10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Kinetics of CNT Growth for Aerogelation in FC-CVD Synthesis
FIONA SMAIL, Brian Graves, Adam M Boies, University of Cambridge
Abstract Number: 1209 Working Group: Materials Synthesis
Abstract The potential for macroscopic assemblies of CNTs to create vast improvements in applications where electrical and/or thermal conductivity, low mass, high strength and high toughness are required continues to accelerate research in the field. The most attractive and scalable route to these materials is the one-step continuous synthesis and collection of elastic aerogels of CNTs, using floating-catalyst chemical vapour deposition techniques. The chemistry is driven by an aerosol of iron-based catalyst nanoparticles containing a small amount of sulphur, produced from precursors such as ferrocene (Fe source) and thiophene (S source), which react with hydrocarbon species to grow CNTs.
Recent deconvolution of the process using aerosol sampling techniques has led to new insights relevant to process development, namely:
- The synthesis of long CNTs capable of bundling to form elastic aerogels is driven by the negative slope of the axial parabolic temperature gradient - The bulk synthesis occurs due to renucleation of Fe-based catalyst particles in the presence of hydrocarbon pyrolysis species - Renucleation of the Fe-based nanoparticles occurs at higher temperatures and lower Fe supersaturation levels than anticipated as S lowers the Fe nucleation barrier, leading to optimal temperature conditions for CNT growth
To harness the benefits from these recent discoveries for future process scale up, much more information is required about the kinetics of the CNT growth processes in this type of system. While the kinetics of CNT growth in fixed-catalyst bed CVD systems are well characterised, many questions remain about the floating catalyst gas phase synthesis as a) this is a much more difficult system to study b) factors such as diffusion-limitations to growth rates do not apply in the same way. Furthermore, the effect of S, identified since the early days of CNT synthesis as a CNT growth promoted, on the growth rate of CNTs has not been quantified.
This presentation will report the application of aerosol sampling techniques and characterisation of CNT products to the challenge of quantifying CNT growth rates and study how a variety of reaction parameters (catalyst particle size, concentration of S, effect of S-precursor choice, nature of carrier gas, reaction temperature etc) influence the kinetics. The results will aid in optimisation of reactor and process design, to maximise production rates of the macroscopic CNT materials so that their use can be explored and implemented in sectors such as the automotive and aeronautic industries, allowing the benefits of these materials to transform our futures.