A pinboard by
Christian Hoecker

Postdoctoral Fellow, University of Cambridge


Understanding and Scale-Up of a Gas Phase Process for Continuous Tailored Carbon Nanotube Synthesis

Manipulating structures that are as small as a few atoms does not only affect their mutual interactions within this small scale ‘nanoworld’, but can also have a strong impact on phenomena occurring in the ‘macroworld’, the scale on which our daily life takes place. ‘Nano’ describes the order of magnitude in which, for example, the growth of fingernails can be measured – about 1 nanometre per second. Among other things, this nanoworld is home of some incredible structures called carbon nanotubes (CNTs). On the nanoscale, individual carbon nanotubes have been shown to possess significantly improved mechanical, thermal and electrical properties compared to existing materials. However, their applications and macroworld impact are thus far limited. Extrapolating the properties of individual carbon nanotubes into macro-scale CNT materials using a continuous and cost effective process offers enormous potential for a variety of applications in fields such as composite materials, coatings and films, microelectronics, biotechnology, energy storage and energy conversion. The floating catalyst chemical vapour deposition (FCCVD) method, subject to my research, bridges the gap between generating nano- and macro-scale CNT material and has already been adopted by industry for exploitation. It is at the interface of chemistry, physics, engineering and materials science, and uniquely transforms a constant flow of precursors into gas-phase synthesised bulk CNT material which can be spun continuously from a reactor. A deep understanding of the phenomena that occur within the FCCVD reactor is essential to producing a desired and tailored CNT product and successfully scaling up the FCCVD process. My work has led to multiple patents and scientific publications. More importantly, it has fundamentally changed the understanding of the FCCVD process and got awarded a £3M research grant for the ‘Advanced Nanotubes Applications and Manufacturing Initiative’, led by our research group (www.anam.eng.cam.ac.uk). To build onto the insights gained within my previous studies, I now explore further how individual CNTs bond and stick to one another. As part of my postdoctoral research I am presenting my work on the cluster formation, or agglomeration, in CNT aerosols, which breaks new ground in the examination of the fundamental dynamics of the FCCVD method, at the American Association for Aerosol Research Conference.


The influence of carbon source and catalyst nanoparticles on CVD synthesis of CNT aerogel

Abstract: The floating catalyst chemical vapour deposition (FC-CVD) method is unique in providing the capability for continuous carbon nanotube (CNT) synthesis at an industrial scale from a one-step continuous gas-phase process. Controlling the formation of the iron-based catalyst nanoparticles is widely recognized as a primary parameter in optimizing both CNT product properties and production rate. Herein the combined influences of pyrolytic carbon species and catalytic nanoparticles are both shown to influence CNT aerogel formation. This work studies the source of carbon in the formed CNTs, the location of aerogel formation, the in-situ behaviour of catalyst nanoparticles and the correlated morphology of the resultant CNTs. Axial measurements using isotopically-labelled methane (CH4) demonstrate that carbon within all CNTs is primarily derived from CH4 rather than some of the early-forming CNTs being predominantly supplied with carbon via thermal decomposition of catalytic precursor components. Quantification of CNT production along the axis of the reactor definitively dispels the notion that injection parameters influence CNT formation and instead shows that bulk CNT formation occurs near the reactor exit regardless of the carbon source (CH4, toluene or ethanol). Supply of carbon to different reactor locations indicates that CNT aerogel formation will occur even when carbon is delivered near the exit of the reactor so long as the carbon source reaches a sufficient temperature (>1000 °C) to induce pyrolysis. These results give an indication of how future large-scale CNT reactors may be optimized and controlled by modifying downstream catalyst and carbon delivery.

Pub.: 29 Nov '16, Pinned: 29 Jun '17