Synthesis of carbon nanotubes at low temperatures as low as 540oC was demonstrated via floating catalyst chemical vapor deposition method. Catalytic decomposition of benzene was employed using ferrocene as a catalyst precursor. In this work, the technique of introducing catalyst particles into the reactor has been developed by using single heating source for both the catalyst and reactor. In-situ monitoring device was attached to the CVD unit to observe the temperature profile in the reactor. CNTs with both types (aligned and entangled) were synthesized with diameter distribution ranging from 10 to 40 nm. The interesting morphology of CNTs produced at relatively low temperature promotes real opportunity to minimize the synthesis temperature of CNTs in the future works.
Keywords Carbon nanotubes; Floating catalyst; Single heating source; low synthesis temperature
Since their first discovery in 1991 (Iijima, 1991), carbon nanotubes have attracted much attention due to their nanoscale dimensions and promising shape as well as their potential properties. Many methods for the synthesis of CNTs have been used and developed (Ajayan, 1992; Ishigami et al., 2000; Lee et al., 2002). Among all synthesis methods, chemical vapor deposition (CVD) is widely used due to its efficient cost and low operating temperatures required (Shyu et al.,2001; Han et al., 2003; Ni et al., 2006). Depending on the way of introducing the metal catalyst into the reactor, the CVD method can be conducted via supporting catalyst or floating catalyst technique. Floating catalyst method (FC-CVD) has gained much popularity due to its simplicity; furthermore, the purification step is not required to recover CNTs from the substrate. In addition, the absence of support material further reduces the number of process steps. Commonly, the synthesis temperature used in the floating catalyst method is ≥ 600oC (Atieh et al., 2006; Han et al., 2006. Othman, 2007). In particular, Atieh et al. (2006) claimed that most of the products obtained at temperature below 600oC were carbon by-products e.g. amorphous carbon. Some studies reported that the synthesis of CNTs produced at temperatures below 600oC is a crucial parameter for integrating CNTs into hybrid electronics (Liao et al., 2006; Devaux et al., 2008). In this paper, the growth of CNTs was conducted at temperatures as low as 540oC using a new approach of introducing catalyst particles into the reactor.
The experiments were carried out in a tubular ceramic tube of 1000 mm length, 40 mm ID and 50 mm OD. The tube was placed inside a two-stage furnace as shown in Figure 1. First furnace is the preheater consisted of three heating elements have an O-ring shapes to heat the raw materials and maintain the temperature in the preheater at 200°C. The second stage is an electrical furnace with 10°C/min heating rate that provides and maintains the reaction set temperature. Three ceramic boats were located...