bluuebunny/crossref_metadata_2025 huggingface dataset:
Frontiers in β″-Alumina Research
Authors: Dunn Bruce , Farrington Gregory C. , Thomas John O.
Published: August 2016

Beta and β″-alumina are remarkable solid electrolytes whose study has been a principal theme in the field of solid state ionics ever since Yao and Kummer first reported the exceptionally high conductivity of sodium β-alumina in 1967. The unusual properties of sodium β-alumina stimulated widespread interest in both the science and technology of high conductivity solid electrolytes. Since Yao and Kummer's seminal work, many solid electrolytes have been explored, but interest in the β and β″-aluminas has endured, principally because of their virtually unique ability to undergo ion exchange in which the sodium ions are replaced by a wide variety of monovalent, divalent, and trivalent cations as well as various protonic species. The β and β″-aluminas thus are not single compounds, but a family of solid electrolytes with diverse properties and potential technological applications.

Kummer first pointed out the ion exchange properties of sodium β-alumina by showing that the sodium ions in the structure can be replaced by different monovalent cations, such as Li+, K+, as well as H(H2O)x+ and NH4+. More recent studies have shown that the ion exchange chemistry of sodium β″-alumina, is far richer than that of sodium β″-alumina. In fact, the sodium ion content of β″-alumina can be exchanged for virtually any +1, +2, or +3 cation in the periodic chart.
Mixed Conductors: Synthesis, Properties, Applications
Authors: Whittingham M. Stanley
Published: August 2016

Only in the last two decades has the full realization been made that many materials can incorporate atoms or ions into their structures around room temperature. This incorporation frequently occurs with minimal structural changes so that the reaction can be reversed by appropriate chemical or electrical means. These materials include metals, inorganics, and organics. The driving force for reaction is a gain in free energy and is frequently associated with a transfer of electron density between the guest and host species. Thus by definition the host material must contain an electronic structure that can be readily oxidized or reduced, and hence for inorganic materials normally contains transition metals with their variable valences, or for organics a delocalized electron system.

The systems described here frequently exhibit both electronic and ionic conductivity, i.e., they are mixed conductors over at least part of their composition range. They tend to have variable composition; this contrasts with solid electrolytes such as β-alumina which may also be nonstoichiometric but are of fixed composition at normal temperatures. Materials in this last category include the β-aluminas and aluminosilicates such as vermiculite and montmorillonite, both of which can be used as electrolytes due to their high ionic conductivity and low electronic conductivity.
Materials for Fusion Energy
Authors: Reuther Theodore C.
Published: August 2016

Materials research and development specifically for potential application in fusion energy development had its origin in the early 1970s, following the impetus of the 1973 report to the President on “The Nation's Energy Future” by Dixie Lee Ray then chairman of the U.S. Atomic Energy Commission. The first scientific conferences on fusion materials took place in the summer and the fall of 1975 at Argonne National Laboratory and at Gatlinburg, Tennessee. Argonne's international conference set a direction for the use and development of irradiation testing facilities for fusion materials which continues today.

In his keynote to the Gatlinburg meeting on “Radiation Damage and Tritium in Fusion Materials,” E.E. Kintner, then deputy director of the U.S. magnetic fusion program, spoke directly to the hearts of the materials community:

“Materials is the Queen Technology of any advanced technical system. The economics eventually depend upon the materials, the reliability depends upon the materials, and the safety depends upon the materials. I assure you that before we are through with fusion, the physicists will give way to the materials engineers as being the leading lights of fusion.”

Kintner spoke from his experience in naval and civilian nuclear power systems, with reference to the special threats of the fusion reactor environment to the integrity of materials, and from practical engineering issues in a broad sense.
Materials Requirements for Experimental Fusion Reactors
Authors: Smith Dale L.
Published: August 2016

The next major step in the development of fusion power involves the design, construction, and operation of an experimental power reactor. The general objective of this type of device is to demonstrate key plasma physics, materials, and engineering performance under conditions that approach those considered necessary to establish the technical feasibility of fusion power. This device is generally perceived to be a tokamak configuration that operates on the deuterium-tritium (D-T) fuel cycle, which would produce several hundred megawatts of fusion power. Although a number of conceptual design studies on this type of device have been conducted, the current effort is focused on the International Thermonuclear Experimental Reactor (ITER) activity, a joint undertaking of the European Community (EC), Japan, the United States, and the Soviet Union, conducted under the auspices of the International Atomic Energy Agency (IAEA).

The development of fusion power as an energy source depends to a large extent on the proper selection of materials for the various components. these materials will be exposed to a wide variety of conditions such as plasma particle and neutron radiation, high thermal fluxes, large thermal and mechanical stress, various chemical environments, and high magnetic fields. In order to achieve the high performance desired for a commercial power reactor, considerable materials development will be required. Because of the relatively near term time scale projected for ITER and the limited objectives, more conventional materials with more extensive data bases will be used where possible. Even so, a substantial materials development program is required to support a test reactor like ITER.
Participants Debate Cold Fusion During MRS Spring Meeting Panel Session
Authors: Siegel R.W.
Published: August 2016

Capping an exciting day at the 1989 Spring Meeting of the Materials Research Society in San Diego, a special three-hour session on “cold fusion” was held Wednesday evening, April 26, following the plenary lecture by two-time Nobel laureate Prof. Linus Pauling. (See “Linus Pauling Addresses MRS in San Diego” elsewhere in this issue.)

The session, the largest session in MRS history with over 1,700 participants, was sponsored by the Society to provide MRS meeting attendees with an unbiased scientific forum for the presentation and discussion of results and issues regarding recent “cold fusion” announcements in the press. The announcements had captivated the world's interest the preceding month while being met with a healthy amount of scientific skepticism. Such skepticism was not lost on the nation's cartoonists, many of whose works on “cold fusion” were shown during the evening's proceedings.

The special session was organized and moderated by Meeting Cochair Richard W. Siegel, with the help of Angelica M. Stacy and Robin F.C. Farrow (also Meeting Co-chairs) and MRS President R.P.H. Chang. A distinguished panel of invited speakers from the nuclear fusion and materials research communities was assembled to discuss the purported fusion of deuterium nuclei dissolved in palladium or titanium at or near room temperatures.
The Basis and Needs for Intelligent Materials Processing
Authors: Apelian Diran
Published: August 2016

The main concept of intelligent materials processing systems is to have online control during processing. Successful implementation of on-line control of materials processing from the total manufacturing point of view involves full integration of design, procurement, control of incoming components, manufacture, assembly, handling, packaging, and distribution.

There are three primary concerns if on-line control of materials processing is to be successful:

1. Definitive understanding of the process. Process models need to be developed which will bring forth an understanding of the processing variables.

2. Sensors that can interrogate the processes in a manner that allows for process control. Sensing is needed throughout the processing steps so that one can determine and measure various indices and the significant parameters … as borne out by physical and mathematical modeling.

3. Armed with the above, process controls are established to compare the on-line feedback obtained from sensors with the process models. When deviations are observed, measures are taken to change the processing variables so that the operation will yield a “quality” product. Intrinsic to process control is a clear definition of the properties required at the end of individual steps and the relation of the intermediate properties to those specified for the material when the total processing is completed. In fact, only in the light of a definition of the properties and the processes is it possible to define the parameters that can be monitored for on-line control.
Modeling of Defects in Silver Halides
Authors: Catlow C.R.A.
Published: August 2016

Modeling methods are now established as a major technique in defect physics and chemistry. Indeed, much of the contemporary understanding of complex defect processes derives from applying these techniques in conjunction with experimental methods.

The silver halides possess unusual defect properties and pose unique challenges to simulation studies. This article aims to outline the general features of defect simulations, and to review the status of their application to the defect properties of silver halides.

Technical aspects of the field have been detailed elsewhere, so this account is brief. An important feature of recent studies of the silver halides concerns developments in interatomic potentials, which will be considered, followed by a presentation and discussion of the calculated defect parameters.

The basis of the simulation techniques is the specification of an interatomic potential model for the system, i.e., an analytical or possibly a numerical description of the energy of the system as a function of atomic coordinates. For polar materials, the model must include the following terms: Coulomb and short-range energies, and ionic polarization.

To evaluate these terms, charges must be assigned to all atoms. In most studies reported to date, the fully ionic model has been used, i.e., integral charges have been assigned. The procedure has been followed in modeling the silver halides. Care must be taken in summing r-1 terms. Simple truncation procedures give unreliable results.
Petrographic Analysis of Archaeological Ceramics
Authors: Childs S. Terry
Published: August 2016

Petrographic analysis is not new to the study of archaeological ceramics, but it is receiving more attention as it is applied to interesting and diverse archaeological problems. Petrography was developed by geologists to identify minerals in rocks. Archaeologists use it to study the minerals that occur in prehistoric clay matrices transformed by heat to a rocklike state.

Petrographic analysis requires a polarizing microscope and a piece of ceramic, called a thin section, 30 microns (0.03 mm) thick. As light from this specialized microscope passes through a mineral, it produces optical properties unique to that mineral. Birefringence and pleochroism are two such properties used to identify minerals, while physical properties such as cleavage and relief are also important discriminators. Several references fully explain these properties and relate them to specific minerals and rocks.

Using petrographic techniques, as many as five materials can be studied in a ceramic—the clay itself, natural inclusions in the clay, purposefully added inclusions, and glazes or slips on the clay surface. Under certain conditions the clay or inclusions may melt and a fifth material, glass, may form. Depending on the research problem to be addressed and the samples available, the petrdgrapher studies one or more of these materials.
Characterization of Grass Phytoliths for Archaeological Analysis
Authors: Mulholland Susan C. , Rapp George
Published: August 2016

The word phytolith means “plant rocks.” Phytoliths are mineral deposits that form in and between plant cells. Any mineral deposit may be considered a phytolith, although most recent research has focused on opaline silica. Silica seems to be widespread in at least some plant families and is resistant to dissolution in a pH less than 9. Silica phytoliths therefore have the potential to be useful microfossils that can be helpful in the documentation of prehistoric environment and economy.

Identifiable shapes rather than amorphous deposits are a necessary characteristic for useful microfossils. Several plant families have long been known to be consistent accumulators of identifiable silica bodies: Gramineae (grass), Cyperaceae (sedge), and Equisetaceae (horsetail). Phytoliths from the Gramineae are especially well known; specialized silica-accumulating cells produce distinctively shaped phytoliths. However, other families have also been shown to produce significant amounts of identifiable phytoliths. Ulmaceae (elm), Fabaceae (bean), Cucurbitaceae (squash), and Compositae (sunflower) are a few examples of dicotyledonous families that commonly produce phytoliths. Some families, such as the Labiatae (mint), have yielded little or no identifiable phytoliths to date. However, further study may indicate phytolith production in particular species.
Arthur von Hippel: The Man Behind the Von Hippel Award
Authors: Dresselhaus M.S.
Published: August 2016

The Von Hippel Award, the most prestigious award of the Materials Research Society was first presented to its namesake, Arthur von Hippel, in 1976. On November 19, 1988, Prof. von Hippel celebrated his 90th birthday, an appropriate occasion to look back on a lifetime of achievement. Through the many testimonials that were heard at his 90th birthday celebration from family, friends, former students and colleagues, emerged a picture of materials science that reflects much that we treasure as the fabric of the Materials Research Society, namely the interdisciplinary approach to materials research.

It has become an annual tradition of MRS to celebrate the achievement of the Von Hippel Award winner, and each year the celebrants begin the ceremony with an affirmation of the efficacy of the interdisciplinary approach. In the early years of the Von Hippel Award, our young students often heard greetings from Prof. von Hippel himself during the opening ceremony. But as the size of the meetings has grown, it has become increasingly difficult for “The Professor” to offer personal greetings. Many young people today yearn for contact with their intellectual heritage. Inspired by this need, the leadership of MRS recommended that a brief article be written for the MRS BULLETIN on reminiscences about Prof. Arthur von Hippel and his legacy of the interdisciplinary approach to materials research.
Deposition Processes
Authors: Messier Russell
Published: August 2016

My introduction in the November MRS BULLETIN to this two-part series on deposition processes discussed the extensive use of thin films in science and technology. That it takes two issues and nine articles to cover this topic — and by no means exhaustively — is testimony to the manifold ways thin films are prepared.

If all deposition processes resulted in the same product, then such extensive coverage would be redundant and unnecessary. Thin films, however, cover a virtual infinity of free energy states — and related crystal structures, micro-structures, defects, defect densities, impurities, compositions, composition modulations, etc. — that are sensitive to the particular deposition process and its conditions. It is this richness of choice that makes thin film science and technology both exciting and, at times, frustrating.

Along with the freedom to extensively vary thin film characteristics, resulting properties and applications comes the difficulty in understanding preparation-characterization-property relations in enough detail to control and reproduce deposition processes.

The November articles covered molecular dynamics computer modeling of nucleation and growth processes, molecular beam epitaxy, organometallic vapor phase epitaxy, and chemical vapor deposition. This month's articles continue the sequence of ways to deposit films, the general direction being toward lower substrate temperatures. Plasmas, which offer both increased flexibility and complexity, are primarily considered. The last article covers thermal plasmas, not to control the vapor deposition but to melt powders which result in a multiple splat-quenched array of particles that form coatings important to industry.
Evaporation Processes
Authors: Bunshah R.F , Deshpandey C.V.
Published: August 2016

Physical vapor deposition (PVD) technology consists of the basic techniques of evaporation deposition and sputter deposition. PVD is used to deposit films and coatings or self-supported shapes such as sheet, foil, tubing, etc. The thickness of the deposits can vary from angstroms to millimeters.

Applications range widely, from decorative to utilitarian and over significant segments of the engineering, chemical, nuclear, microelectronics, and related industries. They have been increasing rapidly because modern high technology demands multiple and often conflicting sets of properties from engineering materials, e.g., combination of two or more of the following: high temperature strength, impact strength, specific optical, electrical or magnetic properties, wear resistance, fabricability into complex shapes, biocompatibility, cost, etc. A single or monolithic material cannot meet such demands. The solution is a composite material, a core material and a coating each having the requisite properties to meet the specifications.

This article will review evaporation-based deposition technologies, theory and mechanisms, processes, deposition of various types of materials, and also the evolution of the microstructure and its relationship to the properties of the deposits.

The first evaporated thin films were probably prepared by Faraday in 1857 when he exploded metal wires in a vacuum. The deposition of thin metal films in vacuum by Joule heating was discovered in 1887 by Nahrwold and was used by Kundt in 1888 to measure refractive indices of such films. In the ensuing period, the work was primarily of academic interest, concerned with optical phenomena associated with thin layer of metals, research into kinetics and diffusion of gases, and gas-metal reactions.
Plasma Spray Deposition Processes
Authors: Herman Herbert
Published: August 2016

The concept of plasma is central to many scientific and engineering disciplines—from the design of neon advertisement lights to fusion physics. Plasmas vary from low density, slight states of ionization (outer space) to dense, thermal plasmas (for extractive metallurgy). And plasmas are prominent in a wide range of deposition processes — from nonthermal plasma-activated processes to thermal plasmas, which have features of flames and which can spray-deposit an enormous variety of materials. The latter technique, arc plasma spraying (or simply, plasma spraying) is evolving rapidly as a way to deposit thick films (>30 μm) and also freestanding forms.

This article will review the technology of plasma spraying and how various scientific disciplines are contributing to both an understanding and improvement of this complex process.

The plasma gun dates back to the 1950s, when it was introduced for the deposition of alloys and ceramics. Due to its high temperature flame it was quickly discovered that plasmas could be used for depositing refractory oxides as rocket nozzle liners or to fabricate missile nose cones. In the latter technique, the oxide (e.g., zirconia-based ceramics, spinel) was sprayed onto a mandrel and the deposited material was later removed as a free-standing form.

The technique's versatility has attracted considerable industrial attention. Modern high performance machinery is commonly subjected to extremes of temperature and mechanical stress, to levels beyond the capabilities of present-day materials. It is becoming increasingly common to form coatings on such material surfaces to protect against high temperature corrosive media and to enhance mechanical wear and erosion resistance. Several thousand parts within an aircraft gas turbine engine have protective coatings, many of them plasma sprayed. In fact, plasma spraying has emerged as a major means to apply a wide range of materials on diverse substrates. The process can be readily carried out in air or in environmental chambers and requires very little substrate surface preparation. The rate of deposit buildup is rapid and the costs are sufficiently low to enable widening applications for an ever increasing variety of industries.
Magnetism in the High Tc Family of Compounds
Authors: Sinha Sunil K.
Published: August 2016

The most intriguing aspect of the new “high Tc” superconductors is that we still have no consensus about the nature of the basic mechanism for superconductivity in these materials, nor about why Tc is so much larger than in conventional superconductors. As is now well known, these materials include compounds of the type La2-xSrxCu2O4-y (where Sr can also be replaced by Ba) in which the maximum Tc attained is between 35 K and 40 K, and of the type YBa2Cu3O7-δ (where Y can also be replaced by most rare-earth atoms) in which the maximum Tc attained is about 98 K. Very recently, new compounds such as Bi2Sr2CaCu2O8+y have been discovered where Tc's of up to 120 K have been observed, but the physical properties of these at the time of writing are much less well known. The interesting thing about all these compounds is that they all result from doping of cupric oxide insulators, and they all contain planes of Cu-O atoms.

Perhaps not entirely by coincidence, high Tc superconductivity thus occurs in a class of materials, namely transition metal oxides, whose electronic ground states are currently least well understood in terms of conventional band theory. It is now generally accepted that the d-shells of transition metals ions (including Cu) have associated with them a fairly large Coulomb repulsion that makes it energetically unfavorable for two holes to be on the same d-shell simultaneously. For Cu, the energy U is estimated to be between 4 and 8 eV. This implies that Cu++ (d9 configuration) is favored, while Cu+++ (d8 configuration) is not. This is in accordance with spectroscopic measurements of these compounds.
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

Diffusion 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.
Selective Etching of GaN from AlGaN/GaN and AlN/GaN Structures
Authors: Grenko JA. , Reynolds CL. , Schlesser R. , Bachmann K. , Rietmeier Z. , Davis Robert F. , Sitar Z.
Published: August 2016

Thick GaN layers as well as AlGaN/GaN and AlN/GaN heterostructures grown by metalorganic vapor phase epitaxy have been photoelectrochemically (PEC) etched in various dilute electrolytes, and bandgap-selective etching has been demonstrated in heterostructures. This result is a significant step forward in the fabrication of group III-nitride devices and one-dimensional photonic bandgap (PBG) structures in the deep UV. Based on initial results from thick GaN layers, a method was developed to achieve self-stopping selective etching of thin GaN layers in AlGaN/GaN and AlN/GaN heterostructures. Selective PEC etching requires the use of a suitable light source with photon energies larger than the bandgap of GaN, but smaller than that of AlGaN or AlN, thus enabling selective hole generation in the GaN layers to be etched. Additionally, it is imperative to use an electrolyte that supports PEC etching of GaN without chemically etching AlGaN or AlN.