Materials and Man's Needs Materials Science and Engineering -- Volume II, The Needs, Priorities, and Opportunities for Materials Research (1975) / Chapter Skim
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6. Opportunities in Materials Research
6. Opportunities in Materials Research
Pages 305-356
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From page 305... ...
As part of its work, this Task Force analyzed and summarized the large number of letters that were received in reply to invitations sent out by COSMAT to scientists and engineers in the materials field seeking their opinions about materials research opportunities. Most of these scientists and engineers were reached through the professional societies.
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From page 306... ...
Society of Automotive Engineers Society for Experimental Stress Analysis Society of Manufacturing Engineers Society of Plastics Engineers The Gordon Research Conferences (1972) through which solicitations were made included: Analytical Chemistry Atomic and Molecular Interactions Chemistry Chemistry Chemistry Chemistry Chemistry Chemistry Chemistry Chemistry Corrosion Crystal Growth Elastomers ~ Environmental Sciences: Air Geochemistry Inorganic Chemistry Ion Exchange Laser Interactions with Matter Natural Products Organic Photochemistry Polymers Science of Adhesion Separation and Purification Technology of Biomaterials Thin Films and Metallurgy of Semiconductors of Molten Salts and Physics of Cellular Materials and Physics and Physics and Physics of Liquids and Physics of Paper and Physics of Solids of Coatings and Films of Inorganic Phosphors
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From page 307... ...
The alternative to understanding at the microstructural and atom-electron level is to rely primarily on empirical methods which, though often expedient and dramatically successful, provide few guides to whether further improvement is possible. Despite the many impressive achievements of materials research there is the awareness that only the surface of scientific capability has been scratched.
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From page 308... ...
As a result, such phenomena as the Gunn effect and laser action in gallium arsenide and light emission from junctions in gallium phosphide are all understandable in terms of the detailed band structures of these materials. In fact, so well accepted have band structure calculations become that the modern, sophisticated solid state electrical engineer, trying to develop a more efficient Gunn effect oscillator, or a laser, or a light emitting diode,
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From page 309... ...
In the area of mechanical properties, an improved understanding of the relation of crystal structure and bonding behavior to crystal plasticity, as well as a refinement in the treatment of fracture mechanics coupled with microstructures, could lead to ceramics which are strong and tough.
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From page 310... ...
(c) Basic studies of novel processing techniques are of paramount importance.
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From page 311... ...
Studies of the behavior of 3d and 4f ions in glassy hosts has produced structural information as well as an understanding of the physics of optical absorption and fluorescence in glassy solids. But in view of the increasing role expected for glass in electronic applications such as optical communications, there is a need for greatly improved understanding of the spectroscopic properties of various ions in various glassy hosts.
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From page 312... ...
The most promising lines for progress for these materials, however, seem not to lie so much in broad "alloy mapping" programs as in devising more efficient and economical processing techniques, as discussed in a later section. These processing techniques are to be based on knowledge of material properties and behavior gathered over the last several decades.
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From page 313... ...
In alloy development for still higher temperature service, there is an attractive possibility for new class of alloys based on the refractory metals. Major problems are similar to those for superalloys (protective coatings, optimum alloying and processing)
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From page 314... ...
In spite of the complexity of this subject, opportunities for fairly well-defined materials research on contact materials do exist. The first such area is that of tarnish film formation.
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From page 315... ...
These areas, however, are judged to be of lesser overall importance than those of arc erosion and tarnish film formation. Plastics Substances, such as cotton, wool, and silk have been known to mankind longer than recorded history.
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From page 316... ...
There is a host of polymers that are glassy at ordinary temperatures. As with the inorganic glasses, many of these materials are valuable for their optical properties.
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From page 317... ...
Protectants function as light screens, ultraviolet absorbers or deactivators. At elevated temperatures the polyolefins, natural rubber and cellulose materials are stabilized by antioxidants that destroy hydroperoxides and inhibit radical chain reactions.
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From page 318... ...
Other examples of potential uses for composites are in copper-clad superconducting filaments for increased critical current carrying capacity, fiber reinforced or dispersion strengthened copper for combination of high strength and electrical conductivity, fiber reinforced magnets for creepresistant high temperature rotors, and the possibilities of using directionallysolidified eutectics for magnetoresistance, electromagnetic and radiation detec tor applications .
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From page 319... ...
The following areas for materials research are noted. Cements Basic research on the physico-chemical properties as a function of composition will enable the custom development of cements designed for specific functions.
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From page 320... ...
materials. The central position in electronic materials is occupied by: Semiconductors Semiconductors are the heart of solid state electronics.
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From page 321... ...
Much work remains to be done on these materials, both on their physical and chemical properties. Furthermore, the techniques for the controlled preparation of single crystals is still rather primitive.
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From page 322... ...
to be exploited, so that economical processing techniques can be developed for fabricating the materials into useful devices. Permanent magnets - Permanent magnets of alloys of cobalt with rare earths have yielded energy products and coercive forces superior to those available in the past.
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From page 323... ...
As yet the magnitude of these effects cannot be predicted from a knowledge of composition and crystal structure. Amorphous magnetic materials - alloys such as Fe-P-C have been prepared in the amorphous state and shown to be ferromagnetic.
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From page 324... ...
Research in chemical additives and preparative techniques, in net flux systems for liquid phase epitaxy film growth and control of chemical vapor deposition processes are expected to provide some of the needed technological advances. Improvement in our detailed understanding of dynamic processes such as the physics of domain wall motion can be expected to increase markedly the technological properties of magnetic materials.
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From page 325... ...
are needed. These improvements can be expected to flow from an understanding of the hydrodynamics of crystal growth, phase equilibria and the connection between the physical chemistry of growth and the physical and chemical perfection of grown materials.
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From page 326... ...
These excited state dipoles contribute to a macroscopic polarization change only in pyroelectric crystals, and intense electrical pulses as short as 6 picoseconds have been generated with the mechanism using picosecond optical pulse evaluation. At the present time measurements of excited state dipole moments and nonradiative relaxation times have been made only for a few transition metal ions in LiNbO3 and LiTaO but these experiments may be extended to any absorbing center (ionic or molecular, electronic or vibrational)
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From page 327... ...
Its crystal structure is curious in that it has both tetrahedrally- and octahedrally-coordinated Ag sites, and is of significantly lower density than the tetrahedral AgI structure. It is this anomalous low density, combined with tetrahedral cation vacancies with shared faces that is typical of all AgI-type conductors.
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From page 328... ...
Liquid Crystals The investigation of the properties and uses of liquid crystalline materials has encountered an explosive revival during the last decade and particularly during the last five years because of their intriguing device applications and the ready availability of room temperature nematic liquid crystals ¢Schiff bases)
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From page 329... ...
Typical research topics in this area include: (i) Surface Architecture - This also includes surface energy and changes which can occur as the result of contact with body fluids; for example, development of monolayers of lipids, proteins, etc.
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From page 330... ...
Although most innovative processing techniques are primarily developed for specific materials and applications, basic research in this area should spawn new approaches. Examples from four major categories of processing are illustrated below.
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From page 331... ...
It must be noted that much of our current materials processing, particularly process metallurgy, suffers from a lack of real-time data acquisition and feedback control and that such control will be a necessary feature of new processes to optimally exploit the research results derived from the modeling and experimental process analysis indicated. The discovery of new processes involving novel chemistry provides a wide-ranging field of research.
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From page 332... ...
Casting Melt spinning - This relatively new technique of casting metal filaments by extruding a liquid jet through a fine orifice may lead to high-speed production of fine wires in a single step. The challenges in this area include hydrodynamics of the liquid jet, chemistry of surface films developed to stabilize the jet, and casting defects, solid state reactions and resultant properties associated with high cooling rates.
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From page 333... ...
Problems of die material ~ or high temperature operation need to be met, and ways may need to be developed to alter the micros tructure to inhibit superplas tic f low during service. Jo ining and Finishing In joining techniques such as diffusion bonding used in fabricating metal matrix composite materials, basic studies of adhesion as influenced by solid state reactions in the presence of heat and pressure, surface films, etc.
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From page 334... ...
, metastable crystal structures (even simple cubic) , and the first metallic glasses, in which crystallization itself is by-passed.
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From page 335... ...
It should be possible to extend these techniques to analyses of deformation of composites, thixocasting, injection molding, nucleation mechanisms in crystal growth, and the terminal phases of processes such as dynamic superplasticity and splat cooling. In contrast to the finite-element methods, the particle-in-cell techniques show their forte in modeling large and complex material displacements and various mixing or transport mechanisms' including turbulent flow fields.
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From page 336... ...
As in the past, future innovation in electronic materials will depend heavily on furthering the art-and science of crystal growth. The search for new crystals with novel properties often occurs beyond the reaches of the predictive power of physical theory and has to rely heavily on intuitive interpolation and extrapolation of trends in the periodic table, atom sizes, crystal structures, bond polarizabilities, etc.
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From page 337... ...
A wide range of crystal growth and preparation techniques is now available: pulling from the melt, hydrothermal growth from hot aqueous solutions, flux growth from other solutions, growth directly from the melt, epitaxial methods for thin films, chemical vapor deposition, ion implantation, etc. Each method offers advantages and disadvantages for a given material, but in all cases the trend is toward greater control over the resulting crystal composition, purity, and homogeneity.
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From page 338... ...
This neglect has produced a significant knowledge gap in design, fabrication and quality control areas where these materials are utilized. Nowhere in electronic materials are such exacting demands made on crystal quality and defect control as in integrated circuit technology.
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From page 339... ...
The hybrid approach to integrated electronics offers an easy vehicle for the introducing and interfacing of optical devices with other more conventional electronic elements. Major opportunities for long term materials research lie in this field of functional electronics.
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From page 340... ...
In the past, nondestructive testing generally meant testing only for geometric size, defects, and some mechanical properties, but it should be interpreted much more broadly -- testing for composition, microstructure, and the full range of physical properties. Basic research in solid-state physics and chemistry, aimed at detecting and understanding certain properties of materials, has spawned many of the modern techniques for nondestructive testing.
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From page 341... ...
There is hope that the same principles can be applied to shorter wavelength lasers such as the 3371A N2 laser or even the recent laser which has operated down to 1161A. With such actual and anticipated developments comes the need for solid materials for optical elements; windows, mirrors' lenses and nonlinear optical elements.
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From page 342... ...
Present research in materials science is developing knowledge concerning the interaction of lasers with materials. Areas such as laser-induced shock strengthening of metal surfaces, laser welding, and machining of ceramics and metals with lasers will benefit from such materials research.
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From page 343... ...
Dynamic Behavior of Defects When dislocations first were directly observed by transmission electron microscopy in the mid 1950 r S ~ great impetus was glyen to both experimental and theoretical study of dislocations in both single crystals and polycrystalline materials of commercial interest. As a result, the treatment of plastic deformation of crystalline materials by dislocation motion and interactions has been greatly facilitated.
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From page 344... ...
. There is little doubt but what high temperature structural strength is directly related to the stability of the three-dimensional network of area type defects, which can be facilitated by solute and particle pinning.
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From page 345... ...
the relevancy of continuum mechanics, as opposed to atomistic analyses of crack propagation, C5) the effect of defect structure and of chemical composition and distribution at the macro and micro layers in the metal, C6)
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From page 346... ...
Research must also determine the effect of alloy composition on film composition and microstructure and then relate these to the problems of the transition from internal to external oxidation, the adhesion and the spelling or corrosion films, the resistance to breakdown of these films, and the mechanism of self healing. More specifically, the following must be studied: the crystallography of the films and the factors that determine crystal size and transitions between the crystalline and amorphous states; the defect structure, the conductivity of and diffusivities within the films and their effect on film growth kinetics; the mechanical properties of corrosion films; the thermodynamics and kinetics of the transformation from one corrosion product to another during high temperature gaseous corrosion of complex alloys.
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From page 347... ...
Microscopic Understanding of Phase Transitions Though the equilibrium crystal structure can be calculated for only a very few simple materials the fundamental ability to predict the abrupt changes in crystal structure that occur as the temperature, pressure or composition is varied is in ayen worse shape. And the most dramatic phase transition of all, namely melting' is still vary much a mystery from a fundamental point of your.
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From page 348... ...
a true microscopic understanding of phase transition mechanisms is lacking -- a truly important challenge for materials research and solid state physics in particular. In martensitic transformations, for example, there is a large body of evidence for preexisting embryos providing sites for nucleation.
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From page 349... ...
More consideration should be given to systems with simple structured and/or inert hosts, such as helium and the other rare gas solids, so as to provide theoretically tractable, experimentally accessible model systems for impurity effects. The possibility of long-range order (e.g.
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From page 350... ...
The effects of lower dimensionality on collective modes, electron and heat transport must be understood. Particularly intriguing is the effect of a microscopic upper limit to the correlation length in certain directions on the critical properties near phase transitions in lower dimensional systems.
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From page 351... ...
The statistical mechanics of this situation, extending with three dimensions over several atomic layers, needs considerable development. While the roughness of a surface on the atomic scale has a major impact on adsorption, surface diffusion and crystal growth processes,very little is yet known about the details of the role of surface roughness in these processes.
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From page 352... ...
The trend towards miniaturization in electronics resulting from economic, reliability and high frequency considerations points towards growing importance of surfaces. The concepts of miniaturization are best embodied in the technology of large scale integrated circuits where surface and grain boundary diffusion often dominate over bulk diffusion processes.
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From page 353... ...
Yet to put the structure-property relationship of polymeric materials on a firm, fundamental, quantitative base~remains a prime challenge to materials research, akin in complexity to the parallel challenge posed by amorphous inorganic materials, perhaps more so. Collective Behavior Perhaps the single most fruitful concept in solid state-physics has been that of the collective mode or elementary '~citation; this concept has permitted the handling of complex many C10 ~ body systems in terms of a very few degrees of freedom.
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From page 354... ...
phase of a spin system. The collective modes of the liquid crystal state are under present investigation and should illuminate that important intermediate regime between welldeveloped long range order (crystal)
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From page 355... ...
Scattering, absorption and fluorescence experiments which have proved so valuable in guiding theories of materials at equilibrium, should soon begin to do the same for nonequilibrium systems. A foretaste of what might be in store is the use of these fast laser pulses for studying shortlived excited states of radicals and molecules with consequent insights into the mechanisms of chemical reactions.
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