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Trajectories of graphitizable anthracene coke and non-graphitizable sucrose char during the earliest stages of annealing by rapid CO\(_2\) laser heating

Summary

CO\(_2\) laser heating (1200–2600 °C, 0.25–300 s) vs 1 h furnace routes compares graphitizing anthracene coke vs non-graphitizing sucrose char during early carbonization. TEM tracks nanostructure; anthracene graphitizes faster. Sucrose char passes through closed-shell fullerenic nanoparticles that open on further heating, producing pores; odd-membered rings are argued present initially rather than generated only by annealing. ReaxFF MD simulates shell unraveling for the sucrose-derived structure. The study connects graphitizability distinctions in carbon materials science to nanoscale curvature and defect topologies that precede long-range graphitic ordering (introduction themes).

Methods

  • Materials: Anthracene vs sucrose precursors carbonized in tube bomb (500 °C, 5 h, ~6.9 MPa autogenous pressure).
  • Furnace: Ar; 25 °C/min to 1200 or 2600 °C, 1 h holds.
  • Laser: 250 W CW CO\(_2\) laser, pulse-width modulated power; multi-wavelength pyrometry + LII/TTH spectroscopy for temperature histories; TEM (FEI Talos 200 kV); XRD d\(_{002}\), Scherrer L\(_a\)/L\(_c\) where applicable.

  • ReaxFF MD (atomistic fragment): LAMMPS ReaxFF on a 2250-atom sucrose-char-inspired fullerenic shell using the CHO combustion ReaxFF extension cited in the article; energy minimization then NVT heating with a Berendsen thermostat to ~3327 °C; 0.1 fs timestep (see PDF for staging in ps/ns).

  • Cross-validation: authors compare laser-heated trajectories to furnace holds by mapping comparable integrated temperature–time exposure to argue kinetic vs thermodynamic control of ordering (methods narrative).

Additional controls. PBC: three-dimensional PBC for the cluster supercell as in standard LAMMPS setups unless the article specifies isolation. Barostat / bulk pressure: N/A — NPT not used for the ReaxFF heating segment summarized. Electric field: N/A — laser heating is thermal; no EFIELD bias in the quoted protocol. Enhanced sampling: N/A — umbrella / metadynamics / replica exchange not reported for this illustrative MD.

Findings

Outcomes. Laser anneals reach comparable end-state nanostructures to furnace holds when temperature–time integrals match, but laser exposes faster early kinetics. Graphitizable anthracene coke orders more rapidly than non-graphitizable sucrose char under similar programs.

Mechanisms. Sucrose char passes through closed fullerenic shells that open to porous morphologies; odd-membered rings are argued to be present early, not only as annealing products. ReaxFF trajectories show shell unraveling consistent with the proposed bottleneck before extended graphene stacking.

Comparisons. TEM micrographs and XRD metrics (d\(_{002}\), Scherrer widths) benchmark the simulation narrative.

Sensitivity / limitations. Heating rate, peak temperature, and hold time shift graphitization extent; ReaxFF carbon chemistry and the single fragment model are approximate—confirm all numbers in pdf_path.

Limitations

ReaxFF carbon chemistry transferability; single atomistic model for complex char; laser heating heterogeneity.

Experimental comparison should account for spatial gradients in laser-heated foils that are averaged differently than furnace isothermal holds—see temperature diagnostics in the PDF.

Carbonization literature context: distinguishing graphitizing vs non-graphitizing precursors remains central to carbon fiber processing; this work adds time-resolved laser access to early annealing stages (introduction framing).

Relevance to group

van Duin-group ReaxFF on carbonization paired with Penn State experimental laser kinetics.

Citations and evidence anchors

  • DOI: 10.3390/c4020036.