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Nanocarbon synthesis by high-temperature oxidation of nanoparticles.

Nomura K, Kalia RK, Li Y, Nakano A, Rajak P, Sheng C, Shimamura K, Shimojo F, Vashishta P - Sci Rep (2016)

Bottom Line: Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment.Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects.This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

View Article: PubMed Central - PubMed

Affiliation: Collaboratory for Advanced Computing and Simulations, Department of Physics &Astronomy, Department of Computer Science, Department of Chemical Engineering &Materials Science, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0242, USA.

ABSTRACT
High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects. This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

No MeSH data available.


Related in: MedlinePlus

High-temperature nSiC oxidation.(a–c) Snapshots from an RMD simulation showing oxidation of a SiC nanoparticle of diameter 10 nm at temperature 2,800 K. A 2 nm-thick slice in the middle of the simulation box is shown in panels (a–c). Yellow, cyan, and red spheres represent silicon, carbon, and oxygen atoms, respectively, in nSiC. For clarity, O2 molecules surrounding nSiC are not shown here. (a) Initial configuration; (b) a porous layer of silica encapsulating carbon products develops after 0.6 ns; and (c) carbon clusters grow further until the core of nSiC is completely oxidized around 1.7 ns. (d) The time evolution of the silica-shell thickness at temperatures 2,400 K (blue) and 2,800 K (red). (e,f) The time evolution of the number of chemical bonds at 2,400 K (e) and 2,800 K (f).
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f1: High-temperature nSiC oxidation.(a–c) Snapshots from an RMD simulation showing oxidation of a SiC nanoparticle of diameter 10 nm at temperature 2,800 K. A 2 nm-thick slice in the middle of the simulation box is shown in panels (a–c). Yellow, cyan, and red spheres represent silicon, carbon, and oxygen atoms, respectively, in nSiC. For clarity, O2 molecules surrounding nSiC are not shown here. (a) Initial configuration; (b) a porous layer of silica encapsulating carbon products develops after 0.6 ns; and (c) carbon clusters grow further until the core of nSiC is completely oxidized around 1.7 ns. (d) The time evolution of the silica-shell thickness at temperatures 2,400 K (blue) and 2,800 K (red). (e,f) The time evolution of the number of chemical bonds at 2,400 K (e) and 2,800 K (f).

Mentions: Figure 1a–c, shows snapshots of the simulation for D = 10 nm at 2,800 K. Here yellow, cyan, and red spheres represent Si, C, and O atoms, respectively. An animation of the oxidation process is shown in Supplementary movie, S1.mov. Starting from a spherical nSiC immersed in an O2 environment (Fig. 1a), initial oxidation produces a silica shell around the unreacted SiC core (Fig. 1b). The overall reaction at high oxygen pressures reads1011


Nanocarbon synthesis by high-temperature oxidation of nanoparticles.

Nomura K, Kalia RK, Li Y, Nakano A, Rajak P, Sheng C, Shimamura K, Shimojo F, Vashishta P - Sci Rep (2016)

High-temperature nSiC oxidation.(a–c) Snapshots from an RMD simulation showing oxidation of a SiC nanoparticle of diameter 10 nm at temperature 2,800 K. A 2 nm-thick slice in the middle of the simulation box is shown in panels (a–c). Yellow, cyan, and red spheres represent silicon, carbon, and oxygen atoms, respectively, in nSiC. For clarity, O2 molecules surrounding nSiC are not shown here. (a) Initial configuration; (b) a porous layer of silica encapsulating carbon products develops after 0.6 ns; and (c) carbon clusters grow further until the core of nSiC is completely oxidized around 1.7 ns. (d) The time evolution of the silica-shell thickness at temperatures 2,400 K (blue) and 2,800 K (red). (e,f) The time evolution of the number of chemical bonds at 2,400 K (e) and 2,800 K (f).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837334&req=5

f1: High-temperature nSiC oxidation.(a–c) Snapshots from an RMD simulation showing oxidation of a SiC nanoparticle of diameter 10 nm at temperature 2,800 K. A 2 nm-thick slice in the middle of the simulation box is shown in panels (a–c). Yellow, cyan, and red spheres represent silicon, carbon, and oxygen atoms, respectively, in nSiC. For clarity, O2 molecules surrounding nSiC are not shown here. (a) Initial configuration; (b) a porous layer of silica encapsulating carbon products develops after 0.6 ns; and (c) carbon clusters grow further until the core of nSiC is completely oxidized around 1.7 ns. (d) The time evolution of the silica-shell thickness at temperatures 2,400 K (blue) and 2,800 K (red). (e,f) The time evolution of the number of chemical bonds at 2,400 K (e) and 2,800 K (f).
Mentions: Figure 1a–c, shows snapshots of the simulation for D = 10 nm at 2,800 K. Here yellow, cyan, and red spheres represent Si, C, and O atoms, respectively. An animation of the oxidation process is shown in Supplementary movie, S1.mov. Starting from a spherical nSiC immersed in an O2 environment (Fig. 1a), initial oxidation produces a silica shell around the unreacted SiC core (Fig. 1b). The overall reaction at high oxygen pressures reads1011

Bottom Line: Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment.Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects.This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

View Article: PubMed Central - PubMed

Affiliation: Collaboratory for Advanced Computing and Simulations, Department of Physics &Astronomy, Department of Computer Science, Department of Chemical Engineering &Materials Science, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0242, USA.

ABSTRACT
High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects. This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

No MeSH data available.


Related in: MedlinePlus