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Research Papers

Direct Synthesis of Nanofibrous Nonwoven Carbon Components: Initial Observations, Capabilities, and Challenges

[+] Author and Article Information
Mark A. Atwater

Department of Applied Engineering,
Safety & Technology,
Millersville University,
Millersville, PA 17551
e-mail: mark.atwater@millersville.edu

Roger J. Welsh, David S. Edwards

Department of Applied Engineering,
Safety & Technology,
Millersville University,
Millersville, PA 17551

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received June 5, 2016; final manuscript received August 31, 2016; published online October 10, 2016. Assoc. Editor: Rajiv Malhotra.

J. Micro Nano-Manuf 4(4), 041004 (Oct 10, 2016) (8 pages) Paper No: JMNM-16-1025; doi: 10.1115/1.4034609 History: Received June 05, 2016; Revised August 31, 2016

Widespread adoption of carbon nanomaterials has been hindered by inefficient production and utilization. A recently developed method has shown possibility to directly synthesize bulk nanostructured nonwoven materials from catalytically deposited carbon nanofibers (CNFs). The basic manufacturing scheme involves constraining carbon nanofiber growth to create three-dimensionally featured, macroscale products. Although previously demonstrated as a proof of concept, the possibilities and pitfalls of the method at a larger scale have not yet been explored. In this work, the basic foundation for using the constrained formation of fibrous nanostructures (CoFFiN) process is established by testing feasibility in larger volumes (as much as 2000% greater than initial experiments) and by noting the macroscale carbon growth characteristics. It has been found that a variety of factors contribute to determining the basic qualities of the macroscale fiber collection (nonwoven material), and there are tunable parameters at the catalytic and constraint levels. The results of this work have established that monolithic structures of nonwoven carbon nanofibers can be created with centimeter dimensions in a variety of cross-sectional shapes. The only limit to scale noted is the tendency for nanofibers to entangle with one another during growth and self-restrict outward expansion to the mold walls. This may be addressed by pregrowing carbon before placement or selective placement of the catalyst in the mold.

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Figures

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Fig. 1

Schematic representation of the reaction chamber used for constrained carbon nanofiber growth

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Fig. 2

The catalyst placement is a critical factor in determining the resulting properties of the nonwoven carbon produced by the CoFFiN process. General relationships between catalyst placement and bulk properties are given here (perspective is from above the mold).

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Fig. 3

XRD pattern from nanofibers produced after 1 h reaction using a Ni–Cu catalyst at 550 °C in 4:1 C2H4:H2. Note: Only select peak positions are identified for carbon in the form of graphite.

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Fig. 4

(a) Electron micrograph of nanofibers produced using a Ni–Cu catalyst at 550 °C in 4:1 C2H4:H2 is shown as-grown without external constraint. (b) High magnification reveals a regular distribution of size and smooth morphology.

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Fig. 5

The mold (a) and resulting nonwoven carbon monolith (b) are shown here. The material can be removed from the mold and further processed to suit a particular application.

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Fig. 6

Carbon nanofibers were successfully integrated into cylindrical molds, with the highest density occurring in (a) a smaller diameter cylinder (2.36 cm ID). In the larger diameter (4.75 cm ID) cylinder (b), carbon nanofibers also filled the mold cross section, but growth was not as uniform along the length.

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Fig. 7

When fibers are only restricted by the tube diameter, they may extend freely along the length without significant integration as shown (a) schematically and (b) pictorially above. (c) By introducing constraint and varying the starting catalyst form, the growth can be controlled.

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Fig. 8

By using carbon preforms, the initial volume of the carbon is greater, but the rate that carbon is deposited is relatively constant

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Fig. 9

Carbon deposition was studied using various catalyst forms and by adding additional constraint. Although all forms resulted in similar kinetics, the final carbon component varied in integrity.

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