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 sp 2 -hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp 2 -type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

Influence of free carbon on the Young's modulus and hardness of polymer‐derived silicon oxycarbide glasses

“…Extrapolation of the hardness fit to zero and 100% free carbon leads to values of 12.1 and 6 GPa, respectively. While the estimated value for the SiOC glass without free carbon (12.1 GPa) is slightly above the typical values reported in the literature (∼10 GPa), the hardness of the free carbon phase matched closely with the reported values ( H = 5.5‐6.0 GPa).…”

“…By extrapolating the linear fit to zero percent of free carbon, the Young's modulus of the “pure” SiC x O 2(1− x ) x = ∼0.4‐0.5 is found to be ∼117 GPa, in good agreement with the Young's modulus values measured on SiOC glasses with negligible amount of free carbon and x = 0.37 . The same fit extrapolated to 100% free carbon estimates an elastic modulus value of the free carbon phase ∼63 GPa which is higher than the value reported for carbon materials derived from pyrolysis of organic resins, which is ∼40 GPa . The lower elastic modulus that the high‐C samples display compared with the low‐C ones could help in rationalizing the experimental evidence of the lower tendency to crack during pyrolysis shown by the high‐C samples.…”

Structure of Carbon Materials Explored by Local Transmission Electron Microscopy and Global Powder Diffraction Probes

“…This is in agreement with the outcome of work published by Guo et al [92] showing ADF STEM images of agglomerated defective sites in the glassy carbon structure. The proposed models were confirmed by direct HRTEM observations for the same series of polyfurfuryl-alcohol based glassy carbons published in Reference [93]. Examples of the microscopic images for glassy carbons pyrolysed at 800 • C, 1500 • C, and 2500 • C are confronted with the structural models in Figure 26.…”

An advanced structural characterization of templated meso-macroporous carbon monoliths by small- and wide-angle scattering techniques

“…Resins are important compounds in the production of many carbon materials, e.g., as binder matrix for carbon fiber-reinforced carbon materials (CFRC), a light-weight material with excellent mechanical properties even at high temperatures. Upon heat treatment, the PF resin is gradually transformed into a non-graphitizing glassy carbon [49,50] consisting of highly cross-linked graphene stacks, which once were thought to be ribbon-like, but are now acknowledged as being of made of highly curved graphene sheets with a high content of fullerene-like structures [51][52][53][54]. Key properties of glassy carbon materials, such as thermal conductivity, chemical resistance, hardness, density, and coefficient of thermal expansion are closely related to the carbon microstructure and the porosity.…”