Novel Method for Filling Graphite Microfibers
Funded by U.S. Army Research Laboratory
Project Summary
In this research program, Aegis Technology aimed to develop and demonstrate a novel class of nano-filling technology to fill a highly conductive metal into hollow graphite microfibers (or namely carbon nanotubes [CNTs]), which would significantly increase the extinction coefficient of the fibers and lead to a variety of military and industrial applications. This nano-filling technology is based on the combination of a selective surface processing technique and an electroless deposition method, which is expected to offer several advantages such as high processing efficiency, good processing consistency, low processing costs, and good production scalability. In addition, based on the latest literature research, we also determined the best methods to synthesize copper/carbon (Cu/C) core/shell nanowires which possess similar a similar structure as Ag filled carbon nanotubes (metal inside, carbon outside). A hydrothermal method (a bottom-up method) was used to synthesize the nanowires, which has multiple benefits including low costs, and ease in operation and scale up. These Cu/C nanowires are expected to have excellent IR extinction performance same as Ag filled carbon nanotubes.
The objective of this Phase I project is to demonstrate the feasibility of implementing the proposed concept to develop highly conductive metallic nano-fillings in carbon nanotubes, through process design, prototyping, and characterization. The primary research activities and results of this Phase I study include: 1) Process development for Ag nano-fillings in carbon nanotubes and synthesis of Cu/C nanowires, 2) Microstructure characterization of Ag-filled carbon nanotubes and Cu/C nanowires, and 3) Extinction performance measurement of Ag-filled carbon nanotubes and Cu/C nanowires.
This Phase I study has successfully demonstrated the feasibility of the proposed concept, and established proper processing procedures and key processing parameters. Continuous Ag nano-fillings with lengths of several microns (e.g. 3 μm or more) have been successfully filled in carbon nanotubes with an average diameter of ~ 130 nm. The Ag nano-fillings have been characterized in detail using a Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Energy-dispersive X-ray Spectroscopy (EDX) to examine their morphology, length, and soundness. In addition, an annealing process was employed to further improve the electrical conductivity of the Ag nano-fillings. Infrared extinction performance measurement was also carried out on the Ag nano-filled carbon nanotubes, which indicates the existence of Ag nano-fillings in carbon nanotubes.
Cu/C core/shell nanowires have also been successfully synthesized using the proposed hydrothermal method. Cu/C nanowires with diameters of ~ 200 nm and lengths of ~ 5 μm have been demonstrated. A nanowire production yield of more than 50% has been achieved. The Cu/C nanowires were characterized by SEM, TEM, and EDX. SEM and TEM images clearly showed the core/shell structure of Cu/C nanowires. EDX analysis indicated that the major composition of the nanowires were copper and carbon, with only a small percentage of oxygen and nitrogen.
The Phase I work accomplished has established a solid basis for future Phase II of this project, which will: (1) further optimize the processing parameters, (2) scale up the processing for large-quantity production, (3) fully characterize the properties of the nano-fillings and Cu/C nanowires at a systematic level, (4) investigate synthesis of Ag/C nanowires, and (5) explore potential applications.