the excited levels of the excited europium activator. The weak coupling increases the probability that excitation energy will be emitted
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering optically rather than by transfer to the crystal without optical radiation. Third, Y2O3 had already been grown by Lefever; its optical transmission had been measured by Lefever and Wickersheim and was known to be appropriate. Fourth, Y2O3 accepts trivalent europium at a trivalent site. In previous laser material, the rare earth had replaced a divalent ion giving rise to charge compensation and therefore a crystal defect for every activator resulting in line broadening. Y2O3: Eu was the only material chosen for initial studies. The extensive and detailed knowledge in hand precluded the need for a systematic empirical search through many materials. Results Lefever was able to grow yttrium-oxide single crystals with europium doping. In order to do so, he had to develop a modification of the flame fusion burner, and then in order to prevent cracking of the crystals he devised a technique for protecting the growing crystal with a coating of powder which reduced thermal gradients in the crystal. Both improvements were patentable. When the first sample of europium-activated yttrium-oxide laser crystal was examined in the spectrograph under ultraviolet excitation, it was immediately evident to the eye that this was a superior red phosphor. Few scientists in any field are privileged to make a discovery in such a dramatic and instantaneous way. Because of the commercial interest in cathode luminescence, apparatus was built to measure the light emitted due to electron bombardment. The europium-doped yttrium oxide was found to emit a red line of brightness comparable to the green phosphor (willemite) under identical excitation conditions. The color was redder than the red TV phosphor in use at that time, accepted high beam currents without saturating, and emitted efficiently even at elevated temperatures. It is important to remember that the objective of the program was development of a hardy, sharp-line laser material, a goal that was achieved. However, as a result of understanding the properties of the material and an awareness of technical requirements for improved phosphors, the potential value of Y2O3: Eu was immediately recognized and, because of program flexibility, efforts were channeled into further work on the phosphor aspect of the material. Much work has been done subsequently by others on rare-earth phosphors for TV applications. Such work was stimulated in large part by the Palo Alto GT&E group and later studies at Sylvania and the GT&E Bayside Laboratories. APPENDIX 3J Sintering of Ceramic Oxides, e.g. Lucalox Better understanding of the driving forces, material-transport mechanisms, and kinetics involved in the sintering of ceramic oxides, has been evolving over the past 30 years. The understanding is not yet complete, but knowledge already grained has led to better control of manufacturing processes and improved properties in many ceramic products.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Early theoretical work that contributed to this progress was that of the Russian theoretical physicist, J.Frenkel, who published a paper in 1945 on “Viscous Flow of Crystalline Bodies Under the Action of Surface Tension.” In 1950, a theoretical physicist at Bell Laboratories, C.Herring, published two papers entitled “Effect of Changes of Scale on Sintering Phenomena” and “Diffusional Viscosity of a Polycrystalline Solid.” At approximately the same time, a third theoretical physicist, F.Nabarro at Bristol University in England, made similar studies and today there are frequent references in the ceramic literature to the “Nabarro-Herring diffusion creep model.” Another major contributor at about this time and continuing to this day was the metallurgist, G.C.Kuczynsky at the University of Notre Dame, who developed quantitative models for sintering rates and checked them experimentally with metal and glass macroscopic spheres as well as with fine powders. He was the first to demonstrate experimentally in metallic systems that mass flow can occur by volume diffusion during sintering. The ceramists, W.D.Kingery and M.Berg in 1955, were the first to do so in oxide systems. However, the person who is responsible for the first commercial product to be developed based on fundamental studies of sintering is the ceramist, R.L. Coble. This occurred around 1958 and the product became General Electric’s Lucalox. This is a transparent polycrystalline aluminum oxide of nearly theoretical density containing 0.1 to 0.25 percent of magnesium oxide concentrated at the grain boundaries which acts as a grain-growth inhibitor. Competitive products are now also available from Coors (“Vistal”), Philips, Sudplastik, and Keramik, etc. The principal application is as envelopes for high intensity, sodium vapor lamps. Related development of useful products has been extended to ceramics whose major components are yttrium oxide (G.E.’s Yttralox for infrared-transmitting windows), magnesium aluminate (possibly a superior material for high-intensity lamp envelopes), and magnesium oxide (for potential applications as transparent armor). It should be noted that all of these compositions are relatively simple. The first extension to more complex materials is the development of the lanthanaum-doped lead zirconate titanate systems (first at Sandia) for purely optical applications such as optical switching, optical memories, and image-display devices. APPENDIX 3K Interdisciplinary Research—An Exploration of Public Policy Issues* Roadblocks to Interdisciplinary Research Professionals trained in a given discipline speak a special language, use their own methodologies and scientific tools, and may consider one part of * Library of Congress, Science Policy Research Division, Prepared for Committee on Science and Astronautics, U.S. House of Representatives, 30 October 1970.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering a research problem significantly different in importance from another disciplinary professional. Disciplinary orthodoxy and differences between disciplines are items which have varying import for the concept and conduct of interdisciplinary research in various institutional settings. Possible issues are outlined and described below: 1. Disciplinary Orthodoxy May Produce Strains in Doing Interdisciplinary Research: The most important and obvious difference is the fact that interdisciplinary research brings together persons with different foci of interest as well as different conceptual systems. These systems have potentialities for integration, but they also have strong tendencies toward competition. A second factor is the differential status of the disciplines. This has a bearing on both the formal and the informal structure of the research team and its administration and plays an important part in determining the handling of the decision-making process. Closely related to this are the expectations, stereotypes, and images, overt and covert, that members of one discipline hold regarding persons trained in other fields. These may have an important bearing on interpersonal relationships. Fourth are the differences in methodology among the disciplines, together with subtle and often unrecognized differences in philosophic orientation and ideology, which tend to have some relationship to disciplinary affiliation and to bring members of some disciplines more closely together than those of others. 2. Disciplinary Differences May Produce a Power Hierarchy, Inhibiting the Conduct of Effective Interdisciplinary Research: When interdisciplinary research takes place within complex research organizations, participants are unlikely to have equal formal or informal status, which would produce strains in the relationships…The differences in background, status, skills, and values that participants bring to the group could lead to a struggle for power. This is a serious problem… There are many difficulties in getting these groups to operate smoothly. When there are struggles for power, research activities probably suffer. Relations of power become involved in making decisions about the selection of problems and techniques and the necessary tests for the validity of results. Each kind of specialist approaches the problem area from his own perspective and is often incapable of understanding the approaches of others; he may interpret the arguments of others as devices to win power, and they may be precisely that. Perhaps a “least common denominator” approach comes to be used in the selection of problems and concepts. When this happens, significant theoretical findings are unlikely to be obtained. 3. Uneven Levels of Development of the Disciplines Involving Interdisciplinary Research Make Collaboration Difficult: The readiness of the particular disciplines to cooperate in a specific problem is an important criterion. To be ready for interdisci
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering plinary research, the disciplines involved must have arrived at a stage of sophistication. This cannot be forced. Even within the same discipline there are great differences in the degree of preparedness to collaborate with areas of neighboring disciplines. Interdisciplinary research cannot be undertaken until and unless there is a feeling of need for help from outside one’s own discipline. 4. Interdisciplinary Research Requires Collaboration in Use of Concepts; and Sharing of Work Tasks With Each Disciplinary Researcher Using the Appropriate Research Techniques: An interdisciplinary team is a group of persons who are trained in the use of different tools and concepts, among whom there is an organized division of labor around a common problem, with each member using his own tools, with continuous intercommunication and re-examination of postulates in terms of the limitations provided by the work of the other members, and often with group responsibility for the final product. …For research to be considered interdisciplinary there must be integration of concepts. Without some integration, the situation is similar to having occasional meetings with people in other disciplines, or even to just reading about what they are doing. One is influenced to some extent by this kind of interdisciplinary exposure, but more than this is needed for a project to be considered interdisciplinary. Difficulties due to disciplinary orthodoxy appear to be most severe in academia as brought out clearly by the following discussion related to interdisciplinary research on environmental quality:* It will not be easy to begin new problem-focused programs at universities, despite the need for trained professionals and the seriousness of the problems, Dr. J.Kenneth Hare, Professor of Geography at the University of Toronto and former President of the University of British Columbia, commented on these difficulties in an open letter: “Let me start, then, with the question of environmental studies in a modern University. We all know the conservative quality of such places, where nothing can easily be done for either the first or the last time. The status quo is defended in depth by the vested interest of a large number of able people. Among these interests are those of the traditional departments and the largely analytical disciplines they profess. Also strong are the numerous special institutes and centers that have got started in spite of the resistance of the departments. When we propose to start up a broad spectrum, synthesizing effort like environmental studies we run fulltilt into all these vested interests. * John S.Steinhart and Stacie Cherniack— “The Universities and Environmental Quality—Commitment to Problem Focussed Education.” A Report to the President’s Environmental Quality Council, Office of Science and Technology, September 1969.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering “We also bang ourselves against the clan-spirit of the traditional faculty groupings. Humanists, social scientists, natural scientists, and professionals like lawyers and engineers may fight like cats within the clan, but they close ranks and hitch up their kilts when someone questions their loyalties. Environmental studies have to involve many of these clans, which are not used to combining in the way required. If we suggest, as I do, that some of them—notably the humanists—may be utterly transformed by such combinations we alarm the timid and anger the Tories among them. “But the greatest hazard in our path is inherent in Lyndon Johnson’s acid query “Therefore, what?” which he threw at a group of professors who had just briefed him on the Middle Eastern situation. The political interest in the environment demands proposals for action—on all time scales, from the immediate assault on pollution problems and other festering sores of today, to the long-term reconstruction of society in a better relation with environment. At present we are not equipped to make such proposals. We are not action-oriented and on every campus there is a dead-weight of opinion that regards action-oriented programs as hostile to the academic life… “I must also stress the incompetence of the established disciplines to tackle society’s real problem. What we mean by a discipline is an agreed tested body of method—usually analytical—that we bring to bear on problems of our own choosing. The essence of our thinking is that we cannot tackle problems that don’t fit the competence of our own discipline. It’s true that we constantly try to enlarge that competence. Confronted with a new problem, we spare no effort to improve our methods. But if we don’t succeed, we don’t tackle the problem, and we tend to condemn colleagues who try.” Lessons for Interdisciplinary Research As discussed earlier the coupling between disciplines can range from loose to tight, i.e., Research workers in different disciplines make a parallel study of various aspects of a single problem and submit separate reports; thanks to this juxtaposition, it is hoped that further light will be shed on the problem under consideration. —Multidisciplinary, loosely-coupled mode. Research workers in different disciplines tackle the same problem simultaneously and synchronize their efforts, exchange findings, and draft separate reports, which will be prefaced by a joint report attempting to integrate all these findings; in this instance what is sought is some degree of convergence, if not through the investigation, then at least in the comparison of findings. Research workers tackle a single problem together, compare their working hypotheses, make a critical assessment of each other’s methods and draft a final joint report. —Interdisciplinary, tightly-coupled mode.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering There appear to be certain characteristics of close collaboration: From the standpoint of the research problem Focus on a single clearly defined problem. Problem definition determined by demands of problem rather than by disciplinary or individual interests. Formulation of the research problem in such a way that all participants can contribute to its solution. Existence of collaborative potential as a result of previous work on the problem by more than one discipline. From the standpoint of theory Acceptance of a unified over-all theory. Acceptance of a common set of hypotheses and assumptions. Agreement on definition of common concepts. Agreement on operational definitions. From the standpoint of methodology Utilization of resources of all relevant disciplines in exploring possible methodologies. Team agreement on most appropriate methodology, including research procedures, relevant variables to be measured or controlled, and methods to be used. From the standpoint of group functioning Team members selected on basis of their ability to contribute to research objectives. Approximate equality of influence exerted by the representatives of one discipline on another. Acceptance of leadership regardless of disciplines from which leader and researchers come. Flexibility of roles. Development and use of a common language. Free communication among all team members.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Free interchange of information about the research, with mechanics for facilitating such interchange when necessary. Sharing of suggestions, ideas, and data among members from different disciplines. Participation of all team members in joint planning of each step of the research. Reciprocal teaching and learning among team members—a continuous learning process. Problem-centered rather than discipline- or individual-centered team activity. Minimum influence on research plans and operations exerted from outside the research team. Willingness of participants to subordinate own methods and interests to achieve project aims. Publication of research reports by the group as a whole, rather than by individual members. Some of these manifestations of close collaboration will be found to some degree in any project. A few projects where the collaboration is very close appear to contain most of them. Strengths and Weaknesses in Interdisciplinary Research The interdisciplinary mode is not a universal panacea. While it is essential for many achievements in complex technology, it has its weaknesses as well as its strengths. Some of these are listed: Weaknesses and dangers; As teams become larger, originality is apt to be stifled. Individual freedom is restricted through the coordination and organization necessary in group research. Interpersonal difficulties are more likely on larger teams. Interdisciplinary team research can be expensive. When an interdisciplinary team is utilized unnecessarily, resources are spent that could be used more effectively.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Closely related to the large investment of money and personnel often required in interdisciplinary research are the pressures for demonstrable results. Interdisciplinary research requires more time in communication, time which might be spent more profitably on the research itself. As teams become larger, more time is needed for administration. The circumstances under which interdisciplinary research is conducted may be distracting. On the positive side: A team of investigators can tackle larger problems than they can individually. Interdisciplinary research generally gives a broader outlook, opens new horizons, and stimulates more people than individual research. The collaborative experience of interdisciplinary research is more than an additive process, the end result more than the sum total of what each of the disciplines could have achieved independently. One of the most important aspects of interdisciplinary work is the fruitfulness of the challenges from one part of the group in stimulating others to mobilize their resources. Interdisciplinary research broadens understanding through having to translate concepts and approaches between disciplines. Interdisciplinary research illuminates borderline areas and enables one to examine problems lying between disciplines that had previously been ignored by the single disciplines. Interdisciplinary work is advocated enthusiastically by some because of the hope and belief that, by requiring reformulation in translatable terms, it will result in an integrated set of constructs and may even produce a new theoretical framework and a new discipline. Interdisciplinary research facilitates the creation of situations that may result in new and productive combinations. An interdisciplinary approach is valuable in contributing specific techniques and skills from various disciplines to each other. The use of specialists in different fields provides a short cut to information.
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Materials and Man’s Needs Materials Science and Engineering: Volume 1 The History, Scope, and Nature of Materials Science and Engineering Interdisciplinary research can be a valuable learning experience that can be utilized effectively for training purposes. Many of the pitfalls and problems of interdisciplinary team research can be minimized or avoided by recognizing them in advance and guarding against them. Interdisciplinary research should never be conducted for the sake of being interdisciplinary. But many of the complex problems facing the investigator require the concerted attack of several disciplines. When used appropriately, the values of interdisciplinary research far outweigh its disadvantages and it should make increasing contributions toward understanding and solving some of the important problems of today.
Representative terms from entire chapter: