Synthesis, microstructure and electrical conductivity of carbon nanotube–alumina nanocomposites L. Kumari a , T. Zhang a , G.H. Du a , W.Z. Li a, * , Q.W. Wang b , A. Datye c , K.H. Wu c a Department of Physics, Florida International University, Miami, FL 33199, United States b Agiltron Inc., 15 Cabot Road, Woburn, MA 01801, United States c Mechanical and Materials Engineering, Florida International University, Miami, FL 33174, United States Received 1 September 2008; received in revised form 12 September 2008; accepted 1 October 2008 Available online 21 October 2008 Abstract Carbon nanotube–alumina (CNT–Al 2 O 3 ) nanocomposites have been synthesized by direct growth of carbon nanotubes on alumina by chemical vapor deposition (CVD) and the as-grown nanocomposites were densified by spark plasma sintering (SPS). Surface morphology analysis shows that the CNTs and CNT bundles are very well distributed between the matrix grains creating a web of CNTs as a consequence of their in situ synthesis. Even after the SPS treatment, the CNTs in the composite material are still intact. Experimental result shows that the electrical conductivity of the composites increases with the CNT content and falls in the range of the conductivity of semiconductors. The nanocomposite with highest CNT content has electrical conductivity of 3336 S/m at near room temperature, which is about 13 orders of magnitude increase over that of pure alumina. # 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sintering; B. Nanocomposites; C. Electrical conductivity; Chemical vapor deposition; Carbon nanotubes 1. Introduction Carbon nanotubes (CNTs) have been investigated exten- sively for the past decade to explore their unique physical properties and many potential applications. One of the most promising uses of CNTs is in the development of nanocompo- sites, where the CNTs are used as novel fillers and binders to improve their mechanical, electrical and thermal properties [1–3]. CNTs have great potential applications due to their very large aspect ratio (1000–10,000) [4], low density, high rigidity (Young’s modulus of the order of 1 TPa) [5,6], and high tensile strength (up to 60 GPa) [7]. In addition, the excellent electrical conductivity (10 6 S/m at 300 K for single-walled CNT (SWCNT) and >10 5 S/m for multi-walled CNT (MWCNT)) [8,9] and thermal conductivity (6600 W/mK for an individual SWCNT and >3000 W/mK for an individual MWCNT) [10,3] make them suitable candidates in preparing nancomposities with new functional properties. Ceramics can sustain high temperature and have high hardness, but the most noted shortcoming is its inherent brittleness and highly insulating behavior, which has limited its extensive applications [11]. Thus CNTs are considered to be a promising component of a new class of CNT–ceramic composites, which may offer high mechanical, electrical and thermal performances unattainable from current composite materials. CNT-reinforced ceramic nanocomposite has become an intriguing field of intense research. Most of the attempts have been made to improve the mechanical properties of composites through incorporating CNTs [12]. The electrical conductivity of CNT–polymer materials due to the percolation of CNT has been widely investigated [2,13–15], but only a few authors have reported the electrical conductivity of CNT–ceramic composites. Flahaut et al. [16] synthesized CNT–Fe–Al 2 O 3 , CNT–Fe/Co–MgAl 2 O 4 , and CNT–Co–MgO composites and measured their electrical conductivity which was in the range of 200–400 S/m owing to the percolation of the CNTs in the matrix material. Zhan et al. [17] obtained an electrical conductivity of 3345 S/m on the 15 vol% SWCNT–alumina nanocomposites, an increase of 13 orders of magnitude over that of pure alumina. Previous reports by Rul et al. [18] and www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 35 (2009) 1775–1781 * Corresponding author. Tel.: +1 305 348 7257; fax: +1 305 348 6700. E-mail address: Wenzhi.Li@fiu.edu (W.Z. Li). 0272-8842/$34.00 # 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2008.10.005