Carbon and Its Allotropes

Carbon is a vital component of life and is present in all forms of organic matter. Belonging to the family of non-metals, each carbon atom has six electrons that occnpy the orbitals Is, 2s and 2p. The mix between the last two atomic orbitals, with a single 2s electron and 2p 1, 2 or 3 electrons, is called hybridization sp where n = 1, 2 or 3, depending on the nnmber of atoms bonded [20]. The other gronp IV elements snch as Si and Ge exhibit primarily only sp hybridization. 

Diamond, however, is a metastable phase of carbon, with lower binding energy (15 eV/mol) [23], Its compact lattice has sp hybridization (tetrahedral structure) that gives an extreme hardness, rather than electrical conductivity. Diamond is an excellent insulator (band gap 8 eV) due to a orbitals (sp ), which, among other properties, will provide a more cohesive and elastic modulus. 

Another condensed phase of carbon, which is of particular interest in the synthesis of CNTs, is so-called amorphons carbon (Fig. 5.1g). This allotrope of carbon contains sp and sp hybridization links and is usually an unwanted byproduct formed during the synthesis of CNTs. 

In the mid-80s, a new crystalline form of carbon was discovered [24] fuller-enes (Fig. 5.1e). This spherical stmctnre has in its simplest form sixty carbon atoms (C60) that are presented in the format of 20 hexagons and 12 pentagons. An excess carbon atom ( 60) in these molecnles distorts the spherical structure of C60, but without changing the number of pentagons. 

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The author and some of his colleagues felt the need for an updated and systematic review of carbon and its allotropes which would summarize the scientific and engineering aspects, coordinate the divergent trends found today in industry and the academic community, and sharpen the focus of research and development by promoting interaction. These are the objectives of this book... 

This book is a review of the science and technology of the element carbon and its allotropes graphite, diamond and the fullerenes. This field has expanded greatly in the last three decades stimulated by many major discoveries such as carbon fibers, low-pressure diamond and efullerenes. The need for such a book has been felt for some time. 

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