ABSTRACT
Thermodynamic functions and electrical resistivity of Pb-Bi eutectic alloy have been measured over wide ranges of specific volume and pressure in the liquid and gaseous state. The experimental data show a crossover from metallic to insulating behavior in the electrical resistivity of the alloy when its specific volume increases. It is found that in the crossover region the constant volume temperature coefficient of resistivity changes sign from positive to negative and passes through zero at a value of the specific volume which is 2.4 times larger than that in normal state. The second salient feature of the alloy revealed by these experiments is that the isochores plotted in the specific internal energy-pressure plane are straight lines. Based on these experimental data and using an earlier developed approach, an equation of state (EOS) of the alloy has been constructed whose accuracy is determined mainly by the errors of the measurements. It is shown that this EOS can be used to obtain direct estimates of the specific volume and pressure at the critical point of the liquid-gas transition as well as the critical volume for the metal-non-metal (M-NM) transition observed in this eutectic. The results indicate that the critical specific volumes for these two transitions are equal, and the M-NM transition can be described by the classical percolation theory.
ABSTRACT
Direct measurements of the functional dependencies of the electric resistivity and the molar volume on enthalpy and pressure have been performed for graphite and liquid carbon. It has been found that for graphite at the pressures P ⩽ 1 GPa the isochoric temperature coefficient of resistance is positive, while for liquid carbon it is negative over the entire pressure range investigated where P = 0.5-3.5 GPa. These observations probably indicate that graphite is a metal whereas liquid carbon is not a metal, so that the melting of graphite under such pressures coincides with a metal-to-nonmetal transition.
ABSTRACT
Tungsten foil strip sandwiched between two sapphire plates was rapidly heated by an electrical current pulse so that it experienced a two-fold thermal expansion in less than 400 ns under increasing dynamic pressure. The dependence of density on specific enthalpy and pressure was investigated for liquid tungsten using two essentially different diagnostic techniques. Based on a comparison of the results with each other and literature data the systematic uncertainty of the measurements has been estimated. The dependence of density on specific enthalpy along the isobar P = 0.1 MPa has been determined for the entire liquid range. The data have been used to evaluate the constant volume specific heat of liquid tungsten and the electronic contribution to it. It has been shown that the contribution attains more than 40% of the total value of the specific heat.
