Low Cost Method for Metal Nano-Coating of Anisotropic Carbon Fibers
Funded by U.S. Army Research Laboratory
Project Summary
In this research program, Aegis Technology was involved in developing and demonstrating a novel class of nano-coating technology in order to synthesize highly conductive metallic nano-coatings around carbon and glass fibers, which would significantly increase the extinction coefficient of the fibers and lead to a variety of military and industrial applications. This nano-coating technology which is based on a modified electroless coating method is expected to offer several advantages including high processing efficiency, good processing consistency, and low processing costs. The processes developed will also be scalable for large-quantity production and applicable for carbon and glass fibers with different diameters.
In Phase I, we have successfully carried out the technical feasibility studies of the proposed concept through process design, prototyping and characterization. The objective of this Phase II project is to further identify the underlying technical issues governing fabrication and performance of nano-coated carbon and glass fibers, and address the issues related with process optimization and scale up. The primary research activities and results of the Phase II study included: 1) Process development and optimization of silver (Ag) and copper (Cu) nano-coatings on carbon and glass fibers; 2) Microstructure characterization and measurement of electrical conductivity, and extinction coefficient of metal nano-coatings; 3) Investigation and design for production scale up of nano-coated fibers; and 4) Production of metal coated carbon and glass fibers, in order to ship a sufficient amount of metal coated fibers to Army Edgewood Chemical Biological Center (ECBC) for aerosol chamber testing.
In Phase II, we systematically investigated Ag and Cu nano-coatings on 3 μm carbon fibers and Ag nano-coatings on glass fibers with different diameters ranging from 6 μm to less than 2 μm. Both small-scale laboratory coating processes 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 processes, good coating results were achieved for all these carbon fibers and glass fibers. For scaled-up batch production processes, Ag coated 6 μm and 5.5 μm glass fibers demonstrated good coating quality and most of the fibers were coated along the entire length without coating breaks. Microstructure characterization, electrical properties, and extinction performance measurements were carried out for the coated fibers. It was found that the scaled-up batch production processes were very successful for Ag coated 6 μm and 5.5 μm glass fibers. These fibers demonstrated dense coating structures and high extinction performance (~30m2/g) with nearly no dropouts, which indicated that most of the fibers were well-coated with continuous Ag nano-coatings during the scaled-up batch production process. The Ag nano-coatings also have good adherence on glass fibers, and it was difficult to find coatings that peeled off under SEM even when the fibers were scratched by sharp tweezers. Ag coated carbon fibers and glass fibers using scaled-up batch productions were also shipped to Engineered Fibers Technology LLC (Shelton, CT) for packing and dispersion testing. We also carried out design and analysis for continuous production pipeline for coating long fibers.
The accomplished Phase II work has established a solid basis for future Phase III of this project, which will lead to commercially available metal coated fibers for MMW obscurant applications.