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Diamond formation through metastable liquid carbon



It is known that carbon melts at temperatures around 4000 K or higher, and, therefore, this will be for the first time, when liquid carbon state formation preserved within diamond is documented in a carbon-carbonate system at the PT-conditions around 8.0 GPa and 2000 K, that is essentially far from the carbon diagram liquid field, so the newly reported liquid carbon was formed by neither fusion nor condensation. Based on a preponderance of such a strong circumstantial evidence, as morphological features of globular glass-like carbon inclusions within the globular-textured host diamond crystals resulting from liquid segregation process under synthesis conditions, it is suggested, that the produced carbon state has general properties of liquid and is formed through agglomeration alongside with diffusion process of carbon within carbonate melt solvent, and, thus, can potentially open a novel route for liquid carbon production and manufacturing of advanced high-refractory alloys and high-temperature compounds at lower than commonly accepted standard temperatures. A new model of diamond formation via metastable liquid carbon is presented. DOI information: 10.1016/j.diamond.2015.12.015 The following personal article link can provide free access to the full text article, which is valid until February 24, 2016:
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Shumilova T.G., Isaenko S.I., Tkachev S.N. Diamond formation through metastable liquid
carbon. Diamond & Related Materials 62 (2016) 42–48.
... The recent discovery of patches of sub-micron diamonds in Libyan desert glass, a high-silica natural glass that is thought to be of cometary origin ( Kramers et al., 2013), lends credence to the ET model for carbonado. This view is supported by the growing lines of evidence for (1) synthetically produced diamondlike glass ( Shumilova et al., 2016a, b); (2) nanodiamond encased in glassy carbon shells in the interstellar media ( Yastrebov and Smith, 2009); and (3) glassy carbon and nanodiamond produced experimentally ( Shiell et al., 2016) and in supernova shock waves ( Stroud et al., 2011). Another supporting fact is the discovery of asteroid 2008 TC 3 , which was tracked upon entering Earth's atmosphere and landed in North Sudan as a fragmented, diamond-bearing ureilite ( Miyahara et al., 2015). ...
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Carbonado diamond is found only in Brazil and the Central African Republic. These unusual diamond aggregates are strongly bonded and porous, with melt-like glassy patinas unlike any conventional diamond from kimberlites-lamproites, crustal collisional settings, or meteorite impact. Nearly two centuries after carbonado's discovery, a primary host rock compatible with the origin of conventional diamond at high temperatures and pressures has yet to be identified. Models for its genesis are far-reaching and range from terrestrial subduction to cosmic sources.
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The book opens the main low connections between the processes of formation and distribution of native carbon in the nature. The modern classification of carbon forms, mechanisms and thermodynamic conditions of formation of carbon mineralization are described. The typomorphic features of carbon mineralization of different genetic types including new natural carbon forms and new localization of rare carbon forms have been written. Tight genetic connection between carbon forms in the nature is proved the one defines joint presence of diamond, graphite, carbyne and hybrid types of carbon. On the basis of carbon paragenesis new criterion of prospecting of origin diamond deposits is offered. The book is intended for scientists and students of geological specialization and material science the one may be useful for specialists working on the problems of prospecting, synthesis and modifying of diamond, graphite and other forms of carbon materials.
A novel sp 3-bonded nanosize domain, known as a diaphite which is an intermediate state between a graphite and a diamond, is generated by the irradiation of visible laser pulse onto a graphite crystal. The sp 3 structure is well stabilized by shear displacement between neighboring graphite layers. We theoretically study the interlayer sp 3 bond formation with frozen shear displacement in a graphite crystal, using a classical molecular dynamics and a semi-empirical Brenner potential. We show that a pulse excitation under the fluctuation of shearing motion of carbons in an initial state can generate interlayer sp 3 bonds which freeze the shear, though no frozen shear appears if there is no fluctuation initially. Moreover, we investigate a pulse excitation under the coherent shearing motion and consequently obtain that the sp 3-bonded domain with frozen shear is efficiently formed. We conclude that the initial shear is important for the photoinduced sp 3 nanosize domain formation.
Diamond genesis can be clarified by estimating the common parental media for diamond and its syngenetic inclusions. Formation of diamond and diamondite in car-bonatitic melts with garnets, clinopyroxenes, carbonates, iron-chromium alloys, and other minerals was confirmed in experiments using diamond-bearing Kokchetav (Kazakhstan) and Chagatai (Uzbekistan) carbonatitic rocks as the starting materials. Experiments on melting equilibrium of an eclogitic garnet-pyrrhotite join at 7 GPa revealed the existence of a nearly complete silicate-sulfide liquid immiscibility. Very low solubility of silicate components in the sulfide melt implies that the melt is not so efficient for syngenesis of diamonds and silicate inclusions, whereas carbonatitic (carbonate-silicate) parental melts can provide syngenesis of diamond and their primary inclusions more viably. The major components of the parental media for diamond syngenesis are carbonates and silicates, and the minor components are oxides, sulfides, phosphates, haloids, carbon dioxide, water, etc. These media are partially or completely molten during diamond formation, and they have compositionally variable major and minor component contents. It is obvious that the parental media for diamond is closely related to the genesis of carbonatitic magmas in the Earth's mantle.
During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells1, graphite has been vaporized by laser irradiation, producing a remarkably stable cluster consisting of 60 carbon atoms. Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1. The C60 molecule which results when a carbon atom is placed at each vertex of this structure has all valences satisfied by two single bonds and one double bond, has many resonance structures, and appears to be aromatic.
Diamond-like carbon (DLC) is a dense, partially sp3 bonded form of amorphous carbon prepared by ion beam or plasma deposition and frequently used as a hard coating material. Its sp3 bonding arises from C+ ions penetrating surface layers and giving a quenched-in density increase. The formation of DLC can be viewed as a phase transition to a denser metastable phase. The atomic structure of DLC consists of a network of sp3 and sp2 sites. The ?r states of sp2 sites control the electronic properties and the connectivity of sp' sites controls the mechanical properties.
Phase composition and nanostructure of layered and irregular massive impact diamond grains from the Popigai astrobleme have been investigated by Raman spectroscopy and high-resolution electron microscopy and the conditions of phase transformations are discussed. Several coexisting carbon phases forming tight aggregates have been found, including cubic and hexagonal diamond polymorphs, graphite, amorphous carbon, fullerene-like/onion-like carbon. The latter is described within impact diamonds for the first time. It is proposed that the formation of onion-like carbon, in both layered and massive impact diamond grains, is connected with high-pressure graphite transformation or post-pressure stress cooling which causes the partial back transformation of diamond nanocrystallites to sp2 carbon. However, a possible relict origin of the fullerene-like carbon from the impacted initial sedimentary rocks with fullerenes and fullerene-like substances, like shungite or coal, can not be excluded. The difference between micro- and nanostructures of layered and irregular massive impact grains is presented.