Industrial Carbon and Graphite Materials. Группа авторов

hypotheses on the genesis of natural graphite existed, but today most of them are outdated. It is currently supposed that organic matter was the origin of most natural graphites with the probable exception of the Sri Lanka (vein‐type) deposits. The origin of vein graphite deposits is still not certain. In regionally metamorphosed (granulitic, charnockitic) rocks, graphite is thought to form epigenetically from carbon‐rich hydrothermal or pneumatolytic solutions as interlocking aggregates of coarse graphite crystals in veins containing 75–100% carbon. Disseminated flake graphite deposits (see Figure 5.5) develop synergetically from carbonaceous material in sedimentary rocks that have been subjected to garnet grade or higher regional metamorphism. Concurrent large‐scale folding of the metasedimentary sequences is common, and fold limbs often host deposits. Deposits are usually stratabound and consist of individual beds or lenses in gneisses, schists, and marbles that are richer in graphite than associated beds [15]. Single flakes may range from 0.5 to 25 mm. The decomposition of compounds, e.g. carbide, carbonates, carbonyl, and cyano compounds, is less important for the genesis of graphite deposits.

Natural graphite is divided into vein type, flake type, and microcrystalline type, often incorrectly called amorphous graphite. Crystallinity, refractoriness, and other properties of natural graphite from different deposits may vary substantially because of differences in the precursor materials and the conditions of metamorphosis. In general, natural graphite is a ductile soft mineral that easily cleaves parallel to the basic layer. The flaky and vein grades show a typical metallic luster; the microcrystalline “amorphous” grades have a duller black appearance. Table 5.2 shows a classification [16, 17]. The host rocks consist of quartz, mica, gneiss, feldspars associated with pegmatite aplite, granite magnetite, and calcite.

Figure 5.5 Scanning electron microscopy (SEM) picture of a flake natural graphite.

Table 5.2 Classification of natural graphite.

	Deposit	Carbon content (%)	Average crystallite diameter (mm)	Origin
Macrocrystalline flakes	Brazil	<60	<0.1	Syngenetic cata‐ and mesozonal metamorphism of sapropelites
	Germany (Kropfmühl)
	China
	Canada
	Malagasy Republic
	Norway
	India
	Zimbabwe
	Russia
	Mozambique
	Tanzania
Macrocrystalline lumps	Sri Lanka	<100	<0.01	Epigenetic, probably pneumatolytic
Mesocrystalline	Austria	30–90	<0.001	Syngenetic metamorphism of sapropelites
	Czech Republic
Microcrystalline	China	30–90	<0.001	Syngenetic, epizonal metamorphism of coals
	Korea
	Russia
	Mexico Austria

5.3 Synthetic Graphite

      According to IUPAC nomenclature [11], the term “synthetic graphite” should be used instead of “artificial graphite.” The IUPAC describes “synthetic graphite” as follows:

      Synthetic graphite is a material consisting of graphitic carbon which has been obtained by graphitization of non‐graphitic carbon, by chemical vapor deposition (CVD) from hydrocarbons at a temperature above 2500 K, by decomposition of thermally unstable carbides or by crystallizing from metal melts supersaturated with carbon.

Figure 5.6 Classification of different forms of carbon according to IUPAC nomenclature. Approved IUPAC terms are printed in italics [11].

Figure 5.6 provides an overview on the recommended IUPAC nomenclature, together with examples for