Superhigh Pressures Research Articles

Nanocages of layered BN: Super-high-pressure nanocells for formation of solid nitrogen

We observed high N contents inside BN fullerenelike multilayered nanocages (ca. 30–100 nm) formed by reacting CNx nanotubes (x⩽0.1) and B2O3 in a N2 atmosphere at 1985–2113 K. High-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy, energy dispersion x-ray spectroscopy, electron diffraction analysis, spatially resolved energy-filtered TEM, and in situ TEM electron irradiation studies suggest that super-high pressures (of several GPa) are generated inside nanocages, responsible of crystallizing gaseous nitrogen trapped within the BN shells. In addition, high-pressure-induced phase transformation of graphiticlike BN into diamondlike cubic BN occurs inside the nanocages. Thus, BN nanocages play an unusual role of super-high-pressure nanocells.

Surface diffusion growth and stability mechanism of BN nanotubes produced by laser beam heating under superhigh pressures

A growth mechanism for BN nanotubes appearing at superhigh pressures under laser beam heating [D. Golberg, Y. Bando, M. Eremets, K. Takemura, K. Kurashima, and H. Yusa, Appl. Phys. Lett. 69, 2045 (1996)] is proposed based upon consideration of the dependence of the energy of adsorption and surface diffusion on the surface curvature. According to this mechanism, the growth of BN nanotubes is due to surface diffusion along the external surface, which also ensures morphological stability of the open end during growth. It is suggested that the observed nanotube heights are limited by the corresponding diffusion length.

Correction of the statistical model of matter near nuclei

A simple method is proposed to overcome the difficulties of the Thomas-Fermi model caused by the inadequacy of the semiclassical approach near nuclei. As a result the divergences of the quantum corrections to the energy and free energy in the origin vanish, the Scott correction appears, and agreement between the statistical model and perturbation theory is restored for superhigh pressures and/or temperatures. A comparison of the refined statistical results with those of band-structure calculations in the high-compression limit and those of the Saha model in the high-temperature limit demonstrates good quantitative agreement.

Interpolation of the thermody namic model for water in the region of uniform and two-phase states

To solve many problems in gasdynamics, a single mathematical description of the thermodynamic properties of water over a wide range of states covering both normal and superhigh pressures and temperatures is necessary. Existing equations of state (e.g., those given in [1–4] etc.) hold over limited ranges of variation of the thermodynamic parameters. In [5] a method is proposed for constructing interpolation equations of state of water and water vapor over a wide range of uniform states, and thermodynamic functions are obtained which describe with satisfactory accuracy the properties of the medium in the pressure range p > 108 Pa (1 Pa = 10−5 bar). In this paper we refine and develop the results obtained in [5] in order to construct a single analytical description of the properties of water in the region of uniform and two-phase states.

Metallization of alkali-halide crystals under superhigh pressures

An estimation, based on thermodynamical considerations, of the pressure under which the NaCl crystal transforms into the metallic state, was carried out. Using the method of composite atomic orbitals, the thermodynamic potentials of dielectric and metallic phases of the NaCl crystal were calculated. The equations of state were obtained for both phases in a wide range of pressures, from 0 to 2000 kbar. From the point of intersection of the curves of thermodynamic potentials of two phases, the determination was made of the pressure of metallization equal to 1350 kbar. The temperature effects were not taken into account.

Thermal reactions of tetrachloroethylene at superhigh pressures

1. The reactions of terrachloroethylene at 10,000–30,000 atm and 150–350° were investigated in presence and absence of peroxides. 2. Under the conditions studies tertrachloroethylene does not polymerize. In 2–6 hours at 300–350° it undergoes almost complete thermal transformation with formation of 40–50% of hexachloroethane and a smaller amount of hexachlorobenzene.