The viscosity of argon at very high pressure, up to the melting line

Thermodynamic or density scaling of the thermal conductivity of liquids

Thermodynamic or density scaling is applied to thermal conductivity (λ) data from the literature for the model Lennard-Jones (12-6) fluid; the noble gases neon to xenon; nitrogen, ethene, and carbon dioxide as examples of linear molecules; the quasi-spherical molecules methane and carbon tetrachloride; the flexible chain molecules n-hexane and n-octane; the planar toluene and m-xylene; the cyclic methylcyclohexane; the polar R132a and chlorobenzene; and ammonia and methanol as H-bonded fluids. Only data expressed as Rosenfeld reduced properties could be scaled successfully. Two different methods were used to obtain the scaling parameter γ, one based on polynomial fits to the group (TV^γ) and the other based on the Avramov equation. The two methods agree well, except for λ of CCl₄. γ for the thermal conductivity is similar to those for the viscosity and self-diffusion coefficient for the smaller molecules. It is significantly larger for the Lennard-Jones fluid, possibly due to a different dependence on packing fraction, and much larger for polyatomic molecules where heat transfer through internal modes may have an additional effect. Methanol and ammonia, where energy can be transmitted through intermolecular hydrogen bonding, could not be scaled. This work is intended as a practical attempt to examine thermodynamic scaling of the thermal conductivity of real fluids. The divergence of the scaling parameters for different properties is unexpected, suggesting that refinement of theory is required to rationalize this result. For the Lennard-Jones fluid, the Ohtori-Iishi version of the Stokes-Einstein-Sutherland relation applies at high densities in the liquid and supercritical region.

Communication: Simple liquids' high-density viscosity

This paper argues that the viscosity of simple fluids at densities above that of the triple point is a specific function of temperature relative to the freezing temperature at the density in question. The proposed viscosity expression, which is arrived at in part by reference to the isomorph theory of systems with hidden scale invariance, describes computer simulations of the Lennard-Jones system as well as argon and methane experimental data and simulation results for an effective-pair-potential model of liquid sodium.

Viscosity of nitrogen measured to pressures of 7 GPa and temperatures of 573 K

Shear viscosities of supercritical nitrogen have been measured to 573 K and 7 GPa (70 kbars). Measurements were made in a diamond-anvil cell with a rolling-ball technique. Individual isotherms are well fitted by a modified Doolittle equation. The data demonstrate a close relation between viscosities and excess entropy; this relation is further explored for the systems argon, oxygen, carbon dioxide, sodium, cesium, and a Lennard-Jones fluid.

Nonviscous metallic liquid Se

Viscosity is one of the fundamental physical properties of liquids; for different melts it varies in an extremely wide range. Selenium is among the first elementary substances to have manifested, at compression, a phase transformation in the liquid state accompanied by melt metallization. Direct measurements by means of a real-time radiography show that the viscosity of liquid Se under pressure drops by 500 times to a very low level of 8 mPa s. This is the first case of viscosity measurements being performed both for a relatively viscous semiconducting state and a low-viscous metallic state of the same liquid substance. The viscosity of the Se melt strongly decreases with pressure along the melting curve in a semiconducting state and experiences a further significant drop at melt metallization. A similar phenomenon is expected to be observed in many chalcohenide, halogenide, and oxide melts.

The shear viscosity of supercritical oxygen at high pressure

Shear viscosities of supercritical oxygen have been measured up to a pressure of 5.7 GPa at 294 K. A modified free-volume expression fits the data within 6% between the limits of the tenuous gas and 4.8 times the critical density. Nitrogen viscosities were found to correspond to those of oxygen through a simple scaling by critical constants. Viscosities were measured in the high-pressure diamond-anvil cell with a rolling-ball technique. The dynamics of a sphere rolling on an inclined plane were investigated in the context of these experiments. The effect of a second surface, situated above the sphere, was experimentally determined.

Determination of potential energy functions of argon, krypton, and xenon via the inversion of reduced-viscosity collision integrals at zero pressure

The pair potential energy functions of argon, krypton, and xenon have been determined via the inversion of reduced-viscosity collision integrals at zero pressure. A comparison of the potentials with the previously determined potentials are included. The viscosity and thermal conductivity of argon, krypton, and xenon at different temperatures and pressures have been calculated and compared with experimental values. The present potentials for argon, krypton, and xenon provide a good overall account of the experimental properties of these compounds, considering the stated uncertainty in the measurements.Key words: potential energy function, collision integral, viscosity, thermal conductivity.