Surface Of Diamond Crystal Research Articles

ВЫБОР ТЕХНОЛОГИИ ПОВЫШЕНИЯ ГИДРОФОБНОСТИ И ИЗВЛЕКАЕМОСТИ АЛМАЗОВ ТРУБКИ "БОТУОБИНСКАЯ"

A promising direction for solving the problem of producing small diamonds is to expand the range of enriched classes and reduce diamond losses through the use of modern technologies. The article presents the results of research on the causes of reduced hydrophobicity of Botuobinskaya tube diamonds and the choice of parameters for preparing the feedstock for the processes of sticky and foam separation, ensuring the restoration of surface properties and extraction of hydrophilized diamonds into concentrate. Studies have shown that the mineral coatings on the surface of diamonds are fragments of primary or modified kimberlites, as well as slurries and films, firmly connected to the surface of diamond crystals. Diamonds from hypergenically altered kimberlites are characterized by the predominance of carbonate and aluminosilicate minerals. It has been shown by the method of unrestricted flotation of diamond-kimberlite samples that the use of mechanical scrubbing is effective enough to remove slurry coatings, but does not provide complete removal of car bonate-aluminosilicate microbreccias firmly bound to the surface of diamonds. As a result of the conducted research, it is shown that for a more complete recovery of small diamonds from kimberlites enriched at the Nyurbinsky GOK, it is advisable to use the processes of mechanical stripping and thermal cleaning of diamonds from hydrophilizing coatings to restore their hydrophobicity. It is shown that the use of a combination of these methods provides an increase in diamond recovery during sticky separation by 14.1 % and during foam separation by 20.4 %. The level of recovery of hydrophilic diamonds (more than 82 %) achieved using foam separation technology allows us to recommend this process for use in improving the technology of enrichment of small classes of diamonds.

Influence of high fluence heavy ion irradiation on the performance of single crystal diamond detectors

Radiation detectors based on diamond are highly favored for particle physics research due to their superior radiation hardness. In this work, the performance of single crystal diamond detectors under high fluence heavy ion radiation has been investigated. After irradiation by Fe13+ and Xe20+ ion beams with a high particle fluence of 1.2 × 1015 cm-2, the properties of unirradiated and irradiated intrinsic single crystal chemical vapor deposition (CVD) diamond detectors are compared by means of the spectroscopic energy resolution, charge collection efficiency (CCE), mobility-lifetime (μτ) product and time response using a 241Am alpha (α) particle source. The experimental results of the unirradiated sample with respect to I-V dark current levels, showed an ohmic behaviour of the Al and Cr/Au contact, CCE of 100%, fast response with a rise time of 750 ps and a fall time of 600 ps as well as drift velocities of 6.67 × 104 m/s and 4.72 × 104 m/s for holes and electrons respectively. In the case of the irradiated samples, the CCE, μτ product and time response pulse amplitude of holes and electrons were all degraded, indicating that high density trappings for both kinds of carriers were created under the diamond crystal surface and the trapping probability of holes and electrons was equal, which was different from the previous reports in the literature where only higher trapping probability of holes were observed under heavy ions irradiation. In particular, the spectroscopic performance as well as μτ product of holes and electrons in Fe13+ irradiated sample decreased more than those in Xe20+ irradiated sample, which implied that the recombination of electrons and holes increased in Fe13+ irradiated sample with greater penetration depth than that in Xe20+ irradiated sample when radiation fluence was up to 1015 cm-2, despite the lower density of lattice vacancies in Fe13+ irradiated sample. Moreover, the rise time of holes was slightly different, but the drift velocity was basically the same as that of the unirradiated sample, and so was that of the electrons. Anyway, the presented results showed that the diamond detectors irradiated by heavy ions at a high fluence of 1015 cm-2 still retained their good spectroscopic and very fast time response properties.

Application of thermal conditioning in foam separation of diamond-containing kimberlites

The mechanism of the heat treatment effect on the surface condition and floatability of diamonds with a high concentration of hydrophilizing surface mineral formations is studied. By the method of X-ray photoelectron spectroscopy (XPS), it is found that when heated to a temperature above 65°C, the processes of thermomechanical destruction of diamond crystal concretions with rock minerals occur, ensuring cleaning of the diamond surface by 20–50 %. It is shown that when the medium is heated to 80–85°C, due to the removal of molecular and ionic forms of carbonic acid from the aqueous phase, the thermochemical dissolution of hydrophilizing films on the surface of diamond crystals is intensified. Heat treatment at a temperature higher than 80°C for 60–120 s allows achieving diamond purification to a degree of 67–90 %. The developed technology of thermal conditioning of the pulp in the cycle of foam separation of diamond-containing material includes its treatment with superheated steam at a temperature of 105–110°C, which allows achieving the required heating intensity (80–85°C), ensuring effective cleaning of the surface of diamond crystals from hydrophilizing mineral formations and, accordingly, increasing their flotation activity. At the same time, the consumption of flotation reagents is decreased by 10–12 % and the circulation of industrial products in the foam separation cycle is reduced. The technology of thermal conditioning in combination with electrochemical conditioning of recycled water of the foam separation cycle provides the increased recovery of diamonds in the final concentrate by 3.9–5.1 %. The developed technological mode of the diamond-containing material preparation for the foam separation process has passed pilot testing and is recommended for industrial application at processing plant No. 3 of Mirny GOK, ALROSA.

Coexistence of carbonyl and ether groups on oxygen-terminated (110)-oriented diamond surfaces

Diamond-based materials have unique properties that are exploited in many electrochemical, optical, thermal, and quantum applications. When grown via chemical vapor deposition (CVD), the growth rate of the (110) face is typically much faster than the other two dominant crystallographic orientations, (111) and (100). As such, achieving sufficiently large-area and high-quality (110)-oriented crystals is challenging and typically requires post-growth processing of the surface. Whilst CVD growth confers hydrogen terminations on the diamond surface, the majority of post-growth processing procedures render the surface oxygen-terminated, which in turn impacts the surface properties of the material. Here, we determine the oxygenation state of the (110) surface using a combination of density functional theory calculations and X-ray photoelectron spectroscopy experiments. We show that in the 0–1000 K temperature range, the phase diagram of the (110) surface is dominated by a highly stable phase of coexisting and adjacent carbonyl and ether groups, while the stability of peroxide groups increases at low temperatures and high pressures. We propose a mechanism for the formation of the hybrid carbonyl-ether phase and rationalize its high stability. We further corroborate our findings by comparing simulated core-level binding energies with experimental X-ray photoelectron spectroscopy data on the highest-quality (110)-oriented diamond crystal surface reported to date.

Selection of recycled water electrochemical conditioning parameters for preparation of diamond-bearing kimberlite for froth separation

The main reason of decreasing diamond recovery through froth separation is their surface hydrophilization by hypergene minerals and technogenic films, crystallized from the supersaturated aqueous phase, fixed on the surface structurally or by adhesion. Various types of physical actions, including thermal and ultrasonic treatment of the initial feed of froth separation, are recommended to increase the diamond-bearing kimberlite beneficiation process performance, providing cleaning of the surface of diamonds due to destruction of their accretions with rock minerals and removal of film hydrophilizing coatings from the surface of diamond crystals. A sample of kimberlite material with a given content of diamonds of 1.5–2 mm in size was used as a subject of research in the process of froth separation. The results of thermodynamic calculations and experimental research have substantiated the necessity of using electrochemical conditioning of recycled water for increasing the efficiency of diamond surface cleaning in froth separation operation when using the process of thermal treatment of initial ore feed. The use of diaphragmless electrochemical conditioning of recycled water increases the efficiency of thermochemical dissolution of hydrophilizing compounds on the surface of diamonds through reducing the concentration of calcium and carbonate ions as well as through shifting the medium pH to 6.1–6.5. The measurements of the limiting wetting angle showed that the maximum effect of increasing the diamond surface hydrophobicity was achieved when heat and electrochemical treatment were used together. Laboratory studies showed the possibility of increasing flotation diamond extraction from 65.7 to 91.4 % through application of electrochemical conditioning of recycled water. The optimum parameters of diaphragmless electrochemical treatment of recycled water of the froth separation cycle in conditions of application of pulp heat treatment: current density of 175–200 A/m2 and power consumption of 1.2–1.5 kWh/m3. Tests carried out at processing plant No. 3 of the Mirny GOK (Mining and Processing Complex) (Mirny, Yakutiya) showed that the application of the developed froth separation process intensification method with the use of thermal treatment of pulp and electrochemical diaphragmless treatment of recycled water allowed increasing the recovery of diamonds of +0.5–2 mm size by 4.9–5.1 %.

Analysis of Distribution of Secondary Minerals and their Associations on The Surface of Diamonds and in Derrivative Products of Metasomatically Altered Kimberlites

The theoretical and experimental studies resulted in establishing regularities in the distribution of secondary minerals and theirassociations in metasomatically altered diamond-bearing kimberlites and products of their processing.Based on integrated mineralogical research, it was found out that the composition of the altered kimberlites and the fine-dispersedclayey slurries formed during their processing constituted the basis of hydrophilic formations on the surface of diamond crystals notrecovered by the methods of grease and froth separation. Particles of these minerals concentrate in fine-dispersed slurry productsof kimberlite ore processing, interact with the crystal surface, reduce their hydrophobic properties and, accordingly, recovery inprocesses of grease and froth separations into concentrates.

Advanced Methods for Modifying the Properties of Separation Media and Mineral Components for More Efficient Separation of Diamond-Bearing Raw Materials

The results of this study proof the effectiveness of combining physical and electrochemical methods to intensify the processing of diamond-bearing ores as shown by:–recovering more diamonds thanks to the synergistic effects of making the diamond crystal surface more hydrophobic in grease recovery and froth flotation;–complete recovery of abnormally luminescent crystals thanks to modifying the spectral and kinetic properties of such crystals in separation by X-ray fluorescence;–lesser use of ferrosilicon thanks to its greater resistance to corrosion induced by interfacing with corrosive water systems.

The Formation of Crystalline Mineral Covers on the Surface of Diamonds and Their Destruction with the Use of Electrochemically Treated Water Products

The composition of the surface of natural diamonds in interaction with minerals and the aqueous phase in the kimberlite deposit and processed ore are studied. The sequence and conditions for the formation of hydrophilic minerals on the surface of diamond crystals under conditions of processing of kimberlites have been determined. Confirmed the mechanism of hydrophilization of diamonds surface comprising formation of hydroxides and oxides of iron as a mandatory initial stage of crystallization. A method of restore the hydrophobicity of diamonds by the impact of electrolysis products of aqueous systems has been proposed, which allows to destruction or subsequent dissolution of minerals aggregate. The use of treated water in the process of froth separation it possible to increase diamonds recovery in the processing plant concentrate by 8.8%.

Laser monitor for imaging single crystal diamond growth in H2-CH4 microwave plasma

We used an active optical system referred to as ‘laser monitor’ based on a copper bromide vapor brightness amplifier for imaging a diamond crystal surface during its synthesis in a microwave plasma in CH4-H2 gas mixture. The approach allows observation of an entire crystal without interrupting the chemical vapor deposition process. It is demonstrated that the broadband plasma background radiation with the brightness temperature of about 3000 K does not interfere with object real-time monitoring at the laser wavelength of 510.6 nm. High quality images obtained using both passive (laser illumination) and active (laser monitor) methods provide information about the surface relief of the growing crystal with resolution of a few tens of micrometer. Each frame is formed through one pulse (about 30 ns), with the maximum frame rate being 20,000 frames/sec.

Analysis and destruction of mineral impurities on the surface of diamond crystals in treatment of current and old tailings at diamond processing plants

Analysis and destruction of mineral impurities on the surface of diamond crystals in treatment of current and old tailings at diamond processing plants

Dry mixing of diamond and n-layered graphene powders substantially different in density and particle size

ABSTRACTIn this paper, the two-stage process of the uniform distribution of n-layer graphenes in a mixture for sintering polycrystalline diamond at high pressures and temperatures is described. Due to the preliminary deposition of a nanopowder layer on the surface of diamond crystals, at the second stage of mixing the uniform application of a layer of the n-layer graphenes powder on the prepared surface and mixture uniform in the properties are achieved. This approach ultimately makes it possible to produce diamond polycrystals stable in properties. In particular, the current-conducting diamond polycrystals are obtained.

Classification of mineral species on the surface of natural diamond crystals

The analytical research has yielded differences in composition of mineral species on the surface of natural diamonds of hyperaltered kimberlites under conditions of diamond ore occurrence and processing. The classification of the mineral species is based on the mineral origin, properties and attachment on the diamond crystal surface.

P-V Centers Behavior in Diamond C(111) Subsurface Layers

Quantum-chemical modeling is used to study the dependence of spin states, geometrical, electronic and energy characteristics of P-V center from its location on the surface of the diamond C(111). The (111) surface of diamond crystal is found to affect the geometrical parameters, charge characteristics and spin density distribution of P-V centers.

Methods to clean the surfaces of diamond crystals

Methods of step-by-step cleaning of contamination of diamond single crystals surfaces have been defined. The main stages of the cleaning: chemical cleaning of the surface, ion etching, and ultrasound cleaning have been discussed. It has been shown that these methods offer a complete cleaning the surfaces of diamond single crystals.

Achieving ultra-hard surface of mechanically polished diamond crystal by thermo-chemical refinement

In the present work, we propose a novel thermo-chemical post-processing method for refining the mechanically polished surface of natural diamond crystal. The deformation mechanisms of diamond crystal during mechanical polishing are elucidated by Raman Spectroscopy corroborated by molecular dynamics simulations. Moreover, the surface mechanical properties of diamond crystal are qualitatively characterized by nanoindentation tests. Our results reveal that under mechanical polishing there are phase transformations from diamond carbons to layered graphite, amorphous sp3 and sp2 hybrided structures occurred in the topmost surface layer, which consequently deteriorates the intrinsic surface strength of diamond crystal. In the following thermo-chemical refinement, the polishing-induced amorphous carbons, layered graphite and internal stress are largely removed through the weak oxidation reaction. It is found that the formation of considerable graphene structures in the topmost surface layer results in an ultra-hard diamond crystal surface with dramatically enhanced hardness and Young's modulus. Our findings shed light on the preparation of natural diamond crystal surface with superior mechanical properties.

Mineral formations on natural diamond surface and their destruction using electrochemically modified mineralized water

The article describes modeling and analysis of formation, attachment and dissolving of mineral substances on surface of diamond crystals. Based on the thermodynamic analysis and experimental research, the author validates deposition of chemical compounds as the main factor to govern mineral formations on natural diamond surface under contact with mineralized water in the occurrence conditions of kimberlite ore and during mining and processing. The efficiency of electrochemically modified water in dissolving and removal of mineral formations from diamond surface is ascertained.

Effect of additive zinc on larger diamond crystal growth

The large single crystal diamonds are successfully synthesized in a NiMnCo-C system with the zinc additive in a series of the experiments at temperatures of 1270-1400 ℃ and pressures of 6.2-6.4 GPa by the temperature gradient growth. Morphology and structural properties of the synthesized diamond are characterized by optical microscope and scanning electron microscopy. The Raman spectrum is used to investigate the crystallization of synthesized diamond. The results show that the colors of synthetic diamond crystals change from yellow to light yellow and nearly disappears with the increase of the zinc additive. There are a large number of irregular pits in the surface of diamond crystal when the zinc additive is increased up to 3.0 wt.%. the Fourier transform infrared spectroscopy spectra reveal that the nitrogen impurity in the synthetic diamond crystal is predominantly in the form of C center (single substitutional nitrogen atoms), and the nitrogen concentration decreases with the increase of zinc additive. Two possibilities that the zinc powders can be used as the nitrogen getter are given. the Raman spectrum shows that the diamond crystallization can be improved when the zinc additive is less than 3.0 wt.%. We believe that our work is greatly helpful for deeply understanding the natural diamond genesis, enriching the types of diamonds, and expanding the application areas of synthetic diamond.

NV centers in diamond: Quantum-chemical modeling

Quantum-chemical modeling is used to study the relationship between the spin states of nitrogen vacancy (NV) centers and their position on a (100) surface or in the bulk of a diamond crystal. The spin density of the NV centers is computed, and the position of the centers on the crystal surface is demonstrated to be energetically more favorable. The (100) surface of diamond crystal is found to affect the geometrical parameters and adsorption properties of NV centers and their spin-density distribution, relative to these properties in the bulk.

Deep ultraviolet diamond Raman laser

We present a synchronously pumped diamond Raman laser operating at 275.7 nm pumped by the 4th harmonic of a mode locked Nd:YVO4 laser. The laser had a threshold pump pulse energy of 5.8 nJ and generated up to 0.96 nJ pulses at 10.3% conversion efficiency. The results agree well with a numerical model that includes two-photon absorption of the pump and Stokes beams and uses a Raman gain coefficient of diamond of 100 cm/GW. We also report on the observation of nanometer scale two-photon assisted etching of the diamond crystal surfaces.

Molecular dynamics study on carbon film deposition

Hydrogen-free carbon film deposition is studied through molecular dynamics (MD) simulation. MD simulation is performed for low-energy carbon particle impacts on carbon surfaces at room temperature. Deposition energy is considered up to E=100eV per carbon atom. Deposited surface is set into amorphous, and (111) surface of diamond crystal is considered in order to compare. For (111) surface, we found three characteristic regions. The deposition frequently results in the shallow trapping in E⩽20eV. In E⩾30eV, the deep trapping occurs about normal incidence, and the reflection appears about grazing incidence. For the amorphous surface, however, the reflection and the deep trapping are suppressed.