Investigation of thermophysical properties of materials at extreme conditions

V. Fortov1, M. Sheindlin1, M. Brykin1, V. Korabenko1, K. Khodakov1 and A. Rakhel1

1Joint Institute for High Temperatures, Russian Academy of Sciences, Russia

Keywords: exploding-wire, laser heating, extreme conditions, critical point
property: density, heat capacity, resistivity, melting temperature
material: carbon, metals, carbides, oxides

The scope of the investigations is related to extension of the temperature/pressure range of co-called thermophysics towards vicinity of the critical points of refractory substances (that means temperatures in the domain of 5000 – 10000 K and pressures in the order of 1 GPa) and stretched even further entering domain of high-energy-density matter.

A special emphasis is placed on different methods of generation of temperatures and pressures in materials and corresponding specific ways of thermophysical properties measurements. The near-critical range of parameters can be covered using “exploding-wire” technique   and various laser heating methods performed at high static pressures. Recent developments in “exploding-wire” technique made it possible to measure enthalpy of some metals vs. temperature in the moderate temperature domain of  2000 - 6000 K within ca. 1-2 us. Very high pressures can be reached by fast heating of flat conductive specimens in the restricted volume. The electrical conductivity was measured in a transition interval from condensed to gaseous state for W, Al, Fe in the pressure range of 1-10 GPa and temperature range of 10-50 kK. A maximum on the temperature dependence of the resistivity of Al along isochors were detected in the so-called “metal - non-metal” transition region. The pressure generated by thermal expansion of a specimen is continuously increasing in course of microsecond heating reaching a value of several GPa. The latter can be successfully monitored by a Ruby crystal attached to a specimen as it was shown in resent experiments.

Laser heating methods are applied for measurements of different properties of non-metal substances and for vaporisation studies. Here, experiments are performed at high static gas pressures of some 0.1 GPa. It was demonstrated that melting points of some refractory ceramics can be measured very precisely due to the clean self-crucible melting in the controlled gas atmosphere. Even the pressure dependence of the melting temperature was obtained for the first time for tungsten and uranium dioxide.     

As for the very high energy densities in matter they can be generated by different methods: by shock and multi-step shock compression, electrical and laser heating and some others.

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