Melting of Shocked Boron Carbide
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Melting of Shocked Boron Carbide A. M. Molodetsa, *, A. A. Golysheva, and G. V. Shilova a
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow region, 142432 Russia *e-mail: [email protected] Received April 27, 2020; revised May 13, 2020; accepted May 13, 2020
The aim of this work is to determine the melting temperature of boron carbide at high shock pressures. To this end, powder boron carbide samples have been compressed by shock waves with an amplitude of 60–80 GPa. Shocked samples have been recovered for the subsequent electron microscopy, X-ray spectroscopy, and Xray diffraction analyses. The event of sample melting has been identified by the disappearance of boundaries between particles of the recovered initially powder sample. The pressure and temperature of shocked particles of boron carbide powder have been calculated using a hydrocode based on the previously developed equations of state for boron carbide and experimental setup materials. The average melting temperature of the boron carbide has been determined as Tml = 1900(500) K at the pressure Pml = 70(10) GPa. DOI: 10.1134/S0021364020120103
1. INTRODUCTION It is well known that boron carbide, being a constructional and functional material in a number of important branches of industry, has a peculiar complex crystal structure. For this reason, fundamental and applied problems concerning boron carbide were studied in numerous works (see [1] and references therein). The behavior of boron carbide at high pressures, in particular, its melting at high pressures, was considered in many of these works because the melting temperature of boron carbide, which is as high as 2720(50) K under normal conditions, decreases with increasing pressure. This was experimentally found in [2], where it was found that the slope of the melting curve at pressures up to 8 GPa is dT /dP = ‒13/6 K/GPa. The melting of boron carbide at high pressures is of both fundamental and applied interest. In particular, armored boron carbide goods are promising protective elements against high pressures and temperatures at shock and laser impacts. In this case, pressures reach tens of gigapascals; consequently, information on the pressure dependence of the melting temperature of boron carbide is required in a wide pressure range (see, e.g., [3]). In this context, the linear extrapolation of the result obtained in [2] predicts that the melting of boron carbide at a pressure of about 50 GPa will occur at a temperature of about 2000 K. More accurate model determinations of the pressure dependence of the melting temperature of boron carbide at megabar pressures were published. In particular, within the one-component melting model, it was shown in [4] that a negative
slope of the melting curve of boron carbide can hold up to 40 GPa, when the melting temperature of boron carbide decreases to 2200 K. Within the two-component melting model in [5], the region of the low-temperature melting of boron carbide is predicted up to 100 GPa and the melting t
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