Continuous Carbon Nanofibers For Nanofiber Composites
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Continuous Carbon Nanofibers For Nanofiber Composites Yuris Dzenis and Yongkui Wen Department of Engineering Mechanics Center for Materials Research and Analysis University of Nebraska-Lincoln Lincoln, NE 68588-0526, U.S.A.
ABSTRACT Continuous carbon nanofibers were manufactured using electrospinning technique. The as-spun polyacrylonitrile (PAN) nanofibers were stabilized and carbonized to convert them into carbon nanofibers. The diameters of typical carbon nanofibers were in the range from 100 - 500 nanometers. Compared to the vapor grown carbon nanofibers, the electronspun carbon nanofibers were continuous, uniform in diameter, and solid. The electrospun nanofiber samples did not require purification. The carbon nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Electron and X-ray diffraction patterns were obtained and analyzed. Nanocomposites of epoxy resin reinforced with as-spun PAN and carbon nanofibers were fabricated and analyzed. The results showed good potential of continuous carbon nanofibers for nanocomposite and other applications.
INTRODUCTION Carbon nanofibers are attracting considerable attention due to their unique physical, mechanical, and chemical properties, including high Young’s modulus and strength, thermal and electrical conductivity, thermal stability, high specific surface area, and many others. They can be used for catalyst support in high temperature and/or corrosive environments, as conductive fillers in composites with electro-magnetic shielding capabilities, and to improve mechanical properties of composites [1]. Most commercially available carbon nanofibers are produced by vapor growth methods [2,3]. This production technique employs a catalyst in the gas phase transported into a heated reactor with a hydrocarbon gas. Pyrolysis of the hydrocarbon in the presence of the catalyst results in the formation of carbon filaments. While the filament lengthens by catalytic growth, non-catalytic chemical vapor deposition of carbon takes place from the hydrocarbon gas on the sides of the filament. Vapor grown carbon fibers (VGCF) have a number of disadvantages for composite applications. (1) They are entangled and disoriented and it is difficult to distribute them uniformly in volume or on surface. (2) Because the catalytic activity of the metal particle is buried in the growing tip of the filament, the filaments cannot grow very long. As a result, the VGCF are discontinuous. (3) Carbon black, tar, and other by-products are formed simultaneously with carbon filaments during pyrolysis of the hydrocarbon gas. As a result, one of the overriding barriers to widespread commercial use of VGCF is excessive cost of their purification. (4) VGCF have multi-wall hollow structure with poor interaction between the graphite layers. As a result, U5.4.1
the fibers can deform telescopically under tensile loading that can substantially reduce their reinforcing capacity. Recently, electrospinning has been shown capable of producing pol
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