Electrical Properties of SbCl 5 , ICl, HNO 3 , and Br 2 Intercalated Pitch Based Carbon Fibers
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ELECTRICAL PROPERTIES OF SbCl 5 , ICI, HN03, INTERCALATED PITCH BASED CARBON FIBERS*
and Br
2
V. NATARAJAN AND JOHN A. WOOLLAM Department of Electrical Engineering, University of Nebraska, Lincoln, NE,
USA
ABSTRACT Highly graphitized pitch based carbon fibers with heat treatment temperatures (HTT) of 2500*C, and 3000C have been intercalated with SbC1 5 , ICI, H1103, and Br 2 . These were reacted either by themselves alone, or in double sequence (e.g. Br 2 followed by SbCl 5 ). The electrical resistivities of individual fibers were then measured in air, and as a function of temperature, to a series of temperatures, to test air and thermal stability. The lowest resistivity found in this sequence so far is 28 micro ohm cm when ICI intercalation was followed by HN0 3 reaction. These conductors are sometimes air stable (depending on intercalant) at room temperature and can be heated somewhat, but begin to deintercalate at much lower temperatures than was found for CuCI2 intercalated fibers [1,2]. In comparison with the CuCl2 reaction with pitch fibers, these intercalants react easily, and the sequential intercalations appear to give lower final resistivities.
INTRODUCTION For aerospace use the reciprocal product of resistivity times density is a relative figure of merit for comparing the usefulness of materials in competition with copper as a conductor. On this basis the resistitity of an intercalated fiber needs to be less than about 6 micro ohm cm. In addition, the final conductor needs to be air and thermally stable, or a simple inexpensive coating developed. In intercalated highly oriented pyrolytic graphite (HOPG), resistivities on the order of 2 micro ohm cm have been reached [3,4]. In intercalated fibers resistivities as low as 3 micro ohm cm have been reached in highly graphitized fibers [5], however these conductors are air reactive. For CuCl 2 intercalated fiber resistivities of 12.7 micro ohm cm were reached, and were air and 0 thermally stable up to 450 K. [1,2]. In the present paper we give results of intercalations by a series of chemical species either reacted individually or sequentially. PROPERTIES OF THE STARTING FIBERS AND INTERCALATION PROCEDURES Host fibers. The starting fibers were formed at Union Carbide by the pitch based process [6,71, but had graphitizing heat treatments above the temperatures normally used for commercial fibers. Thus our samples with heat treat0 0 ments of 2500 C, 2750 C, and 3000°C were made especially for scientific studies, includinq the work presented in this paper. They have Young's moduli of 92 x *Research supported by Grant NAG-3-95 from the NASA Lewis Research Center, Cleveland, Ohio.
Mat. Res. Soc. Symp. Proc. Vol.
20 (1983) @Elsevier Science Publishing Co.,
Inc.
46
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The starting resistivities averaged 390 106 PSI, and strength of 29x10 PSI. 0 0 micro ohm cm for 2500 C HTT, 225 micro ohm cm for 2750 C HTT, and 190 micro 0 ohm cm for 3000 C HTT. Higher HTT increases the graphitic order. Intercalation reactions. All of the species (SbCI 5, ICl, HNO , and B
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