THERMODYNAMICS OF ALLOTROPIC MODIFICATIONS OF CARBON - SYNTHETIC DIAMOND, GRAPHITE, FULLERENE C-60 AND CARBYNE

摘要

In an adiabatic vacuum calorimeter, a temperature dependence of heat capacity of four allotropic modifications of carbon, viz, synthetic diamond, graphite, carbyne and fullerene C-60, has been studied in the (5-340) K range. The diamond sample studied is a commercial crystalline product containing impurities, according to a certificate, in an amount less than 1%; graphite is a spectrally pure crystalline substance with 99.9999 mass% of carbon; the carbyne sample with the content of carbon 99.5% is almost amorphous; crystalline fullerene C-60 has the content of a main substance ca. 99.98%. From the experimental data obtained for all objects under study, the thermodynamic functions C-p(0), H-0(T)-H-0(0), S-0(T) and G(0)(T)-H-0(0) have been calculated over the (0-340) K range. The calculation results and literature data on enthalpies of combustion have been used to calculate standard thermochemical parameters of formation Delta(f)H(0), Delta(f)S(0), Delta(f)G(0) of synthetic diamond, fullerene C-60 and carbyne from graphite at T = 298.15 K and p = 101.325 hPa. A comparison of thermodynamic properties of the allotropic carbon modifications has been made and the order of their thermodynamic stability has been found to be: carbyne (a) > graphite (cr) > diamond(cr) > fullerene C-60(cr). [References: 14]