Arthur Sloan
Rice University
This proposal focuses on improving growth processes for carbon nanotubes (CNTs) as an enabling technology for lightweight CNT yarn conductors and CNT-based composites. Its primary objective is refining the understanding of the dynamics of CNT growth via the floating catalyst chemical vapor deposition (FCCVD) method. This will serve as a means to improve process efficiency and the quality of produced CNTs. Specifically, improvements to CNT aspect ratio (length/diameter) and crystallinity are desired. Its secondary objective is to investigate the use of the FCCVD process for the simultaneous production of CNTs and hydrogen from methane. This could provide a scalable alternative to steam-methane reforming for the production of hydrogen for use as rocket propellant.
Improving the quality of available CNT is an important step in realizing the property milestones laid out in TA10.2.3.1 and TA10.1.1.1. The properties of these and other macroscale applications of CNTs scale with the quality of the CNTs used in their manufacturing. Current CNT production methods remain poorly characterized from an engineering standpoint. This has resulted in an inability to
commercially produce CNTs that allow macroscale applications to reach any significant fraction of the properties of individual CNTs. The FCCVD process is one of the most promising methods to grow CNTs in a manner suitable for industrial production, but more studies of internal processes like reaction kinetics and heat and mass transport phenomena are needed. The FCCVD process can be operated with a variety of hydrocarbon feedstocks, including methane. The result is solid carbon in the form of CNTs and hydrogen gas, which may easily be collected and used as fuel. This hydrogen has, up until recently, been largely ignored as byproduct of the reaction. Creating a process optimized for the simultaneous production of CNTs and hydrogen will build upon and go beyond the studies proposed in the pursuit of the primary goal.
A variety of techniques will be used to study internal processes of FCCVD and their effect on the produced CNTs. The high temperatures used in FCCVD will necessitate a combination of in situ condition measurements and sample collection, model experimental systems, and finite element modeling to build a holistic understanding of the process internals. Produced CNTs will be characterized using the spectroscopic, microscopic and thermogravimetric techniques common in the study of CNTs. These include Raman spectroscopy, transmission electron microscopy, and thermogravimetric analysis.