The composition of the fluid phase in inclusions in synthetic HPHT diamonds grown in system Fe–Ni–Ti–C (original) (raw)
Related papers
Doklady Earth Sciences, 2020
Data on the interaction of the Fe-Ni melt with CaCO 3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography-mass spectrometry (GC-MS). Diamonds were synthesized from graphite. During the interaction of the Fe-Ni melt with CaCO 3 , CaFe oxides and (Fe, Ni) 3 C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.
Spectroscopic study of HPHT synthetic diamonds, as grown at 1500°C
Diamond and Related Materials, 2002
The distribution patterns of colour and photoluminescence in synthetic HPHT diamonds, grown in the Fe -Ni -C system at 15008C, have been studied by absorption and luminescence spectroscopy. A strong inhomogeneity in the spatial distribution of nickel and nitrogen impurity defects and nickel -nitrogen complexes of variable structure have been found. There is a wellpronounced periphery zone of yellow colour due to donor nitrogen and a much lighter internal area of Ia type, where A-type nitrogen defects and different nickel -nitrogen complexes are predominant. The strong S2, S3 yellow -green luminescence related to NE1 -NE3 defects is partly absorbed in the 450 -550-nm region with re-emission in vibronic systems with 727-and 746-nm zero-phonon lines in the near-IR region. The spatial distribution of optically active defects, analysed with ESR data on their structure taken into account, and the absence of polarisation in optical absorption are consistent with the 'annealing' model for complex defect formation. ᮊ (A. Yelisseyev).
C
With its exceptional strength characteristics, diamond has some mechanical drawbacks, significant brittleness being among them. In particular, some HPHT-grown diamonds crack when the extreme parameters inherent to the diamond growth process gradually decrease. The cracking is caused by excessive stress due to the poor plastic properties of the diamond growth catalytic medium at certain stages of reducing the pressure and the temperature. An insulating container with the growth cell and heating circuit fragment inside can also make a significant contribution to the probability of cracking. This paper considers the possibility of minimizing the mechanical stress in the growth cell and, consequently, in the diamond crystal by choosing the optimal trajectory for the decrease in the pressure and temperature from diamond growth conditions to normal conditions.
An Updated Chart on The Characteristics of HPHT-Grown Synthetic Diamonds
Gems & Gemology, 2004
A new chart, supplementing the one published in the Winter 1995 issue of Gems & Gemology, summarizes the features of both as-grown ("non-modified") and treated ("modified") synthetic diamonds currently in the gem market (that is, those grown by the high pressure/high temperature technique). It includes photographs of visual features, information about visible-range absorption spectra, and illustrations of growth-structure patterns as revealed by ultraviolet fluorescence imaging. The chart is designed to help gemologists recognize the greater variety of laboratory-created diamonds that might be encountered today.
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.
The change of Fe–Ni alloy inclusions in synthetic diamond crystals due to annealing
Diamond and Related Materials, 2000
The influence of annealing under high P᎐T parameters on the inclusions of Fe᎐Ni alloys in synthetic diamond crystals was studied. The experimental annealing of the grown diamond crystals was held under a pressure of 6.5᎐7.0 GPa, at temperatures of 1700᎐2200ЊC and the duration of the experiments was 1᎐30 h. Depending on the annealing temperature, the color of diamonds changed, along with the corresponding variations of their IR spectra, i.e. diamond of Ib type transformed into Ia type. The form of metal inclusions, entrapped by diamonds, varied, they experienced change of their faces with their orientation in one direction, in accordance with the temperature gradient in the reaction cell. Besides, the migration of the inclusions of the Fe᎐Ni alloy within diamond volume in the direction of higher temperatures took place. The mechanism of metal inclusions' migration in diamond as a result of recrystallization in the gradient field of temperatures is considered. The assumption about possible participation of carbon-containing melt of transition metals at the early stage of natural diamonds crystallization with further recrystallization and self-purification of diamonds from the transition metals' inclusions during the long period of their existence in the Earth's mantle at high temperatures and pressures was made. ᮊ
Effect of nitrogen impurity on the dislocation structure of large HPHT synthetic diamond crystals
Journal of Crystal Growth, 2014
The real structure of the {111} sectors of large single synthetic diamond crystals with different nitrogen contents has been studied by the selective etching method: (1) nitrogen-gettered diamonds with nitrogen impurity content at a level of 1-2 ppm, (2) diamond crystals grown without additives with nitrogen impurity of 180-220 ppm and (3) diamonds nitrogen alloyed during growth up to the concentrations of 550-600 ppm. All diamond crystals have been grown by the temperature gradient method using the high pressure apparatus of "split-sphere" type (BARS) at T¼1350 1C, P¼5.7 GPa and (100) seed crystal. It is found that the density of dislocations increases from 85 cm À 2 to 4.0 Â 10 3 cm À 2 and the total length of planar defects increases from 30 to 300 μm/cm 2 as the nitrogen content in the crystals increases up to 600 ppm. It is shown that partial dislocations are the dominant dislocations (60-90%) in all the crystals studied. A proportion of perfect dislocations increases as the nitrogen content in crystals, and correspondingly, the dislocation density increase. Possible causes for the increase of the extended defects density in the synthetic diamond crystals with the nitrogen impurity concentration rise are discussed.
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
Spectroscopic investigation of Bellataire and Iljin HPHT treated diamonds
A number of near colorless and fancy color HPHT treated diamonds with various cutting shapes from Bellataire (USA) and Iljin (South Korea) Companies were carefully studied in the GIT_GTL by using both standard gemological instruments and advanced spectroscopic techniques. Microscopic examination of diamonds from both sources reveals some features commonly found in the HPHT treated diamonds; such as strain pattern, small feather-like fractures, dark inclusions. The Bellataire HPHT treated diamonds used in this study (14 samples) weigh from 0.19 to 0.34 ct. in different cutting styles. Color grades of these diamonds range from J to M with IF to SI1 clarity grades. The Infrared spectra (FTIR) indicate that all of them are of type IIa diamonds (Nitrogen free to below the detection limit of FTIR). The Photoluminescence spectra (PL) show peaks at 637 (NV -) and 575 (NV 0) nm and the ratio of 637/575 PL peak is generally greater than 1. In addition, there seems to be some relationships bet...