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

Glass-like carbon is a well known carbon form that still poses many challenges for structural characterization owing to a very complex internal atomic organization. Recent research suggests that glassy carbon has a fullerene-related structure that evolves with the synthesis temperature. This article reports on direct evidence of curved planes in glassy carbons using neutron and X-ray diffraction measurements and their analysis in real space using the atomic pair distribution function formalism. Changes in the structure including the degree of curvature of the non-graphitizing glassy carbons as a function of the pyrolysis temperature in the range 800-2500°C (1073-2773 K) are studied using optimized models of the atomic structure. Averaged models of single coherent scattering domains as well as larger structural fragments consisting of thousands of atoms were relaxed using classical molecular dynamics. For such models the diffraction intensities and the pair distribution functions were computed. The compatibility of the computer-generated models was verified by comparison of the simulations with the experimental diffraction data in both reciprocal and real spaces. On the basis of features of the developed structural models for glass-like carbons, the origin of the properties such as high strength and hardness and low gas permeability can be better understood. [ABSTRACT FROM AUTHOR]