Thermodynamics of allotropic modifications of carbon: Synthetic diamond, graphite, fullerene C60 and carbyne

Abstract

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. 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 functionsC 0 p ,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 Δ f H 0 , Δ f S 0 ,Δ f G 0 of synthetic diamond, fullerene C 60 and carbyne from graphite at T=298.15 Kand p=101.325 kPa. 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)