Abstract
This work aimed to identify and address the main challenges associated with fabricating large samples of carbon foams composed of interwoven networks of carbon nanofibers. Solutions to two difficulties related with the process of fabricating carbon foams, maximum foam size and catalyst cost, were developed. First, a simple physical method was invented to scale-up the constrained formation of fibrous nanostructures process (CoFFiN) to fabricate relatively large foams. Specifically, a gas deflector system capable of maintaining conditions supportive of carbon nanofiber foam growth throughout a relatively large mold was developed. ANSYS CFX models were used to simulate the gas flow paths with and without deflectors; the data generated proved to be a very useful tool for the deflector design. Second, a simple method for selectively leaching the Pd catalyst material trapped in the foam during growth was successfully tested. Multiple techniques, including scanning electron microscopy, surface area measurements, and mechanical testing, were employed to characterize the foams generated in this study. All results confirmed that the larger foam samples preserve the basic characteristics: their interwoven nanofiber microstructure forms a low-density tridimensional solid with viscoelastic behavior. Fiber growth mechanisms are also discussed. Larger samples of mechanically-robust carbon nanofiber foams will enable the use of these materials as strain sensors, shock absorbers, selective absorbents for environmental remediation and electrodes for energy storage devices, among other applications.
Highlights
Testing and developing applications of novel carbon-based materials, including carbon nanotubes, nanofibers, and graphene, is limited by the difficulty of synthesizing sufficient quantities of high-quality, low-cost material
The development of a process for growing relatively large scale carbon nanofiber foams (CNFF) is best understood in terms of three phases of development
In the first phase (Section 3.1), it was clearly demonstrated that a simple strategy would not produce a mold-filling, high-quality fiber foam
Summary
Testing and developing applications of novel carbon-based materials, including carbon nanotubes, nanofibers, and graphene, is limited by the difficulty of synthesizing sufficient quantities of high-quality, low-cost material. The only mechanically-robust carbon fiber foams that exist at large scale are composites, containing both carbon fiber and polymeric materials [10,11,12,13]. The constrained formation of fiber nanostructures (CoFFiN) [14,15] provides a means to generate pure carbon fiber foams with mechanical and thermal stability. As demonstrated in the present work this limitation was a natural consequence of the complexity of growing large scale carbon fiber foams. The success of the scale-up process outlined in the present paper, and the concomitant development of Fibers 2016, 4, 9; doi:10.3390/fib4010009 www.mdpi.com/journal/fibers
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