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Low-temperature carbonization of polyacrylonitrile/graphene carbon fibers: a combined ReaxFF molecular dynamics and experimental study

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Uncorrected proof PDF (Rajabpour_Carbon_2020_lowT_carbonization_galley.pdf). The version-of-record PDF and primary curation: 2020rajabpour-carbon-174-2-low-temperature-carbonization.

Summary

Polyacrylonitrile (PAN)-derived carbon fibers are workhorse structural materials; graphene additives are explored to catalyze carbonization chemistry so that high mechanical properties can be achieved at lower furnace temperatures, saving energy and processing cost. This Carbon article couples ReaxFF reactive MD of oxidized PAN models with graphene inclusions to accelerated-temperature trajectories with experimental carbonization of PAN versus PAN/graphene fibers at 1250 °C versus 1500 °C setpoints. The simulation narrative emphasizes graphene edges and heteroatom (N/O) functionality as nucleation sites that promote ring alignment and graphitic cluster formation relative to oxidized PAN alone. Experiments report large gains in tensile strength and Young’s modulus for graphene-containing fibers carbonized at 1250 °C compared with neat PAN at 1500 °C, framing the low-temperature processing advantage.

Methods

ReaxFF MD constructs oxidized PAN systems with graphene; NVT equilibration 60 ps at 300 K precedes snapshot selection (five frames from the last 5 ps at 1 ps spacing). Snapshots are heated to 2200, 2500, or 2800 K at 10 K/ps, then held 1 ns per target temperature to sample high-temperature chemistry on accessible MD timescales. Integration uses 0.25 fs timesteps (validated vs 0.10 fs at 2800 K in SI) and a Berendsen thermostat (100 fs damping). Experiments carbonize fibers and report mechanical properties (abstract values). The Carbon abstract states explicitly that graphene edges together with N and O heteroatoms act as catalytic seeds that expedite all-carbon ring alignment as precursors to graphitic structure growth—this is the MD mechanism paired with the 1250 °C vs 1500 °C mechanical comparison.

MD application (ReaxFF). Same reactive molecular dynamics protocol as on [[2020rajabpour-carbon-174-2-low-temperature-carbonization]]: NVT 60 ps at 300 K; five snapshots; 10 K/ps ramp to 2200–2800 K; 1 ns at each T; 0.25 fs; Berendsen thermostat (100 fs damping). PBC 3D supercells of oxidized PAN + graphene (atom counts in VOR PDF if galley text is thin). Barostat / NPT: N/A — as in the summarized protocol. Electric field: N/A — Replica / metadynamics: N/A — not used.

Findings

MD supports a mechanism in which graphene edges plus N/O groups seed graphitic growth and alignment pathways faster than oxidized PAN without graphene under the modeled conditions. Experiments quote ~91% higher tensile strength (632 → 1207 MPa) and ~101% higher Young’s modulus (88 → 177 GPa) for PAN/graphene at 1250 °C versus PAN-only at 1500 °C (abstract numbers). Together, the simulation story and mechanical data motivate graphene as a processing aid that can partially decouple ultimate fiber properties from the maximum furnace temperature, subject to microstructure and precursor chemistry details outside the MD cells.

Sensitivity and corpus honesty: MD uses 2200–2800 K as kinetic acceleration; furnace temperatures in experiment differ. This uncorrected proof may lack final pagination; use [[2020rajabpour-carbon-174-2-low-temperature-carbonization]] for VOR citation and stable mechanical table.

Limitations

Simulations use elevated temperatures to accelerate chemistry relative to furnace schedules; quantitative mapping to factory protocols requires caution. Proof-PDF lacks final pagination/typesetting; cite 2020rajabpour-carbon-174-2-low-temperature-carbonization for stable locators.

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