A Viable Method for Metal Nano-Coating of Graphite Microfibers
Funded by U.S. Army Research Laboratory
Project Summary
In this SBIR program funded by U.S. Army Edgewood Chemical Biological Center (ECBC), Aegis Technology is aimed to develop and demonstrate a novel class of nano-coating technology to synthesize highly conductive metallic nano-coatings around carbon micro/nanofibers including nanotubes, which would significantly increase the extinction coefficient of the fibers and lead to a variety of military and industrial applications. This nano-coating technology based on a modified electroless coating is expected to offer the advantages such as high processing efficiency, good processing consistency, and low processing cost, which is also scalable for large-quantity production and applicable for carbon nanofibers/tubes with different diameters/lengths. After we successfully carried out the technical feasibility studies of the proposed concept in previously accomplished Phase I, in this Phase II, Aegis has further identified the underlying technical issues governing fabrication and performance of nano-coated carbon nanofibers/tubes, and addressed the issues related with process optimization and scale up.
In Phase II, we systematically investigated Ag nano-coatings on ASI 130 nm carbon nanofibers, Helix 20-40 nm, 40-60 nm, and 60-100 nm carbon nanotubes, and PMMA polymer nanofibers. Both small-scale laboratory coating process and scaled-up batch production were explored in detail. Different coating temperatures, coating times, coating solution ratios, and batch production masses were investigated. For small-scale laboratory coating process, good coating results were achieved for all these carbon nanofibers/tubes and polymer nanofibers. The coating processes were also scaled-up to 3-5 grams per batch. It was found that good coatings could be achieved for batch mass less than 3 grams. The nano-coatings synthesized are characterized in detail by Scanning Electron Microscope (SEM) to examine their thickness, morphology and soundness. The optimization of coating processes resulted in nano-coatings with improved morphology and microstructures. Other property measurements of the Ag nano-coated carbon nanofibers/tubes showed that the Ag nano-coatings displayed very good adherence to the nanotubes. The coated carbon nanofibers/tubes were also measured for extinction performance. However, an extinction peak was not observed due to the wide length distribution of the nanofibers/tubes, which suggested that it is necessary to develop graphite nanofiber/tubes with well controlled, specific length. The modeling and simulation, conducted by our technical partner, Prof. Charles Bruce at New Mexico State University (NMSU), also suggested that the graphite material (e.g. high-conductivity carbon nanofibers) only with the required relatively narrow length distribution have optical properties peak in the visible to near IR spectrum (2-4 µm) and far IR producing attenuation from 8-12 µm.
In addition, as suggested by ECBC and NMSU, Aegis has also carried out two additional development efforts. One is to investigate the intercalation of previously used graphite material (carbon nanofibers) with Bromine, suggested by Prof. Prof. Charles Bruce. The other is to silver coat titanium dioxide fibers, suggested by Dr. Brendan DeLacy, which were chosen to be filtered to limit the length distribution. Aegis has all successfully processed/coated these materials as suggested. However the length distribution of these fibers materials processed was still far from ideal.
In this accomplished Phase II, Aegis has achieved the technical goal as set for this project, by successfully developing and demonstrating a viable method for metal nano-coating of graphite microfibers. However, the successful application of this technology developed still depends upon the availability of carbon microfibers with desired length that can be well controlled within a narrow length distribution.