A Scalable Technique for the Synthesis of Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) are a form of crystalline carbon with extraordinary mechanical, chemical, physical and electrical properties. Consequently, CNTs have been used in a broad range of applications, e.g. electronics, polymeric additives and structural materials. However, the lack of a suitable large-scale manufacturing technique continues to inhibit their widespread use. Of the three established synthesis methods for CNTs: i) chemical vapour deposition (CVD), ii) laser ablation, and Hi) arc discharge, CVD based techniques show the greatest promise for economically viable, large-scale synthesis. In particular, the fluidised bed CVD (FBCVD) technique (where the CVD reaction occurs within a fluidised bed of catalyst particles) has the potential to produce high quality CNT, inexpensively, in large quantities. In this work, we review the existing literature on CNT synthesis via FBCVD and demonstrate that no systematic study of the key parameters has been undertaken. Specifically, we show that there is no clear relationship between key experimental variables (e.g. temperature, pressure) and CNT properties (e.g. CNT diameter, length) and yield, when the results of several studies are compared. We support these findings with experiments investigating the influence of key variables. The successful scale-up of any process requires detailed understanding of key process parameters and their interactions. Hence, further research to optimise the purity, yield and selectivity of the synthesised CNTs is required.