Evolution of glassy carbon under heat treatment : correlation structure-mechanical properties

Abstract

In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp2-hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth- like structure with sp2-type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.