Direct and repetitive growth cycles of carbon nanotubes on stainless steel particles by chemical vapor deposition in a fluidized bed Carole E. Baddour * , D. Chester Upham, Jean-Luc Meunier Department of Chemical Engineering, McGill University, 3610 University St., Montre ´al, Que ´bec, Canada H3A 2B2 ARTICLE INFO Article history: Received 23 November 2009 Accepted 19 March 2010 Available online 25 March 2010 ABSTRACT Carbon nanotubes are synthesized directly on stainless steel (SS) 304 particles (ø70 lm) by chemical vapor deposition (CVD) in a fluidized bed system (FBCVD) without the addition of an external catalyst. The direct growth method was originally developed for a fixed thermal CVD furnace, it is shown here it can be extended to FBCVD in a demonstration of the ease of scale up of the direct growth method. The growth method is compliant with SS particles substrate microstructures in the form of dendrites. It is also shown the SS particles can be successfully recycled for a second growth sequence without having to repeat the particle pre-treatment. Ó 2010 Elsevier Ltd. All rights reserved. The unique properties of carbon nanotubes (CNTs) have shown great promise in developing new devices and improv- ing current technologies. Current CNT applications include and are not limited to, electrodes and sensors [1,2], fuel cells [3], reinforcements in high performance composites [4,5] and lithium ion batteries [6,7]. CNTs are expected to bring forward innovations in many other fields if lower prices are achieved by large scale production. Large scale synthesis of CNTs is performed in fluidized bed chemical vapor deposition (FBCVD) reactors. Currently, several large scale production facilities use FBCVD in France (Arkema), the USA (SouthWest Nano) and China (Chengdu Organic Chemicals). The FBCVD technique offers enhanced mass transfer, continuous opera- tion and ease of scale up. In addition, FBCVD provides a homogenous environment and eliminates stagnant areas, thus enabling all the catalyst particles to be exposed to the feed gases and take part in the reaction process [8]. The cata- lytic systems for FBCVD consist of a metal (typically Fe, Ni, Co or mixtures thereof) loaded onto support particles such as Al 2 O 3 , SiO 2 , or La 2 O 3 . These catalytic particle systems are pre- pared by CVD, impregnation, co-precipitation and sol–gel. The metal loading ranges from 0.5% w/w to 96% w/w, depending on the preparation method used. Synthesis temperatures range from 500 to 850 °C and carbon sources include, but are not limited to, C 2 H 2 ,C 2 H 4 and CH 4 [9]. Here, we present a direct method for producing CNTs on stainless steel (SS) 304 particles (/70 lm) in a FBCVD reactor, with the opportu- nity to recover and reuse the SS 304 particles for multiple growth processes. The direct growth method was originally developed for a fixed thermal CVD setup [10], and it is shown here to be extended to a FBCVD setup. The technique de- scribed in [10] simply involves a hydrochloric acid treatment step followed by a heat treatment to prepare the SS substrate for CNT growth. The SS itself provides the active sites neces- sary for CNT growth thus there is no need for the addition of any external catalyst precursor. The CNTs produced were characterized by Scanning and Transmission Electron Micros- copy (SEM and TEM), Thermo-Gravimetric Analysis (TGA) and Raman Spectroscopy. The FBCVD reactor is illustrated in Fig. 1. The setup con- sists of a 40 mm ID quartz cylinder 304.8 mm in length, which is positioned on top of a 48 mm SS distributor disk. The dis- tributor disk rests on top of a SS nozzle with a maximum diameter of 40.5 mm. The gases enter from this nozzle. This assembly is located inside a 610 mm-long quartz tube (50 mm ID). Silicon stoppers are positioned on both ends of the longer quartz tube, allowing gases to enter from the bot- tom and exit from the top. A 3-mm thick layer of alumina wool is placed between the inner and outer quartz tubes. The setup is surrounded by a Barnstead Thermolyne 21100 vertical tube furnace. The SS particle preparation involves cleaning in acetone in an ultrasonic bath and etching in hydrochloric (HCl) acid (35–38% Reagent Grade) for 5 min. The minimum fluidization velocity of the SS particles is 0.028 m/s. The powders (65 g) are then inserted in the FVCVD reactor and are subjected to a 30 min heat treatment at 850 °C in an Ar atmosphere at a flowrate of 1000 sccm. Afterwards, the temperature is reduced to the synthesis temperature of 0008-6223/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2010.03.031 * Corresponding author: Fax: +1 514 398 6678. E-mail address: carole.baddour@mail.mcgill.ca (C.E. Baddour). 2652 CARBON 48 (2010) 2644 – 2673