bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer-Based Modeling in Materials Science
Authors: Dodson Brian W. 
Published: August 2016

In principle, all materials science problems are easy to solve. One describes the system using quantum mechanical wave functions, solves the Schrödinger equation using the appropriate boundary conditions, and converts the result into the microscopic and/or macroscopic observables of interest. Unfortunately, carrying out this program is usually many orders of magnitude too difficult. As a result, various approximations and simplifications are introduced to obtain descriptions having the minimum complexity to describe a given class of phenomena. (A simple example is the treatment of lattice vibrations in solids using a ball-and-spring description.) Such a simplified description is called a model.Due to the complexity of virtually all problems concerning materials, it is fair to say that the use of models is ubiquitous in materials science. In many situations, however, models sufficiently complex to describe the phenomena of interest are too difficult to be solved analytically. The computer has played an essential role in obtaining descriptions of material behavior based on such complex models. Traditionally, the amount of computer power available has restricted such models to idealized problems, which are then used as prototypes for the actual problems. Recently, however, the role of modeling has expanded to include treatment of specific and realistic materials problems. Development of these new classes of applications has been driven by the tremendous increase in computer power which has become available to the average researcher. The increase in computer capacity has catalyzed implementation of more realistic descriptions of material response.
EXAFS Studies of Semiconductor Microstructure
Authors: Bunker Bruce A. 
Published: August 2016

Extended X-Ray Absorption Fine Structure (EXAFS) is a technique capable of probing local structure in condensed- matter systems, determining distances, coordination numbers, and species of atoms near an x-ray excited atom. Further, this information is obtained separately for each constituent atomic species. EXAFS can be applied equally well to crystals, alloys, or even systems having no long-range order such as liquids, gases, and amorphous materials.Here we review EXAFS spectroscopy and its use in studying semiconductors. First, we show EXAFS in the study of impurities to determine the local environment of Fe implanted in Si. Second, we show how EXAFS can be used to determine local structural distortion in diluted magnetic semiconductors. We next demonstrate that EXAFS can determine the nature of the phase transition in ferroelectric Pb1-x Gex Te, where the transition is revealed to have an order-disorder character in contrast to GeTe where the transition is purely displacive. The theme of these examples is that EXAFS can determine the relative positions of atoms in condensed matter and that the short-range order as determinedn by EXAFS often differs from the long-range order or theoretical expectations.In the EXAFS technique, one measures the x-ray absorption coefficient as a function of x-ray energy. The absorption spectrum shows a number of x-ray edges corresponding to the threshold of excitation of core electrons from the sample's various atomic species. At energies above each of these edges, oscillations in the absorption coefficient are due to backscattering of the photoelectron from the neighboring atoms.
Materials Science of Polymers
Authors: Thomas Edwin L. 
Published: August 2016

This issue of the MRS BULLETIN is devoted to a class of materials undergoing a transition from a period in which they were viewed primarily as cheap substitutes for other materials into a new period where polymers are seen as high tech, value-added materials in their own right. The six articles included here focus on a portion of the wide range of topical areas concurrently at the frontiers of polymer materials science.Polymers are molecules consisting of a large number of units (mers) covalently connected to form macromolecules of very high molar mass (upwards of 106). Polymer chemists have learned how to make an almost endless variety of highly complex yet well- defined macromolecules utilizing a wide variety of monomers. Once polymer physicists and materials scientists depended on industry to provide samples (which were far from model materials to work on). Today, significant improvements in chemical synthesis and a growing collaborative effort between polymer chemists and materials scientists have resulted in the availability of extremely well-defined materials (molecular weight distribution, composition, sequence of monomer types along the chain backbone, stereochemistry of these units and overall molecular architecture, e.g., branching vs. linear) for the attainment of novel properties and the investigation of structure-property relationships. Given the sophistication of current polymer synthesis, it is now possible to test structure-property hypotheses systematically and to rationally design macromolecules to form specified microstructures and provide desirable physical properties.The typical mental image conjured by the word polymer is an entangled mass of cooked spaghetti. This is in fact very appropriate for the class of flexible chain polymers in the noncrystalline state. The pioneering work of P.J. Flory in elucidating the nature of such materials, e.g., polymer melts and amorphous polymers above their glass transition temperature, made crucial use of the essentially Gaussian behavior of the end-to-end distance vector of a flexible chain polymer in the condensed state.
Observation of Defects in Crystalline Polymers by HREM
Authors: Martin David C. , Thomas Edwin L. 
Published: August 2016

The importance of crystalline defects in determining the macroscopic properties of metals, ceramics, and semiconductors is well known. Crystalline polymers also exhibit defect structures, but analyzing of defects in polymers is more difficult because the topological connectivity of the covalently bonded polymer chains means that solid polymers typically exhibit larger amounts and types of disorder than crystals of low molar mass molecules. Imaging is also more complex because of the inherent electron beam sensitivity of these typically organic materials. Recent developments in synthesis and processing have made it possible to achieve very highly ordered polymer systems. Defects in these materials will undoubtedly play a critical role in determining mechanical properties, optical behavior, and transport properties such as electrical conductivity.Direct imaging techniques are particularly important for studying defects because the typically low volume fraction of defects in the crystalline phase makes diffraction experiments difficult if not impossible. Also, in diffraction information about the relative orientation of individual crystallites is lost. It is not surprising, then, that High Resolution Electron Microscopy (HREM) has become extremely important for studying defects in inorganic materials systems. HREM studies of polymers have been limited by the beam sensitivity of organic compounds. Recently, however, high voltage instruments, low dose techniques, and image processing procedures have made it possible to obtain lattice images in systems with beam sensitivities as low as 0.003 C/cm2 (2 e-/A2).This review discusses the nature of defects in crystalline polymer systems and illustrates how proper application of high resolution imaging techniques promises to answer questions in polymer morphology.
Diffusion in Polymer Alloy Melts
Authors: Green Peter F. , Kramer Edward J. 
Published: August 2016

AbstractDiffusion in polymer alloys or blends can be used to extract information on the fundamentals of the dynamics of individual polymer chains in the melt and the thermodynamics of the interaction between unlike polymer species. The dynamics of individual chains are available from measurements of the tracer diffusion coefficients, D*, of the various species while the thermodynamics of interaction, represented by the Flory parameter, x, can be obtained from measurements of the mutual diffusion or interdiffusion coefficient, D. We will show that these quantities can be measured conveniently by forward recoil spectrometry (FRES), an ion beam analysis technique that can determine the concentration versus depth profile of polymers labeled with deuterium diffusing into unlabeled polymer matrices.For high enough molecular weight of the matrix, the tracer diffusion coefficient of both species in the blend scale as D0N−2, where N is the number of monomer segments per diffusing chain; the constant D0, however, can differ by more than 104 for chemically different molecules diffusing in the same blend, suggesting that conventional concepts of chain dynamics in melts, such as monomer friction coefficients, need to be reexamined. The mutual diffusion coefficient is controlled by the faster species in the blend (the one with the larger D*N product) in agreement with what was found in metallic alloys (but in sharp disagreement with the “slow” theory of mutual diffusion which predicts that the slower species controls). Since the combinatorial (ideal) entropy of mixing of polymers is low, the thermodynamic driving force for diffusion is dominated by enthalpy and excess entropy of mixing (x) to a degree unprecedented for atomic or small molecule systems. This means that one can observe not only a thermodynamic “slowing down” of diffusion when x becomes positive as one nears the spinodal but also a large thermodynamic “speeding up” of diffusion when x is negative. Measurements of mutual diffusion turn out to be one of the most sensitive methods available for measuring x.
Enthusiasms and Realities in Advanced Materials
Authors: Gilman J.J. 
Published: August 2016

Tom Read arrived at Columbia University on the same day that I did in 1948. He was a new professor in the School of Mines and I was a new graduate student. He was more than just a new professor. He was exceptional for that time. His father, T.T. Read, had been famous as an archeological metallurgist and professor at Columbia when the School of Mines was the premier school of its kind in the country. A measure of its eminence is that Irving Langmuir chose to study there rather than in a standard chemistry department.The younger Tom Read had studied physics at Columbia under Shirley Quimby, one of the few solid-state physics professors of the time (pre-transistor). After graduation he worked at the Frankford Arsenal and at the Westinghouse Research Laboratories, where he and Frederick Seitz wrote their definitive review of the mechanisms of the plastic deformation of solids.When he came back to Columbia as a professor, Tom Read's physics background made him almost unique among metallurgy professors. And, he had the zeal of a crusader — he was determined to teach fundamental knowledge rather than recipes. His techniques were often novel.For example, one semester we were to learn about ferromagnetism. But he had trouble finding a good American text, so he announced that we would study both ferromagnetism and German using the famous book by Becker and Doring called Ferromagnetisms. As a result, I have never forgotten the essentials of ferromagnetism.
Growth and Fractal Structure of Ceramic Precursors
Authors: Keefer Keith D. 
Published: August 2016

Ceramic precursors are the chemical constituents of ceramic materials in a form in which they can be manipulated and shaped prior to processing to form a dense body. Generally these precursors are finely ground crystalline materials such as oxides or clays. Recently, however, much effort has focused on preparing precursors by chemical rather than mechanical means. The goal is to prepare purer, more homogeneous, and more reactive precursors than mixed crystalline powders. A wide variety of chemical processes have been devised to grow ceramic precursors, including powders formed by precipitation reactions, gels formed by hydrolysis and condensation reactions, and gas phase pyrolysis, to name just a few. Due to the random nature of the growth processes, these precursors often have structures wholly unlike their mechanically derived counterparts on both an atomic and a “macromolecular” scale. Random growth and structure and the effect of these structures on the subsequent processing of ceramics is an area of growing interest.Random structures are inherently more difficult to describe and study than are the ordered, periodic structures of crystals. With the exception of a few special cases, such as random walk polymers, little of a quantitative nature could be said about them until the development of fractal geometry and the accompanying realization that the structures which result from many random growth processes are, in fact, fractal.
Whisker-Reinforced Ceramic Matrix Composites
Authors: Homeny J. , Vaughn W.L. 
Published: August 2016

Whisker-reinforced ceramic matrix composites have recently received a great deal of attention for applications as high temperature structural materials in, for example, advanced heat engines and high temperature energy conversion systems. For applications requiring mechanical reliability, the improvements that can be realized in fracture strength and fracture toughness are of great interest. Of particular importance for optimizing the mechanical reliability of these composites is the effect of the whisker/matrix interfacial characteristics on the strengthening and toughening mechanisms. Whisker reinforcements are primarily utilized to prevent catastrophic brittle failure by providing processes that dissipate energy during crack propagation. The degree of energy dissipation depends on the nature of the whisker/matrix interface, which can be controlled largely by the matrix chemistry, the whisker surface chemistry, and the processing parameters.It is generally believed that a strong interfacial bond results in a composite exhibiting brittle behavior. These composites usually have good fracture strengths but low fracture toughnesses. If the interfacial bond is weak, the composite will not fail in a catastrophic manner due to the activation of various energy dissipation processes. These latter composites tend to have high fracture toughnesses and low fracture strengths. Generally, the interface should be strong enough to transfer the load from the matrix to the whiskers, but weak enough to fail preferentially prior to failure. Thus, local damage occurs without catastrophic failure. It is therefore necessary to control the interfacial chemistry and bonding in order to optimize the overall mechanical performance of the composites.
Up Close: Immobilization of High-Level Nuclear Waste at the Savannah River Plant
Authors: Plodinec M.J. 
Published: August 2016

At the Savannah River Plant (SRP), construction of what will be the world's largest solidification facility for nuclear waste has been under way since 1983. Beginning in 1990, the nearly 100 million liters of liquid high-level nuclear waste now stored on the site will be made into a durable borosilicate glass in this Defense Waste Processing Facility (DWPF).In developing a slurry-fed melting process for the DWPF, we made advances in understanding both glass processing and glass durability. This article focuses on what we learned and what further advances are likely to be made.Generally speaking, the goal of any glass technologist is to make a good glass and to make it well. In the glass industry a good product is whatever people will buy. To make it well means, above all, to make the product as economically as possible. Thus, the commercial glass technologist will control the composition of the melter feed material very closely to ensure that only the components necessary for glass performance are included, and in the least expensive form possible. The commercial glass technologist may also tolerate low yields or specify several stages of post-melt processing if it is necessary to produce a product to demanding specifications.To the nuclear waste glass technologist, however, a good product is one which will be stable in geologic environments for millions of years.
Up Close: Innovative Materials Development, Preparation, and Testing at Ames Laboratory
Authors: David V. 
Published: August 2016

Ames Laboratory, operated by Iowa State University for the U.S. Department of Energy (DOE), was established in 1947 to conduct basic research with particular emphasis on new materials.Like the other national laboratories, Ames Laboratory was created in consequence of contributions made to the Manhattan Project. It was in Ames, early in World War II, that two college professors and a group of graduate students resolved a problem that had proved intractable to industry. Within months of Pearl Harbor, Frank Spedding and Harley Wilhelm devised a practical method for the large-scale production of pure uranium. While teaching industry how to do it, Ames furnished 1,000 tons of uranium for the Manhattan Project.In the postwar years, processes were developed at Ames Laboratory for the production of metals such thorium, vanadium, and chromium that were considered exotic at the time. The processes were adopted by industry and most are still in use today.Based on Spedding's earlier research, a pilot plant was built at Ames that produced 100-pound batches of the 15 rare earth elements in unprecedented purity. To tap a research source of 15 new metals, for these elements were hardly known before, would have been a triumph; but because each one in this family of the “fraternal fifteen” differs from its neighbor by a single electron, the research prospect revealed was virtually unbounded.
Materials Education—A Renewal
Authors: Liedl G.L. 
Published: August 2016

Materials have always been interwoven throughout the very fabric of man's history. The present reawakening to the value and importance of materials, however, has become a dominant factor in manufacturing, national security, international competition and trade, consumer products (quality and reliability), and even education. Other renewals of interest have occurred over the centuries, probably beginning with the formation of the first pot from clay. These renewals were associated with discoveries such as copper, iron, and the transistor. However, in the past 40 years the base for renewed interest has broadened.A true coupling of science and engineering into the field of materials was probably initiated in the 1940s and 1950s. Emphasis at that time was on metals and the “new” semiconductors, with an interest that incubated and grew to where their central position in national economies and man's daily life was recognized. In 1970 the National Academy of Sciences appointed a committee to conduct a comprehensive analysis and assessment of the field of “materials science and engineering.” The COSMAT report which resulted from that study had a dramatic impact on the field and has been a frame of reference for the past 17 years. These years have seen a virtual explosion of ideas, processes, and materials in the field.
Views on a Comprehensive Materials Science and Engineering Education Program
Authors: Abbaschian G.J. , Hollow P.H. 
Published: August 2016

Educational programs in materials science and engineering (MSE) departments must be comprehensive, addressing the main theme of structure-property-processing-application relationships in all materials. In addition, the programs must be dynamic in order to improve materials according to the requirements of our society. Dynamic materials limits and societal needs require the materials field to change constantly over relatively short times. In this respect, education in MSE differs substantially from that in traditional departments such as chemistry, physics, mechanical and chemical engineering, and even the more narrow fields of metallurgical, ceramics and polymer engineering.It may be argued that all departments, scientific or engineering, are dynamic because they are constantly changing and maturing. Obviously, though, departments close to maturity change less rapidly than young departments. MSE, a young department, is changing rapidly from both steady evolutionary growth as well as quantum changes in scope (e.g., electronic materials). In fact, advances in MSE have necessitated a redefinition of scope for other fields. A good example is the field of computers and communication, which is directly tied to the growth, processing, and characterization of high purity semiconductor materials. The opposite is true as well (e.g., high transition temperature superconducting materials). The old adage of “a good design will be limited by the materials available” is true. As such, MSE plays a dual role—simultaneously advancing and impeding progress in other areas of science and engineering.
Views on an Electronic Materials Education
Authors: Chin G.Y. 
Published: August 2016

Electronic materials constitutes a sub-field of materials. Therefore the issues raised concerning an electronic materials education must necessarily be viewed in the broader context of a comprehensive materials education. Yet electronic materials do differ from other subfields in several ways.First, unlike the traditional metals, ceramics and polymers, which are defined primarily by chemical composition, electronic materials are defined by functions, i.e., they are used in devices that provide electronic functions. As such, electronic materials encompass metals, ceramics, and polymers as well as semiconductors.Second, workers employed in electronic materials industries come from a diverse set of academic disciplines. They are physicists, chemists, chemical engineers, electrical engineers, and mechanical engineers as well as metallurgists, ceramists, and materials science and engineering (MSE) graduates. Thus activities in the electronic materials industries represent an extreme case of interdisciplinary activity which is characteristic of MSE.Third, the electronic materials industries play a dominant role in world economy today and the technology is changing at a dizzying pace. Thus issues in education in electronic materials become more challenging than other subfields and may require fresh and nontraditional approaches.When speaking of electronic materials, one generally thinks of semiconductors, such as silicon and more recently gallium arsenide, that are used in microelectronic devices.
Up Close: Materials Research at Carnegie Mellon
Authors: Mahajan S. , Berry G.C. 
Published: August 2016

Materials research is a long-standing tradition at Carnegie Mellon. Since its inception as Carnegie Technical Schools in 1906, the metallurgy program has flourished on the campus. Evolving from a single department involved in metals research formed in 1906, leading-edge, interdisciplinary materials research has grown considerably, with materials-related research now carried out in many departments. These include Chemical Engineering, Chemistry, Civil Engineering, Electrical and Computer Engineering (ECE), Mathematics, Mechanical Engineering, Physics, and Mellon Institute (an affiliate of the University), and, of course, Metallurgical Engineering and Materials Science (MEMS). It is beyond the scope of this article to cover every aspect of materials-related research at Carnegie Mellon. Consequently, we have decided to concentrate on materials and topics of particular interest to MRS members.The current research pertaining to materials at Carnegie Mellon can be broadly classified by material type into three categories: metals and alloys, polymers, and electronic and magnetic materials.The major thrust on research in metals and alloys is in MEMS. In addition, there are a number of complementary efforts in Chemical Engineering and Mechanical Engineering. For example, Prof. Sides of Chemical Engineering is evaluating electrolytic extraction of aluminum from its ores, while Professors Prinz, Sinclair, Steif, Swedlow, and Wright of Mechanical Engineering are examining the macroscopic flow behavior of metals and alloys and its relevance in manufacturing engineering. Prof. Prinz is also interested in vibratory compaction of metal powders, both from experimental and modeling points of view.