Synthesis of Carbon Nanotubes on Macroporous Kaolin Substrate via a New Simple CVD Method

Abstract

In the present paper, a new simple chemical vapor deposition (CVD) method was investigated for synthesis of carbon nanotube (CNT) films on macroporous kaolin substrates (in mullite phase) using cyclohexanol and ferrocene as carbon source and catalyst, respectively. Effect of growth temperature on structure of the CNT films was also investigated by SEM images. Growth of a novel structure of the CNTs at 600°C on the macroporous kaolin substrate was succeeded. The novelty of these CNTs lies in their heart-like caps. At 650°C, CNTs were grown perpendicular on the macroporous surface of kaolin substrate. At higher temperatures (700, 750, 800°C), a quite different structure of CNT films was obtained. This interesting structure is composed of a continuous mat like thin film of long CNTs grown horizontally over the entire surface of macroporous kaolin substrate, and some casually overgrown humps. Various structures such as carbon fibers, helical CNTs and Y junction CNTs were observed in the overgrown humps. The results demonstrate ability of the proposed CVD method to perform growing of the CNT films with interesting structures on the macroporous kaolin substrates. We then perform a sensitivity analysis of the ignition time and ignition length to changes in the initial deposit thickness and gas flowrate under various conditions using the averaged model. We have found that the ignition time and ignition length are most sensitive to changes in deposit thickness when the deposit thickness and exhaust temperature is low. Also, the ignition time is relatively insensitive to changes in gas flow rate, but the ignition length is most sensitive to changes in gas flow rate at low exhaust temperatures. These studies are useful towards the ultimate development of a predictive particulate emissions control system for diesel-fueled vehicles.