Fabrication of Activated Carbon Fibers/Carbon Aerogels Composites by Gelation and Supercritical Drying in Isopropanol
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Bo Zheng and Jie Liu Department of Chemistry, Duke University, Durham, North Carolina 27708
Steve Weiss, Jackie Y. Ying, Mildred S. Dresselhaus,a) and Gene Dresselhaus Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
Joe H. Satcher, Jr. and Theodore F. Baumann Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (Received 5 April 2003; accepted 5 August 2003)
Activated carbon fiber/carbon aerogel (ACF/CA) composites were fabricated by gelling a mixture of ACF and resorcinol and furfural, followed by supercritical drying of the mixture in isopropanol. The product then went through carbonization in a nitrogen atmosphere. The fabrication conditions, such as the mass content of R–F, the content of the ACF added, and the gelation temperature, were explored. The textures and pore structures of the ACF/CA composites thus obtained were characterized using transmission electron microscopy, scanning electron microscopy, and a surface area analyzer. The mechanical properties of the samples were assessed primarily through compressive tests. The experimental results indicated that the added ACF disperses uniformly in the resulting ACF/CA composites. The carbon matrix of the ACF/CA composites also consisted of interconnected carbon nanoparticles with sizes in the range of 20 to 30 nm. The ACFs can reinforce the related carbon aerogels when they originally have low mass density and are weak in mechanical strength. When large amounts of ACF were added to the composites, the micropore area and micropore volume of the composites increased, but their external surface area decreased. The mesopore volumes and the related diameters and mesopore size distributions of the ACF/CA composites were mainly affected by the mass density of the composites. The micropore sizes of all the composites were sharply concentrated at about 0.5 nm.
I. INTRODUCTION
Generally, carbon aerogels are fabricated through the sol-gel polymerization of resorcinol with formaldehyde in aqueous solution, followed by exchanging with an organic solvent such as acetone, and then exchanging with liquid CO2 and drying under CO2 supercritical conditions, and finally carbonizing at elevated temperatures under a N2 atmosphere.1 Recently we developed a new fabrication method for carbon aerogels by synthesizing and supercritical drying an organic aerogel in isopropanol. Based on our previous studies,2 we have found that this polymerization system presents a very rapid a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 12, Dec 2003
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cross-linking speed, so that the gelation time is usually several minutes. Around the gel point, it takes only several seconds for the transition of the polymerization system from a liquid into a solid. The rapid consolidation of this new method allows us to synthesize a composite of activated carbon fiber (ACF) and organic aerogel, because the rapid consolidation wil
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