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

Abstract

Electrical conductivities were measured for methane, benzene, and polybutene shock compressed to pressures in the range 20 to 60 GPa (600 kbar) and temperatures 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 chemical decomposition into diamondlike, defected C nanoparticles and fluid H2 and their relative abundances (C:H2), 1:2 for methane and 2:1 for benzene. The measured conductivities suggest that conduction flows predominately through the majority species, H2 for methane and C for benzene. These data also suggest that methane is in a range of shock pressures in which dissociation increases continuously from a system which is mostly methane to one which has a substantial concentration of H2. Thermal activation of benzene conductivities at 20–40 GPa is probably caused by thermal activation of nucleation, growth, and connectivity of diamondlike, defected C nanoparticles. 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 saturates. The electrical conductivity of polybutene (1:1) is very low. While the mechanism is unknown, one possibility is that the electronic bandgap of whatever species are present is large compared to the temperature. Electrical conductivity measurements are proposed as a way to determine the melting curve of diamondlike C nanoparticles at 100 GPa pressures.

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

“…On the other hand, shock experiments suggest no chemical reactivity up to 26 GPa and 3,200 K (ref. 18). The discrepancy between the results obtained by LH DAC, shockwave, MD and thermodynamics may arise from various assumptions in modelling as well as from kinetic, catalytic and analytical problems in the experiments.…”

Optical properties of methane to 288GPa at 300K

“…The refractive index of diamond, n d , as a function of pressure has been computed by quantum mechanical methods [33]. The computed value of n d at zero pressure is less than the experimental value by 0.073 but the computed initial slope agrees with the experimental value [34]. We, therefore, use the theoretical n d (P) relation with 0.073 added at all pressures in this study.…”

“…Actually sufficient pressure ineluctability leads to a presence of diamond cupping. The effect of the cupping has been nicely discussed by van Straaten and Silvera [46] which demonstrates the deterioration of the pattern due to this effect. In addition, there is a small stress gradient in the sample at very high pressure in the present case but there is always a large radial stress gradient in the diamond at the surface at very high pressures (except at r ¼ 0).…”

Chemical processes in the deep interior of Uranus

“…The con- 9 and the SU data of Nellis et al 4 are single-shock data, whereas the water data of Chau et al 8 are from multiple-shock data. Also shown for comparison purposes are the single-shock data for methane 10 and ammonia 9 . The dashed line is a guide for the eyes.…”

“…Figure 1a shows the electrical conductivity data of SU as a function of pressure. For a useful comparison, the electrical conductivity data for individual constituents [8][9][10] that make up the interior of Uranus (water, ammonia and methane) are also shown in Figure 1. The previous single-shock data on SU showed a five order of magnitude increase in electrical conductivity from ambient to about 50 GPa and reached the value of ~20 (Ω-cm) − 1 The higher pressure data in this work shows that the electrical conductivity of SU continues to increase monotonically by a of factor 3 between 50 to 191 GPa.…”