Condensation from plasmas has been shown to yield very fine, high purity powders from even the most refractory materials. Elementary particles in these powders are often single crystals, as fine as 50 nm diameter. These particles vary widely in agglomeration state; in some systems they are essentially independent, while in others hard agglomerates as large as several microns are observed. In this article the geometric aspects of reactor design which are thought to influence these powder structures are reviewed, along with three case studies in powder microstructure. Finally, the structure of the “typical” plasma powder is compared with expectations from alternative preparation routes.

The development of new, energy-efficient processing strategies for ceramic fabrication has become a rapid growth field over the last ten years. Most of these strategies rely on minimizing diffusion requirements during densification by improving both the chemical homogeneity and the initial density of the powder compact to be consolidated; both requirements dictate unusual care in the synthesis of the starting powders. In the oxide systems most extensively studied to date, the required powders can often be produced by precipitation from aqueous solutions and/or emulsions. In the carbide and nitride systems widely envisaged for the next generation of structural applications, these techniques are difficult and gas-phase synthesis routes appear more attractive. In fact, even the leading practitioners of the precipitation arts write enthusiastically of aerosol synthesis methods for the oxides.

Two recent DOE information exchanges exemplifying the breadth and depth of materials research supported through BES/DMS were held at Los Alamos National Laboratory, New Mexico, on June 15-16 and at Sandia National Laboratory, Albuquerque, New Mexico on June 17-18, 1987. The Division of Materials Sciences (DMS), Office of Basic Energy Sciences (BES), U.S. Department of Energy, holds annual information exchanges at each of the national laboratories. Representatives of all DOE national laboratories as well as representatives of other government, academic, and industrial laboratories are invited to attend the information exchanges.

The LANL meeting was opened by laboratory director Sig Hecker, who set the stage for a day and a half of technical presentations concerning BES-supported research at Los Alamos. Organizing the meeting and chairing the first day's session was James L. Smith, chairman of LANL's Center for Materials Science. A wide variety of topics were covered. Leading off was Zachary Fisk, who discussed correlated electrons and high Tc superconductivity. He described work on both heavy fermion systems and the new ceramic oxide superconductors.

Subsequent presentations dealt with localized vibrational modes (soliton-like) which can be sustained in solids showing both dispersion and nonlinear effects. Thermal physics and quantum fluids were described and a novel acoustic dilution refrigerator concept was demonstrated. Studies designed to elucidate the structure of molecular solids were also discussed.

Rapid progress in the development of new electronic materials and the steady maturation of silicon-based technologies has resulted in a host of novel electronic devices in which the active region of the structure is confined to an interface or a surface. The chemical, electronic, and physical characterization of surfaces and interfaces in semiconductors and insulators is of critical importance to manufacturing process control as well as to the fundamental electron physics and materials science which support microelectronic device research.

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.

I would like to express my gratitude to the Awards Committee and its chairman for bringing me here today. One of the effects, and not the least, of this award is to call on my earliest recollections from the United States. In the Fall of 1956, I arrived in Boston at the Massachusetts Institute of Technology (MIT) as a postdoctoral fellow in the laboratory of Prof. von Hippel. My stay in the Materials Research Laboratory of MIT was a determining influence in my future work.

The many-body problem is the study of the effects of interaction between bodies on the behavior of a many-body system. The importance of the many-body problem derives from the fact that almost any real physical system is composed of a set of interacting particles. Another essential aspect is that the many-body problem is not a branch of solid-state or atomic or nuclear physics but deals with general methods applicable to all many-body systems.

Because of the complexity of the many-body problem, one of the preferred solutions is simply to ignore it. One can always say, “Let us admit that the particles forming the system do not interact or that their interaction is so weak that the effect can be considered negligible.” In many cases, this method produced good results, and one of the great mysteries is why.

This article will provide information about chemical processes which rely on the heat evolved during reaction to synthesize and, in some cases, to simultaneously density single-phase or composite ceramic materials. Although the basic concept underlying these processes is simple, the high temperature reactions are complex and require careful study with individual systems before their potential as fabrication processes can be fully realized.

Many reactions between solids involving elements and/or compounds, or between solids and gases are highly exothermic. Listed in Table I is a selected group of typical chemical reactions accompanied by their calculated adiabatic temperatures. As a general rule any reaction with an adiabatic temperature ~2000°C or over can be reacted under combustion conditions. For example, suppose that a cold-pressed cylindrical compact of titanium and boron powder (Eq. 1) is ignited at the top surface with a convenient source of heat such as a laser. From the igniting surface a combustion wave rapidly self-propagates down the compact, transforming the reactants into the TiB2 product. Figure 1 shows a Ti and C powder compact where the combustion wave has progressed about halfway down the compact.

The changes in Electron Spectroscopy for Chemical Analysis (ESCA) equipment since 1982 have significantly expanded the range of applications and general utility of the technique. Most of these changes center around improvements in spatial resolution although there have also been improvements in speed and energy resolution. The implications of these changes extend beyond the obvious ability to obtain information from small features on samples.

The three major approaches to controlling spatial resolution are: (1) defined area x-ray sources, (2) limited field-of-view electron analyzers, and (3) imaging electron analyzers. Each of these will be reviewed briefly and their salient features contrasted. These advances in the instrumentation have brought about the following benefits to users of the ESCA technique: (1) ability to analyze small features, (2) rapid depth profiling, (3) multiple samples, and (4) improved charging control. Examples are included.

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.

Fundamental principles and experimental procedures for fully utilizing the power of Auger analysis are discussed. Topics include: quantitative analysis, high resolution imaging, depth profiling, and noise reduction. These studies reveal several improvements that might be expected in the immediate future and how they might be achieved. Some knowledge of Auger spectroscopy is assumed, but references on theory, principles, instrumentation, and applications are cited.