High-yield growth and morphology control of aligned carbon
nanotubes on ceramic fibers for multifunctional enhancement
of structural composites
Namiko Yamamoto
a
, A. John Hart
a,b,
*
, Enrique J. Garcia
a
, Sunny S. Wicks
a
, Hai M. Duong
a
,
Alexander H. Slocum
b
, Brian L. Wardle
a
a
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 41-317,
Cambridge, MA 02139, USA
b
Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
ARTICLE INFO
Article history:
Received 18 May 2008
Accepted 20 October 2008
Available online 5 November 2008
ABSTRACT
We present an in-depth study of CNT growth on commercially-available woven alumina
fibers, and achieve uniform growth of dense aligned CNTs on commercially-available
cloths up to 5 · 10 cm in area. By systematically varying the catalyst concentration, catalyst
pre-treatment time, and sample position within the tube furnace, we isolate key factors
governing CNT morphology on fiber surfaces and classify these morphologies as related
to the processing conditions. Synthesis employs a low-cost salt-based catalyst solution
and atmospheric pressure thermal CVD, which are highly attractive approaches for com-
mercial-scale processing. The catalyst solution concentration determines the uniformity
and density of catalyst on the fibers, H
2
exposure mediates formation of catalyst clusters,
and thermal decomposition of the reactant mixture activates the catalyst particles to
achieve uniform aligned growth. Under conditions for aligned CNT growth, uniform radi-
ally-aligned coatings are achieved with shorter CNT length, and these split into ‘‘mohawks’’
as the CNT length increases. Radially-aligned growth for 5 min adds a typical CNT mass
fraction of 3.8% to the initial sample mass, and a uniform morphology exists throughout
the weave. Composites prepared by standard layup techniques using these CNT ‘‘fuzzy’’
alumina fibers are attractive as integral armor layers having enhanced ballistic and impact
performance, and serve as a model system for later implementation of this technology
using carbon fibers.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
While there are numerous methods for controlling carbon
nanotube (CNT) growth on planar substrates such as silicon
wafers, applications of CNTs in structural composites neces-
sitate integration of CNTs with three-dimensional arrange-
ments of advanced fibers. In comparison to dispersion of
CNTs in epoxies [1] followed by impregnation of fibers, direct
growth of CNTs on fiber substrates [2–4] is an alternative and
more promising approach to achieve uniform CNT distribu-
tion throughout a composite. In such ‘‘fuzzy-fiber’’ reinforced
plastics (FFRP), CNTs form nanoscale mechanical connections
among adjacent fibers, which also serve as electrically and
thermally conductive pathways throughout the composite.
0008-6223/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbon.2008.10.030
* Corresponding author: Address: Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI
48109-2125, USA. Fax: +1 734 864 5751.
E-mail address: ajohnh@umich.edu (A. John Hart).
CARBON
47 (2009) 551– 560
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon