TECHNICAL PAPER Study of the Variables in the Synthesis of Carbon Nanotubes by the Spray Pyrolysis of Benzene–Ferrocene Mixtures Shamik Chaudhuri 1,2 • Ritayan Chatterjee 1,3 • Dinabandhu Ghosh 1 Received: 17 January 2015 / Accepted: 1 May 2015 Ó The Indian Institute of Metals - IIM 2015 Abstract Pure multiwalled carbon nanotubes were syn- thesized by the spray pyrolysis of benzene–ferrocene mixtures at 1173–1273 K. Several variables were studied: temperature, ferrocene concentration in benzene, pump (feed) rate of benzene–ferrocene mixture, and flow rate of carrier gas (argon). Characterization of the CNTs and the effects of the variables were studied with the help of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermo- gravimetry. The yield and morphology of CNT was found to be optimum at 1273 K. The effect of temperature on the yield of CNT is explained thermodynamically. Also, the standard Gibbs energy of formation of C 6 H 6 (s), which is a new thermodynamic data, is generated. Ferrocene con- centration affected the yield inversely. The pump rate controlled the number of walls of the CNT produced and the control of argon flow rate helped to achieve proper alignment of the CNTs. Keywords Carbon nanotubes  Ferrocene  Spray pyrolysis  Raman spectroscopy  Yield  Morphology 1 Introduction Materials with novel properties are an integral part of our society. Without these materials many different forms of technologies could not be developed. Carbon nanotubes (CNTs) are one such material with novel properties that can improve modern technology. CNTs consist of a rolled graphene sheet (a hexagonal carbon layer with sp 2 bond between individual carbon atoms) with diameters of nanometer size and length up to several micrometers, yielding a high aspect ratio of up to 132,000,000:1. CNTs form in three main categories: single-walled nanotube (SWNT), double-walled and multi-walled nanotubes (MWNTs) [1]. Because of their superior properties such as high mechanical strength, hardness, novel electrical and thermal properties, the CNTs have a vast field of applica- tions [2–6]. Some of the promising applications of the CNTs are as electrodes for electrochemical double layer capacitors, field emitters, nanoelectronic devices, for hy- drogen storage, in composite materials, etc. [7–13]. CNTs are generally synthesized by electric arc discharge method, laser ablation method, catalytic chemical vapour deposition (CCVD), flame analysis, spray pyrolysis, etc. [14–19]. The architecture and chirality of CNTs produced by these methods are greatly influenced by thermodynamic conditions, catalysts used and molecular composition of condensed phases [20]. In the first two methods, high temperature processes are involved and high quality nan- otubes can be produced. However, the yields are poor and not adaptable for large scale production. In contrast, the CCVD method has been proven to be a preferred route for the large scale production. Spray pyrolysis is com- paratively inexpensive and one of the latest methods to produce CNT. In this method, a liquid hydrocarbon such as benzene, toluene, or xylene, etc., is used as carbon & Shamik Chaudhuri shamikjumet@gmail.com; schaudhuri@research.jdvu.ac.in 1 Department of Metallurgical and Materials Engineering, Jadavpur University, Kolkata 700032, India 2 Centre of Excellence in Phase Transformation and Product Characterization: TEQIP, Jadavpur University, Kolkata 700032, India 3 Department of Applied Sciences, Haldia Institute of Technology, Haldia 721657, West Bengal, India 123 Trans Indian Inst Met DOI 10.1007/s12666-015-0547-3