A. M. Molodets

Electrical resistivity of plastic insulation at megabar shock pressures

This paper presents the results of experimental determination of the electrical resistivity of an insulating polymer composition (Teflon film and high-vacuum leak sealant) under stepwise shock compression at pressures up to 150 GPa. The data obtained can be used in experiments to measure the electrical conductivity of materials in this range of shock pressures.

Shock-wave studies of anomalous compressibility of glassy carbon

The physico-mechanical properties of amorphous glassy carbon are investigated under shock compression up to 10 GPa. Experiments are carried out on the continuous recording of the mass velocity of compression pulses propagating in glassy carbon samples with initial densities of 1.502(5) g/cm3 and 1.55(2) g/cm3. It is shown that, in both cases, a compression wave in glassy carbon contains a leading precursor with amplitude of 0.135(5) GPa. It is established that, in the range of pressures up to 2 GPa, a shock discontinuity in glassy carbon is transformed into a broadened compression wave, and shock waves are formed in the release wave, which generally means the anomalous compressibility of the material in both the compression and release waves. It is shown that, at pressure higher than 3 GPa, anomalous behavior turns into normal behavior, accompanied by the formation of a shock compression wave. In the investigated area of pressure, possible structural changes in glassy carbon under shock compression have a reversible character. A physico-mechanical model of glassy carbon is proposed that involves the equation of state and a constitutive relation for Poisson’s ratio and allows the numerical simulation of physico-mechanical and thermophysical properties of glassy carbon of different densities in the region of its anomalous compressibility.

Thermophysical properties of the polymorphic modifications of lithium hydride in the megabar shock pressure range

The region of a high electrical conductivity of lithium hydride is experimentally determined in the pressure range 100–150 GPa and the temperature range 2000–3000 K of multiple shock compression. This result is used to construct thermodynamic potentials for the two polymorphic modifications of lithium hydride (B1, B2), and these potentials make it possible to calculate its thermophysical properties in the shock pressure range 80–1200 GPa. The calculated and experimental results are analyzed to determine the B1 ↔ B2 equilibrium line for the polymorphic modifications of lithium hydride at pressures up to 300 GPa and temperatures up to 2000 K.

Electroconductivity and pressure–temperature states of step shocked C60 fullerite

A study of electrophysical and thermodynamic properties of C60 single crystals under step shock loading has been carried out. The increase and the following reduction in specific electroconductivity of C60 fullerite single crystals at step shock compression up to pressure 30 GPa have been measured. The equations of state for face centred cubic (fcc) C60 fullerite as well as for two-dimensional polymer C60 and for three-dimensional polymer C60 (3D-C60) were constructed. The pressure–temperature states of C60 fullerite were calculated at step shock compression up to pressure 30 GPa and temperature 550 K. The X-ray diffraction studies of shock-recovered samples reveal a mixture of fcc C60 and a X-ray amorphous component of fullerite C60. The start of the formation of the X-ray amorphous component occurs at a pressure P m≈ 19.8 GPa and a temperature T m≈ 520 K. At pressures exceeding P m and temperatures exceeding T m, the shock compressed fullerite consist of a two-phase mixture of fcc C60 fullerite and an X-ray amorphous component presumably consisting of the nucleators of polymer 3D-C60 fullerite. The decrease in electroconductivity of fullerite can be explained by the percolation effect caused by the change of pressure, size and number of polymeric phase nuclei.

Equation of state of polytetrafluoroethylene for calculating shock compression parameters at megabar pressures

Semi-empirical equations of state (thermal and caloric) are obtained to calculate not only the kinematic parameters (shock wave velocity, particle velocity, and reverberation of waves) but also the thermodynamic parameters (temperature, pressure, and compression) of monolithic and porous polytetrafluoroethylene at high shock pressures. The equations of state are used to model wave interaction in shock-wave experiments using the developed hydrocode. The equations are verified by comparison simulation results with published results of experiments and the data of our shock compression tests of solid and porous samples of PTFE in the range of 10–170 GPa.

Structural Transformations of Amorphous Carbon (Glassy Carbon) at High Shock Pressures

Amorphous carbon (glassy carbon) samples were shock compressed up to 80 GPa and temperatures up to 1700 K for several microseconds. Glassy carbon samples before and after an explosive action are analyzed by X-ray diffraction, electron microscopy, and electron-probe microanalysis. It is shown that as a result of microsecond shock pressure exposure, glassy carbon is compacted to ρCG ≈ 2.3(5) g/cm3 and is partly transformed into a graphite-like nanomaterial with a cellular structure. At the level of crystallites, the density of glassy carbon increases via a decrease in the interplanar spacings and an increase in the crystallite thickness and width. Spheres from 20 nm to 80 μm in diameter are found to be formed during shock-wave compression of glassy carbon in a copper container and high-temperature shock heating posteffects. Spheres 20 μm in diameter consist of a copper-rich core and a carbon shell.

Electrical conductivity and equations of states of β-rhombohedral boron in the megabar dynamic pressure range

The pressure dependence of the conductivity of boron under conditions of a stepwise shock compression of megabaric range is studied. With this purpose, the following problems have been solved. The conductivity of boron has been measured in the range of dynamic pressures, where boron has different high-pressure phases. The equations of state of β-rhombohedral and amorphous boron have been constructed in a megabaric pressure range. The thermodynamic states of boron in the conditions of these experiments are calculated, which, in combination with the measurement data, made it possible to determine the change in the boron conductivity in the conditions of strong stepwise shock compression at dynamic pressures to 110 GPa. The increase in the conductivity of polycrystalline boron at megabar pressures is interpreted as a result of a nonmetal–metal transition.

Equations of state and melting curve of boron carbide in the high-pressure range of shock compression

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.

Semiempirical description of thermophysical properties of lithium deuteride at high pressures and temperatures

The semiempirical expression of the free energy of lithium deuteride in the form of an analytical function of volume and temperature for the pressure range of 0–100 GPa and at 200–2000 K was developed. The thermodynamic description was based on experimental data of thermophysical properties at normal conditions and lithium deuteride Hugoniot. The predictive calculations of a set of thermophysical properties of lithium deuteride at high pressures (including shock conditions) and temperatures were performed. A comparison of isotherms, isobars, heat capacity, and thermal conductivity with literature experimental data was presented. The results made it possible to consider, compare, and coordinate the data on the shock and isothermal compression of lithium deuteride at high pressures and temperatures from a unified point of view.

Equations of state of silver azide and calculation of its Hugoniots

The thermal and caloric equation of state of the orthorhombic phase of silver azide are presented. For this material, pressure-temperature relations along the Hugoniots of the material with different porosity and shock velocity-particle velocity relations are calculated. The calculations are performed for pressures up to 3 GPa and temperatures of 300–500 K, particle velocities of up to 0.4 km/s, and initial porosity of 1–1.5. The relative positions of the Hugoniots and equilibrium lines of polymorphic transformations of silver azide in the indicated region of thermodynamic variables is discussed.