M. van Thiel

Equation‐of‐state data for molecular hydrogen and deuterium at shock pressures in the range 2–76 GPa (20–760 kbar)a)

Dynamic equation‐of‐state data for D2 and H2 were measured in the pressure range 2–76 GPa (20–760 kbar) using a two‐state light‐gas gun. Liquid specimens were shocked from initial states near the saturation curve at 20 K. Maximum compression was sixfold over initial liquid density at a calculated temperature of 7000 K for D2. The data is discussed in terms of the theory of Ross et al., which includes an effective intermolecular pair potential, molecular vibration, free molecular rotation, and molecular dissociation.

Shock compression of liquid carbon monoxide and methane to 90 GPa (900 kbar)

Dynamic equation‐of‐state data for liquid CO and CH4 were measured in the shock pressure range 5–92 GPa (50–920 kbar) using a two‐stage light‐gas gun. The liquids were shocked from initial states near their saturation curves at 77 and 111 K for CO and CH4, respectively. The experimental technique used to double‐shock CH4 is described. The CO data were examined by using three theoretical models: (1) a chemically nonreactive model, (2) a quasi‐chemical‐equilibrium model that allows CO to dissociate into gaseous species and graphite, and (3) a chemical‐equilibrium model that also includes a dense carbon phase which exists at higher pressures and temperatures than graphite. This dense phase is assumed to be diamond. Our analysis shows that at low pressure chemical equilibrium takes much longer than a typical shock passage time. As a consequence, the experimental data initially follow the nonreactive Hugoniot to pressures well beyond the chemical dissociation limit. Both the experimental data and the Hugoniot computed with case (3) agree satisfactorily at high pressure. Further consequences of these observations to high‐explosive studies are discussed. The theoretical analysis for the CH4 data was presented in an earlier paper.

Equation-of-state, shock-temperature, and electrical-conductivity data of dense fluid nitrogen in the region of the dissociative phase transition

The dissociative phase transition of fluid nitrogen at pressures in the range 30–110 GPa (0.3–1.1 Mbar), temperatures in the range 4000–14 000 K, densities up to 3.5 g/cm3, and internal energies up to 1 MJ/mol was investigated by shock compression. Equation‐of‐state, shock‐temperature, and electrical‐conductivity experimental data are presented and analyzed in detail.

Shock Compression of Argon

Liquid argon has been shock compressed from two initial states at 86°K and 2 bar, and 148.2°K and 70 bar. The highest pressure of 700 kbar and temperature of 13 000°K were obtained by reflecting a shock wave with a pressure of 270 kbar from a tungsten wall. These shock loci allow a test of the interatomic potential over a wide region and show that the potential can be represented by a sum of pair interactions up to a pressure of 400 kbar. The pair potential is furthermore found to be considerably less repulsive at small interatomic distances than the 12‐power repulsive law. In fact, an exponential form yields good results up to 360 kbar. Above this pressure range the reflected‐shock data require a large change in the potential form which is interpreted to be due to a pressure‐induced electronic transition to the conduction band. Calculations show that a discontinuity in the Hugoniot data at 50 kbar and 1200°K could be identified with the melting line. This temperature corresponds to three times the highes...

Shock compression of liquid hydrogen

High explosives have been used to shock liquid hydrogen to 39 500 bars, 5·2 cm3/g and an estimated temperature of 1100°k from an initial state near the normal boiling point, 20·5°k and 14·1 cm3/g. How far the melting curve and the equation of state can be pursued by shock wave experiments is discussed. The derived intermolecular potential between two hydrogen molecules is shown to be inadequately represented by the previously postulated Lennard-Jones 6–12 potential in the repulsive region between 2·0 and 2·7 A. The power of the inverse intermolecular distance is shown instead to be 8·5 in that region if a purely repulsive potential is used.

Theoretical description of the graphite, diamond, and liquid phases of carbon

A three-phase equation-of-state model, to be used in high-pressure high-density simulations of systems containing carbon, is described for the system graphite-diamond-liquid. The solid phases are represented by cold lattice and thermal energy terms. Simple additivity of the energy terms is assumed and the cold curve is a modified Birch form. Liquid states for diamond and graphite are obtained by a previously described scaling model. The actual Gibbs free energy of the liquid state uses the free energy of these liquids in a mixture model that includes an entropy of mixing and a pressure-dependent strain term. It is noted that the thermal expansion coefficient and the Grüneisen gamma increase faster above 3000 K than the usual approximation for the volume dependence would predict. The result is a phase diagram that fits all available data.

Corresponding states at small interatomic distances

By measuring the thermodynamic properties of condensed rare gases in single shock experiments to pressures of about 400,000 atmospheres, it has been established within the present (approximately 2%) accuracy that argon and xenon are in corresponding states up to about 200,000 atmospheres. At higher pressures strong deviations from corresponding states become apparent, which can be traced to large-scale thermal excitation of electrons in xenon to the conduction band across a pressure-narrowed energy gap. Corresponding states behavior implies that deviations from pair-wise additivity of the intermolecular potential may be neglectedi). Therefore the pair potential derived from the data should and indeed does agree with the results obtained from molecular beam scattering within the experimental accuracys). Also gratifying is the close agreement with the theoretical pair potential derived from the Thomas-Fermi-Dirac theory a). The intermolecular potential for the class of substances following corresponding states behavior must furthermore be of the form of an energy scaling parameter, E, multiplied by a universal function of the intermolecular distance. This universal function, however, is poorly represented by the customary inverse twelfth power of the intermolecular distance, but can be approximated quite well by a less repulsive exponential function. The single shock experiments were carried out on liquid xenon in an analogous manner as they had been previously on liquid argon4). The corresponding initial conditions for argon and xenon were taken, respectively, to be 86.O”K, 1.88 atm and 165.2”K, 2.24 atm5). Since the initial, unshocked states of argon and xenon are in corresponding states, their Hugoniots should coincide when plotted in terms of reduced quantities (quantity divided by its value at the critical point), if corresponding states behavior continues to be obeyed. The heavy inert gases were chosen since they are the most likely substances to obey corresponding statesr). They had previously been found to obey this rule quite wells) from measurements on the normal solid and lower density states, that is for properties which depend heavily on the

Shock compression of deuterium to 900 Kbar

Abstract An experimental program to compress liquid deuterium with a two-stage gun is described. A xenon standard was used to check the adequacy of the EOS of the Dural container in the 7000 (1.7 Mbar) to 3000° K (0.0 Mbar) range. The agreement is reasonable. Further work on this standard is in progress to improve the accuracy. The target design parameters were checked with some sound speed measurements which confirm the liquid-like behavior of Dural at the temperatures, pressures, and strain rates of these experiments. The uncertainties of the results are analyzed and tabulated with the data. Comparison between the molecular and the metallic equations of state indicates a small volume change on metallization due to the high compressibility of the molecular phase vis-a-vis the metallic phase.

Electrical conductivity and equation of state of shock‐compressed liquid oxygen

The electrical conductivity of shock‐compressed liquid oxygen has been measured in the dynamic pressure range 18–43 GPa(180–430 Kbar). A double‐shock equation‐of‐state point was also measured. The data and Hugoniot calculation, based on a chemical equilibrium model, indicate that liquid oxygen partially dissociates and forms a two‐component conductive fluid. Details of the experimental design are given and the data are discussed in terms of electronic transport in disordered systems.

Measurement of Elastic and Plastic Unloading Wave Profiles in 2024‐T4 Aluminum Alloy

Velocities for one‐dimensional release waves in 2024‐T4 aluminum alloy have been obtained between 30 and 132 kbar. Stress‐time records were obtained with piezoresistive manganin gauges. The release wave clearly showed the existence of two release systems. The leading edge of the release wave was 27% faster than the bulk sound velocity calculated from the ideal fluid model. The second release system was identified by a change in slope of the release wave profile. The peak velocity of this release system did correspond more closely to the hydrodynamic bulk sound velocity. These results imply elastic behavior of aluminum at high pressure. The shape of the release wave, however, cannot be fitted by a perfect elastic‐plastic model, thus pointing out the need of a more elaborate description.