Experimental study of liquid carbon

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.

Experimental investigation of linear thermal expansion of pyrolytic graphite at high temperatures

“…From the analysis of the obtained experimental data follows that the expansion of pyrolytic graphite in a direction perpendicular to the basal plane agrees within the measurement accuracy with data [5] obtained from non-isobaric heating, as well as calculated data [3]. The experiments also show that the temperature dependence of the expansion of pyrolytic graphite corresponds with the experimental data available in the literature for T < 3300 K [2] up to a temperature of about 4000 K, after which it shows a slightly more intense growth.…”

“…Dependence of the relative density of pyrolytic graphite on temperature in comparison with the literature data [2,3,5]. Thus, the average volume coefficient of thermal expansion at the temperature interval 3300-4800 K can be calculated as ̅ = ┴ + 2 ║ = 5,76 * 10 (3) Assuming that the approximation of the CTE of pyrographite in a direction perpendicular to the layers near the melting point is closer to the experimental data obtained than the approximation by the constant, one can obtain the density and expansion at this temperature.…”

“…Hence the CTE of pyrolytic graphite in a direction parallel to the layers in the temperature range 3300-4800 K can be taken equal to ║ = 4,65 * 10 . From the obtained dependences of the relative expansion of pyrolytic graphite in directions perpendicular and parallel to the basal plane one can calculate the dependence of graphite density on temperature in the temperature range 3000-4800 K. Figures 7 shows the relative density of pyrographite versus temperature in comparison with literature data [2,3,5]. Experimental points correspond to a pressure of 1 kbar (i.e.…”

“…The existing experimental data on the volumetric expansion of graphite in the temperature range up to the melting temperature are either calculated [3,4] or obtained in experiments in non-isobaric conditions, as in [5]. The difficulty of isobaric experiments with graphite is explained by the abovementioned features, as well as by the active sublimation of carbon, which intensifies at the temperatures above 3000 K. Thereby it was required to develop an experimental technique that makes it possible to obtain data on the thermal expansion of graphite materials in the temperature range 3300-5000 K.…”

“…In figure 7 a linear function is used to approximate the CTE in the direction perpendicular to the layers. To calculate the dependence of the density on the energy introduced in [5] the dependence of the specific enthalpy on temperature for graphite published in the GSSSD [7] was used.…”