The realization of schemes for measuring rapidly changing resistances in dynamic (explosive) experiments is considered. Practical schemes of two-wire and four-wire resistance measurement techniques are presented. The results of the application of the described techniques in an explosive experiment are presented.

Metastable superconducting-like behavior of rhombohedral Bi samples exposed to surface oxidation under special conditions has been observed below the critical temperature range of 15-35 K. The ac magnetic susceptibility and electrical resistance measurements imply that the superconductivity appears in the Bi/Bi2O3 interfacial layer formed at the surface of the samples.

Abstract Spall strength of zirconium heated by a strong shock wave to thousand-degree temperatures and that underwent transformations into denser polymorphic modifications was determined. Pressure profiles at the sample–soft barrier boundary were measured in spall experiments under flat one-dimensional loading. The equations of state of three polymorphic modifications of zirconium were constructed in the pressure range up to 50 GPa. Thermodynamic states of zirconium, which were calculated under conditions of experiments, in combination with results of measurements of pressure profiles, made it possible to determine the spall strength of zirconium heated in the shock compression–unloading cycle. The spall strength of zirconium was –2.8(7) GPa at 1027(70) K. Experimental pressure profiles were analyzed using the results of mathematical modeling of the performed experiments.

Spall strength of zirconium heated by a strong shock wave to thousand-degree temperatures and that underwent transformations into denser polymorphic modifications was determined. Pressure profiles at the sample–soft barrier boundary were measured in spall experiments under flat one-dimensional loading. The equations of state of three polymorphic modifications of zirconium were constructed in the pressure range up to 50 GPa. Thermodynamic states of zirconium, which were calculated under conditions of experiments, in combination with results of measurements of pressure profiles, made it possible to determine the spall strength of zirconium heated in the shock compression–unloading cycle. The spall strength of zirconium was –2.8(7) GPa at 1027(70) K. Experimental pressure profiles were analyzed using the results of mathematical modeling of the performed experiments.

Superconducting at 38 <= T <= 55 K metastable Mo/MoO3-x, 0 <= x <= 0.25, interfaces have been prepared by means of a redox reaction of Mo-metal with powdered alpha-MoO3. The ac magnetic susceptibility and electrical resistance measurements suggest that the Mo/MoO3-x interfacial layer is consisting of weakly connected superconducting regions.

Mixture of Na and WO3 at a molar ratio of 1:1 has been subjected to a shock-wave pressure of similar or equal to 20 kbar, followed by vacuum-encapsulating and quenching of the product to liquid nitrogen. The ac magnetic susceptibility of the samples has revealed metastable superconductivity with T-c approximate to 40 K. Comparison of the ac susceptibility measured at different magnetic fields and frequencies infers that the superconductivity arises within the weakly linked superconducting regions formed during the shock-wave pressure treatment.

Целью исследования являлось определение барической зависимости удельной электропроводности бора в условиях ступенчатого ударного сжатия мегабарного диапазона. Для достижения этой цели решены следующие задачи. Измерена электропроводность образцов бора в области динамических давлений, где существуют различные фазы высокого давления этого элемента. Построены уравнения состояния beta-ромбоэдрического бора и аморфного бора в мегабарном диапазоне давлений. Рассчитаны термодинамические состояния бора в условиях выполненных экспериментов, что в комплексе с результатами измерений позволило определить изменение удельной электропроводности бора при сильном ступенчатом ударном сжатии в области динамических давлений до 110 GPa. Увеличение электропроводности поликристаллического бора в области мегабарных давлений истолковано как следствие перехода неметалл-металл. Работа выполнена при поддержке Госкорпорации Росатом" в рамках контракта N Н.4х.44.9Б.16.1012 от 01.03.2016 г. DOI: 10.21883/FTT.2017.07.44603.001

We have constructed the equations of state for crystalline boron carbide B 11 C (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.

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.

We performed experiments on shock compression up to pressures of 36 and 50 GPa of mixed samples of silicon nitride and potassium bromide, placed between copper plates that serve as walls of a recovery ampoule. For comparison, similar experiments were carried out by the conventional compression of a mixture of silicon nitride and copper powder. The loading of the samples was fulfilled by means of aluminum flyers accelerated by products of explosion to a few kilometers per second. The pressure profiles prior to a shock wave entering the sample and after its runout were measured with the use of manganin sensors. It is found that for the configurations of the experimental assembly used, the pressure in the samples, accumulated by circulating the shock wave, reaches the desired value before unloading. Based on estimates of the rate of heat transfer between the components, it is shown that thermal equilibrium can be set during the existence of high pressure in the mixed samples. Within the framework of the single-temperature medium model, the equations of state of the samples are derived, and the temperatures of their shock compression are calculated. Using these equations, we performed numerical simulations that showed good agreement with the experimental data.

A mixture of Al and alpha-Al2O3 has been subjected to a shock-wave pressure of similar or equal to 170 kbar, followed by vacuum-encapsulating and quenching of the product to liquid nitrogen. The ac magnetic susceptibility measurements of the samples have revealed metastable superconductivity with T-c approximate to 37 K, characterized by glassy dynamics of the shielding currents below Tc. Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial granular layer formed between metallic Al and its oxide due to the shock-wave treatment. (C) 2015 Elsevier B.V. All rights reserved.

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.

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.

A mixture of Mg and MgO has been subjected to a shock-wave pressure of ≈170 kbar. The ac susceptibility measurements of the product has revealed a metastable superconductivity with Tc ≈ 30 K, characterized by glassy dynamics of the shielding currents below Tc. Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial layer formed between metallic Mg and its oxide due to the shock-wave treatment.

The C60 fullerite has been Ca-intercalated under high pressure up to 240 kbar induced by a pressure shock wave. Magnetometric measurements have revealed superconductivity of the as-prepared sample at 9.9 K. The sample relaxed under normal conditions in the helium atmosphere has exhibited traces of superconductivity with the onset at T = 30 K.