Electrical conductivities of methane, benzene, and polybutene shock compressed to 60 GPa (600 kbar)

Electrical conductivities were measured for methane, benzene, and polybuten e shock compressed to pressures in the range 20 to 60 GPa (600 kbar) and te mperatures in the range 2000 to 4000 K achieved with a two-stage light-gas gun. The data for methane and benzene are interpreted simply in terms of ch emical decomposition into diamondlike, defected C nanoparticles and fluid H -2 and their relative abundances (C:H-2), 1:2 for methane and 2:1 for benze ne. The measured conductivities suggest that conduction flows predominately through the majority species, H-2 for methane and C for benzene. These dat a also suggest that methane is in a range of shock pressures in which disso ciation increases continuously from a system which is mostly methane to one which has a substantial concentration of H-2. Thermal activation of benzen e conductivities at 20-40 GPa is probably caused by thermal activation of n ucleation, growth, and connectivity of diamondlike, defected C nanoparticle s. At 40 GPa the concentration of these C nanoparticles reaches a critical density, such that further increase in density does not have a significant affect on the cross-sectional area of conduction and, thus, conductivity sa turates. The electrical conductivity of polybutene (1:1) is very low. While the mechanism is unknown, one possibility is that the electronic bandgap o f whatever species are present is large compared to the temperature. Electr ical conductivity measurements are proposed as a way to determine the melti ng curve of diamondlike C nanoparticles at 100 GPa pressures. (C) 2001 Amer ican Institute of Physics.