Different Forms of Carbon

Elucidation of the phase relationships between the different forms of carbon is a difficult field of study because of the very high temperatures and pressures that must be applied. However, the subject is one of great technical importance because of the need to understand methods for transforming graphite and disordered forms of carbon into diamond. The diagram has been revised and reviewed at regular intervals [59-61] and a simplified form of the most recent diagram for carbon [62] is in Fig. 5. 

It is outside the scope of this Chapter to undertake a comprehensive review of structure-property relationships for the different forms of carbon. However, a limited comparison of properties is useful for illustrating the influence of chemical bonding upon the properties of diamond, graphite and Buckminsterfullerene, Qo, Table 4. Carbynes are omitted from the comparison since insufficient is known of their properties. 

In graphite, a different form of carbon, atoms are bonded to each other in such a way that a hexagonal structure is formed in a plane. Each carbon atom is bonded to three other carbon atoms with an angle of 120° between the bonds. The bonding involves sp2 - sp2 hybrid overlap and this gives rise to layers. 

Harry Kroto, Richard Smalley, Robert Curl, and their colleagues discover a different form of carbon, Cgg, also known as buckminsterfullerene or buckyball. ... 

The difference of about 2% carbon in case of the lower rank bituminous coal does not appear to be entirely caused by cumulative errors in assessing the different forms of carbon. Remarkably, (Table VI) the amount of carbon retained in char consequent on prior dehydrogenation (and which according to our interpretation represents the sum of aromatic and hydroaromatic car-... 

Further work is required to determine the nature of the different forms of carbon formed on Ni/Zr02 catalysts during C02 reforming. 

Adsorption on mica and plane surfaces of salts. Adsorption on different forms of carbon. ... 

Figure 17. Reactivities of different forms of carbon against oxidation in 5% oxygen in Ar (100%) as function of temperature. The carbon black was FW-1 (Degussa), the graphite natural graphite powder AF (Kropfmuhl).

Usually, the vaporization of the entire carbon sample prior to conversion is not required in this type of reaction. It will do if a sufficiently large number of carbon atoms are mobilized and settle at a new equilibrium position. This may be achieved by thermal vibrations at elevated temperatures, but the so-called knock-on effects at particle bombardment or irradiation may serve to the same end. In the sections below, the products of thermal treatment and of various irradiations will be presented starting from different forms of carbon. All these procedures have in common that normally a heterogeneous mixture of products is obtained. Still these may often be prepared in macroscopic amounts, thus presenting the opportunity to study the physical and chemical properties of onion-like carbon materials. 

FIG. 14. Overview of different forms of carbon, diamond, graphite, Ceo and crystals of Cso... 

In the past five decades there has been a large volume of literature in the study of carbon reactions with oxygen-containing gases, and the central issue is the determination of the active sites on carbon so that the kinetics of carbon can be correlated for different forms of carbon based on the active sites existing on these carbons. Since the groundbreaking work of Laine, Vastola, and Walker [7], this area has been somewhat dormant until recently, when further advances have been made [4-6,8,9,73-76]. 

Dandekar and co-workers investigated the surface chemistry of three different forms of carbon, (i.e., activated carbon, graphitized carbon fibers and diamond powder) by means of TPD combined with TR spectroscopy [236]. The samples were studied as-received as well as after either a nitric acid treatment to introduce oxygen functional groups on its surface or a... 

Because C50 clusters were so preferentially formed, the group proposed a radically different form of carbon, namely, nearly spherical CgQ molecules. They proposed that the carbon atoms of Cgo form a ball with 32 faces, 12 of them pentagons and 20 hexagons ( FIGURE 12.47), exactly like a soccer ball. The shape of this molecule is reminiscent of the geodesic dome invented by the U.S. engineer and philosopher R. Buckminster Fuller, so Cgo was whimsically named buckminsterfullerene, or buckyball for short. Since the discovery of C q, other related molecules of carbon atoms have been discovered. These molecules are now known as fullerenes. 

On a museum shelf, you see a beautiful clear diamond and a piece of black graphite side by side. You know that these two specimens have exactly the same chemical composition (pure carbon, C), and that experiments at very high pressures and temperatures have succeeded in changing graphite into diamond. But how is it that these two different forms of carbon can exist side by side for years, while the two different forms of H2O cannot ... 

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