Crystalline forms of carbon

AH graphite has crystal stmcture but only certain kinds and sizes of natural graphites are commercially classified as crystalline, a term used for import duty purposes. Throughout this article reference is made separately to dake, vein (lump or high crystalline), and amorphous forms, all of which are essentially the same crystalline form of carbon. However, fine stmctured graphites (cryptocrystalline (2)) have been classified as amorphous. 

Graphite is a denser crystalline form of carbon. Graphite anodes are prepared by heating calcined petroleum coke particles with a coal tar pitch binder. The mix is then shaped as required and heated to approximately 2 800°C to convert the amorphous carbon to graphite. Graphite has now superseded amorphous carbon as a less porous and more reliable anode material, particularly in saline conditions. 

It is well known that the stable crystalline form of carbon at ambient conditions is graphite, which is fully sp hybidized. The synthesis of the fully sp -hybridized crystalline diamond is performed at high temperatures and pressures. So, the production of metastable carbon solids with a high fraction of sp -hybridized... 

The commonest crystalline forms of carbon, cubic diamond and hexagonal graphite, are classical examples of allotropy that arc found in every chemistry textbook. Both diamond and graphite also exist in two minor crystallographic forms hexagonal diamond and rhombohedral graphite. To these must be added carbynes and Fullerenes, both of which are crystalline carbon forms. FulleTenes are sometimes referred to as the third allotrope of carbon. However, since Fullerenes were discovered more recently than carbynes, they are... 

Table 4. Some properties of crystalline forms of carbon...

Carbon electrodes can be made from a number of various crystalline forms of carbon. The two most common versions are the carbon paste electrode and the glassy carbon electrode. In Chapter 11, devoted to the electrochemistry of biological functions, it will be seen that pyrolytic graphite electrodes have also found wide application. Recently, attempts to use carbon-nanotube electrodes have been also proposed.9... 

The crystalline form of carbon known as graphite, is composed of stacked hexagonal networks of C atoms. The generalized structure of such a network is identical to that presented in Fig. 2.1 as the ideal array for silicate sheets. The graphite sheet is simpler in that only one atom, C, is located at the... 

Physical Form. A crystalline form of carbon made from high-temperature treatment of coal or petroleum products same properties as natural graphite it is chemically inert... 

A.l 1 Calculate the average density of a single carbon atom by assuming that it is a uniform sphere of radius 77 pm and that the mass of a carbon atom is 2.0 X 10 23 g. The volume of a sphere is f-nr , where r is its radius. Express the density of carbon in grams per cubic centimeter. The density of diamond, a crystalline form of carbon, is 3.5 g-cm 3. What does your answer suggest about the way the atoms are packed together in diamond ... 

Before 1985, six crystalline forms of carbon were known two forms of graphite, two forms of diamond, and chaoit and carbon (VI) discovered in 1968 and 1972, respectively. In addition a number of almost pure amorphous forms exist, such as polyacetylene (7.60) and cumulene (7.61) and recently a number of interesting nanostructured forms of carbon have been produced (Section 15.8). The year 1985 marked the discovery of the fullerenes, which represent the only truly pure molecular form of carbon, are produced under very extreme conditions as carbon vapour condenses in an atmosphere of an inert gas such as helium. Harold Kroto s interest in this chemistry originated with microwave spectroscopic studies of the atmosphere of stars and interstellar dust clouds. Kroto wanted to try to reproduce in the laboratory spectra of carbon... 

C Graphite is one of the crystalline forms of carbon. TWo of the distinctive properties of graphite arc ... 

Amorphous carbon is a general term that covers non-crystalline forms of carbon such as coal, coke, charcoal, carbon black (soot), activated carbon, vitreous carbon, glassy carbon, carbon fiber, carbon nanotubes, and carbon onions, which are important materials and widely used in industry. The arrangements of the carbon atoms in amorphous carbon are different from those in diamond, graphite, and fullerenes, but the bond types of carbon atoms are the same as in these three crystalline allotropes. Most forms of amorphous carbon consist of graphite scraps in irregularly packing. 

There are three main crystalline forms of carbon with well-defined lattice parameters (i.e. having long-range order) graphite, diamond and the fullerenes. Graphite is the stable form at ambient temperature and pressure. Its normal structure is shown in Figure 9.1. 

One method involves the microwave-induced removal of hydrogen from methane (CH, swamp gas) in a very sparse gas phase so that carbon atoms, stripped of most of their hydrogen, can settle out on the substrate and start building diamond crystals. In the past, the diamonds formed in this process were tiny and only suitable for industrial applications, but lately gem-quality crystals have been grown. The artificial diamond is virtually indistinguishable from the natural diamond because they are both just a crystalline form of carbon. 

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