Peter A. Willis

Gas-phase production of carbon single-walled nanotubes from carbon monoxide via the HiPco process: A parametric study

We have demonstrated large-scale production (10 g/day) of high-purity carbon single-walled nanotubes (SWNTs) using a gas-phase chemical-vapor-deposition process we call the HiPco process. SWNTs grow in high-pressure (30–50 atm), high-temperature (900–1100 °C) flowing CO on catalytic clusters of iron. The clusters are formed in situ: Fe is added to the gas flow in the form of Fe(CO)5. Upon heating, the Fe(CO)5 decomposes and the iron atoms condense into clusters. These clusters serve as catalytic particles upon which SWNT nucleate and grow (in the gas phase) via CO disproportionation: CO+CO⇒CO2+C(SWNT). SWNT material of up to 97 mol % purity has been produced at rates of up to 450 mg/h. The HiPco process has been studied and optimized with respect to a number of process parameters including temperature, pressure, and catalyst concentration. The behavior of the SWNT yield with respect to various parameters sheds light on the processes that currently limit SWNT production, and suggests ways that the producti...

SWNT and MWNT Reinforced Carbon Nanocomposite Fibrils

In this study the feasibility of using the more economically viable MWNT as an alternative to the high cost, low available SWNT was examined. Both SWNT and MWNT were electrostatically assembled into continuous aligned nanocomposite fibrils through a coelectrospinning process in order to increase the strength and toughness of polyacrylonitrile (PAN)-derived carbon fibers. It was found that the effectiveness of CNT in reinforcing the PAN precursor is highly dependent on the dispersion and the alignment of the CNT. Alignment of CNT has been achieved in the fibers through flow, confinement and charge induced during the electrospinning process. The presence of the CNT in the electrospun fiber was verified using Raman Spectroscopy and HRTEM. The local alignment of the CNT along the fiber direction was also observed using HRTEM. PAN and CNT was successfully co-electrospun with fiber diameters in the range of 40 nm to greater than a micrometer. With the addition of 1 wt. % SWNT, a two-fold increase in strength and modulus was obtained. The addition of 1 wt% MWNT increased the failure strength by 28%, the modulus by 20%, and a more than 100% increase in strain at failure was obtained in the as-spun nanofibers mat. These encouraging results show that MWNT are an attractive alternative to SWNT. Co-electrospinning of CNT and PAN demonstrates a promising pathway to produce the next generation of high performance carbon fibers that will help bridge dimensional and properties gap between nanoscopic and macroscopic structures.