Finite Element Analysis of Convection in Growth Cell for Diamond Growth Using Ni-Based Solvent

Thermal-electricaJ-fluid coupled finite element analyses are performed in the model of the growth cell in a high-pressure and high-temperature （HPHT） cubic apparatus in which the large diamond crystal can be grown by using Ni-based solvent with temperature gradient method （TGM）. The convection in the Ni-based solvent with different thicknesses at 1700-1800 K is simulated by finite element method （FEM）. The experiments of diamond crystal growth are also carried out by using Ni-based solvent at 5.7GPa and 1700-1800K in a China-type cubic high pressure apparatus （CHPA）. The simulation results show that the Rayleigh number in the solvent is enhanced obviously with the increasing solvent thickness. Good quality diamond single crystal cannot be grown if the Rayleigh number in the solvent is too high.     

Differential structure on κ-Minkowski spacetime realized as module of twisted Weyl algebra

The differential structure on the κ-Minkowski spacetime from Jordanian twist of Weyl algebra is constructed, and it is shown to be closed in 4-dimensions in contrast to the conventional formulation. Based on this differential structure, we have formulated a scalar field theory in this κ-Minkowski spacetime.     

Structural phenomena in glassy carbon induced by cobalt ion implantation

Glassy carbon (GC) was implanted by 150 keV Co⁺ ions to the doses of 1×10¹⁶ (low dose) and 1×10¹⁷ ions/cm² (high dose). The low dose implantation results in GC structure disordering with formation of amorphous carbon (a-C). Analysis of Rutherford backscattering (RBS) and Raman spectra has revealed 15 at.% of sp³-bonded C atoms in the a-C structure. The in-pane size of sp² clusters was estimated to be 1.1 nm. On the contrary, the high dose ion implantation results in ordering of the a-C structure. Content of the sp³ atoms in a-C was reduced to about 5% and, respectively, the in-plane sp² cluster size was increased up to 2.8 nm. Together with the a-C structure ordering the Raman spectra identifies formation of transpolyacetylene (TPA)-like chains after the high-dose Co⁺ implantation. In parallel, RBS suggests an enhanced diffusion of the implanted cobalt within the modified carbon layer. Correlation of the RBS and Raman results argues a driving role of cobalt diffusion in the TPA-like chains formation and a-C ordering. Great surface roughening observed after the high dose Co⁺ implantation suggests also the pronounced cobalt clustering causing large flux of “free volume” to the surface.     

Milling and dispersion of multi-walled carbon nanotubes in texanol

Rheological results were used to determine the optimum type of dispersant and its concentration for six commercial dispersants for the dispersion of multi-walled carbon nanotube (MWCNT) agglomerates in texanol. An unsaturated polycarboxylic acid copolymer (BYK P-104) exhibited the optimum performance with the lowest MWCNT slurry viscosity in texanol. The cutting and dispersion efficiencies of MWCNTs with 20 wt.% of BYK P-104 dispersant were compared using conventional ball milling and high energy milling, whereby the latter was found to be more effective. High energy milling for 2 h produced a large portion of MWCNT agglomerates smaller than 150 nm, showing a drastic increase in slurry viscosity due to the dispersion into individual CNTs. On the other hand, 120 h ball milling was required to achieve the agglomerate size of 300 nm with less viscosity increase upon milling. Decrease in the degree of MWCNT crystallinity was observed by both milling, even though 2 h high energy milling showed slightly less damage than 120 h ball milling based on XRD and Raman spectroscopy results.     

Mode selective control of flow turbulence

We study spin transport in normal/ferromagnetic/normal/ferromagnetic.../normal graphene superlattices, which can be realized by putting a series of magnetic insulator bars on top of a graphene sheet. Owing to magnetic proximity effect, local exchange splittings will be induced in the graphene sheet, effectively forming a magnetic graphene superlattice. The spin polarization of tunneling conductance and the magneto resistance (MR) exhibit oscillatory behavior with the gate voltage. The superlattice structure leads to an enhanced spin polarization and MR ratio, making the magnetic graphene superlattice become very promising in spintronics applications.     

Alkylation of imidazole under ultrasound irradiation over alkaline carbons

N-Alkyl-imidazole has been synthesized by sonochemical irradiation of imidazole and 1-bromobutane using alkaline-promoted carbons (exchanged with the binary combinations of Na, K and Cs). The catalysts were characterized by X-ray photoelectron spectroscopy, thermal analysis and N₂ adsorption isotherms. Under the experimental conditions, N-alkyl-imidazoles can be prepared with a high activity and selectivity. It is observed that imidazole conversion increases in parallel with increasing the basicity of the catalyst. The influence of the alkaline promoter, the reaction temperature, and the amount of catalyst on the catalytic activity has been studied. For comparison, the alkylation of imidazole has also been performed in a batch reactor system under thermal activation.     

Microstructure of high-pressure-synthesized diamonds under rapid quenching and electron irradiation

A type of synthetic diamond single crystal about 0.4–0.5 mm in dimension prepared under high pressure–high temperature (HPHT) in the presence of a FeNi molten catalyst was quenched from HPHT and irradiated with 300 keV electrons at room temperature. Transmission electron microscopy was employed to examine the microstructure of the diamond single crystal before and after electron irradiation. It was found that there exists a large amount of cellular interfaces in the quenched diamond sample, which indicates the growth condition of the diamond under HPHT. Hexagonal dislocation loops about several tens of nanometers in dimension were observed in the high-pressure-synthesized diamond single crystal before electron irradiation, which strongly suggests that a number of vacancies were quenched-in due to rapid quenching from high temperature at the end of diamond synthesis, and were aggregated in the synthetic diamond to form vacancy disks on the (111) plane, the collapse of such vacancy disks forming vacancy-type dislocation loops. After electron irradiation, it was found that defect clusters present as interstitial-character dislocation loops were formed in the electron-irradiated region of the diamond. The interstitial dislocation loops grow with increase of the irradiation time. The present study, in comparison to previous work on ion implantation on diamond, indicates that electron irradiation does not induce a phase transformation but produces interstitial dislocation loops due to the migration of interstitial atoms and vacancies. The result of the study directly indicates that interstitials and vacancies in diamond are mobile at room temperature under electron irradiation. Nitrogen, as the most important kind of impurity contained in the HPHT as-grown diamond, probably acts as nucleation of the interstitial loops. Received: 16 November 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: yinlw@sdu.edu.cn