Composition of Hydrocarbons in Synthetic Diamonds Grown in a Fe—Ni—C System (according to Gas Chromatography—Mass Spectrometry Data) (original) (raw)
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The light volatile impurity elements hydrogen and nitrogen have been directly measured for the first time in synthetic diamonds. Hydrogen was measured by counting the gamma ray yield from the 'H(19F, oy)i60 nuclear resonance reaction; nitrogen was measured using the positron annihilation technique based on the i4N((u, n)"F nuclear reaction. The volatile element concentrations from the suite of synthetic diamonds are compared to those obtained using the same techniques in a suite of natural type lb diamonds.
Experimental study of intake of gases by diamonds during crystallization
Journal of Crystal Growth, 1999
The composition of gases in diamond crystals, grown at the multi-anvil apparatus "BARS" in the Fe-Ni-C system under pressure 55-60 kbar, temperature 1300°C-1500°C, has been studied. The source of the gases in experiments was their natural admixture in the parent metal-carbonic schist. The gases occurred in diamonds in the scattered form in the zones of the crystal imperfections as well as in the form of three-dimensional inclusions with the size of 5-40 mkm. The composition of gaseous impurities in diamond has been studied by heating the crystals in He atmosphere under 600°C with the following chromatographic analysis of the emanated gases on the content of H O, CO , CO, H , N
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In the last decade, progress in diamond growth by chemical vapor deposition (CVD) has resulted in significant improvement in the quality of synthetic single crystals. This article reports on the gemological and spectroscopic features of six synthetic type IIa diamonds grown for research purposes at the French Laboratoire d'Ingénierie des Matériaux et des Hautes Pressions (LIMHP-CNRS), and compares their diagnostic features to CVD-grown diamonds from other producers. Three of the six samples were nitrogen doped, whereas the other three were classified as high purity. A number of characteristics that are diagnostic of CVD synthetic diamond were present in the nitrogen-doped crystals, despite an absence of defect-related absorption features in the infrared region. Identification of the high-purity samples was more complicated, but it was still possible based on features in their photoluminescence spectra, their distinctive birefringence, and characteristic luminescence images.
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Results are presented for synthesis of the diamond phase of carbon during detonation of the high-temperature explosive benzotrifuroxan (BTF)-C6N606. The detonation products of this nonhydrogenic explosive have a high temperature which initially falls in the region of thermodynamic stability of the liquid phase of carbon. A two-stage synthesis process is proposed: drops of liquid carbon with diameters O. 1-1.0 I~m are formed initially, and these drops subsequently crystallize into the diamond structure. The experimental results given here confirm this hypothesis.
Carbonatitic mineralogy of natural diamond-forming fluids
Earth and Planetary Science Letters, 2010
Keywords: diamond fluid inclusion X-ray diffraction vibrational spectroscopy mineralogy carbonatite A suite of 20 cuboid fibrous diamonds from the Democratic Republic of Congo was studied to determine mineral phases crystallized from diamond-forming fluids that were trapped as inclusions in diamonds. We identified minerals and non-crystalline components using their compositional trends in the electron microprobe analyses of inclusions, an innovative bulk X-ray diffraction analysis and characteristic FTIR and Raman peaks. The DRC diamonds contain fluid inclusions of the Ca-carbonatitic-silicic composition. Most common phases precipitated from the fluid are found to be high-Si micas (90-30% of the solids volume), complex non-crystalline Na-Ca-Mg-Fe carbonate matter and apatite (together 5-70%), leaving a residual aqueous solution of K, Cl and carbonate ions and gaseous CO 2 . A notable absence of carbonate minerals in bulk X-ray diffraction patterns combined with the vibrational spectroscopy observations on the C-O bonds indicates that C may be included in dissolved or amorphous carbonate matter. The modes of the most abundant phases are controlled by chemical trends of the bulk fluid compositions. Other relatively rare ∼ 30 minerals, including various minerals with structural and coordinated H 2 O, are detected by the vibrational spectroscopic and X-ray analyses. The fluid also contains some hydrocarbons associated with the carbonate material. The presence of some rare minerals and exotic compositions of solid-solution minerals in the fluid suggest crystallization from a closed system with high salinity-high aH 2 O-high aCO 2 composition that persisted to relatively low temperatures and pressures. The bulk of the fluid crystallized in the diamond stability field (P b 7 GPa, T b 950°C), but continued to form hydrocarbons, accessory and deuteric phases down to 200°C and 0.2 GPa. Overall, the mineralogy of the fluid resembles carbonatite.
Some aspects of diamond synthesis
Diamond and Related Materials, 1993
We have studied the structural properties of new carbon phases involved in diamond synthesis at both high and low pressure. X-ray diffraction analysis of graphite after a high pressure, high temperature treatment (about 5.5 GPa, 1900-2100 K with FeNi catalyst) showed the presence of a new carbon phase (H-12)o.3 , which plays a key role in the growth of diamond crystals. Experimental examination of the metallic surface on chemical vapour deposited diamond suggests the existence of a new carbon phase. We propose a hypothetical new carbon phase H-8, with a hexagonal unit cell (a = b = 2.543 A; c = 8.82 A). The present paper reports the results obtained in the study of a heterogeneous Fe-Ni-C system at high pressure in the presence of a small amount of hydrogen. A hereditary effect and low miscibility of molten hydrogenated nickel were observed. Diamond crystals have been grown within the bulk heterogeneous FeNi solvent catalyst.
Unravelling aspects of the gas phase chemistry involved in diamond chemical vapour deposition
Physical Chemistry Chemical Physics, 2001
We describe laser and mass spectroscopic methods, and related modelling studies, that have been used to unravel details of the gas phase chemistry involved in diamond chemical vapour deposition (CVD) using both H/C (i.e. and H/C/O (e.g. gas mixtures, and comment on the relative advantages hydrocarbon/H 2) C O 2 /CH 4) and limitations of the various approaches. In the case of the more extensively studied systems hydrocarbon/H 2 we pay particular emphasis to investigations (both experimental, and 2-and 3-dimensional modelling) of transient species like H atoms and radicals, their spatial distributions within the reactor and the ways in CH 3 which these distributions vary with process conditions, and the insight provided by such investigations into the chemistry underpinning the diamond CVD process. These analyses serve to highlight the rapid thermochemical cycling amongst the various hydrocarbon species in the reactor, such that the gas phase composition in the vicinity of the growing diamond surface is essentially independent of the particular hydrocarbon source gas used. Such applies even to the case of hot Ðlament activated gas mixtures, C 2 H 2 /H 2 for which we show that radical formation (hitherto often presumed to involve heterogeneous CH 3 hydrogenation steps) can be fully explained in terms of gas phase chemistry. Diamond growth using H/C/O-containing gas mixtures has traditionally been discussed in terms of an empirically derived HÈCÈO atomic phase composition diagram (P. K. Bachmann, D. Leers, H. Lydtin and D. U. Wiechert, Diamond Relat. Mater., 1991, 1, 1). Detailed studies of microwave activated gas mixtures, accompanied by simpler CO 2 /CH 4 zero-dimensional thermochemical modelling of this and numerous other H/C/O-containing input gas mixtures, provide a consistent rationale for the " no growth Ï, " diamond growth Ï and " non-diamond growth Ï regions within the HÈCÈO atomic phase composition diagram.