Bonding carbon allotropes

Effective Doping in Novel sp Bonded Carbon Allotropes... 

Fig. 4. EEL spectra of (a) graphite and (b) diamond. These carbon allotropes represent different spectra sp bonding especially exhibits 7c -excitation peak lower than the o -excitation peaks (modified from ref. 16).

The different structures of the carbon allotropes lead to widely different properties. Because of its three-dimensional network of strong single bonds that tie all atoms in a crystal together, diamond is the hardest known substance. In addition to its use in jewelry, diamond is widely used industrially for the tips of saw blades... 

C60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in circumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature-low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented. 

For strong Pt fixation on CNM surface it is necessary to introduce functional groups, preferable from ones are -COOH, -OH and quinoid. The diversity of carbon allotropic forms and types of bonds between carbon atoms causes the different approaches to inculcation of a functional groups on CNM surface. 

The first of these is the canonical name when this allotrope is considered alone however, because an infinite number of carbon allotropes can be formed by replacing congruently placed single bonds in graphite or diamond with acetylenic linkages of the second form, this name is also important. 

Most of the carbon in the Allende C3V chondrite is present in elemental form, rather than as polymer or extractable organic compounds (Breger et al., 1972). It was originally called amorphous carbon , since it is amorphous to x-rays. However, recent work shows it to be carbyne (Whittaker et al., 1980 Hayatsu et al., 1980b) a triply bonded, linear allotrope of elemental carbon. Carbyne exists in at least 10 varieties, ranging between graphite and diamond in hardness and density (Whittaker, 1978 and references therein). 

Carbon is the basis of all life on earth, and without a doubt, one of the most versatile elements known to man. More than ten million carbon compounds are known today, many times more than that of any other element. Carbon itself exists in several allotropes. Its flexible electron configuration allows carbon to form three hybridization states which lead to different types of covalent bonding. The most representative macroscopic forms of carbon are graphite and diamond. In 1985, Kroto et al. discovered a third carbon allotrope, the fullerenes. While their experiments aimed at understanding the mechanisms by which long chained carbon molecules are formed in interstellar space, their results opened a new era in science - the beginning of nanotechnology. 

Carbon materials liave particular characteristics due to differences in chemical bond formation. Allotropic forms of carbon drat luive been discovered can be categorized into five types from file standpoint of the type of hybridization of the valence orbitals (1) sp -hybridization (2) sp -hybridization (3) sp-hybrid-ization (4) mixed hybridization (sp + sp ) and (5) a valance state characterized by a fractional degree of hybridization (sp , where 1 diamond-like carbon, and fullcrcnes correspond to groups (1), (3), (4), and (5), respectively. 

The properties of carbon allotropes depend on the arrangement of the atoms and how they are bonded to each other. 

The combination of sp , sp and sp hybridized atoms can give rise to a large number of carbon allotropic forms and phases, but only carbon solids based on all sp (diamond) and sp (graphite, fullerene) hybridization are well known and characterized [1]. In addition there are innumerable transitional forms of carbon where sp and sp hybridization bonds co-exist in the same... 

Linear carbon chains with sp hybridization have been proposed to be present in the interstellar medium [2-4]. These chains can be constituted by alternate single (C-C) and triple (C=C) bonds (polyynes) or double (C=C) bonds (poly-cumulenes) and have been proposed as building blocks for carbynes, a carbon allotrope [5],... 

Carbon is the most versatile element in forming allotropes. Organized or unorganized, atoms of carbon can take on an incredible number of arrangements, each different from the other and each forming a different allotrope. With all their diversity, these substances have one thing in common they are made up solely of covalently bonded carbon atoms. 

Another allotrope of elemental carbon is diamond. Besides being blinded by the brilliance of a cut diamond, you should know that diamond is the hardest natural substance. It s often used on the tips of cutting tools and drills. Can the structure of diamond explain its hardness Look at the model of diamond. Every carbon atom is attached to four other carbon atoms which, in turn, are each attached to four more carbon atoms. Diamond is one of the most organized of all substances. In fact, every diamond is one huge molecule of carbon atoms. This organization of covalently bonded carbons throughout diamond accounts for its hardness. If you tried to write... 

This threadlike allotrope of carbon is organized into long spirals of bonded carbon atoms. Each spiral contains 300 to 500 carbon atoms. It s produced by using a laser to zap a graphite rod in a glass container filled with argon gas. The allotrope splatters on the glass walls and is then removed. Because they conduct electricity, these carbon filaments may have uses in microelectronics. Some linear acetylenic carbons may eventually form ftillerenes, whereas others form soot. 

Strelnitskii et al. 32) reported a superdense carbon allotrope (4,100 kg-m ) obtained as carbon films formed by radio-frequency condensation of carbon plasmas on cooled substrates the crystalline phase, obtained along with amorphous phase, was studied by electron diffraction and revealed a primitive rhombohedral unit cell with 8 carbon atoms, hence this phase was called Cs, and its structure, as proposed by Stankevich et al. [33] and Biswas et al. [34], involved cubes connected by single bonds (supercubane). Burdett and Lee [9] found the supercubane structure to be less stable than diamond if the constituting atoms have 4 or less electrons per atom, but more stable for electron-rich systems (i. e. >4 electrons per atom). Johnston and Hoffmann [35], observing discrepancies in the crystallographic analysis and the unusual bond length distribution, found that a likely alternative structure for Cs is the body-centered BC-8 structure adopted by the high-pressure y- Si allotrope. 

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