Thermodynamic Properties and Similarity of Stacked-Cup Multiwall Carbon Nanotubes and Graphite

The heat capacity of stacked-cup multiwall carbon nanotubes (MWCNTs) was measured in an adiabatic calorimeter over the temperature range of (5 to 370) K. Results are compared with literature data on various samples of CNTs and other carbon allotropes. The relatively large scatter of the heat capacity data for CNTs is discussed. The energy of combustion for MWCNTs was determined by combustion calorimetry, and the enthalpy of formation was found to be Δf H°m = (0.6 ± 0.9) kJ·mol–1. It is demonstrated that the thermodynamic properties of MWCNTs at T > 200 K are close to those of graphite. Equilibria of the synthesis of MWCNTs were considered.