Skip to content

Metal-nanotube composites as radiation resistant materials

Summary

Reactive molecular dynamics with ReaxFF studies helium transport in nickel containing carbon nanotubes (CNTs), motivated by radiation-induced helium swelling and embrittlement in structural materials where He bubbles degrade ductility. The simulations compare defect-free versus vacancy-containing CNT models to separate interface trapping from fast outgassing along CNT interiors when wall defects exist. Helium is represented with Morse-type van der Waals interactions to Ni and C atop the reactive Ni/C/H ReaxFF core, enabling physisorption-limited ingress without spurious chemistry at the He pair level. Adri C. T. van Duin is a coauthor.

Methods

  • Code: LAMMPS large-scale reactive MD.
  • Potential: ReaxFF parametrization combining Ni/C/H with noble-gas interactions; He interacts with Ni and C via van der Waals (Morse) terms with combination-rule parameters (as described in the article).
  • Integration / ensemble: Time step 0.5 fs; NPH dynamics with Nose-Hoover thermostat coupling and barostat-style anisotropic stress control implemented via the LAMMPS stress tensor (damping 500 fs) plus periodic temperature rescaling every 10 steps (values stated in the paper).
  • System: Atomistic supercell with Ni matrix, embedded CNTs, and explicit He loading; vacancies introduced in CNT walls to mimic radiation defects; helium diffusion tracked at metal–CNT interfaces and along CNT cores. Periodic boundary conditions (PBC) apply in three dimensions as in standard LAMMPS bulk models.
  • Duration: per-protocol production times in ps/ns are tabulated in Appl. Phys. Lett. (N/A — not copied into this note).

Findings

  • For pristine (defect-free) CNTs, helium diffuses along metal–CNT interfaces and accumulates there; no helium penetration through perfect CNT walls is observed, consistent with impermeable graphene-like barriers in the model.
  • With vacancies in CNT walls, helium can enter CNT interiors, where nanotubes act as one-dimensional “nano-chimneys” enabling outgassing and reducing bubble nucleation in the metal relative to scenarios without such escape paths.
  • The authors argue metal–CNT composites can improve radiation tolerance when helium swelling / embrittlement is limiting, by providing fast escape pathways for helium relative to bulk Ni without CNTs.

Relative to bulk Ni without CNTs, embedding changes He partitioning and escape kinetics under the same loading assumptions. Vacancy density in CNT walls is the main structural lever between interface-only transport and nano-chimney outgassing. Figure-level He fields and stress targets are in papers/Gonzalez_CNT-Ni-chimney_2016.pdf; idealized interfaces and absent collisional defect production are caveats in Limitations and the APL text.

Limitations

Classical reactive MD cannot capture full defect production under irradiation; vacancies are introduced phenomenologically. Atomistic length/time scales require upscaling to engineering microstructures and dose rates; He production rates are not modeled explicitly.

Relevance to group

Direct van Duin co-authorship; demonstrates ReaxFF for He transport in Ni–carbon nanocomposite geometries relevant to nuclear materials concepts.

Citations and evidence anchors

Reader notes (navigation)

Pair this Appl. Phys. Lett. entry with broader nuclear materials MD corpora by noting that He transport here is classical physisorption-limited and does not include radiation damage cascade physics or H/He co-diffusion at grain boundaries. CNT diameters and Ni matrix dimensions should be read from the APL figures when scaling flux estimates.