Quantitative Chemical Analysis Throughout the FC CVD Process as a Route to Reliable Fibre Production and Research

Abstract

Carbon nanotube fibre production through the Floating Catalyst – Chemical Vapour Deposition (FC-CVD) process has been developed at Cambridge University for 14 years by the Macromolecular Materials Laboratory (MML) group. Since then research has focused on lab-scale processes and fibre property optimisation. Continued research has been stymied by unreliable reactor performance and repeatability. Investigations were therefore undertaken to expand instrumentation and process control capabilities on the reactor, and furthermore to investigate the reaction mechanics of the process in order to deepen our understanding and enable further improvement of fibre properties. Improved process control has been achieved through a Fourier-Transformed Infra-Red spectrometer integrated into the gas line to monitor the precursor feedstocks in real time. This has revealed the erratic and inaccurate behaviour of precursor delivery, held as responsible for the reactor’s poor performance up to this point. Precursor delivery reliability has now been greatly improved but can more importantly be corrected for live when making fibre, which has enabled the publication of a major study into predicting fibre properties [1]. Further work, sampling reactor furnace gases at four positions (the first time this has been reported), has produced novel insight into the gas chemistry of the FC-CVD process. While ferrocene and thiophene precursors decomposed too rapidly to study, contributing only small quantities of common gases, hydrocarbon and alcohol precursors produced a variety of chemical species that varied with reaction parameters of dispensing quantity and hydrogen flow rate. Furnace gases from toluene in particular showed significant quantities of benzene deep in the laminar flow zone, and reduced levels of methane, ethene and acetylene, which were further lowered when higher flow rates carried more intact benzene deeper into the furnace. This effect and other observations about gaseous precursor products have been related to MML publications with conclusions drawn about CNT reaction mechanisms.