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Niobium carbide composites were obtained by sintering niobium powder and detonation nanodiamond at high pressure (7 GPa) and high temperature (∼1990 °C) for several tens of seconds. The resulting composites demonstrate a set of distinct reflections from the NbC phase in the X-ray diffraction pattern and exhibit superconducting properties at temperatures below 11.4 K.

Several papers published in Elsevier and Springer journals in 2020–2021, in which there were numerous violations of standards concerning citation practice in scientific papers, are analyzed. These papers deal with high-thermal-conductive diamond/metal composites. The examples under consideration mainly concern composites prepared via deposition of tungsten coatings onto diamond particles. The revealed errors and distortions in citations are indicated and classed. The examples given may be useful to a wide range of readers (authors, reviewers, editors) as illustrations of the data distortion encountered in scientific publications due to incorrect citation

The aim of this work was (i) to develop an untraditional method of alumina doping that ensures low sintering temperature and (ii) to obtain dense engineering ceramics with good mechanical properties by conventional sintering. A nanostructured coating of manganese–titanium oxides was applied to α-Al2O3 micropowder particles using liquid-phase synthesis of Mn–Ti–O–C–H xerogel and its annealing. The alumina modified in this way was sintered at 1300–1400 °C in air. The sintering process was accompanied by the formation of manganese metatitanate MnTiO3. The sintered samples have the relative density of about 97%, the bending strength of ≥ 260 MPa, and the Vickers microhardness of ≥ 16 GPa. The longitudinal and transverse sound velocities were measured, from which the Poisson’s ratio of 0.24 and the Young’s modulus of ≥ 360 GPa were calculated. Modification with MnTiO3 precursors yielded higher mechanical properties of ceramics than modification with a ready MnTiO3 coating. The results are compared with the properties of Al2O3 doped with Mn–Ti–O formulations in other studies, and of industrial alumina ceramics.

An overview of research on the synthesis of manganese titanates is presented. The xerogel of Mn–Ti–O–C–H composition was synthesized from manganese acetate and titanium tetrabutylate via liquid-phase method using organic solvents. The calcination of xerogel in air at 450 °C and 700 °C yielded manganese titanate precursors in the form of a nanostructured mixture of Mn2O3 and TiO2. Annealing at 1000 °C, manganese metatitanate MnTiO3 was obtained. Reference experiments with initial reagents included, separately, thermal decomposition of Mn(CH3COO)2×4H2O and the product of Ti(OC4H9)4 hydrolysis. The composition, structure, and properties of the products were studied using X-ray diffraction, scanning electron microscopy, elemental analysis, diffuse reflectance IR Fourier spectroscopy, thermogravimetry, and by measuring specific surface area. The data presented by these different techniques are basically consistent with each other (with an increase in the annealing temperature, an increase in globule size and decrease in specific surface area are observed; structuring occurs within the long- and short-range order; the size of the crystallites does not exceed that of the globules; elemental composition correlates with phase composition; the endothermic character of the reaction of MnTiO3 formation at 900 °C is confirmed by a thermodynamic calculation). Nevertheless, some unexpected effects were revealed (based on the FTIR diffuse reflection spectra, mixed oxide Mn–Ti–O is formed in the surface layer of particles already at 450 °C and 700 °C; etc.). Application of the proposed technique for modifying Al2O3 powders, with the aim of implementing low-temperature sintering of corundum ceramics, is discussed.

We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3–4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

The electron paramagnetic resonance (EPR) spectra of triplet centers in detonation nanodiamonds (DNDs) and diamond single crystals of submicrometer size, synthesized from those DNDs at high pressures and temperatures, are studied. In the EPR spectra of DNDs, signals from negatively charged nitrogen- vacancy centers (NV)/sup(-) with a g factor of g1 = 4.24 and multivacancies with g2 = 4.00 are observed. The signals from (NV)/sup(-) centers disappear in the spectra of diamond single crystals, and a quintet signal with g = 4.00 is detected at the position of the signal from multivacancies. Analysis of the shape and position of the quintet’ lines showed that this ESR signal is due to the pairs of nitrogen substitution centers in diamond, separated from each other by distances not exceeding 0.7 nm, between which a strong exchange interaction takes place. A comparison of the experimental data and the simulation results allows determining the spin-Hamiltonian parameters of the exchange-coupled pairs of paramagnetic impurity nitrogen atoms.

Boron doped diamond (BDD) was synthesized under high pressure and high temperature (HPHT) of 7 GPa, 1230 °C in a short time of 10 s from a powder mixtures of detonation nanodiamond (DND), pentaerythritol C 5 H 8 (OH) 4 and amorphous boron. SEM, TEM, XRD, XPS, FTIR and Raman spectroscopy indicated that BDD nano- and micro-crystals have formed by consolidation of DND particles (4 nm in size). XRD showed the enlargement of crystallites size to 6–80 nm and the increase in diamond lattice parameter by 0.02–0.07% without appearance of any microstrains. Raman spectroscopy was used to estimate the content of boron atoms embedded in the diamond lattice. It was found that the Raman diamond peak shifts significantly from 1332 cm −1 to 1290 cm −1 without appearance of any non-diamond carbon. The correlation between Raman peak position, its width, and boron content in diamond is proposed. Hydrogenated diamond carbon in significant amount was detected by IR spectroscopy and XPS. Due to the doping with boron content of about 0.1 at%, the electrical conductivity of the diamond achieved approximately 0.2 Ω − 1 cm −1 . Reaction mechanism of diamond growth (models of recrystallization and oriented attachment) is discussed, including the initial stages of pentaerythritol pyrolysis and thermal desorption of functional groups from the surface of DND particles with the generation of supercritical fluid of low-molecular substances (H 2 O, CH 4 , CO, CO 2 , etc.), as well as byproducts formation (B 2 O 3 , B 4 C).

Diamond single crystals synthesized from powder detonation nanodiamonds (DNDs) by means of treatment at high pressures (P ~ 7 GPa) and temperatures (T > 1300°C) have been studied by electron paramagnetic resonance (EPR). A key feature of treatment (high-pressure high–temperature (HPHT) sintering) is the use of low molecular weight alcohols in the process. The appearance of a hyperfine EPR signal structure due to “paramagnetic nitrogen” (P1 centers) is explained by the growth of submicron and micron diamond single crystals from DND nanocrystals by the oriented attachment and coalescence mechanism. Such growth and coarsening of crystals appreciably decreases the concentration of paramagnetic centers, the presence of which hinders the detection of a hyperfine structure in the EPR signal from P1 centers, in the near-surface areas of coalesced and grown together DND particles. It has been shown that the concentration of paramagnetic defects of all types decreases to ~3.1 × 1018 g–1 (~60 ppm) during HPHT treatment at T = 1650°C. This causes the successful identification of P1 centers, whose fraction is no less than ~40% of the total amount of paramagnetic centers in microcrystals synthesized by HPHT sintering.

Possibility of growth of diamond single crystals from nanodiamond particles by oriented attachment mechanism under influence of organic substances has been suggested and experimentally confirmed. It has been found that diamond single crystals ranging up to 1.5 μm are formed from the 4–5 nm nanodiamond particles at high pressures and high temperatures treatment (HPHT; P ~ 7 GPa, T ~ 1300 °C). It has been experimentally shown that the necessary condition for the formation of the diamond single crystals is an addition of substances containing C H groups into HPHT chamber. The formation of the diamond single crystals has been confirmed by several experimental methods, including Raman scattering, scanning electron microscopy (SEM) and electron energy loss spectroscopy (EELS). Analysis of experimental results has shown that mechanism of oriented-attachment growth is responsible for formation of diamond single crystals. A model explained details of the mechanism has been suggested.

The content of nitrogen-vacancy (NV−) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size

For the first time it has been experimentally shown that a powder of detonation nanodiamonds (DND) and a saturated acyclic hydrocarbon, mono- or dibasic alcohol, used as the reaction mixture after treatment at high pressures (5–8 GPa) and high temperatures (1300–1800°C) results in the formation of diamond single crystals up to 15 micron in size. The Raman spectrum indicates that the diamonds have a perfect of crystal structure. It has been suggested that the oriented attachment mechanism is responsible for growth of micrometer-size diamond single crystals out of DND particles with sizes of about 5 nm under these technological conditions.

On the basis of experimental data on thermal conduction and sound velocity in composites obtained by sintering detonation nanodiamonds with the crystallite size of 4–5 nm and diamond micropowders with a grain size of about 10 μm at a high pressure (5–7 GPa) and high temperature (1200–1800°C), mechanisms of heat transfer in such structures are suggested. These mechanisms are shown to be different in composites of micro- and nanoparticles. In composites of micrometer particles, the conventional macroscopic mechanism of phonon propagation is active. In composites with a grain size of a few nanometers, the main contribution comes from thermal resistance on grain boundaries.

Using pressureless infiltration of copper into a bed of coarse (180 μm) diamond particles pre-coated with tungsten, a composite with a thermal conductivity of 720 W/(m K) was prepared. The bending strength and compression strength of the composite were measured as 380 MPa. As measured by sound velocity, the Young's modulus of the composite was 310 GPa. Model calculations of the thermal conductivity, the strength and elastic constants of the copper–diamond composite were carried out, depending on the size and volume fraction of filler particles. The coincidence of the values of bending strength and compressive strength and the relatively high deformation at failure (a few percent) characterize the fabricated diamond–copper composite as ductile. The properties of the composite are compared to the known analogues — metal matrix composites with a high thermal conductivity having a high content of filler particles (~60 vol.%). In strength and ductility our composite is superior to diamond–metal composites with a coarse filler; in thermal conductivity it surpasses composites of SiC–Al, W–Cu and WC–Cu, and dispersion-strengthened copper. Keywords: Metal matrix composite, Thermal conductivity, Strength, Elastic constants

The possibility of fabricating ‘aluminum – carbon nanofibers’ compact materials by hot pressing at a pressure of 5 GPa and a temperature of 480 – 980°C is studied. It is shown that aluminum carbide forms in the case of hot pressing above 720°C. The hardness of the hot-pressed aluminum – carbon nanofibers’ composite material is 80% higher than that of pure aluminum at a satisfactory ductility.

The aluminum-carbon nanofiber compacted materials fabricated by hot pressing are studied. The carbon content and the compacting temperature are shown to affect the hardness of the aluminum-carbon nanofiber compacted composite material: the hardness increases from 30 to 57 HB when the carbon nanofiber concentration increases from 0 to 1.5 wt %. The chemical state of the composite components is studied by X-ray photoelectron spectroscopy. Carbon nanofibers transform into an amorphous modification at a temperature of 980°C, which corresponds to the decrease in the hardness. Aluminum carbide Al4C3 is found to form, and its content increases monotonically in the hot pressing temperature range from 720 to 1370°C.

Different aspects of applications of electron paramagnetic resonance (EPR) based techniques including high frequency (HF) electron spin echo (ESE), electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) approaches to study diamond nanostructures are examined.

The modification of graphite used in diamond synthesis with low concentrations of the fullerene C60-C70 extract (from 0.045 to 0.225 wt % of graphite mass) in the presence of a Ni-Mn metal catalyst at a pressure of 5 GPa in the temperature range 1600–1800 K is found to decrease the activation energy of the graphite-diamond phase transition from 160 ± 40 to 100 ± 40 kJ/mol.

Using the steady-state heat flux method, the effective thermal conductivity λ of a particle bed is measured at room temperature, varying the external load P on the bed in the range of 3–30 kPa. Grains of various forms (debris, pebble, cubo-octahedral) and balls of different materials (polypropylene, sodium chloride, ceramics, diamonds, metals) of which the thermal conductivity of the solid measures 0.2–1500 W/(m K) are used. From the experimental dependencies λ(P) = λ0 + Δλ(P), values for effective thermal conductivity in the absence of contact heat conduction λ0 and contact conductivity Δλ(P) are found. The analysis allowed us (a) to refine further our earlier evaluation (in the first part of this study Abyzov et al. (2013)) of the adequacy of models which do not take account of contact thermal conductivity (the differential effective medium model and those of Gusarov et al., Raghavan–Martin, Chiew–Glandt/Gonzo, Kunii et al., Zehner–Schlunder) and (b) to assess the capabilities provided by a number of models of contact thermal conductivity (those of Dul’nev–Sigalova, Kaganer, Gusarov and others). A model with nominally flat rough contacts between particles in the bed is proposed, which describes the observed effects for contact thermal conductivity.

We studied the photoluminescence of MEH-PPV polymer films and a MEH-PPV/DND nanocomposite after exposure to gamma irradiation from a radioisotope source of cesium-137 with doses of 0.5–12.2 kGy for H2O and their relaxation processes after exposure to the maximum dose. Exposure to gamma irradiation leads to the formation of new structural units in MEH-PPV/DND, which are similar in structure to the structural units of the conductive PPV polymer. A microscopic model is proposed that describes the evolution of MEH-PPV/DND photoluminescence in the context of the formation of bonds between aliphatic radicals of polymers and the surface of detonation diamond.

The thermal conductivity of packed beds of various materials (metals, ceramics, superhard materials, polymers, etc.) is measured by the steady-state heat flux method at room temperature in air. Powders and granular materials are used, with particle sizes ranging mainly from 50 μm to 1.5 mm, with various particle shapes (debris, pebble, cubo–octahedral single-crystals, regular spheres), the thermal conductivity of the solid ranging widely from 0.15 to 1500 W/(m K). Experimental data and model calculations of the effective thermal conductivity of the bed are compared, including dependences on bed porosity and particle size. Both classical and more recent models are involved, such as the differential effective medium model and those of Raghavan–Martin, Kunii et al., Zehner–Schlunder, Gusarov et al., Hsu et al., Batchelor–O’Brein, and some others, which allow analytical calculations. The adequacy of the models is reviewed in connection with the properties of the disperse materials (particle shape etc.), based on the concepts of the absence or presence of contact thermal conductivity in the bed.

Sintered oriented nanodiamond arrays with the extremely high concentrations of the nitrogen-vacancy (NV) centers (up to 103 ppm) were investigated by the W-band (94 GHz) electron spin echo electron paramagnetic resonance techniques. The NV centers were fabricated by the high-pressure high-temperature sintering of detonation nanodiamonds (DND) without the post or prior irradiation of the samples. The processes of polarization and recovery of the equilibrium population of the spin sublevels by optical and microwave pulses have been examined at room temperature in high magnetic fields corresponding to the fine-structure transitions for the NV defects at 94 GHz (3,250–3,450 mT). A long spin coherence time of 1.6 μs and spin–lattice relaxation time of 1.7 ms were measured. The results were compared with those obtained on the NV centers fabricated by the irradiation and subsequent annealing of the commercially available bulk diamonds. It was shown that the relaxation characteristics of the NV defects were similar in the both types of the samples despite the extremely high concentrations of NV defects and isolated nitrogen donors in the sintered DND.

Different aspects of applications of electron paramagnetic resonance (EPR) based techniques including high frequency (HF) electron spin echo (ESE), electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) approaches to study diamond nanostructures are examined.

A composite material with a high thermal conductivity is obtained by capillary infiltration of copper into a bed of diamond particles of 400 μm size, the particles having been pre-coated with tungsten. The measured thermal conductivity of the composite decreases from 910 to 480 W m−1 K−1 when the coating thickness is increased from 110 to 470 nm. Calculations of the filler/matrix thermal boundary resistance R and the thermal conductivity of the coating layer λ i using differential effective medium, Lichtenecker’s and Hashin’s models give similar numerical values of R and λ i ≈ 1.5 W m−1 K−1. The minimal thickness of the coating h ∼ 100 nm necessary for ensuring production of a composite while maximizing its thermal conductivity, is of the same order as the free path of the heat carriers in diamond (phonons) and in copper (electrons). The heat conductance of the diamond/tungsten carbide coating/copper interface when h is of this thickness is estimated as (0.8–1) × 108 W m−2 K−1 and is at the upper level of values characteristic for perfect dielectric/metal boundaries.

The structure of detonation diamonds sintered at a high pressure (7 GPa) and temperatures of 1200–1700°C has been investigated by small-angle neutron scattering. It is shown that sintering leads to an increase in the particle size from 6 to 30 nm and established that this increase is due to the chainlike oriented attachment of particles. This study supplements the oriented-attachment model, which was suggested based on the X-ray diffraction spectra of detonation nanodiamonds (DNDs) sintered under the same conditions.

We show that nitrogen is the main impurity contained in detonation nanodiamonds at a concentration of 16,000 ppm. The content of nitrogen-vacancy NV− centers in these nanodiamonds is about 2.7 ppm, which is the largest of all known types of nanodiamonds of size less than 10 nm with artificially created NV− centers. The removal of graphite-like fragments from the nanodiamond surface allowed us to detect the characteristic photoluminescence of the NV− color centers in individual nanodiamond aggregates of sizes from 50–100 to 500–700 nm. We have further confirmed the detection of the negatively charged NV− through the observation of a strong decrease in the photoluminescence intensity when an external magnetic field is applied. Such an effect results from the optically detectable magnetic resonance of the electronic spin triplet ground state of NV− that cannot be observed in other emitting defects in a similar spectral range, including the neutral NV0 centers.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band and at high-frequency W-band (95 GHz) have been used to study natural diamond nanocrystals, detonation nanodiamond (ND) with a size of ∼ 4.5 nm and detonation ND after high-temperature, high-pressure sintering with a size of ∼ 8.5 nm. Isolated nitrogen centers N0 and nitrogen pairs N2 + have been detected and identified, and their structure has been unambiguously determined by means of the high frequency EPR and ESE in natural diamond nanocrystals. In detonation ND and detonation ND after sintering, isolated nitrogen centers N0 have been discovered in nanodiamond core. In addition EPR signals of multivacancy centers with spin 3/2 seem to be observed in nanodiamond core of detonation ND.

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W2C–WC. The average roughness, R a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m−1 K−1 are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 107 W m−2 K−1. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.

Sintering of detonation nanodiamonds (DND) has been studied at a pressure of ∼ 7 GPa in the 700–2000 °C temperature range. The X-ray coherent-scattering regions in DND have been found to grow with increasing sintering temperature. It is shown that diamond crystallites grow by the oriented attachment mechanism. It is demonstrated that the increase of thermal conductivity of the composites thus obtained is initiated by variation of the heat conductance of the boundaries separating DND crystallites.

A giant concentration of nitrogen vacancy defects has been revealed by the electron paramagnetic resonance (EPR) method in a detonation nanodiamond sintered at high pressure and temperature. A high coherence of the electron spins at room temperature has been observed and the angular dependences of the EPR spectra indicate the complete orientation of the diamond system.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band (9.4 GHz) and W-band (94 GHz) have been used to study defects in natural diamond nanocrystals, detonation nanodiamond (ND) with a size of  4.5 nm and detonation ND after high-pressure high-temperature (HTHP) sintering with a size of  8.5 nm. Based on identification of atomic nitrogen centers N0 and nitrogen pairs N2+ detected by means of the high frequency EPR and ESE in natural diamond nanocrystals, atomic nitrogen centers N0 have been discovered in nanodiamond core in detonation ND and detonation ND after sintering. In addition EPR signal of multi-vacancy centers with spin 3/2 seems to be observed in diamond core of detonation ND.

X-ray photoelectron spectroscopy data confirm that the surfaces of detonation-diamond particles contain complexes consisting of nitrate ions bound to surface defects of substitutional nitrogen in the diamond lattice or to structural units of type C(sp3)–NH3+ on the surface. Etching with argon ions easily removes the nitrate-ion complexes from the surface of the detonation diamonds without damaging their crystal lattice. Analysis of a sample’s IR absorption spectra before and after thermal heating at 350°C makes it possible to distinguish on the spectrum two lines (narrow and wide) with close-lying frequencies (1384.9 and 1372 cm−1), caused only by the different degree of bonding of the nitrate ions to underlying surface sites that contain nitrogen in tetrahedral sp3 coordination. The narrow line with higher peak intensity corresponds to an almost quasi-free state of an isolated nitrate ion on the surface of the detonation diamonds in the composition of a complex already damaged during moderate heating or during other low-energy treatments. Detonation-diamond particles with chemisorbed nitrate ions are unique markers that allow themselves to be easily detected in solid deposits of suspensions and solutions.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band and at high-frequency W-band (95 GHz) have been used to study defects in natural diamond nanocrystals, detonation nanodiamond (ND) with a size of ∼4.5 nm and detonation ND after high-temperature, high-pressure sintering with a size of ∼8.5 nm. Atomic nitrogen centers N 0 and nitrogen pairs N 2 + have been detected and identified and their structure has been unambiguously determined by means of the high frequency EPR and ESE in natural diamond nanocrystals. In detonation ND and detonation ND after sintering atomic nitrogen centers N 0 have been discovered in nanodiamond core. In addition EPR signal of multi-vacancy centers with spin 3/2 seems to be observed in diamond core of detonation ND.

A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.

Individual nitrogen centers N0 and nitrogen pairs N2+ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N0 nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.

Experimental data are used in an attempt to unravel the mechanism underlying the effect of modification of a graphite blend by fullerenes on the diamond synthesis at high pressures and temperatures in the presence of metal catalysts. Diamonds have been synthesized under different conditions in a wide range of temperatures and at different pressures, and the effects of blend modification by fullerenes and by addition of natural microcrystalline diamonds to a blend on the diamond synthesis at high pressures and temperatures have been compared.

We studied the sintering mechanisms and thermal conductivity of composites based on well purified detonation nanodiamonds (ND) prepared by Dr. Aleksenskii A.E. The thermal and electrical conductivities of composites from natural diamonds of 10–14 μm in size were also examined. Both types of composites were sintered at high pressures (5.0–7.0 GPa) and high temperatures (1200–2300 °C) for 10–25 s. It was found that the thermal conductivity of composites from natural diamonds increased as the sintering temperature approached the diamond–graphite equilibrium in the pressure range of 4.5–6.5 GPa because of the interdiffusion of the diamond particles. Above the phase equilibrium temperature, the thermal conductivity was observed to decrease due to the sample bulk graphitization. The maximum value of this parameter for the ND samples was observed at approximately 1900 °С. Higher temperatures caused sample damage at lowered pressures, which seems to be due to the ND transition to the nondiamond carbon phase possessing a lower density. When we added 5 wt.% of С60 fullerene to the initial ND, the diamond transition to a nondiamond carbon-like state occurred at a temperature below 1400 °С and the thermal conductivity increased from 50 to 100 W/(m·K). Thermal conductivity was found to be about 50 W/(m·K) for the ND samples and about 500 W/(m·K) for the microdiamonds. © 2008 Elsevier B.V. All rights reserved.

The thermal conductivity of composites sintered from natural microdiamond (5–7 and 10–14 μm) and nanodiamond powders under pressure of ∼ 6.0 to 6.5 GPa at the temperature ∼ 1000 to 2000 °C for 6–20 s was measured in a steady heat flow in the temperature range of 50–200 °C. It was found that the thermal conductivity of nanodiamond composites produced in these conditions was less than 10 W/(m⁎К) while that of natural microdiamonds was as high as 500 W/(m⁎К).

We investigated formation of carbon nanofibers grown by chemical deposition (CVD) method using an acetylene-hydrogen mixture on the surface of micron-sized aluminum powder particles. To obtain uniform distribution of the carbon nanostructures on the particles we deposited nickel catalyst on the surface by spraying from the aqueous solution of nickel nitrate. It was found that increasing the time of the synthesis lowers the rate of growth of carbon nanostructures due to the deactivation of the catalyst. The Raman spectroscopy measurements confirm the presence of disordered carbon corresponding to CNFs in the specimen. X-ray photoelectron spectroscopy showed the presence of aluminum carbide in the hot pressed samples. An aluminum composite material prepared using 1 wt.% CNFs obtained by uniaxial cold pressing and sintering showed 30% increase in the hardness compared to pure aluminum, whereas the composites prepared by hot pressing showed 80% increase in the hardness. Composite materials have satisfactory ductility. Thus, the aluminum based material reinforced with carbon nanostructures should be appropriate for creating high-strength and light compacts for aerospace and automotive applications and power engineering.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7355

The paper reports on the effect of a fullerene co-catalyst on high pressure – high temperature (HPHT) synthesis of diamond from graphite. It is shown that the co-catalyst increases the diamond yield by a factor of 1.30–1.45 at relatively low pressure (4.5 GPa) and temperature (about 1200 °C).

The possibility of creating single-crystalline materials in the boron-carbon-nitrogen system has been studied. The thermal conductivity of composites obtained by sintering a mixture of natural microcrystalline diamond powder with cubic boron nitride at high pressures (up to 7 GPa) and high temperatures (up to 2600°C) has been measured. To within sensitivity of the X-ray diffraction, no new C-N and/or B-C-N compounds are formed at the interphase boundaries in the system under consideration.

To measure the thermal conductivity of particle beds, a specially designed cuvette is inserted into the chamber of an ITP-MG4 device fitted with a vertical heat flux sensor. The cuvette with a transparent wall makes it possible to reduce the amount of test material to 25 cm3, to monitor visually the uniformity of a charge, to determine the bulk density of the particle bed (and to increase it if necessary using vibrocompaction) and to apply external pressure to the bed from 2.5 to 30 kPa. Using various continuous-solid and particulate materials as references, a calibration equation is obtained for thermal conductivity in the range of 0.03–1.1 W (m K)−1. To eliminate thermal contact resistance when measuring references, the end faces of glass specimens with a departure from flatness of up to 50 μm are wetted with water. To model the calibration, a calculation is carried out by the electrical circuit analogy. The calculated curve is close to the experimental points if a value for the contact thermal resistances r# = 2 × 10−3 m2 K W−1 is taken. Values of r# calculated by the Yovanovich model, based on the known roughnesses of the contact surfaces of the cuvette and the solid specimens, are an order of magnitude lower due to the decisive influence of nonflatness and not surface roughness at the low pressures used. The conditions under which our measurements were made are compared with the instructions of Russian, American and international standards for the measurement of thermal conductivity by the steady-state heat flow method (specimen size, flatness of working surfaces, etc). The sources of measurement inaccuracy and ways to improve the technique are examined.