PERGAMON Carbon 39 (2001) 91–100 Formation of vapor grown carbon fibers with sulfuric catalyst precursors and nitrogen as carrier gas * Y.Y. Li, S.D. Bae, A. Sakoda , M. Suzuki Institute of Industrial Institute of Science, University of Tokyo,7-22-1 Roppongi, Minato-ku, Tokyo 106-8558, Japan Received 22 November 1999; accepted 13 March 2000 Abstract Vapor grown carbon fibers (VGCFs) with a maximum length of 2 cm and a diameter of a few micrometres have been fabricated by a conventional thermal deposition method at 10008C using ferric sulfate or ferrous sulfate as catalyst precursors, nitrogen as carrier gas, benzene as the source of carbon and a ceramic tube as substrate. Experiments employed a feeding gas of 27 wt.% benzene vapor and 73 wt.% nitrogen with a flow rate of 13.9 ml/min for a deposition time of 5 to 90 min on a ceramic substrate coated catalyst precursor from a 0.5 M aqueous solution. It was found that the combination of the sulfuric catalyst and nitrogen is capable of producing VGCFs satisfactorily. Observation about the nucleation phenomenon of catalyst, the lengthening and thickening of the VGCFs, reveals that catalyst particles with a mean diameter of 78 nm were generated at 10008C while carbon filaments were firstly found after 10 min carbon deposition. In addition, the lengthening and thickening of the VGCFs were confirmed to occur simultaneously in the growth process.  2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibers; Carbon filaments; B. Chemical vapor deposition; Pyrolysis; C. Scanning electron microscopy 1. Introduction late 19th century. Schutzenberger et al. [6] reported that carbon filaments were found accidently in carbonaceous Vapor-grown carbon fibers (VGCFs), cylindrical and soot and films while the thermal decomposition of hydro- hollow-cored carbon fibers with a catalytic particle in the carbons was studied. Almost at the same time, Hughes and tip of the core, are generally fabricated by thermal vapor Chambers [7] patented the manufacture of ‘hair-like deposition using a mixture of gaseous hydrocarbons and carbon filaments’ as electric lamp filaments. Further carrier gas on a substrate seeded with metallic-based studies of VGCFs have been carried out extensively since catalysts at temperatures around 10008C. Under proper the early 1960s. This is because of, partly, the demand for experimental conditions, the length of VGCFs could be up low cost and as-produced short carbon fibers to replace to several centimetres whereas the diameter could be a few polyacrylonitrile (PAN) and pitch-based carbon fibers. micrometres. Many proposed growth mechanisms of Research interests of VGCFs include materials (precursor, VGCFs were reviewed by Serp and Figueiredo [1]. The catalyst and substrate), new techniques, characterization mechanisms consist of (1) nucleation of catalyst, (2) [8,9] and modeling [10–12]. Hydrocarbons such as ben- lengthening of VGCF and (3) thickening of VGCF [2–5]. zene, acetylene [13], toluene [14], propylene [15], 1- In general, materials required for the formation of VGCFs methylnaphthalene, methane and ethylene [16,17] have include (1) precursor (hydrocarbon), (2) carrier gas (usual- been studied as the source of carbon. Based on these ly hydrogen), (3) catalyst (usually metal particles) and (4) approaches, benzene was recommended as the most effec- substrate. The history of VGCFs can be traced back to the tive precursor [17] for the formation of VGCFs. In order to find active catalysts, transition metals such as iron [18,19], nickel [20], vanadium and molybdenum [21] were investi- gated while ceramic, graphite [22], stainless steel [23,24] *Corresponding author. Tel.: 181-3-3402-6231; fax: 181-3- or copper–nickel [25] was examined, respectively, as 3408-1486. E-mail address: sakoda@cc.iis.u-tokyo.ac.jp (A. Sakoda). suitable substrates for fabricating VGCFs. Baker et al. [18] 0008-6223 / 01 / $ – see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(00)00082-8