Glassy Carbon, NIST Standard Reference Material (SRM 3600): Hydrogen Content, Neutron Vibrational Density of States and Heat Capacity
Ronald L. Cappelletti, Terrence J. Udovic, Hui Li, Rick L. Paul
The neutron vibrational density of states has been determined for two forms of commercial glassy carbon and found to differ significantly, depending on the heat treatment of the samples, which affects the hydrogen content. Samples heat-treated at high temperatures contain little hydrogen and their spectra closely resemble that of graphite. Using a continuous cooling method, the heat capacity of a sample of this form of glassy carbon was measured from 20 K to 300 K and compared to the contribution calculated from the neutron vibrational density of states from 1 meV to 225 meV of the same material, showing quantitative agreement. Thus the heat capacity of high temperature heat-treated glassy carbon can be accounted for in terms of the contribution of atomic vibrations. The heat capacity of powdered graphite was also measured in this work and correspondingly was found to be very similar to that of this form of glassy carbon. Comparison is also made to earlier heat capacity measurements in the literature on a similar glassy carbon sample from a completely different source, finding good agreement.