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About this book

This book was begun after three of the present authors gave a series of in­ vited talks on the subject of the structure and properties of carbon filaments. This was at a conference on the subject of optical obscuration, for which submicrometer diameter filaments with high length-to-diameter ratios have potential applications. The audience response to these talks illustrated the need of just one scientific community for a broader knowledge of the struc­ ture and properties of these interesting materials. Following the conference it was decided to expand the material presented in the conference proceedings. The aim was to include in a single volume a description of the physical properties of carbon fibers and filaments. The research papers on this topic are spread widely in the literature and are found in a broad assortment of physics, chemistry, materials science and engineering and polymer science journals and conference proceedings (some of which are obscure). Accordingly, our goal was to produce a book on the subject which would enable students and other researchers working in the field to gain an overview of the subject up to about 1987.

Table of Contents

Frontmatter

1. Introductory Material on Graphite Fibers and Filaments

Abstract
The purpose of this book is to review the physical properties of carbon filaments and fibers. These materials have been developed in the last 25 years, and new types are still being discovered and tested. It is hoped that in this book we will demonstrate that scientifically interesting and technologically important physical research has been, and can be carried out on these novel materials.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

2. Synthesis of Graphite Fibers and Filaments

Abstract
This chapter considers the methods by which the various types of fibers are produced. It is noted that ex-polymer fibers are produced by methods which lie in the area of applied polymer chemistry. Several reviews of their manufacture have been written. Therefore, only a brief description of their preparation is given here, enabling the reader to relate structural features to growth methods. The methods of growing CCVD filaments is considered in greater detail. The growth of the CCVD filaments in lengths of hundreds of millimeters has not been reviewed previously. It is emphasized that commercial carbon fibers are manufactured from polymers, and that one type (ex-PAN) dominates the commercial market, though low cost isotropic pitch fibers are also beginning to find wide application in high bulk, low performance applications. The present review of fiber growth would therefore seem to be out-of-balance with respect to current commercial utilization. However, the most interesting physical experiments have been carried out on the newer CCVD fibers, thereby providing the rationale for the balance we have chosen.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

3. Structure

Abstract
The main types of carbon filaments have been introduced in the previous chapter, and a brief description has been given of their principal structural features. This chapter considers the main types of measurements that have been carried out to elucidate their structure. In all cases, unless otherwise stated, it is assumed that the basic structural unit is the hexagonal plane of carbon atoms in the honeycomb arrangement. In highly perfect filaments, these planes are stacked in a regular ABAB (graphitic) sequence, while in less perfect filaments, the stacking is random (turbostratic). For disordered filaments, the planes are bent, or twisted, and defects such as vacancies, interstitials, dislocations, grain boundaries, voids, impurities, etc., are present. The purpose of structural information is, as far as possible, to characterize the basic structural unit and the defects which are present. This chapter will therefore attempt to show in each case what structural information can be achieved by each of the characterization techniques.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

4. Lattice Properties

Abstract
The lattice dynamics of a material are intimately connected with the elastic coefficients, which control the mechanical properties. The lattice dynamics in turn determine the phonon dispersion relations, which control the specific heat and thermal expansion, and strongly affect the transport properties through carrier scattering processes. Since the lattice dynamics for carbon fibers have not been considered explicitly, the results for crystalline graphite have conventionally been used with some modifications to take into account the small crystallite size, the high concentration of defects and the general disorder which are all prevalent in carbon fibers [Lespade et al. 1982]. To explain certain aspects of transport phenomena in carbon fibers (Chap. 8), the dispersion relations for crystalline graphite in the long wavelength approximation are used to treat electron-phonon scattering.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

5. Thermal Properties

Abstract
To date, there have been no direct measurements of the specific heat of carbon fibers. The only heat capacity work on carbon fibers known to us is the differential scanning calorimetry study carried out on a number of ex-PAN, ex-pitch and vapor grown carbon fibers before and after bromination [Jaworske et al. 1987]. This work was directed toward relating the degree of structural order to the threshold for intercalation and is discussed in Sect. 10.1.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

6. Mechanical Properties

Abstract
The most important applications of carbon fibers utilize their high strength-to-weight ratio, and therefore mechanical properties are of special technological interest (see Table 1.1). Some idea of the potential strength of carbon fibers can be gleaned from R. Bacon’s [1960] study of carbon whiskers, in which he found extensional moduli of 800 GPa [120 Msi (megapounds per square inch)] and breaking stresses of 20 GPa (3 Msi). Since typical tensile strengths of steels are 1 GPa, and their densities are about four times that of carbon, the potential of carbon fibers as structural materials is clear (see Tables 1.1 and 6.1). Actual tensile strength values realized in commercial fibers are lower than those of carbon whiskers, but still offer significant advantages over conventional metals.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

7. Electronic Structure

Abstract
The wide range of structures that occur in carbon filaments is described in Chap. 3, in terms of microstructures, lattice defects and impurities. This range of structures in turn implies that a wide range of electronic structures can occur. At one extreme, where the filaments are graphitic, the electronic structure approximates that of single crystal graphite. At the other extreme, where the filaments can be modeled as an inhomogeneous mixture of partially aligned polymeric molecules, a model based on the electronic structure of macromolecules is more appropriate. In between these two extremes, disorder of various kinds modifies the electronic structure in several ways.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

8. Electronic and Magnetic Properties

Abstract
The electronic structure of carbon fibers was introduced in Chap. 7. This chapter explores the electronic and magnetic properties of carbon fibers, beginning with equilibrium, and then considering steady state properties. It is quite useful to consider similarities in the properties of fibers to those of bulk carbons, with perturbations derived from the special structural features of the fibers. This can produce effects which are unique to carbon fibers. In turn, this allows information to be deduced about their electronic structure, and in some cases, their microstructure. In fact, some electronic effects are particularly sensitive to certain structural features, and provide valuable probes of structural defects.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

9. High Temperature Properties

Abstract
Very few measurements have been reported in the open literature on the structure and properties of carbon fibers above room temperature [Rowe and Lowe 1977; Sheehan 1987]. However, there is a somewhat larger literature on the properties of carbons at elevated temperatures [Lutcov et al. 1970; Tanaka and Suzuki 1972; Null et al. 1973; Leider et al. 1973]. Some high temperature properties of fibers can be estimated by analogy to bulk graphite results, and this approach will be used in this section where results on fibers are lacking.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

10. Intercalation of Graphite Fibers and Filaments

Abstract
Intercalation compounds are formed by the insertion of atomic or molecular layers of a guest chemical species between layers in a host material such as graphite. Numerous reviews and conference proceedings on graphite intercalation compounds (GICs) are available [Vogel and Hérold 1977; Hérold 1979; Vogel 1980; Dresselhaus and Dresselhaus 1981; Pietronero and Tosatti 1981; Nishina et al. 1981; Solin 1982; Hérold and Guérard 1983; Dresselhaus et al. 1983, 1986; Eklund et al. 1984; Dresselhaus 1987]. The intercalation process occurs in highly anisotropic layered structures where the intraplanar binding forces are large in comparison with the interplanar binding forces. The guest species in an intercalation compound exhibits order, in contrast to doping where the guest species tends to occupy random locations. Intercalation provides the host material with a means for controlled variation of many physical properties over wide ranges. Intercalation can proceed with either donor intercalants which transfer electrons to the graphite host material or with acceptors which receive electrons from the graphite.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

11. Ion Implantation of Graphite Fibers and Filaments

Abstract
Ion implantation is an important technique for modifying material properties through the introduction of impurity atoms or the creation of lattice defects in a controlled way. The technique is important in the semiconductor industry for making p-n junctions by, for example, implanting n-type impurities into p-type host materials. From a materials science point of view, ion implantation allows essentially any element of the periodic table to be introduced into the near-surface region of essentially any host material, with quantitative control over the depth and composition profile of the impurity by proper choice of ion energy and fluence (i.e., the total number of implanted ions per unit area of sample). Furthermore an important application of ion implantation is in the synthesis of metastable alloys which could not be produced by other means.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

12. Applications of Graphite Fibers and Filaments

Abstract
This chapter considers some applications of carbon fibers. This topic is not treated exhaustively. Instead, an attempt is made to give an overview, with emphasis given to those applications which involve physical principles.
Mildred S. Dresselhaus, Gene Dresselhaus, Ko Sugihara, Ian L. Spain, Harris A. Goldberg

Backmatter

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