An intermetallic Fe–Zr catalyst used for growing long carbon nanotube arrays Haibo Zhao a , Philip D Bradford b , Xin Wang b , Wei Liu b , Tzy Jiun Mark Luo b , Quanxi Jia c , Yuntian Zhu b , Fuh-Gwo Yuan a, ⁎ a Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, 27695, United States b Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, 27695, United States c Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, 87545, United States abstract article info Article history: Received 23 April 2010 Accepted 26 May 2010 Available online 1 June 2010 Keywords: Carbon nanotube Chemical vapor deposition Fe–Zr Metallic nanoparticles containing single and binary components have been known for their catalytic properties to grow carbon nanotube (CNT) arrays. In this paper, an intermetallic catalyst consisting of iron and zirconium was used to grow millimeter long, well aligned arrays. The Fe–Zr catalysts enabled the growth of 1.7 mm-long carbon nanotube arrays in 45 min. A comparison with pure iron catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. SEM images showed the different growth behaviors for Fe–Zr and Fe catalysts. The long, uniform CNT arrays grown here have potential applications in many advanced composites. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) have garnered extensive attention because of their excellent thermal, mechanical and electrical properties [1]. CNTs can be grown using various techniques, however, the production of ultra long (in the range of millimeters) CNTs is usually accomplished by chemical vapor deposition (CVD) on nano-particle catalyst covered substrates to produce aligned CNT arrays [2–4]. These arrays have been shown to be advantageous when extremely large aspect ratio and alignment of CNTs are desirable. Arrays have been the precursor for spinning high specific strength fibers [5–8], which are promising for future high strength composite materials [6–8]. The alignment inherent to the arrays has shown the potential for producing composites with vertically aligned CNTs which provide through-thickness multifunctionality to the composites [9–11]. Arrays have also been used as a raw material for making buckypapers that contain much longer CNTs than are normally achieved [12]. These CNT buckypapers could be used as reinforcement for advanced composite materials. Achieving continuous growth of CNTs on a catalytic substrate is the ultimate goal of many research groups and will not be realized until all of the issues facing continuous growth are addressed. An important issue hindering the continuous growth of CNT arrays is the thermal stability of the catalyst particles. Growth of CNTs at higher temperature produces CNTs with smaller diameter and fewer defects [13,14], and defect-free CNTs with small diameters are the strongest materials known [15]. However, at higher temperatures self-diffusion of metal particles will enlarge the sizes of catalyst particles, which is well known as “Ostwald Ripening”. In addition, small particles tend to agglomerate into larger, lower spatial-density particles during the CNT growth [16]. Atomic-scale in-situ observation of carbon nanotube growth reveals that catalysts are very mobile at the CNTs growth temperature [17]. For example, iron particles are almost quasi-liquid and can change their shape dramatically in seconds [17]. To overcome this challenge, many efforts have been taken to seek more stable catalysts [18–22]. Numerous catalysts have been successfully used in the growth of carbon nanotubes. These catalysts include single element metal and their binary alloys, such as Fe, Co, Co–Mo and Ni [18–22]. However, none of these catalysts shows a high thermal stability, and the CNT growth stops at a relatively short time. Attempts to grow longer nanotube arrays without any other assistance, such as water vapor-assisted growth, have only reached limited success thus far [18–22]. In this work, a new intermetallic catalyst, Fe–Zr, was used to grow 1.7 mm-long CNT arrays without water assistance in 45 min. To our best knowledge, pure zirconium alone cannot catalyze CNT growth. Multiple motivations exist for utilizing the intermetallic catalyst. First, the non-reactive zirconium will decrease the activity of the catalyst, which might help to reduce the amorphous carbon formation which usually is the main culprit for quenching carbon nanotube growth [23]. Another function of Zr is to form intermetallic bonds with Fe. These strong bonds may stabilize the catalysts and thus reduce the catalysts susceptibility to coarsening. Consequently, the catalysts may remain active longer to increase the CNT array growth time and ultimate height. Materials Letters 64 (2010) 1947–1950 ⁎ Corresponding author. Tel.: + 1 919 515 5947; fax: + 1 919 515 5934. E-mail address: yuan@ncsu.edu (F.-G. Yuan). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.05.045 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet