Diamond Nanocomposites Research Articles

СИНТЕЗ НАНОКОМПОЗИТА НА ОСНОВЕ ИМПАКТНЫХ АЛМАЗОВ И КАРБИДА КРЕМНИЯ В УСЛОВИЯХ ВЫСОКИХ ДАВЛЕНИЙ И ТЕМПЕРАТУР

The article studies the structure, phase composition and physicomechanical characteristics of the nanocomposite based on impact diamonds. It is shown that the additions of a binder based on SiC and Si lead to reduction of the defectiveness of the nanocomposite and increase in the uniformity of its structure compared to the material without additives. Moreover, increase in the binder content also leads to the inversion of the structure type of the nanocomposite from polycrystalline to matrix. It is established that the addition of amorphous carbon black and boron affects the refinement of the nanocomposite matrix structure due to the formation of secondary finedispersed nanostructured SiC and boron carbide. Preliminary mechanical activation of the reaction mixture leads to structural changes in the synthesized material in comparison with the material obtained without the use of mechanical activation. In this case, the hardness of the samples obtained under comparable synthesis modes increases, which is associated both with the formation of a fine-grained structure of the material and with the phase transformation of lonsdaleite to diamond. An analysis of the microhardness and heat resistance of the obtained samples makes it possible to conclude that the achieved level of physicomechanical parameters of the diamond nanocomposite allows it to be used in a stone-processing tool for treating medium hard rocks.

Core–Shell Composites Based on Partially Oxidized Blend of Detonation Synthesis Nanodiamonds

The results of a study on the production of graphite–diamond nanocompositions by partial oxidation of a detonation synthesis blend in aqueous solutions of nitric acid under pressure in the temperature range 120–230°C are presented. A part of the graphite shell was subjected to selective oxidation. According to the results of kinetic studies in a 400 mL autoclave, an oxidation process scheme is proposed, which is based on a radical chain reaction involving nitrogen dioxide and carbon of graphite/graphene shell on the surface of the particles. The synthesis conditions for the main types of graphite–diamond nanocomposites of various oxidation states are determined. On a pilot installation in a swinging titanium autoclave of a 12 L capacity, experimental batches of the product were accumulated, which made it possible to assess the possibility of scaling the developed laboratory process.

Production of Polycrystalline Materials by Sintering of Nanodispersed Diamond Nanopowders at High Pressure. Review

The investigations dealing with the problems of forming polycrystalline materials with a high level of physical-and-mechanical properties using the method of diamond powder sintering at high pressure have been considered. The compacting mechanism of diamond nanopowders of different genesis under exposure to high pressure and high temperature is described, special features of pore structure formations are considered, and the critical role of the specified factor in sintering is shown. The need of degassing and modification of the diamond particle surface during the preparation for sintering is noted. The effectiveness of tungsten and its compounds is shown as an activating addition for producing wear-resistant thermostable diamond nanocomposites.

Development of Composite Poly(Lactide-co-Glycolide)- Nanodiamond Scaffolds for Bone Cell Growth.

There are relatively few nanotechnologies that can produce nanocomposite scaffolds for cell growth. Electrospinning has emerged as the foremost method of producing nanofibrous biomimetic scaffolds for tissue engineering applications. In this study diamond nanoparticles were integrated into a polymer solution to develop a nanocomposite scaffold containing poly(lactide-co-glycolide) (PLGA) loaded with diamond nanoparticles. To investigate the effect of adding diamond nanoparticles to PLGA scaffolds, primary human mesenchymal stem cells (hMSCs) were seeded on the scaffolds. The cytocompatibility results showed that addition of diamond nanoparticles did not impinge upon cell proliferation, nor was there a cytotoxic cellular response after 9 days in culture. Scanning electron microscopy, transmission electron microscopy, atomic force microscopy and confocal microscopy enabled qualitative characterization of the fibres and revealed cell morphology and number. Furthermore, surface roughness was measured to evaluate diamond nanoparticle modifications, and no significant difference was found between the diamond nanocomposite and pure polymer scaffolds. On the other hand, bright spots on phase images performed by atomic force microscopy suggested a higher hardness at certain points on fibers of the PLGA-nanodiamond composites, which was supported by nanoindentation measurements. This study shows that PLGA nanofibers can be reinforced with nanodiamond without adversely affecting cell behaviour, and thus it sets the foundation for future application of these scaffolds in bone tissue engineering.

Synthesis of novel superhard materials under ultrahigh pressure

Superhard materials are solids whose Vickers hardness is beyond 40 GPa. They have wide applications in industry such as cutting and polishing tools, wear-resistant coatings. Most preparations of superhard materials are conducted under extreme pressure and temperature conditions, not only for scientific investigations, but also for the practical applications. In this paper, we would introduce the recent progress on the design and preparations of novel superhard materials, mainly on nanopolycrystalline diamond, B-C-N superhard solid solutions, and cubic-Si3N4/ diamond nanocomposites prepared under ultrahigh pressure and high temperature (HPHT), using multi-anvil apparatus based on the hinged-type cubic press. Bulk materials of all these superhard phases have been successfully synthesized and are systematically tested. We emphasize that ultrα-HPHT method plays an important role in the scientific research and industrial production of superhard materials. It provides the driving forces for the light elements forming novel superhard phases as well as the way for sintering high-density nanosuperhard materials.

Reinforcement effect of nanodiamond on properties of epoxy matrix

Epoxy/nanocrystalline diamond nanocomposites composites were prepared by dispersing ultrasonically, 0.4, 0.7, 1.0, and 4.0 wt% acid‐treated nanocrystalline diamond (NCD) powder in epoxy matrix. Fourier infrared spectroscopy was utilized to study the moieties attached to the nanodiamond particles. The trace elements present in NCD powder before and after acid treatment were analyzed by ion beam techniques. Thermomechanical properties of the nanocomposites showed that incorporation of low content (0.4 wt%) of nanodiamond powder into epoxy matrix enhanced the storage modulus, loss modulus, and hardness by ∼68, ∼55, and ∼86%, respectively, over neat epoxy. By increasing the concentration of modified NCD to 0.7 wt% resulted in lower values of hardness and thermomechanical properties but still remain higher than neat epoxy. An increasing trend in properties was again observed at 4 wt% concentration of modified nanofiller. The glass transition temperature was up shifted to ∼110°C over neat epoxy. The mechanisms responsible for enhanced properties of epoxy matrix are also discussed in detail. POLYM. COMPOS., 34:811–818, 2013. © 2013 Society of Plastics Engineers

Disorder and optical gaps in strained dense amorphous carbon and diamond nanocomposites

We employ empirical tight-binding simulations on strained tetrahedral amorphous carbon and diamond nanocomposite networks. For each applied strain, the optoelectronic properties are monitored through the absorption coefficient and the dielectric function. These lead to the optical gaps and are able to quantify the amount of disorder in the structures. We compare our results to those of unstrained nanostructured diamond and amorphous carbon (a-C) phases and link the degree of disorder in these materials to their structural details as a function of the external load. The atomic rearrangements and distortions imposed by the external strain in these structures are directly observable in their optoelectronic properties. We thoroughly discuss the interplay between increased external strain, structural and topological disorder, atomic rearrangements and their effect on the calculated optoelectronic properties.

Atomistic Factors Governing Adhesion between Diamond, Amorphous Carbon and Model Diamond Nanocomposite Surfaces

Complementary atomic force microscopy (AFM) measurements and molecular dynamics (MD) simulations were conducted to determine the work of adhesion for diamond (C)(111)(1 × 1) and C(001)(2 × 1) surfaces paired with carbon-based materials. While the works of adhesion from experiments and simulations are in reasonable agreement, some differences were identified. Experimentally, the work of adhesion between an amorphous carbon tip and individual C(001)(2 × 1)–H and C(111)(1 × 1)–H surfaces yielded adhesion values that were larger on the C(001)(2 × 1)–H surface. The simulations revealed that the average adhesion between self-mated C(001)(2 × 1) surfaces was smaller than for self-mated C(111)(1 × 1) contacts. Adhesion was reduced when amorphous carbon counterfaces were paired with both types of diamond surfaces. Pairing model diamond nanocomposite surfaces with the C(111)(1 × 1)–H sample resulted in even larger reductions in adhesion. These results point to the importance of atomic-scale roughness for adhesion. The simulated adhesion also shows a modest dependence on hydrogen coverage. Density functional theory calculations revealed small, C–H bond dipoles on both diamond samples, with the C(001)(2 × 1)–H surface having the larger dipole, but having a smaller dipole moment per unit area. Thus, charge separation at the surface is another possible source of the difference between the measured and calculated works of adhesion.

Nanoindentation of model diamond nanocomposites: Hierarchical molecular dynamics and finite-element simulations

Complementary molecular dynamics (MD) and finite-element (FE) simulations of model diamond nanocomposites (MDN) subjected to nanoindentation were undertaken to understand how contact behavior pertaining to the surface morphology of MDN surfaces can be spanned from the molecular to the continuum scale. The MD simulations determined that the behavior inside the contact region is influenced by atomic-scale features on the tip and surface, indent location, grain tilt and roughness of the MDN surfaces. In addition, if the atomic-scale surface morphology is treated as a surface roughness within the FE simulations, the same grain orientations, and similar elastic properties are used for both MD and FE simulations, there is reasonable agreement between the contact pressures for relatively low indentation loads and shallow substrates. For larger loads, the contact pressures from the FE simulations deviate somewhat from the MD results near the center of the contact. The contact behavior for length scales that are prohibitive for MD models (e.g., deep substrates) was also examined using FE simulations. This allowed for a detailed investigation of how contact conditions and stick-slip events within the contact evolve as a function of contact pressure and continuum surface stresses.

Peculiar dynamics and elastic properties of hybrid semi-interpenetrating polymer network–3-D diamond nanocomposites

Polyurethane–poly(2-hydroxyethyl methacrylate)-3-D nanodiamond (PU–PHEMA–ND) composites were studied using combined CRS/DSC/AFM approach. The peculiar behavior and the pronounced heterogeneity of their glass transition dynamics were revealed. Two opposite tendencies for changing dynamics by 3-D NDs, with prevailing sharp suppression of motions, and three-fold increasing elastic properties were shown. Maximal effects were found at minimal ND content of 0.25wt%. This was associated, besides the improved dispersion/spatial distribution of NDs, with formation of thoroughly cross-linked nanocomposite network, due to the double hybridization resulting in a low rheological percolation threshold and the synergistic effect in dynamics.

Probing the sp 2 dependence of elastic moduli in ultrahard diamond films

The structural and elastic properties of diamond nanocomposites and ultrananocrystalline diamond films (UNCD) are investigated using both empirical potentials and tight-binding schemes. We find that both materials are extremely hard, but their superb diamondlike properties are limited by their sp 2 component. In diamond composites, the sp 2 atoms are found in the matrix and far from the interface with the inclusion, and they are responsible for the softening of the material. In UNCD, the sp 2 atoms are located in the grain boundaries. They offer relaxation mechanisms which relieve the strain but, on the other hand, impose deformations that lead to softening. The higher the sp 2 component the less rigid these materials are.

ZnO nanowire and amorphous diamond nanocomposites and field emission enhancement

ZnO nanowires were fabricated on the amorphous diamond thin layer on silicon substrates using thermal chemical vapor transport and condensation (CVTC) without any metal catalysts. The remarkable enhancement of the field emission of the nanocomposites by ZnO nanowires covered amorphous diamond was found compared to that of the intrinsic amorphous diamond, suggesting the probability of decorating amorphous diamond by fabricating one-dimensional nanostructures on its surface, which could largely improve the field emission by modifying surface microstructures. Associated with surface chemical reactions, a vapor–solid mechanism of ZnO nanowires nucleation and growth on amorphous diamond was established.

Structure, stability, and stress properties of amorphous and nanostructured carbon films

Structural and mechanical properties of amorphous and nanocomposite carbon are investigated using tight-binding molecular dynamics (TBMD) and Monte Carlo (MC) simulations. In the case of amorphous carbon (a-C), we show that the variation of sp 3 fraction as a function of density is linear over the whole range of possible densities and that the bulk moduli follow closely the power–law variation suggested by Thorpe. We also review earlier work pertained to the intrinsic stress state of tetrahedral (ta-C) amorphous carbon. In the case of nanocomposites, we show that the diamond inclusions are stable only in dense amorphous tetrahedral matrices. Their hardness is considerably higher than that of pure amorphous carbon films. Fully relaxed diamond nanocomposites possess zero average intrinsic stress.

Synthesis and Electrochemical Characteristics of a Nanocomposite Diamond Electrode

A nanocomposite material with novel electrochemical properties was synthesized by immersing a platinum wire into the dense zone of the 1-2% CH 4 /H 2 plasma in a microwave chemical vapor deposition reactor. Raman analysisof the deposit indicated the presence of nanocrystalline diamond, graphite, and amorphous sp 3 carbon. Notably, the characteristic broad shoulder between 1350 and 1550 cm - 1 attributable to amorphous sp 2 carbon was absent. Growth of freestanding submicrometer-thick whiskers containing diamond and graphite nanocomposite was observed. The nanocomposite material, without any prior surface pretreatment, showed high reversibility (ΔE p < 100 mV) for dopamine redox reactions in 0.1 M KCl solution.

Mechanism of the formation of a diamond nanocomposite during transformations of C60 fullerite at high pressure

The results of an investigation of the transformation of C60 fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported. It is found that treatment of fullerite C60 at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp 3) and graphitic (sp 2) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading to the transformation of C60 fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites are discussed.

Nanocrystalline diamond: Effect of confinement, pressure, and heating on phonon modes

Micro- and nanocrystalline systems exhibit properties that differ markedly from bulk systems. Diamond, a prototypical system, demonstrates a broadening, shift, and emergence of Raman phonon modes that are believed to originate from finite-size effects. Such information should be useful in constraining confinement models developed to describe the state of these mesoscopic systems. For example, previous investigations have analyzed crystallite size and stresses in scientifically and technologically relevant environments, including chemical-vapor-deposition diamond films and diamond nanocomposites. We have experimentally measured the effect on the diamond Raman phonon modes due to confinement, pressure, and heating effects. At ambient pressure, we present Raman measurements for diamond crystallites ranging from 6 nm to 10 \ensuremath{\mu}m, which were synthesized by both static and dynamic techniques. The Raman spectra obtained from the statically synthesized samples exhibit a characteristic strong and narrow diamond band, while those dynamically synthesized exhibit both diamond and graphiticlike features. A redshift of the diamond Raman band is observed for decreasing particle size. However, the pressure dependence of the phonon is about the same as that for the bulk system up to 30 kbar for crystallite sizes between 6 and 10 nm. Our measurements also indicate that heating effects from the incident laser dramatically affect the measured Raman spectra. This result leads us to an explanation for discrepancies among previously published results. We show that crystallite size and stress information cannot be determined without compensating for heating effects. Lastly, the phonon confinement model is able to explain the shifts of the Raman modes with size.