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Materials 2014, 7(5), 3820-3833; doi:10.3390/ma7053820
Article

Carbonized Micro- and Nanostructures: Can Downsizing Really Help?

1,*  and 2
1 Department of Aerospace Engineering, Texas A and M University, 3409 TAMU College Station, TX 77843-3409, USA 2 Department of Material Science and Engineering, Texas A and M University, 3003 TAMU College Station, TX 77843-3003, USA
* Author to whom correspondence should be addressed.
Received: 6 March 2014 / Revised: 4 April 2014 / Accepted: 25 April 2014 / Published: 14 May 2014
(This article belongs to the Section Advanced Composites)
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Abstract

In this manuscript, we discuss relationships between morphology and mechanical strength of carbonized structures, obtained via pyrolysis of polymeric precursors, across multiple length scales, from carbon fibers (CFs) with diameters of 5–10 µm to submicron thick carbon nanofibers (CNFs). Our research points to radial inhomogeneity, skin–core structure, as a size-dependent feature of polyacrylonitrile-based CFs. This inhomogeneity is a surface effect, caused by suppressed diffusion of oxygen and stabilization byproducts during stabilization through skin. Hence, reducing the precursor diameters from tens of microns to submicron appears as an effective strategy to develop homogeneous carbonized structures. Our research establishes the significance of this downsizing in developing lightweight structural materials by comparing intrinsic strength of radially inhomogeneous CFs with that of radially homogeneous CNF. While experimental studies on the strength of CNFs have targeted randomly oriented turbostratic domains, via continuum modeling, we have estimated that strength of CNFs can reach 14 GPa, when the basal planes of graphitic domains are parallel to nanofiber axis. The CNFs in our model are treated as composites of amorphous carbon (matrix), reinforced with turbostratic domains, and their strength is predicted using Tsai–Hill criterion. The model was calibrated with existing experimental data.
Keywords: carbon nanofibers; carbon fibers; turbostratic domains; skin–core inhomogeneity carbon nanofibers; carbon fibers; turbostratic domains; skin–core inhomogeneity
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Naraghi, M.; Chawla, S. Carbonized Micro- and Nanostructures: Can Downsizing Really Help? Materials 2014, 7, 3820-3833.

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