Preface

In 1994 the Oak Ridge National Laboratory hosted an American Carbon Society Workshop entitled "Carbon Materials for Advanced Technologies". The inspiration for this book came from that workshop. By late 1995 a suitable group of contributors had been identified such that the scope of this book would be sufficiently broad to make a useful contribution to the literature.

Carbon is a truly remarkable element which can exist as one of several allotropes. It is found abundantly in nature as coal or as natural graphite, and much less abundantly as diamond. Moreover, it is readily obtained from the pyrolysis of hydrocarbons such as resins and pitches, and can be deposited from the vapor phase by cracking hydrocarbon rich gases. In its various allotropic forms carbon has quite remarkable properties. Diamond possesses the highest thermal conductivity known to man and is prized as a gem stone. Both of these attributes result from the high degree of crystal perfection and bond strength in the diamond lattice. Graphite possesses extreme anisotropy in the bond energies of its crystal lattice, resulting in highly anisotropic physical properties. The most recently discovered allotrope of carbon, C60 or Buckminsterfullerene, has been the subject of extensive research, as have the related carbon nanotubes and nanostructures.

Engineered carbons take many forms. For example, cokcs, graphites, carbon and graphite fibers, carbon fiber - carbon matrix composites, adsorbent carbons and monoliths, glassy carbons, carbon blacks, carbon films and diamond like films. Many of these engineered carbon forms are discussed in this book, especially with respect to their applications in technologically advanced systems. Moreover, this book contains accounts of research into the uses of novel carbons. Modem day applications of carbon materials are numerous. Indeed, the diversity of carbon applications are truly astounding, and range from the mundane (e.g., commodity adsorbent carbons or carbon black), to the exotic (e.g., high modulus carbon fibers that enable the lightweight stiff composite structures used in airframes and spacecraft).

Chapter 1 contains a review of carbon materials, and emphasizes the structure and chemical bonding in the various forms of carbon, including the four allotropes diamond, graphite, carbynes, and the fullerenes. In addition, amorphous carbon and diamond films, carbon nanoparticles, and engineered carbons are discussed. The most recently discovered allotrope of carbon, i.e., the fullerenes, along with carbon nanotubes, are more fully discussed in Chapter 2, where their structure-property relations are reviewed in the context of advanced technologies for carbon based materials. The synthesis, structure, and properties of the fullerenes and nanotubes, and modification of the structure and properties through doping, are also reviewed. Potential applications of this new family of carbon materials are considered.

Detailed accounts of fibers and carbon-carbon composites can be found in several recently published books [1-5]. Here, details of novel carbon fibers and their composites are reported. The manufacture and applications of adsorbent carbon fibers are discussed in Chapter 3. Active carbon fibers are an attractive adsorbent because their small diameters (typically 6-20 |am) offer a kinetic advantage over granular activated carbons whose dimensions are typically 1-5 mm. Moreover, active carbon fibers contain a large volume of mesopores and micropores. Current and emerging applications of active carbon fibers are discussed. The manufacture, structure and properties of high performance fibers are reviewed in Chapter 4, whereas the manufacture and properties of vapor grown fibers and their composites are reported in Chapter 5. Low density (porous) carbon fiber composites have novel properties that make them uniquely suited for certain applications. The properties and applications of novel low density composites developed at Oak Ridge National Laboratory are reported in Chapter 6.

Coal is an important source of energy and an abundant source of carbon. The production of engineering carbons and graphite from coal via a solvent extraction route is described in Chapter 7. Coal derived carbons and graphites are first reviewed and the solvent extraction of coal using N-methyl pyrrolidone is described. The characteristics of cokes and graphites derived from solvent extracted pitches and feedstocks are reported. The modification of the calcined cokes by blending the extracted pitches, and/or by hydrogenation of the pitch, and subsequent control of graphite artifact properties are discussed.

Applications of activated carbons are discussed in Chapters 8-10, including their use in the automotive arena as evaporative loss emission traps (Chapter 8), and in vehicle natural gas storage tanks (Chapter 9). The use of evaporative loss emission traps has been federally mandated in the U.S. and Europe. Consequently, a significant effort has been expended to develop a carbon adsorbent properly optimized for evaporative loss control, and to design the on board vapor collection and disposal system. The manufacture of activated carbons, and their preferred characteristics for fuel emissions control are discussed in Chapter 8, along with the essential features of a vehicle evaporative loss emission control system.

The use of activated carbons as a natural gas storage medium for vehicles is attractive because the gas may be stored at significantly lower pressures in the adsorbed state (3.5 - 4.0 MPa) compared to pressurized natural gas (20 MPa), but with comparable storage densities. The development of an adsorbed natural gas storage system, and suitable adsorbent carbons, including novel adsorbent carbon monoliths capable of storing >150 V/V of natural gas, are reported in Chapter 9. Moreover, the function and use of a guard bed to prevent deterioration of the carbon adsorbent with repeated fill-empty cycling is discussed.

The application of activated carbons in adsorption heat pumps and refrigerators is discussed in Chapter 10. Such arrangements offer the potential for increased efficiency because they utilize a primary fuel source for heat, rather than use electricity, which must first be generated and transmitted to a device to provide mechanical energy. The basic adsorption cycle is analyzed and reviewed, and the choice of refrigerant-adsorbent pairs discussed. Potential improvements in cost effectiveness are detailed, including the use of improved adsorbent carbons, advanced cycles, and improved heat transfer in the granular adsorbent carbon beds.

Chapter 11 reports the use of carbon materials in the fast growing consumer electronics application of lithium-ion batteries. The principles of operation of a lithium-ion battery and the mechanism of Li insertion are reviewed. The influence of the structure of carbon materials on anode performance is described. An extensive study of the behavior of various carbons as anodes in Li-ion batteries is reported. Carbons used in commercial Li-ion batteries are briefly reviewed.

The role of carbon materials in nuclear systems is discussed in Chapters 12 and 13, where fusion device and fission reactor applications, respectively, are reviewed. In Chapter 12 the major technological issues for the utilization of carbon as a plasma facing material are discussed in the context of current and future fusion tokamak devices. Problems such as surface sputtering, erosion, radiation enhanced sublimation, radiation damage, and tritium retention are addressed. Carbon materials have been used in fission reactors for >50 years. Indeed the first nuclear reactor was a graphite "pile" [6], The essential design features of graphite moderated reactors, (including gas-, water- and molten salt-cooled systems) are reviewed in Chapter 13, and reactor environmental effects such as radiation damage and radio lytic corrosion are discussed. The forms of carbon used in fission reactors (graphite, adsorbent carbon, carbon-carbon composites, pyrolytic graphite, etc.) are reviewed and their functions described.

Graphite is a widely used commodity. In addition to it nuclear role, graphite is used in large quantities by the steel industry as arc electrodes in remelting furnaces, for metal casting molds by the foundry industry, and in the semi-conductor industry for furnace parts and boats. Graphite is a brittle ceramic, thus its fracture behavior and the prediction of failure are important in technological applications. The fracture behavior of graphite is discussed in qualitative and quantitative terms in Chapter 14. The applications of Linear Elastic Fracture Mechanics and Elastic-Plastic Fracture Mechanics to graphite are reviewed and a study of the role of small flaws in nuclear graphites is reported. Moreover, a mathematical model of fracture

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