MODEL OF POLYMORPHIC TRANSFORMATION IN A SHOCK WAVE. 1. CARBON
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MODEL OF POLYMORPHIC TRANSFORMATION IN A SHOCK WAVE. 1. CARBON S. A. Kinelovskii
UDC 536.424.1
Abstract: This paper presents a model describing polymorphic phase transition in a shock wave based on experimental data on shock compression of a material. It is assumed that the phase transition in a non-porous material is of martensitic type and occurs in a stationary shock wave that arises in the immediate vicinity behind the first shock wave. Conditions for the occurrence of this shock wave are determined. The model has been tested for non-porous pyrolytic graphite. It has been shown that the model adequately describes the experimental results obtained in various studies for this type of graphite. Keywords: polymorphism, shock wave, graphite, diamond, phase transition. DOI: 10.1134/S0021894420040161
INTRODUCTION The propagation of a shock wave in a crystalline material can lead to a polymorphic transition—the change in the atomic structure of the material. According to [1], the formation of new crystalline modifications in short periods of time ∼10−7 is one of the most interesting issues of the physics of shock waves and the physics of high pressures. This paper considers the shock-wave polymorphism of carbon, i.e., the graphite–diamond transition, which has been investigated for over 50 years. During this period, a large number of papers have been published dealing with the study of the influence exerted on this phase transition by various factors, such as the method of preparation and structure of samples, their initial density and temperature, methods of shock-wave generation, etc. A review of these works are presented in [2–7]. Based on an analysis of the results of previous studies, a number of conclusions can be drawn related to the subject of this work. 1. For graphite of various types, the shock pressure and velocity at the beginning of the phase transition and the time Δt of completion of the phase transition vary significantly. For example, in the case of pyrolytic graphite, pressure values of ∼40 GPa [8] or 34 GPa were reported [9], and in the case of pressed porous samples, 18–23 GPa [8–10]. The estimated time in which graphite is converted to diamond or a diamond-like highpressure phase ranges from Δt ≈ 10−8 s [10, 11] to Δt ≈ 3 · 10−7 s [12], the latter value corresponding to compressed porous graphite. These differences are usually explained by different mechanisms of transformation for various types of graphite.
Lavrent’ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia; [email protected]. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 61, No. 4, pp. 141–150, July–August, 2020. Original article submitted March 2, 2020; revision submitted March 2, 2020; accepted for publication March 2, 2020. c 2020 by Pleiades Publishing, Ltd. 0021-8944/20/6104-0623
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2. It is generally accepted that the phase transition in shock-loaded graphite is indicated by the formation of a two-wave structure which arises in a certain range of velociti
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