Graphitization of Carbons

Charcoals and various carbon blacks show great variability of their structure and properties as a function of the carbonaceous starting material and the preparation conditions [3, 11]. The graphitization of carbon, which is required to achieve a high corrosion resistance, lead to materials of more homogeneous structures and properties, allowing a good reproducibility of reactions. 

The authors (iSl) and Kmetko (ISS) have confirmed definitely, from electron micrographs, that graphitization of carbon blacks of low surface area produces polyhedral particles. 

Carbon materials used for the commercial synthesis of carbon fluoride include natural graphite, petroleum coke, activated carbon, carbon black and carbon fiber. Experimental carbon materials include residual carbon, exfoliated graphite, fullerenes and other unique carbons and carbon inserts. The degree of graphitization of carbon material varies continuously, so it is not simple to define the exact boundary between carbon and graphite. The product formed... 

A review of the graphitization of carbons, containing 183 references, has been published.20 The influence of doping by boron on the graphitization of carbons has been the subject of an exhaustive investigation 21 a new mechanism for the graphitization process has been developed.21... 

Other fillers also produce variable degrees of crystallinity depending on their surface treatment. Carbon black is such an example. Graphitization of carbon black may increase surface crystallinity by 30%." ... 

Paredes, J.I., Burghard, M., Mardnez-Alonso, A., and Tascon, J.M.D. (2005). Graphitization of carbon nanofibers visualizing the stmctural evolution on the nanometer and atomic scales by scanning tunneling microscopy. Appl. Phys. A, 80, 675-82. 

Table 2. Effects of graphitization of carbon black on reinforcement...

Aromatic carbon seems to be one of the major structural defects in amorphous SiC phases resulting from polymers. It stays in the SiC as amorphous carbon up to 1300 °C as shown by Raman studies. Graphitization of carbon usually occurs at temperatures higher than 2000 °C. 

Y. Hishiyama, M. Inagaki, S. Kimura and S. Yamada, "Graphitization of carbon fiber/glassy carbon composites". Carbon, 12 249-258.1974. 

F. J. Maldonado-Hodar, C. Moreno-CastiUa, J. Rivera-UtriUa, Y. Hanzawa, and Y. Yamada, Catal5dic Graphitization of Carbon Aerogels by Transition Metals, Langmuir, 16, pp. 4367-73, 2000. 

The degree of graphitization of carbon precursors such as those shown in Table 4.1 varies considerably, depending on whether a coke or a char is formed, as will be shown in the following sections. 

The narrowed PSD in the case of Salix viminalis wood-originated carbon occurs in relatively limited range of carbonization temperatures (600-700°C) and its hmited duration (typically 1 hr + 1 hr). More severe carbonization conditions leads to a collapse of this specific system of pores (Gorska, 2009 Ohata et al., 2008) due to graphitization of carbon matrix. 

The MPL often suffers more severe carbon corrosion and hydrophobicity loss than the substrate layer, because it is closer to the corrosive substances produced in membrane and CL (e.g., H2O2, HF). Similar to the carbon powders in the catalyst layer, graphitization of carbon powders in MPL also enhances the corrosion resistance. The hydrophobic material (e.g., PTFE) can also protect the carbon from corrosion. Wood and Borup (Wood et al., 2009) found that no significant structure change occurred in MPL after 664 h of durability test at 1 A cm. In order to enhance the durability, Gore CARBEL CL MPL uses PTFE as substrate filled with carbon black (like the concept of reinforced membrane), and it showed good durability in a PEM fuel cell life test (Cleghorn et al., 2006 Wood et al., 2009). 

S. I. Hirano, K. Nakamura, and S. Somiya, Graphitization of carbon in presence of calcium compounds under hydrothermal condition by use of high gas pressure apparams. In Hydrothermal Reactions for Materials Science and Engineering, S. Somiya, Editor, Elsevier, London, 331-336,1989. 

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