Glass melting has changed very little in general principles since the earliest times, still being produced in fireclay pots or crucibles—even up to the present day. In Europe, experiments to melt glasses in tank furnaces began about 1700 A.D., but this became an important form of glass manufacture after Siemens introduced the regenerative furnace in 1870. This design was the basis for the development of modern furnaces and there is still a considerable similarity to the original.

Until the late 1920s the glass contact refractories used in tank furnaces were based on fireclay or sandstone blocks. About this time important changes began when sillimanite and fusion-cast mullite refractories became available. However, because of the higher cost of fusion-cast refractories the introduction of these materials was delayed and they did not come into general use for lining the glass melting tank until the late 1940s.

The high performance of tank furnaces today is related to a number of factors such as improved furnace design and regeneration, but the most significant has been an improved melting rate brought about by the use of higher temperatures. This has only been achievable as a result of the improved quality of fusion-cast and other refractory materials, such as those used in the furnace superstructure and regenerators. Garstang showed that there has been a steady increase in melting temperatures in the container glass industry. In data going back to 1920, there has been an increase from about 1300°C to some 1590°C. Bondarev showed that the increase in production achieved by using higher temperatures reduces the specific consumption of fuel.

Although cracks in structural components are, in general, highly undesirable, not all of them are detrimental to the life of the structure. To determine precisely how detrimental the crack actually is, one must characterize several crack parameters, particularly the location, size, shape, and orientation with respect to the applied stress. With these parameters and the magnitude of the applied stress, the driving force on the crack can be calculated by determining the stress intensity factor K or the stress intensity range ΔK. Most inspections today are performed in a scanning mode. If indications of some anomaly appear, the inspection is concentrated on these locations; and, if the response verifies the presence of a flaw, the size, shape, orientation of the flaw and the potential for future growth of the flaws are determined. This process is now termed “quantitative nondestructive evaluation” (QNDE).

This short review is devoted to recent advances in the characterization of cracks in various stages of development. The increase in sophistication in instrumentation and the use of computers for data analysis and interpretation has been dramatic and will certainly continue.

In the laboratory, compliance gauges and electrical potential drop methods are now extensively used for crack length and shape measurements. Acoustic methods are being widely used in industry as nondestructive testing and evaluation tools because they are relatively easy to apply to real structures.

The Fusion Reactor Materials Program in the United States began in about the mid-1970s, in a world sensitized to energy production needs by the 1973 Arab Oil Embargo. In the program's early stages, materials problems were recognized to be as important as any of the other problems facing this new energy technology. The effects of irradiation on the behavior of materials to be used in the first-wall and blanket structure were of particular concern. Today, although the economic and political realities that define energy needs have changed, fusion energy still remains an important part of our vision for a better future. Global environmental effects such as the “greenhouse effect” from increased CO2 in the atmosphere and acid rain, coupled with safety concerns about fission reactors, make fusion very attractive as a clean and safe energy source.

Over the past 10 years, the range of candidate materials for structural application in fusion reactors has expanded to include new martensitic and ferritic steels with reduced activation characteristics, vanadium alloys, ceramics, and composite materials. However, because austenitic stainless steels are easily fabricated, nonmagnetic, reasonably strong and tough, commercially available, and familiar, they also remain as candidate materials for fusion. They have also been extensively studied for use in various fission reactor systems as well. The austenitic and stainless properties of Fe-Cr-Ni alloys and steels were discovered during 1900–1915. Commercial grades like AISI types 304 and 316 stainless steels were developed prior to World War II. The effects of irradiation on materials have been studied since 1942, when Eugene P. Wigner anticipated that fission fragments and energetic neutrons would damage crystalline materials by displacing atoms to create point defects (vacancies and interstitials).

There are many methods of depositing thin film materials: thermal evaporation, sputtering, electron or laser beam evaporation, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE). A good survey of many of the deposition methods appears in the 1988 November and December issues of the MRS BULLETIN. One method not included in that survey, however, is metalorganic deposition (MOD), a powerful method for depositing a variety of materials.

Metalorganic deposition is not to be confused with metalorganic chemical vapor deposition (MOCVD), which is a gaseous deposition method. MOD is a nonvacuum, liquid-based, spin-on method of depositing thin films. A suitable organic precursor, dissolved in solution, is dispensed onto a substrate much like photoresist. The substrate is spun at a few thousand revolutions per minute, removing the excess fluid, driving off the solvent, and uniformly coating the substrate surface with an organic film a few microns thick. The soft metalorganic film is then pyrolyzed in air, oxygen, nitrogen, or other suitable atmosphere to convert the metalorganic precursors to their constituent elements, oxides, or other compounds. Figure 1 shows a schematic of the deposition process including a prebake and annealing (if necessary).

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.

One of the newer tendencies in materials science has been to tailor-make classical products (long associated with old applications) with controlled properties for special uses, especially in high technology. Preparing dispersed systems in which all particles have nearly uniform size (monodisperse solids) is a typical example. This goal can be achieved in some cases through cleverly controlled particle growth from a liquid medium. Examples of such preparations include gold colloids prepared by Zsigmondy and later by Turkevich et al., sulfur sols obtained by LaMer, metal oxides and hydrous oxides prepared by Matijević et al., silica, etc. These dispersions have been used either to check theories of colloid science, or to a lesser extent, for industrial purposes. In the case of fine metal particles, a uniform size distribution associated with a low degree of agglomeration, and sometimes the spherical shape, appear as particularly convenient characteristics for certain applications. The production of conductive inks or pastes for electronic materials and for the preparation of conductive paints are particularly good examples.

In so-called thick film technology, conductive inks and pastes are screen printed on a ceramic substrate in order to form, after firing, a conductive film with a thickness less than 10 μm. This technique is, for instance, used to form the network in hybrid integrated circuits or the internal electrodes of multilayer ceramic capacitors.

Metallic powders in thick film compositions are usually precious metals (Au, Ag, Pt, Pd), their mixtures, or alloys. Cheaper metals such as copper or nickel are tested and may be potential substitutes for precious metals in different specific applications. Powders for thick film composition are mainly obtained through chemical precipitation from aqueous or organic solutions, which yield high purity powders. Modification of precipitation parameters (such as the nature and the concentration of the starting metallic compound and of the reducing agent, reaction temperature, viscosity of the medium) and the addition of additives and surfactants, can often be used to control particle size and agglomeration.

Over the past few years, we have developed a new process for preparing finely divided metal powders of easily reducible metals (such as precious metals and copper) or less reducible metals (such as cobalt, nickel, cadmium, or lead) by precipitation in liquid polyols. This reaction will be used as an example in order to discuss the mechanism of formation of uniform micrometer and submicrometer size metal particles by precipitation reactions.

Over the past 10 to 20 years, cathodo-luminescence microscopy (CLM) has become an important, standard technique for studying many geological materials, but its application to ceramic material has not been fully realized. CLM has been found to be especially valuable in determining original porosity in carbonate rocks, a feature that was extremely important in determining the ability of petroleum and related fluids to migrate through the rocks and concentrate in the favorable structures where petroleum is found today. CLM constitutes one of the most significant techniques employed in the exploration for petroleum, but the results of those investigations remain largely unpublished in company files. A number of investigations have discussed the application of cathodoluminescence (CL) to studies of porosity in carbonates.

Other applications of CLM to geology involve metals exploration. Halos of red CL feldspar in the rocks around carbon-atite deposits, which may contain rare earths, copper, and other metals, contrast with feldspar crystals with blue or blue-green CL that are distal from the ore deposits. Dolomite associated with lead-zinc ores may exhibit growth zoning by CL that can be used to trace the path of the ore fluids for distances of 100 miles or more. The detection of host rock limestone alteration in the Tri-State zinc-lead district, potassic and argillic alteration at the Henderson molybdenite mine, and ore guides in other metallic deposits by CL was discussed by Hagni.

The very high sensitivity of silver halide photographic emulsions is the result of a surprisingly high quantum efficiency in the formation of the latent image, combined with a large amplification of the stored optical signal upon photographic “development.” The efficient formation of the latent image can be traced to the effects of an unusual set of physical properties of silver bromide and silver chloride, involving the electron energy band structure, the dynamics of photoelectrons, the nature and mobilities of the ionic point defects, and the existence of a sub-surface electric field.

Despite the current availability of a wide variety of optical recording systems, the standard silver halide photographic emulsion continues to offer a unique combination of sensitivity, resolution, tone quality, convenience, and economy. This article will outline the physical processes that operate in forming the image. It will emphasize the unusual set of properties of silver bromide and silver chloride that are involved, and that impart to the process its extraordinary efficiency. Only black-and-white images will be considered, but the same basic imaging process is involved in color photography as well.

This discussion is, of necessity, brief and often qualitative, but more complete treatments of the scientific aspects of the photographic process can be found in the other articles in this issue of the MRS BULLETIN, as well as in the bibliography.

Developing materials that resist degradation when exposed to neutrons is a key element in international programs to demonstrate the engineering and economic viability of fusion power. An additional requirement is that these materials exhibit low-induced long-lived radioactivity in order to enhance fusion power's environmental (and economic) attractiveness. This article briefly overviews current efforts to develop reduced activation structural alloys for fusion reactor applications.

A specific objective of the U.S. Fusion Materials Program is that all reactor components will meet the requirements for near-surface burial. Presently, this is interpreted to mean that all radioactive waste should satisfy Part 61 of Title 10 of the U.S. Code of Federal Regulations (10CFR61), prepared by the Nuclear Regulatory Commission (NRC). Specific activity limits are placed on particular long-lived radionuclides, which, when combined with activation calculations for conceptual fusion devices, place constraints on material compositions. Regulation 10CFR61 was prepared to cover low-level waste produced by the fission reactor industry; it has been necessary to extend it, in principle, to include additional radionuclides. Unlike anticipated waste from a fusion industry, only a small fraction of the fission waste stream is activated metals; hence, the applicability of the regulation is questionable. Further analysis of the probable disposal method for fusion wastes is needed, along with consideration of maintenance and decommissioning scenarios.

The discovery and demonstration of molecular shape-selective catalysis in zeolitic silicate structures has led to a large segment of new catalytic science as well as to chemical process technologies with broad impacts on industry and society. Manmade catalysts are beginning to acquire skills of molecular structure selectivity and activity seen in the world of enzymes.

All our activities, including those of life itself, are dominated by the presence and action of ever transforming molecules. Heat alone transforms them but, basically, decomposes them indiscriminately. Catalysts, on the other hand, can direct transformations with meticulous selectivity as if to preserve a continuing purpose and order, and life itself. However, manmade catalysts, although the major tool of the chemical industry, have been highly simplistic and crude in their discriminatory capabilities. For example, we have solid acidic catalysts called cracking catalysts that will break carbon-carbon bonds. They have been employed for decades in the petroleum fuels industries and represent the largest volume of any manufactured catalyst. They will rather indiscriminately break C—C bonds in nearly any aliphatic organic structure, with only some structural preference for tertiary over secondary over primary carbon links.

In another class of manmade catalysts, molecules with unsaturated bonds are hydrogenated by a variety of metal-based catalysts. This addition of hydrogen proceeds nearly regardless of where the bond occurs in the structure. Or, take a synthesis reaction, such as that of xylenes from the addition of methanol to toluene. The usual acidic catalysts will add the new methyl group in any and all of the three possible isomeric positions to produce ortho-, meta-, and para-xylenes.

The preparation, utilization, and understanding of high polymers represents one of the great triumphs of chemistry and materials science in the 20th century. Synthetic polymers have traditionally been used as structural materials and electrical insulators. Biopolymers often exhibit interesting electrical response phenomena. A recent article in the MRS BULLETIN, for example, discussed piezoelectric properties of both synthetic and biopolymer systems. The newer, synthetic electroactive polymeric materials, however, represent one of the most exciting current areas of polymer materials science.

Many synthetic ionic polymer materials are known; perhaps the first were the polyelectrolytes and crosslinked ion exchange materials. These are materials whose backbone contains charges of one sign, balanced by small counter ions of the opposite sign. Such polyelectrolytes have found very important applications in analytical chemistry, water purification, and chemical processing.

Complexes, in which salts are dissolved in neutral polymer hosts, have until recently received less attention. The area of polymer/salt complexes became extremely active following the work of P.V. Wright, who first clearly showed that polyethylene oxide (PEO) is an excellent polymer host for a number of salts, and that the resulting solid polymer/salt complexes are electrical conductors. M. Armand broadened the investigation of electrical properties of polymer/salt complexes and pointed out that these materials might be useful in electrochemical devices, especially batteries.

This article will discuss the formation, properties, behavior, and applications of polymer electrolytes and mixed conductors—that is, polymeric materials in which charge is transported either by ions or by ionic and electronic charge motion. Our concentration will be on solvent-free materials—materials in which no small molecule solvents are present. There is substantial interest, and substantial progress, in the area of solvent-swollen polymer electrolytes.

Before the pioneering work of Bednorz and Müller in finding superconductivity near 30 K in lanthanum-barium-copper oxide,. oxide superconductors were well known, but perhaps not fully appreciated. Most anomalous among those superconductors was the perovskite structure material BaPb0.75Bi0.25O3, with a superconducting transition temperature (Tc) of 12 K2 and a surprisingly low density of states at the Fermi level. The increases in Tc for copper-oxide-based materials continue to generate worldwide excitement, but from both a chemical and theoretical point of view, high Tc superconductivity observed in a noncopper containing material is also of considerable interest.

Recently we found that the simple cubic perovskite compound Ba0.6K0.4BiO3 displays a superconducting transition temperature near 30K—a Tc considerably higher than that of conventional superconductors and surpassed only by copper containing compounds. This material is in stark contrast to the now well-known copper oxides for two reasons: (1) superconductivity occurs within the framework of a three dimensionally connected bismuth-oxygen array (and not a 2-d array as in the Cu-O based compounds) and: (2) there are no magnetic fluctuations present in the chemical system, either in the superconductor itself or in the nonsuperconducting end member compound, eliminating the possibility that the high Tc might be caused by magnetic interactions. The parent compound BaBiO3 is, however, of considerable interest due to the presence of a structurally frozen charge disproportionation of the bismuth atoms, considered by many to be the electronic equivalent of the antiferromagnetism observed in the nonsuperconducting cuprate host compounds.

The ideal undistorted perovskite ABO3 structure consists of a regular array of equally dimensioned BO6 octahedra sharing all corner oxygens with neighboring equivalent octahedra, with 180° B-O-B angles.

Magnetic particles are important not only in the technology, but also in the function of some biosystems. In addition, they are of great scientific interest in developing a better understanding of magnetic phenomena. Ever since magnetic recording media were first prepared, extensive efforts have been made to produce improved magnetic dispersions. The particle s for magnetic media must be of single domain, high saturation magnetization, and proper coercive force. However, the magnetic interactions between such particles are very strong, and stable dispersions are difficult to obtain. Originally, their use was limited to audio tapes, but presently they are employed in a variety of applications. Thus, small particles of different magnetic properties are constituents of magnetic fluids.

In 1975, magnetic particles were identified in the bodies of some bacteria, which can navigate along geomagnetic fields. It is also believed that certain animais have the ability to detect a magnetic field due to the presence of magnetic particles in their cells.

Techniques are being developed to introduce new functions to materials by incorporating magnetic particles. For example, magnetic particles that are encapsulated by nonmagnetic compounds (e.g. polymers) or particles are used for binding and separating enzymes from reactant mixtures. Efforts are under way to use magnetic particles in drug delivery Systems and for diagnosis.