| Popis: |
The results of measurements of thermal conductivity, electric resistivity and heat capacity of graphites with density of 1·9 g/cm3 and higher in the temperature range 50–2500°K are presented. On basis of the modified Debye equation average crystal parameters for the graphites investigated are calculated. It is concluded that irrespectively of the degree of perfection of the graphite lattice Umklapp processes markedly affect the thermal conductivity beginning from T= 120–140°K. It is shown that the curve of the thermal conductivity vs. temperature at T > 140°K is exponential, the exponent power changing at the excitation of the stiff modes of atomic vibrations. In terms of the experimental data, the following thermodynamic functions: enthalpy, thermodynamic potential at 100, 150, 200, 250, 300°K, as well as at the standard temperature 298·15°K are calculated. The thermodynamic functions of pyrolytic carbon heattreated at 3000°C are recommended as standards for comparative evaluation of thermodynamic state of various artificial graphites. |
