Well-ordered graphite

Figure 8. TEM micrographs of well-ordered graphite produced at 1200°C. 

Fig. 1. Carbon-phase diagram where A, solvent-catalyzed diamond growth B—G, diamond formation diiecdy from graphite C, graphite formation from diamond, D, approximate region where formation of Lonsdaleite occurs from well-ordered graphite crystals (7,8). To convert GPa to atm, multiply by...

The composition varies with the heat treatment and the end point according to x-ray diffraction studies it is a form of carbon that reconverts to well-ordered graphite on heating to 1800°C. Before the use of x-rays, chemists used the Brodie reaction to differentiate between graphitic carbons and turbostratic carbons. Turbostratic carbons yield a brown solution of humic acids, whereas further oxidation of graphite oxide produces mellitic acid (benzenehexacarboxylic acid) [517-60-2], C12H6012. 

Endo M, Oshida K, Kobori K, Takeuchi K, Takahashi K. Evidence for glide and rotation defects observed in well-ordered graphite fibers. J Mater Res 1995 10 1461-1468. 

A practical situation is shown in Fig. 26. The carbon 1 s data of HOPG as reference are compared to those of a chemically etched graphitized carbon black sample. The defective graphitized carbon surface exhibits a significantly wider main line at almost the same position as the well-ordered graphite (cleaved and annealed in UHV [90]). It can be seen that the neglect of the line asymmetry invariably causes the erroneous detection of additional lines in the range l-2eV above the peak... 

The foregoing discussion serves to show that disordered carbon structures are oxidized more readily than well-ordered graphite planes and that dislocations and active sites provide nucleation points for attack of the carbon crystallite. Another factor that must be considered is that dispersed electrocatalysts, such as platinum, on the carbon surface are not benign. The electrocatalysts interact with the carbon causing local oxidation or corrosion, i.e., the platinum catalyzes the corrosion of the carbon itself. In the presence of oxygen, which is the condition under which the electrocatalyst will operate, reduction intermediates from the oxygen (e.g., HOj) can have an accelerated corrosion effect. 

Cokes are formed by the carbonization of most aromatic hydrocarbons and a few polymers as mentioned above and are readily converted into a well-ordered graphite structure. 

The coke-former aromatic hydrocarbons listed in Table 4.1 and shown in Fig. 4.2, i.e., naphthalene, einthracene, and acenaphtalene, are linear with a coplanar structure that has no preferred growth direction. This structural feature and the formation of a mesophase mentioned in Sec. 2.3 are the major factors in the easy conversion of theturbostratic structure into well-ordered graphite planes.1 1... 

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