Composites of Carbon Filaments Made from Methane
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Composites of Carbon Filaments Made from Methane Xiaoping Shui, Xuli Fu, Martin Segiet and D.D.L. Chung Composite Materials Research Laboratory, University at Buffalo The State University of New York, Buffalo, NY 14260-4400, U.S.A. ABSTRACT Polymer-matrix and cement-matrix structural composites containing discontinuous carbon filaments (diameter = 0.1 µm) that were made catalytically from methane were developed for structural and electromagnetic functions. The composites were particularly attractive for electromagnetic interference shielding and radio wave reflection, due to the skin effect and the small diameter of the filaments. Coating the filaments with nickel by electroplating further enhanced the electromagnetic performance. However, the composites were not attractive for structural functions other than vibration damping, due to the large amount of interface between the filaments and the matrix. An effective configuration for the damping function involved using the filaments as an additive between the laminae of continuous conventional carbon fibers in a polymer-matrix structural composite. INTRODUCTION Submicron diameter carbon filaments are mainly those that are grown catalytically from carbonaceous gases at 500-700°C [1,2], although they include the nanotubes, which typically have diameter in the nanometer range. Due to the higher yield in production, the former is more abundant than the latter and applications involving the former are more well developed than those involving the latter. Submicron carbon filaments are to be distinguished from conventional carbon fibers, which are made by pyrolysis of pitch or polymer. They are also to be distinguished from vapor grown carbon fibers (VGCF), which are prepared by pyrolysis of carbonaceous gases to non-catalytically deposit carbon on catalytically grown submicron diameter carbon filaments at 950-1100°C [3,4]. Carbon filaments differ from both conventional and vapor grown carbon fibers in their small diameter. Conventional carbon fibers typically have diameter around 10 µm and VGCF have diameters up to 10 µm. Both carbon filaments and VGCF are not continuous, though the latter can be longer than the former. In contrast, conventional carbon fibers can be continuous. In spite of the discontinuous nature of carbon filaments, the aspect ratio can be quite high, due to the small diameter. In this work, carbon filaments are intertwined and have a morphology that resembles cotton wool. Moreover, they are disordered crystallographically, though they exhibit a fishbone morphology for the carbon layers. Each filament has an axial hollow channel in the middle, due to the catalyst particle used in the filament growth. The filaments were grown by Applied Sciences Inc. (Cedarville, Ohio) from methane, using an iron catalyst. The filament diameter is 0.15 µm. In this paper, the term “filaments” refers to filaments of submicron diameter, whereas the term “fibers” refers to fibers of diameter greater than 1 µm.
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COMPOSITE MATERIALS FOR STRUCTURAL APPLICATIONS Structur
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