Static synthesis of microdiamonds from a charge containing nanodiamonds

The effect of detonation nanodiamonds (DNDs) [5] on the graphite-diamond phase transition at high pressures and temperatures has been experimentally studied. It is established that adding DNDs to a graphite-based charge for the diamond synthesis provides for a ～1.4 times higher conversion of graphite into diamond even at relatively low pressures (4.5–5.5 GPa) and temperatures (1250–1500°C). DND additives also modify the size distribution of microcrystalline diamonds.     

Modeling of temperature fields in the growth volume of the high-pressure cell of the six-punch high pressure apparatus in growing of diamond crystals by <Emphasis Type="Italic">T</Emphasis>-gradient method

Based on the finite element method a computer model is developed to determine the heat state of the six-punch high-pressure apparatus with a high-pressure cell for growing structurally perfect diamond single crystals. The temperature fields in the high-pressure cell were calculated during the growing diamond single crystals depending on the internal and outside diameters of graphite current shunt, which allows us to change the temperature at the characteristic points of high pressure cell by 20–110°C, horizontal and vertical temperature drops in a growth volume by 3–18°C and the temperature gradient in it by 0.17–2.0 deg/mm. Based by the calculations of temperature fields, the experiments were conducted and the diamond single crystals up to 5 mm in size were obtained. The crystals quality depends on the place in the growth volume and corresponds to the calculated data.     

Special features of self-organization of ultradispersed diamond at high pressures and temperatures

The behavior of ultradispersed diamond (UDD) particles at high pressure and temperature has been studied experimentally. Products from UDD only, from UDD with boron added, from UDD with boron and the liquid phase added have been analyzed. The possibility to obtain bulk well-faceted single crystals in sizes up to 10 μm as a result of the self-organization of UDD nanoparticles of size ≈ 5 nm in a liquid phase, which does not solve carbon, has been found for the first time.     

Defect-and-impurity state of type Ib diamond single crystals of cubic habit

Type Ib diamond single crystals of size to 5–6 mm and to 2.4 carats in weight have been grown at high pressures and temperatures. The defect-and-impurity state and dislocation structures of these crystals have been studied using the IR and optical microscopies as well as the method of the selective etching. To produce type Ib crystals of cubic habit has been made possible by the minimization of the growing temperature. Defect regions in the form of a cone with the basis 0.2–1.8 mm in diameter and 0.5–2.5 mm in height are contained by these crystals. The study of the cone-shaped defect regions using the selective etching showed that at the exposure on the faces the etching pits are of the tetragonal shape and the dislocation density in them exceeds the density of dislocations in crystals that were grown under the usual conditions by 70 to 100 times. The observed defect regions are formed in the course of the diamond crystals growth as the temperature decreases by ~ 30–35°C at the crystallization front because of the increasing heat sink in the direction of a seed crystal.     

Self-organization of ultradisperse diamond particles heated at high pressures

Diamond single crystals with decahedral and icosahedral faceting and dimensions of 50–80 nm have been obtained by high-temperature high-pressure treatment of an ultradisperse detonation-synthesized diamond (UDD) powder. It is concluded that the growth of diamonds is related to the oriented association of initial UDD nanoparticles, the driving force of which is the tendency of the system to the state of minimum surface energy. The crystal habit is determined by the crystal morphology of UDD nanoparticles, which possess regular polyhedral shapes and flat facet morphology.     

Self-organization processes and sedimentation stability in detonation nanodiamond suspensions

Problems related to the stabilization of suspensions prepared from a dry detonation nanodiamond (DND) powder have been studied. Secondary DND suspensions have been obtained and factors influencing their stability with respect to sedimentation have been analyzed. It is shown that the self-organization of particles in DND suspensions in combination with their periodic ultrasonic treatment can be used to convert the maximum possible mass fraction of DND particles in secondary suspensions into nanodimensional (5–100 nm) forms.     

Defect-and-impurity state of diamond single crystals grown in the Fe–Mg–Al–C system

Special features of the formation of the defect and impurity states of diamond single crystals grown in the Fe–Mg–Al–C growth system by the temperature gradient method at the pressure 7.2–8.2 GPa and temperature 1700–1900°C have been investigated. It has been shown that as the magnesium content of the growth system increases, the type of the grown crystals changes in the following sequence: IIa → IIb.     

Effect of the Surface Modification of Synthetic Diamond with Nickel or Tungsten on the Properties of Copper–Diamond Composites

Tungsten- and nickel-containing coatings have been produced on the surface of synthetic diamond crystals by rotary chemical vapor deposition (RCVD) using tungsten hexacarbonyl, W(CO)₆, and nickelocene, Ni(C₅H₅)₂, as gaseous precursors. The thickness, composition, and morphology of the coatings have been shown to depend on the RCVD process duration and reactant concentrations in the vapor phase. The synthetic diamond microcrystals with tungsten- and nickel-containing coatings have been used to produce copper–diamond heat-conducting composites. Powder mixtures containing 50 vol % diamond with a particle size of 50, 100, or 200 μm have been consolidated by spark plasma sintering or hot pressing. It has been shown that the highest relative density (97%) and thermal conductivity (340 W/(m K)) are offered by the composites produced by spark plasma sintering using tungsten carbide-coated 50-μm diamond crystals.     

Special features of the diamond crystallization in the Mg–Zn–B–C system

The diamond crystallization in the Mg–Zn–B–C system occurring in the diamond thermal stability region have been considered. The phase transformations, which take place during the preparation of the alloy–solvent for carbon and its structure, the diamond crystallization and properties of the resultant diamond crystals have been studied. The formation of the acceptor centers and inclusions in diamond crystals caused by the addition of boron into the growth system have been considered. It has been found that the use of the diamond powder produced in this system for abrasive machining surfaces of sapphire parts makes it possible to increase the machining efficiency and quality as compared with that of the powder produced in the Ni–Mn–C system.     

Kinetics of diamond single crystal growth in Fe-Co solvents doped with titanium and zirconium

The growth kinetics of structurally perfect single crystal in the Fe-Co -C solvents with additions of Ti (1.81–5.35 at %) and Zr (0.64–6.30 at %) has been studied in the temperature range from 1380 to 1680°C at a pressure of 5.5–6.1 GPa. Concentration limits of the formation of diamond single crystals of types Ib, IIa, and an intermediate type Ib + IIb have been established. Defect-and-impurity state, habit, and special features of capturing solvent inclusions by the growing single crystals have been studied. Boundaries of the regions of variations of the habit, the degree of structure perfection, and capture of inclusions as a function of pressure and temperature have been defined in the p,T diagram of carbon.     

Synthesis, structure, and physical properties of boron-doped diamond

Microcrystalline boron-doped diamond powders consisting of octahedrally faceted crystals have been synthesized in the C-H-B system at a pressure of 8 GPa and temperatures above 2000 K. The presence of boron has been shown to reduce the parameters of diamond synthesis compared to the binary system C-H (naphthalene). One possible reason for the reduction in synthesis parameters is the formation of less perfect graphite in the boron system in an intermediate step of diamond synthesis. At B/(C + B) ratios of about 5–10 at % in the C-H-B (naphthalene + boron) system, superconducting diamond microcrystals have been synthesized.     

Ordered porous diamond films fabricated by colloidal crystal templating

We have developed a colloidal crystal templating method for preparation of diamond films with 2D and 3D ordered porous structures. The technological process involved breaks down into (a) impregnation into the pores of silica colloidal crystal (opal) films of detonation nanodiamond (DND) particles from their hydrosol; (b) microwave plasma-enhanced chemical vapor deposition (MWPECVD) regrowth with diamond of pores with high DND filling; (c) Ar(+) ion dry etching of fragments of shells of coalesced diamond crystallites which form in the course of MWPECVD on the surface of the SiO(2) beads making up the outer surface of a film and (d) wet etching of the SiO(2) template in aqueous HF solution. The final samples are either connected to the substrate or free-standing films of various thicknesses having 2D or 3D ordered porous structures. The morphology of the diamond films fabricated by this method replicates the pore network of the opal template. Raman measurements confirm the diamond structure of the synthesized ordered porous material.     

Effect of the titanium doping of the Fe—Co—C solvent on the nitrogen content of diamond single crystals grown at high pressures and temperatures

Diamond single crystals have been grown experimentally in Fe—Co-based alloys—solvents for carbon with a titanium content varying from 1 to 2 wt %. Average growth rates and morphological features of the grown crystals have been defined; the defect-and-impurity states and characteristics of macroinclusions have been analyzed. It has been found that an increase of titanium content of the Fe—Co—C solvent from 1 to 2 wt % brings about a change of the single crystal type from Ib to IIa. The use of the solvent having 1.5 wt % of titanium allows growing diamond single crystals of mixed Ib + IIb types.     

Structure and hardness of octahedral natural diamond single crystals depending on the HPHT treatment conditions

The structure evolution of octahedral natural diamond single crystals has been studied depending on the HPHT treatment using Raman scattering and infrared spectroscopy. It has been found that the formation of a polycrystalline diamond capsule around a single crystal at p = 8 GPa and T = 1500°C gives rise to a combined structural-stressed state in the single crystal due to its plastic strain. This state has been manifested by a significantly (more than double) broadening of the characteristic line of diamond (1332 cm^?1) in the Raman spectrum and the increase of a single crystal hardness from 105 to 120 GPa.     

Nanodiamond-based nanolubricants for motor oils

Over the last few years, interest in applications of nanoparticles as lubricant additives has steadily grown due to the demonstrated reduction in friction and wear of nanoparticle-containing lubricant formulations (so-called nanolubricants). Particularly, studies of motor oils containing a “green” all-carbon additive, detonation nanodiamond (DND) particles, revealed their positive impact on the performance of lubricant compositions and fuel economy in engine tests. In the current review we discuss critical issues toward successful implementation of DND in nanolubricants: role of DND structural characteristics, stability of colloids of DND in oils, DND compatibility and synergism with other additives in commercial oils, mechanisms of DND impact on the properties of lubricants. Owing to the abrasive nature of diamond, DND-based nanolubricants must be carefully engineered in order to avoid increased wear of the friction surfaces and get full benefit from significantly reduced friction of well-polished surfaces.     

Distribution of local deformations in diamond crystals according to the analysis of Kikuchi lines profile intensities

The histogram method has been proposed to determine strains in diamond crystals by the analysis of reflection electron diffraction bands in Kikuchi patterns. The anisotropy has been defined of the local strain distribution on the surface of two diamond samples produced by the temperature gradient method in the Fe-Al-C system and by growing on a surface of a statically synthesized diamond single crystal (Ni-Mn-C) in the Mg-C + Bor system.     

Stress and dislocations in diamond–SiC composites sintered at high pressure,high temperature conditions

Diamond–silicon carbide composites were sintered at 10 GPa and three different temperatures: 1600, 1800, and 2000 °C. Distributions of residual surface stresses in diamond crystals were obtained by the analysis of Raman band shifts and splitting. It was noted that stresses concentrate around points of contacts between diamond crystals. Average stress increase with increasing sintering temperature. Complementary information on average sizes of crystallites, concentration of stacking faults, and population of dislocations in both diamond and SiC were obtained from X-ray diffraction profile analysis. It was observed that for both diamond and silicon carbide phases the average crystallite sizes decrease. The population of dislocations in the diamond phase increases with increasing sintering temperature and the population fluctuates in the SiC phase. Concentration of stacking faults was significant only in SiC.     

Special features of the formation of a microrelief on the surface of diamond single crystals when grown in solvent based on an iron-cobalt-zirconium alloy

It has been shown that when growing diamond single crystals in the diamond thermodynamic stability region using solvents based on iron-cobalt-zirconium alloys virtually all crystal faces exhibit microrelieves, which represent the combination of valleys and peaks, whose depth and height do not exceed several micrometers. The origin of the microrelief has been caused by the features of the solvent crystallization and phase transformations in it as the temperature decreases. A liquid solvent is crystallized as a mixture of elongated grains of composition (Fe, Co)₃C with interlayers of α-solid solution of eutectic composition between them, which results in the formation of valleys and peaks on the crystal surface. Cooling the solvent leads also to the formation of microscopic diamond single crystals and precipitation of excess graphite from the α-solid solution of composition (Fe, Co)₃C. The relief observed on faces of the grown crystals is of the surface nature only.     

Nitrogen and Luminescent Nitrogen‐Vacancy Defects in Detonation Nanodiamond

An efficient method to investigate the microstructure and spatial distribution of nitrogen and nitrogen‐vacancy (N‐V) defects in detonation nanodiamond (DND) with primary particle sizes ranging from approximately 3 to 50 nm is presented. Detailed analysis reveals atomic nitrogen concentrations as high as 3 at% in 50% of diamond primary particles with sizes smaller than 6 nm. A non‐uniform distribution of nitrogen within larger primary DND particles is also presented, indicating a preference for location within the defective central part or at twin boundaries. A photoluminescence (PL) spectrum with well‐pronounced zero‐phonon lines related to the N‐V centers is demonstrated for the first time for electron‐irradiated and annealed DND particles at continuous laser excitation. Combined Raman and PL analysis of DND crystallites dispersed on a Si substrate leads to the conclusion that the observed N‐V luminescence originates from primary particles with sizes exceeding 30 nm. These findings demonstrate that by manipulation of the size/nitrogen content in DND there are prospects for mass production of nanodiamond photoemitters based on bright and stable luminescence from nitrogen‐related defects.     

Boron-doped diamond single crystals for probes of the high-vacuum tunneling microscopy

The results of studying the structure of diamond single crystals grown by the temperature gradient method with the aim to obtain samples having maximum uniform characteristics for manufacturing probes for scanning electron microscopes with a specified axial orientation and controlled distribution of the dopant have been considered. It has been shown that the use of similar probes in scanning tunneling microscopy decreases the probability of incidental tunneling channels with participation of the surface states caused by the presence of boron atoms in the diamond structure and increases the reliability of experimental data. The high stability of monocrystalline diamond probes and the possibility to attain the atomic resolution with the help of them have been demonstrated by the investigations of the (0001) graphite plane using scanning tunneling microscopy.