New functional forms have been developed for multiparameter equations of state for non- and weakly polar fluids and for polar fluids. The resulting functional forms, which were established with an optimization algorithm which considers data sets for different fluids simultaneously, are suitable as a basis for equations of state for a broad variety of fluids. The functional forms were designed to fulfil typical demands of advanced technical application with regard to the achieved accuracy. They are numerically very stable and their substance-specific coefficients can easily be fitted to restricted data sets. In this way, a fast extension of the group of fluids for which accurate empirical equations of state are available is now possible. This article deals with the results found for the polar fluids CFC-11 (trichlorofluoromethane), CFC-12 (dichlorodifluoromethane), HCFC-22 (chlorodifluoromethane), HFC-32 (difluoromethane), CFC-113 (1,1,2-trichlorotrifluoroethane), HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane), HFC-125 (pentafluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-143a (1,1,1-trifluoroethane), HFC-152a (1,1-difluoroethane), carbon dioxide, and ammonia. The substance-specific parameters of the new equations of state are given as well as statistical and graphical comparisons with experimental data. General features of the new class of equations of state such as their extrapolation behavior or their numerical stability and results for non- and weakly polar fluids have been discussed in preceding articles.

Equations of state for technical applications. III. Results for polar fluids

The scattering cross section of gaseous argon as a function of electron energy (2-300 meV) has been redetermined from the temperature dependence of the thermal electron mobility ${\ensuremath{\mu}}_{\mathrm{th}}$. The cross section at $\ensuremath{\epsilon}l10$ meV is larger than previously reported. The threshold drift velocity above which electron heating occurs is ${v}_{d}^{\mathrm{thr}}\ensuremath{\approx}100$ m/s in the low-density gas at 121 K; the ratio of ${v}_{d}^{\mathrm{thr}}$ to the speed of sound is $\frac{{v}_{d}^{\mathrm{thr}}}{c}\ensuremath{\approx}0.5$, characteristic of energy loss by elastic collisions. In the dense gas at $\frac{n}{{n}_{c}}\ensuremath{\gtrsim}0.2$, where ${n}_{c}$ is the critical density: (1) the value of $n{\ensuremath{\mu}}_{\mathrm{th}}$ increases; (2) the maximum in the plot of $\ensuremath{\mu}n$ against field strength $\frac{E}{n}$ shifts to lower $\frac{E}{n}$; (3) the temperature coefficient of ${\ensuremath{\mu}}_{\mathrm{th}}$ at constant density increases. (1) is due to the mutual screening of the attractive, long-range scattering interactions; (2) is due to (1) and the constant "saturation" drift velocity; (3) is due to quasilocalization of the electrons. Quasilocalization or enhanced scattering in the coexistence vapor and liquid is significant at $0.2\ensuremath{\lesssim}\frac{n}{{n}_{c}}\ensuremath{\lesssim}1.6$, and maximizes near $\frac{n}{{n}_{c}}=0.6$. Quasilocalization occurs to a smaller extent in argon than in xenon at the same $\frac{n}{{n}_{c}}$ and $\frac{T}{{T}_{c}}$. The low-energy wing of the Ramsauer-Townsend effect is obliterated by screening at $n\ensuremath{\ge}1.0\ifmmode\times\else\texttimes\fi{}{10}^{22}$ molecule/${\mathrm{cm}}^{3}$ in both argon and xenon, which corresponds to $\frac{n}{{n}_{c}}=1.2$ in the former and 2.0 in the latter. The maximum in ${\ensuremath{\mu}}_{\mathrm{th}}$ occurs at 1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{22}$ molecule/${\mathrm{cm}}^{3}$ in both liquids, corresponding to $\frac{n}{{n}_{c}}=1.5 \mathrm{and} 2.4$, respectively. The magnitude of the maximum in ${\ensuremath{\mu}}_{\mathrm{th}}$ is reasonably interpreted by the Lekner zero-scattering-length model, but it is not yet possible to explain quantitatively the density at which the maximum occurs. The drift velocities at high fields, $\frac{E}{n}g5$ mTd ($5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}$ V ${\mathrm{cm}}^{2}$/molecule) little affected by density up to $\frac{n}{{n}_{c}}=1.6$ in argon. At higher density the drift velocities increase. Relatively large densities are required to affect the behavior at these fields because the scattering cross section in the vicinity of the Ramsauer-Townsend minimum is low (\ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$).

Electron transport in gaseous and liquid argon: Effects of density and temperature

The elastic moduli of nine metals, argon, krypton, xenon, silver bromide and benzene are examined as functions of isobaric dilatation from absolute zero to the melting point and in the melt. The isothermal bulk modulus, and in many cases the two shear moduli, each have a Gruneisen-type dependence on crystal volume. In all except the inert gases the isothermal bulk modulus is continuous with respect to volume through the melting expansion and in every case one of the shear moduli falls continuously to a value sufficiently close to zero at the volume of the melt at the freezing point, that fluidity results by thermal activation. The Born-Durand elastic-instability melting hypothesis is therefore essentially correct except that the shear modulus vanishes in the melt at the melting point rather than in the solid.

The volume dependence of elastic moduli and the Born-Durand melting hypothesis

Thermodynamic properties of liquid argon at high pressures, calculated from PVT and sound-velocity data

Simultaneous measurements of the density and electrical conductivity have been carried out for expanded liquid Hg in the temperature and pressure range up to 1500°C and up to 2200 bar. At densities below 10 g/cm 3 the temperature coefficient of the conductivity at constant volume increases appreciably with decreasing density. Anomalous behaviours are found in the thermodynamic properties such as equation-of-state and isothermal compressibility when the metallic Hg is transformed to a nonmetallic state. Structural changes in the metal-nonmetal transition range are discussed in connection with the observed thermodynamic properties.

E. Vangeel

Papers

Sound velocity measurements in liquid argon as a function of pressure and temperature

Experimental investigation of the sound velocity in the critical region of argon