Diamond Mode Research Articles

Thermal resistance of PCD materials with borides bonding phase

In these studies, one group of PCD materials has been prepared using diamond powder and 10 wt % of TiB2 and the second batch of the PCD material has been prepared using a mixture of diamond powder with 5 wt % of TiB2 and 2 wt % of Co. The materials have been sintered using a Bridgman-type high-pressure apparatus at 8.0 ± 0.2 GPa and a temperature of 2000 ± 50 °C. Thermogravimetric (TG) measurements and Differential Thermal Analysis (DTA) have been carried out for diamond micropowders, TiB2 bonding phase, and sintered composites. The coefficients of friction for diamond composites in a sliding contact with an Al2O3 ceramic ball have been determined from the room temperature up to 800°C. Material phase compositions were analyzed for initial samples and after wear tests, at the temperature of 800°C. Raman spectra of diamond composites with borides bonding phases, observed for the first-order zone center modes of diamond and graphite during heating up to 800°C in air have been presented. Thermal properties have been compared with the commercial diamond-cobalt PCD. It has been found that diamond with TiB2 and Co is the most resistant to the hardness changes at elevated temperatures and this material maintains the high hardness value up to 800°C but it has a high coefficient of friction.

Calculation methods of investigating the surface layer of thin-walled shafts hardened by methods of surface plastic deformation

Calculation methods of investigating the residual stress-strain state of the surface layer of shafts hardened by shot peening and diamond burnishing are discussed in the paper. Shafts manufactured at aircraft plants are mostly thin-walled. In addition high requirements are imposed on the accuracy of their geometric dimensions and shape. Ensuring the fatigue resistance of shafts is achieved by applying hardening treatment. Hardening treatment residual stresses result in residual deformation of shafts often exceeding manufacturing tolerances. The models and approaches proposed in this paper make it possible to predict computationally the residual stress-strain state of the surface layer after diamond burnishing as well as technological residual deformations of the shafts caused by residual stress. They also allow adjusting the modes of shot peening and diamond burnishing at the stage of process development. The work was carried out for a shaft made of VT-22 and EP517-SH materials. The results of the investigation show that the use of preliminary numerical analysis of treatment modes makes it possible to ensure residual deformations of the most critical sections of the shafts and seating surfaces for bearings within manufacturing tolerances and also to reduce tensile residual stress on the shaft surface after diamond burnishing.

Numerical investigation of compressive behaviour of luffa-filled tubes

The behaviour of luffa and luffa-filled tubes under uniaxial compression was investigated numerically using finite element analysis (FEA) and analytically by theoretical models. The FEA models were validated against experimental data. Parametric study was carried out using the validated FEA models to examine the effects of the density of luffa, the thickness to diameter ratio of tube and the cross-sectional topology of luffa core. It was found that the optimal density of the luffa as filler for the luffa-filled tubes was closely related to the optimal density of the luffa sponge. It increased with the increase of the thickness to diameter ratio of the tube. The cross-sectional topology of the filler material had a negligible effect on the specific energy absorption per unit mass even when the deformation pattern of the luffa-filled tube was changed from the diamond mode to the concertina one.

From Photons to Phonons and Back: A THz Optical Memory in Diamond

Optical quantum memories are vital for the scalability of future quantum technologies, enabling long-distance secure communication and local synchronization of quantum components. We demonstrate a THz-bandwidth memory for light using the optical phonon modes of a room temperature diamond. This large bandwidth makes the memory compatible with down-conversion-type photon sources. We demonstrate that four-wave mixing noise in this system is suppressed by material dispersion. The resulting noise floor is just 7×10(-3) photons per pulse, which establishes that the memory is capable of storing single quanta. We investigate the principle sources of noise in this system and demonstrate that high material dispersion can be used to suppress four-wave mixing noise in Λ-type systems.

Energy Absorption of Thin-Walled Square Tubes With a Prefolded Origami Pattern—Part I: Geometry and Numerical Simulation

Thin-walled tubes subjected to axial crushing have been extensively employed as energy absorption devices in transport vehicles. Conventionally, they have a square or rectangular section, either straight or tapered. Dents are sometimes added to the surface in order to reduce the initial buckling force. This paper presents a novel thin-walled energy absorption device known as the origami crash box that is made from a thin-walled tube of square cross section whose surface is prefolded according to a developable origami pattern. The prefolded surface serves both as a type of geometric imperfection to lower the initial buckling force and as a mode inducer to trigger a collapse mode that is more efficient in terms of energy absorption. It has been found out from quasi-static numerical simulation that a new collapse mode referred to as the completed diamond mode, which features doubled traveling plastic hinge lines compared with those in conventional square tubes, can be triggered, leading to higher energy absorption and lower peak force than those of conventional ones of identical weight. A parametric study indicates that for a wide range of geometric parameters the origami crash box exhibits predictable and stable collapse behavior, with an energy absorption increase of 92.1% being achieved in the optimum case. The origami crash box can be stamped out of a thin sheet of material like conventional energy absorption devices without incurring in-plane stretching due to the developable surface of the origami pattern. The manufacturing cost is comparable to that of existing thin-walled crash boxes, but it absorbs a great deal more energy during a collision.

Optical properties of impact diamonds from the Popigai astrobleme

Impact diamonds from Popigai astrobleme were found to consist of different carbon phases: cubic and hexagonal diamond with sp3 bonding according to X-ray structural analysis as well as amorphous, crystalline and disordered graphite with sp2-bonding (Raman scattering). The sizes of graphite domains vary from 10 to 100nm. Fundamental absorption edge for Popigai impact diamonds is shifted ~0.5eV to lower energies in comparison with kimberlite diamonds (5.47eV) as a result of the lonsdaleite input, in good agreement with ab initio calculations (Eg=5.34 and 4.55eV for 3C cubic and 2H hexagonal diamonds, respectively). Yellowish color of impact diamonds is due to Rayleigh light scattering on structural defects whereas graphite is responsible for gray to black coloring. In the mid-IR region there is a multi-phonon absorption of 3C diamond in the 1800 to 2800cm−1 range and some new bands at 969, 1102, 1225, and 1330cm−1 in the one-phonon region. Micro-Raman study shows inclusions of side noncarbon minerals (quartz, magnetite, and hematite) some of which contain Cr3+ impurity. The vibration modes of cubic diamond and lonsdaleite exhibited in the Raman spectra were elucidated by the first-principles studies. Popigai impact diamonds demonstrate a broad-band luminescence in 2.1, 2.38, and 2.84eV components similar to that for nanocrystal polycrystalline 3C diamond. All emissions are excited at band-to-band transitions whereas the last two are observed also at excitation into 2.4 and 3.0 bands supposedly as a result of intracenter processes within the H3(NVN) and NV0 centers.

AXIAL CRUSHING OF TRIANGULAR TUBES

In the present paper, the mechanical behavior of large deformation of a regular equilateral triangular tube under quasi-static axial crushing is reported, which is a polygon with an acute angle and odd number of sides. Based on the results from nonlinear finite element analysis (FEA), a new type of inextensional basic plastic collapse folding element is proposed to describe the plastic progressive collapse. The progressive folding around the stationary horizontal hinges and inclined traveling hinges are involved to develop the new basic folding element. Two types of inextensible deformation modes are discovered, i.e., diamond mode and rotational symmetrical mode. The average crushing load for each mode is predicted from the super-folding element theory, which was proposed from the previous investigation on the axial crushing of square columns. A rigid-plastic material model and a kinematically admissible model are involved in this theory. The results are further validated against experiments. The approximate quasi-static theoretical predictions for the mean crushing loads of triangular tubes provide reasonable agreement with the corresponding experimental results.

Light-weight thin-walled structures with patterned windows under axial crushing

Patterned windows are introduced to the thin-walled square tubes to reduce the weight while maintaining the mechanical property of the original tube. The topological pattern design is studied under axial compressing condition. Experimental results show that these windowed tubes have enhanced crushing performance over the conventional tube, with 63% as the maximum reduction in the initial peak load and 54% as the maximum increase in the specific energy absorption. Parametric study is conducted by using a finite element analysis to investigate the effect of the size of windows on tubes' collapse characteristics. Three collapse modes, the symmetric, extensional and diamond modes, are distinguished. Tubes collapsing in the diamond mode perform less well in terms of both the energy absorption and SEA, while those with the symmetric or extensional mode generally show an increase in SEA.

Multidisciplinary optimization of collapsible cylindrical energy absorbers under axial impact load

In this article, the multi-objective optimization of cylindrical aluminum tubes under axial impact load is presented. The specific absorbed energy and the maximum crushing force are considered as objective functions. The geometric dimensions of tubes including diameter, length and thickness are chosen as design variables. D/t and L/D ratios are constricted in the range of which collapsing of tubes occurs in concertina or diamond mode. The Non-dominated Sorting Genetic Algorithm-II is applied to obtain the Pareto optimal solutions. A back-propagation neural network is constructed as the surrogate model to formulate the mapping between the design variables and the objective functions. The finite element software ABAQUS/Explicit is used to generate the training and test sets for the artificial neural networks. To validate the results of finite element model, several impact tests are carried out using drop hammer testing machine.

Crush Can Behaviour as an Energy Absorber in a Frontal Impact

The work presented is devoted to the investigation of a state-of-the-art technological solution for the design of a crush-can characterized by optimal energy absorbing properties. The work is focused on the theoretical background of the square tubes, circular tubes and inverbucktube performance under impact with the purpose of design of a novel optimized structure. The main system under consideration is based on the patent US 2008/0185851 A1 and includes a base flange with elongated crush boxes and back straps for stabilization of the crush boxes with the purpose of improvement of the energy-absorbing functionality. The modelling of this system is carried out applying both a theoretical approach and finite element analysis concentrating on the energy absorbing abilities of the crumple zones. The optimization process is validated under dynamic and quasi-static loading conditions whilst considering various modes of deformation and stress distribution along the tubular components. Energy absorbing behaviour of the crush-cans is studied concentrating on their geometrical properties and their diamond or concertina modes of deformation. Moreover, structures made of different materials, steel, aluminium and polymer composites are considered for the material effect analysis and optimization through their combination. Optimization of the crush-can behaviour is done within the limits of the frontal impact scenario with the purpose of improvement of the structural performance in the Euro NCAP tests.

Determination of ultrathin diamond films by Raman spectroscopy

AbstractThe study of Raman spectra of recently predicted ultrathin diamond films (diamanes) with nanometer thickness, transformed from multilayered graphenes by the adsorption of hydrogen is presented. Here we studied the phonon spectra of diamane structures in detail by ab initio method, especially the Raman and infrared (IR) vibrational modes. In particular, two‐layered diamanes display Raman peaks near 1110, 1260, 1320, 2860 cm−1, and three‐layered diamanes have a broad region (1110–1340 cm−1) of Raman shifts and peaks near 2830–2860 cm−1. The spectra are radically distinguished from the similar spectra of one to three layered graphenes and graphane. magnified imageLeft side: Atomic structure and vibration pattern of optical modes of ultrathin diamond (diamane). Right: Phonon densities of the states of graphane and diamanes.

Macroscopic non-classical states and terahertz quantum processing in room-temperature diamond

Researchers investigate the optical phonon modes of bulk diamond at room temperature. Ultrafast Raman scattering measurements show an extended and highly non-classical state in the optical phonon modes of bulk diamond. The researchers also demonstrate a terahertz-bandwidth quantum memory based on transient ultrafast Raman scattering from the optical phonons.

Deformation and energy absorption of aluminum foam-filled tubes subjected to oblique loading

Research to quantify the energy absorption of empty and foam-filled tubes under oblique loading with different loading angles and geometry parameters was carried out. Tests on circular tubes made of aluminum alloy AA6063 under quasi-static axial or oblique loading were performed. The collapse behavior of empty, foam-filled single and double tubes was investigated at loading angles of 0°, 5°, 10° and 15° with respect to the longitudinal direction of the tube. The tubes were fixed at both ends and oblique load was realized by applying a load at the upper end of a pair of specimens. When the foam-filled tubular structures subjected to oblique quasi-static loading, some new deformation modes, such as spiral folding mode, irregular extensional folding mode and irregular axi-symmetric or diamond deformation mode, were identified and ascribed to the bending of tubes and shearing of foam filler, as well as the interaction between the tubes and the foam. The energy absorption characteristics of empty and foam-filled single and double tube structures with respect to the load angle and wall thickness are determined. It is found that the energy-absorbing effectiveness factors of the circular tube structures with aluminum foam core are significant higher than those of the empty tubes and the energy absorption capacity of the foam-filled double tubes is better than that of the empty and foam-filled single tubes.

Structure of diamond nanoparticles grown by chemical vapor deposition

We studied the structure of diamond nanoparticles grown by chemical vapor deposition. SEM images show that the material contains cubic, hexagonal, and possibly icosahedral structures ranging in size from 10 to 200nm. Raman spectroscopy shows bands, which are characteristic of crystalline diamond, E2g mode of hexagonal diamond, a-C, and graphite.

Carbon-Based Nanostructures Obtained in Water by Ultrashort Laser Pulses

An ultrashort (100 fs) Ti:Sapphire pulsed laser has been employed in order to produce nanostructures by pulsed ablation of a graphite target in water. Different (10−100−1000 Hz) repetition rates have been used, and the features of material produced have been investigated by surface enhanced Raman spectroscopy (SERS) and scanning electron microscopy (SEM). SERS spectra show that a broad asymmetric band associated with diamond-like carbon (DLC) is observed when repetition rates of 10 or 100 Hz are used. On the contrary, ablated species produced with 1 kHz pulses present a narrow peak at 1333 cm−1, the typical mode of diamond, which is, however, embedded in a DLC band centered at 1540 cm−1. SEM images show the presence of dispersed octahedral-shaped structures having a size from 1 to 5 μm, in the case of 10 or 100 Hz repetition rates, and agglomerates of particles having a dimension below 300 nm, when 1 kHz pulses are used.

Superconductivity of p-type diamond (001) and (111) thin films: Ab initio calculations

The surface structure, electronic properties, lattice dynamics, and the electron–phonon coupling for p-doped diamond (001)-(2 × 1) and (111)-(2 × 1) thin films have been extensively investigated using ab initio methods within the virtual crystal approximation. The calculations of p-doped diamond thin films strongly favor dimer reconstruction of diamond surfaces. The physical origin of superconductivity of diamond (001)-(2 × 1), respectively, and (111)-(2 × 1) thin films which is higher than that of bulk diamond is systematically studied. It is showed that surface vibrational modes of diamond (001)-(2 × 1) surfaces give main contributions to superconducting transition temperature T c , while T c of diamond (111)-(2 × 1) surfaces is attributed to the combined action of surface and bulk vibrational modes. Therefore, at the highest concentration (13.98 × 10 21 cm − 3 ) T c ≈ 56.5 K of diamond (111)-(2 × 1) surfaces is about twice as high as that of bulk and diamond (001)-(2 × 1) surfaces.

Multiple Defect Modes in Diamond Photonic Crystal

Defect frequencies, degeneracy and mode field patterns of defect modes in diamond based photonic crystal (PC) are analyzed. An efficient method to create multiple defect frequency levels in the photonic band gap by degeneracy lifting is proposed. The degenerate dipole mode is split into two defect frequency levels by upsetting the symmetry about the origin. The diamond PC with our proposed defect structure has four defect frequency levels with two dipole and two quadrupole mode field patterns. It is shown that non-degenerate monopole and hexapole modes can be obtained by pulling up the acceptor levels from the dielectric band in diamond photonic crystals. Our proposed structure has a monopole and a hexapole mode that are very close in frequency. However, C6v symmetry of the triangular lattice guarantees their non-degeneracy.

Energy absorption of pressurized thin-walled circular tubes under axial crushing

By pressurizing cellular materials, honeycombs, or thin-walled structures, their energy absorption can be greatly enhanced, and this enhancement can be controlled by the applied pressure. This concept shines light on the possibility of achieving adaptive energy absorption. To investigate the effect of internal pressure on energy absorption of thin-walled structures, this paper presents a study of axial crushing of pressurized thin-walled circular tubes. In the experiments, three groups of circular tubes with radius/thickness ratio R/ t=120–200 were axially compressed under different pressurizing conditions. The results show that with an increase of internal pressure, the deformation mode switches from diamond mode with sharp corners to that with round corners, and eventually to ring mode. In diamond mode, the mean force of the tubes increases linearly with internal pressure. The enhancement comes from two mechanisms: direct effect of pressure and indirect effect due to interaction between pressure and tube wall. After the deformation switches to ring mode, the enhancement resulting from the second mechanism becomes weaker. Based on experimental observations, the deformation mode, energy dissipation mechanisms as well as interaction between internal pressure and tube wall are analyzed theoretically and the theoretical results are in good agreement with the experimental ones.

Elementary excitations in Si, Ge, and diamond time reversal affected

The Space Symmetry and the Time Reversal Symmetry of vibrational modes in Si, Ge and diamond are investigated. Using Space Symmetry we have derived the Lattice Mode Representation. Reducing it onto phonon species we obtain the symmetry allowed phonons and their degeneracies. Using reality test for irreducible representations according to those the phonons are classified we determine which modes are Time Reversal affected. Comparison with experimental data obtained by neutron scattering is made. The effect of Time Reversal Symmetry on electrons in the conduction band and holes in the valence band as well as on excitons is briefly discussed.

Diamond formation in carbonate-silicate-sulfide-carbon melts: Raman- and IR-microspectroscopy

An experimental study on diamond nucleation and growth in a carbon solution in multicomponent carbonate, carbonate-silicate, silicate and sulfide melts was performed using a high-pressure toroidal anvil-with-hole cell with graphite resistive furnace. The boundary conditions of diamond spontaneous crystallization and seeded growth are determined for all the diamond growth media with the use of the PT diagram of diamond crystal growth. A density of diamond nucleation in the studied carbonate, carbonate-silicate, silicate, and sulfide melts with dissolved carbon exceeds (3.0–5.0) × 10 2 nuclei/mm 3 with a maximum around 1.0 × 10 5 nuclei/mm 3 at formation of polycrystalline “diamondite”. Raman spectra of quenched carbonate-carbon, carbonate-silicate-carbon, silicate-carbon and sulfide-carbon melts contain bands relating to the region of C-C stretching modes in diamond and graphite microphases. FTIR spectra show that nitrogen defects in the carbonate-synthetic diamond are characterized with the mixed Ib-IaA type and reveal a high nitrogen concentration (up to 850 ppm).