Diamond formation

Fig. 1. Carbon-phase diagram where A, solvent-cataly2ed diamond growth B—G, diamond formation direcdy from graphite C, graphite formation from diamond, D, approximate region where formation of Lonsdaleite occurs from weU-ordered graphite crystals (7,8). To convert GPa to atm, multiply by...

The presence of water vapour in the ingoing gas irrixmre has been found to suppress the formation of graphite and dins to favour diamond formation. The significant change in composition when water vapour is added, is the presence of carbon monoxide in about half the proportion of hydrogen atoms. 

There is a clear difference in syngenetic inclusions in diamond crystals between (2) and (3), indicating a difference in the chemical environments of diamond formation. 

H. Yamaoka, M. Akaishi, and S. Yamaoka, Diamond formation in the graphite-MgO-HjO system. Advanced Materials 96, Tsukuba, NIRIM, 1996, pp. 245-50... 

Figure 15.7 is reproduced with permission from R. H. Wentorf Jr., Diamond Formation at High Pressures , taken from Advances in High-Pressure Research, Vol. 4, R. H. Wentorf, Jr., editor, Academic Press, London, 1974, pp. 249-281. 

Galimov, E. M. 1991 Isotopic fractionation related to kimberlite magmatism and diamond formation. Geochim. Cosmochim. Acta 55, 1697-1708. 

The tendency for diamond formed under nonfluid conditions to be influenced by the structure of the precursor carbon can be noted when hydrocarbons are decomposed at 12 GPa. Aliphatic hydrocarbons, which already posses tetrahedral carbon bonding, seem to slowly lose hydrogen and approach cubic diamond. Purely aromatic molecules such as anthracene change to graphite, then finally to diamond at higher temperatures. Adding aliphatic carbon atoms to the molecules or the mixture favors diamond formation at lower temperatures. 

Then a mixture of diamond and cobalt powders was placed into the cell and subjected to pressure and temperature. Liquid cobalt that wetts diamond is pulled out of the compact if the volume occupied by cobalt somewhat exceeds the total volume of pores which remained after shrinkage of diamond powder. When liquid metal is in contact with a graphite heater, the current flow at first increases due to a total drop of the system electric resistance and then decreases because of diamond formation in the heater. In this case, the shrinkage value corresponds to the volume of cobalt in the powder. 

Towards the end of the 18 century a British chemist, Smithson Tennant, showed that diamonds are composed of nothing but carbon a discovery that gave a more scientific direction to synthesis efforts. By the beginning of the 19 century, it was known that carbonaceous materials, heat and pressure are required for diamond formation. Finally, success in artificial synthesis was achieved in the middle of the 20 century by two routes the High Pressure High Temperature (HPHT) route leading to the formation of diamond grit and the Low Pressure... 

Russian group of Derjaguin et al., by irradiating ultrafine graphite powder with a CO laser beam, and was later confirmed by Roy et al. Various other researchers have reported diamond synthesis by similar techniques (e.g., 24-27). Diamond formation by laser ablation of graphite too has been claimed (e.g., 28, 29). 

Cartigny P., Harris J. W., and Javoy M. (1998a) Eclogitic diamond formation at Jwaneng no room for a recycled component. Science 280, 1421—1424. 

Pal yanov Y. N., Sokol A. G., Borzdov Y. M., Khokhryakow A. F., and Sobolev N. V. (1999a) Diamond formation from mantle carbonate fluids. Nature 400, 417-418. 

Hermann J. and Green D. H. (2001) Experimental constraints on melt-carbonate interaction at UHP conditions a clue for metmorphic diamond formation In Fluid/Slab/ Mantle Interactions and Ultrahigh-P Minerals (eds. Y. Ogasawara, S. Maruyama, and J. G. Lion). Waseda University, Tokyo, pp. 31—34. 

Sobolev N. V. and Shatsky V. S. (1990) Diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation. Nature 343, 742—746. 

It is clear that all these results give only indirect evidence for tlie rneclianisrn of diamond formation in detonation of explosives. In order to confirm the hypotheses suggested above, experimental evidence is necessary. Because of the complexity of detonation products, the very short duration of the detonation process, and the very high pressure and temperature in the detonation zone of... 

Figure 12.21. Surface morphologies of the Ir substrates, which were BEN-treated and then subjected to diamond formation step. The times are the periods of the BEN treatments [407].

The mechanism of diamond formation by the LPSSS method using metal catalyst is considered to be similar to that of heteroepitaxial growth of diamond on Pt(lll) and Ir(lOO) described in Sections 12.1 and 12.2, because a metal-C H complex seems to be involved in the nucleation process. An advantage of the LPSSS method in view of engineering is that substrates with complex shapes could be coated with diamond. 

Diamonds formed by this route would contain inclusions containing either free sulphur, or sulphur compounds, or both on oxidation, gaseous sulphur oxy-compounds would be formed, which could be detected mass spec-trometrically. No evidence of sulphur was found, and so this proposed route to natural diamond is not thought to be responsible for the formation of all natural diamonds. The data are limited by the amount of diamond oxidized (16 g), and so the possibility of some diamond formation by this route cannot be ruled out.11... 

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