Insights into carbon nanotube growth using an automated gravimetric apparatus

Abstract

The development of an automated chemical vapour deposition micro-reactor based on a thermogravimetric analyser is presented. This apparatus was used to investigate carbon nanotube (CNT) growth. Gas flow and reaction modelling highlighted problems with current systems and demonstrated why experimental results are currently apparatus specific. Modelling also indicated that the large-scale production of chiral selective CNTs cannot be achieved in current systems using hydrocarbons. The apparatus provided unprecedented insight into the synthesis of CNTs. Catalyst reduction does not reach completion, probably due to alumina stabilisation of iron oxides, and any discrete pre-reduction step is detrimental to final carbon yield. Any CNT nucleation period was solely attributable to carbon source or H2 supply restrictions, and growth and final yield were highly dependent on deposition rates within the initial period. The apparatus high throughput capabilities were used for a two-stage optimisation protocol. An optimum carbon yield of >40gC/gFe·h was found at 700°C with 20% C2H4 and 80% H2, comparable with the highest reported literature values. A new method to selectively accelerate, slow, or even stop, CNT growth rates using ‘carrier’ gas modulation is also demonstrated.