Equations of state and melting curve of boron carbide in the high-pressure range of shock compression
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Equations of State and Melting Curve of Boron Carbide in the High-Pressure Range of Shock Compression A. M. Molodets*, A. A. Golyshev, and D. V. Shakhrai Institute for Problems in Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia *e-mail: [email protected] Received September 13, 2016
Abstract—We have constructed the equations of state for crystalline boron carbide B11C (C–B–C) and its melt under high dynamic and static pressures. A kink on the shock adiabat for boron carbide has been revealed in the pressure range near 100 GPa, and the melting curve with negative curvature in the pressure range 0– 120 GPa has been calculated. The results have been used for interpreting the kinks on the shock adiabat for boron carbide in the pressure range of 0–400 GPa. DOI: 10.1134/S1063776117030049
1. INTRODUCTION A large number of publications are devoted to analysis of the properties of boron carbide in the range of high pressures and temperatures, including extreme conditions of shock compression (see [1–12] and references therein). The part of boron carbide investigations dealing with applications is closely related to the problem in fundamental research into the physics of boron carbide and its structural transformations in the megabar pressure range. The first articles on shock compression of almost monolithic polycrystalline boron carbide samples [1, 2] were published in the 1970s. The kinks on the shock adiabat for boron carbide were investigated in [2–4], where assumptions were made concerning phase transformations of crystalline boron carbide under shock compression. The state of the art in the physical properties and phase transformations of shock-compressed boron carbide in the pressure range up to 90 GPa was summed up in [5]. The kinks observed on the shock adiabat in the coordinates of mass velocity u vs. shock wave velocity D indicated, first, a high (about 15 GPa) yield stress and, second, that the phase transformation occurred with a decrease in the specific volume in the pressure range of 40–50 GPa. It turned out that it was difficult to determine the pressure of phase transformation of shock-compressed boron carbide more exactly because of a considerable spread in experimental data due to the difference in the stoichiometric compositions, porosities, and the methods in sample preparation. In addition, the fact of phase transformation with a jumpwise change in the volume under a shock compression of the crystalline boron carbide was not confirmed in experiments on static
compression [8], in which a smooth (kink-free) highpressure isotherm for boron carbide was registered up to 80 GPa, and the physical reason for the phase transformation in shock-compressed boron carbide remained unclear. The solutions to these problems were proposed in publications on molecular-dynamic simulation of shock compression of crystalline boron carbide [9, 10]. It was shown that, in the presence of high shear stresses of 1D shock compression, the angle in triatomic carbon–boron ch
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