Research ArticleMATERIALS SCIENCE

Compressed glassy carbon: An ultrastrong and elastic interpenetrating graphene network

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Science Advances  09 Jun 2017:
Vol. 3, no. 6, e1603213
DOI: 10.1126/sciadv.1603213
  • Fig. 1 XRD and sp2/sp3 component of compressed GCs (Com.GCs) measured at ambient conditions.

    The Com.GC numbers (1 to 4) and Diamond + Com.GC represent the samples recovered after compressing GCs at 25 GPa and temperatures of 400°, 600°, 800°, 1000°, and 1200°C, respectively. (A) The graphite-like interlayer distances for compressed GCs gradually reduced with the increase of synthesis temperatures. The S(q) data are unscaled but successively shifted from the raw GC data by 0.6 units in the vertical axis. The insets show Franklin’s model of nongraphitizing carbon (11), ordered graphite structure with standard interlayer distance of 3.35 Å, and the bulk morphology of recovered sample rods. (B) EELS change showing the decreased sp2 component in the compressed GCs relative to the raw material. The pink and light blue regions represent 1s-π* and 1s-σ* transitions of carbon, respectively.

  • Fig. 2 Nanoscale structure of compressed GCs.

    (A) Raw HRTEM image showing the interpenetrating graphene networks with long-range disorder and short-range order (also see fig. S3). The local order has a lateral dimension of 1 to 5 nm and exhibits lattice spacings of 3 to 5 Å. (B) Schematic linkage types between the graphene layers. The layers are distinguished by different colors, that is, light and dark gray, respectively. Under pressure, the sp3 bonds colored by yellow are readily formed at the curved surfaces of graphene layers with different orientations (top) and are also easily formed between the interlayers (center). In addition, orderly buckled graphene sheets would form the short-range ordered carbon nanolattice (bottom).

  • Fig. 3 Indentation hardness and elastic recovery of compressed GCs.

    (A) The indentation hardness as a function of applied load. The loads of 1.96, 4.9, 7.84, and 9.8 N were applied, respectively. (B) The loading/unloading-displacement curves of compressed GCs showing the high elastic recovery. (C) Hardness and elastic recovery of compressed GCs in comparison with common ceramics, polymers, and metals estimated from the nanoindentation testing (see Materials and Methods). The compressed GCs have an unprecedented combination of hardness and elastic recovery.

  • Fig. 4 Compressive stress-strain curves and specific strength of compressed GCs.

    (A) The compressed GCs exhibit high compressive strength up to 9 GPa and large axial elastic strains near 3%. The Young’s moduli E are derived from the linear stress-strain relationship before yield. The inset shows a schematic of the measurement method in the DAC. (B) The specific compressive strength of compressed GCs in comparison with available data on known ceramics, polymers, and metals (2, 3). When normalized by density, the compressed GCs are about two to four times stronger than commonly used carbon fibers, cemented diamond, cemented cubic BN, SiC, and B4C.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1603213/DC1

    fig. S1. XRD of compressed GCs recovered after compressing raw GC at pressures of 10 to 25 GPa and temperatures of 600° to 1200°C.

    fig. S2. SAED patterns of compressed GCs measured at different length scales.

    fig. S3. Local order in compressed GC.

    fig. S4. The sp3 component of compressed GCs measured at ambient condition.

    fig. S5. The sp3 component of compressed GC and microstructure of raw GC.

    fig. S6. UV Raman spectroscopy of compressed GCs.

    fig. S7. The loading/unloading-displacement curves of compressed GCs in comparison with raw GC, Cu, and MgO.

    fig. S8. The loading/unloading-displacement curves, indentation hardness, and elastic recovery of compressed GCs synthesized at moderate pressures and temperatures.

    fig. S9. The loading/unloading-displacement curves, hardness, Young’s modulus, and indentation elastic recovery of compressed GC at varied loading, holding, and unloading times.

    fig. S10. Indentation morphology after unloading three-sided pyramidal Berkovich diamond indenter, showing significant elastic recovery.

    fig. S11. Optical images of the indentations on diamond and Com.GC-2 after unloading a four-sided pyramidal diamond indenter.

    fig. S12. Mohs hardness of compressed GC (Com.GC-3) characterized with qualitative scratch tests.

    fig. S13. Axial compressive stress-strain relations established in a simple DAC.

    fig. S14. Compressive strength tests for standard materials including type I and II GCs in a simple DAC.

    fig. S15. Comparison of thermal stability of compressed GC (Com.GC-3) with raw GC at air and inert argon (Ar) or nitrogen (N2) conditions, respectively.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. XRD of compressed GCs recovered after compressing raw GC at pressures of 10 to 25 GPa and temperatures of 600° to 1200°C.
    • fig. S2. SAED patterns of compressed GCs measured at different length scales.
    • fig. S3. Local order in compressed GC.
    • fig. S4. The sp3 component of compressed GCs measured at ambient condition.
    • fig. S5. The sp3 component of compressed GC and microstructure of raw GC.
    • fig. S6. UV Raman spectroscopy of compressed GCs.
    • fig. S7. The loading/unloading-displacement curves of compressed GCs in comparison with raw GC, Cu, and MgO.
    • fig. S8. The loading/unloading-displacement curves, indentation hardness, and elastic recovery of compressed GCs synthesized at moderate pressures and temperatures.
    • fig. S9. The loading/unloading-displacement curves, hardness, Young’s modulus, and indentation elastic recovery of compressed GC at varied loading, holding, and unloading times.
    • fig. S10. Indentation morphology after unloading three-sided pyramidal Berkovich diamond indenter, showing significant elastic recovery.
    • fig. S11. Optical images of the indentations on diamond and Com.GC-2 after unloading a four-sided pyramidal diamond indenter.
    • fig. S12. Mohs hardness of compressed GC (Com.GC-3) characterized with qualitative scratch tests.
    • fig. S13. Axial compressive stress-strain relations established in a simple DAC.
    • fig. S14. Compressive strength tests for standard materials including type I and II GCs in a simple DAC.
    • fig. S15. Comparison of thermal stability of compressed GC (Com.GC-3) with raw GC at air and inert argon (Ar) or nitrogen (N2) conditions, respectively.

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