ABSTRACT
I. Introduction 2
II. Structure and Stability of Fullerenes 2
III. Structure of Carbon Nanotubes and Nanoparticles 4
IV. Structure of Chars (Nongraphitizing Carbons) 7 A. Background 7 B. Early Models 10 C. Evidence for Fullerene-like Structures in Chars 13 D. A New Model for the Structure of Char 15
V. Structure of Glassy Carbon 18
VI. Structure of Carbon Fibers 21
VII. Soot and Carbon Black 22 A. Background 22 B. Structure of Soot Particles 24
VIII. Spherulitic Graphite in Cast Iron 28 A. Background 28 B. Structure of Spherulitic Graphite 29
IX. Naturally Occurring Forms of Carbon 32 A. Carbon from Geological Deposits 32 B. Carbon in Meteorites 33
X. Discussion 34
References 36
The discovery of C60 in 1985, and subsequent identification of fullerene-related structures such as carbon nanotubes and nanoparticles, has stimulated a large volume of research. To date, most of this research has concentrated on the remarkable properties of the new carbons themselves. Carbon nanotubes in particular have been shown to have quite exceptional mechanical and electronic properties, which could have a significant technological impact [1]. However, the knowledge gained as a result of fullerene research may be equally important in providing us with a fresh perspective on forms of carbon that have been known for many years. Charcoal, or char, for example, has been used in various ways for millennia, and is currently of enormous importance in purifying water and air supplies [2-4]. Yet despite a huge amount of research, many questions remain about the atomic structure of char and the exact reasons for its remarkable adsorptive properties. Recently, detailed studies of chars both before and after high-temperature heat treatments have provided evidence that they might contain fullerene-related elements. There are also reasons to believe that the class of chars known as glassy carbons may have a fullerene-like structure. In this chapter we assess the evidence that well-known forms of carbon may have structures related to those of the fullerenes. A detailed discussion is given of the structure of chars (nongraphitizing carbons) and of the various models for their structure that have been put forward since the classic work of Rosalind Franklin. In subsequent sections, the structure of glassy carbon, carbon fibers, soot (carbon black), and graphitic particles in spherulitic graphite cast iron are considered. The evidence that fullerenes or fullerene-like structures may be present in naturally occurring forms of carbon is then summarized. To begin, an outline of the main structural features of fullerenes, carbon nanotubes, and carbon nanoparticles will be given, together with a brief discussion of their stability.
