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A STUDY OF ThE ELECTRICAL AND MECHANICAL PROPERTIES OF ALKALI METAL INTERCALATED GRAPHITE FIBERS D.D. DOMINGUEZ, I.L. LAKSHMANAN, E.F. BARBANO, AND I.S. MURDAY Code 6170, Naval Research Laboratory, Washington, D.C. 20375, USA.

ABSTRACT Individual graphite fibers (TP 4104B and GY-70) were intercalated with alkali metals using the two-zone vapor transport method commonly used to prepare alkali metal intercalated graphite. The progress of the reaction was followed in situ by measuring the electrical resistances of the fibers as the temperature difference (AT) between the fiber and the metal was decreased stepwise. These measurements showed that the ease and extent of intercalation are related to fiber graphitization. Without exposure to air, the temperature dependence of the resistances of the intercalated fibers were also measured from -196°C to 400°C. The measurements showed that the intercalated fibers have a metallic dependence on temperature. Tensile strength measurements on the intercalated fibers showed that intercalation of the heavy alkali metals is deleterious.

INTRODUCTION Although intercalation has been known to increase the a-axis conductivity of graphite for more than 50 years, it has only been studied as a means of improving the conductivity of carbon fibers for the past 15 years. These investigations have dealt with many different fibers and intercalants. As a result, it is difficult to predict the extent to which a given fiber conductivity can be improved by intercalation. Questions about the mechanism(s) of electrical conductivity in fibers remain unanswered. Conclusions regarding the effect of intercalation on fiber mechanical properties are not clear. In an attempt to answer some of these questions, we have undertaken a systematic study of two highly graphitized carbon fibers to see how intercalation affects their electrical and mechanical properties. In this paper we will examine potassium and cesium intercalation of these fibers and see how the intercalation of these alkali metals will alter the conductivity of the fibers, their temperature dependence, and their tensile strengths. EXPERIMENTAL The two highly graphitized carbon fibers chosen for this study are TP 4104B, a pitch-based fiber (Union Carbide, specific resistivity ca. 200gf cm, Young's modulus 100 million psi) and Celion GY-70, a polyacrylonitrile (PAN) - based fiber (Celanese Corporation, specific resistivity ca. 5000 cm, Young's modulus 77 million psi). Prior to use, the surfaces of these fibers were prepared by heating the fiber bundles in air at ca. 4000C for one minute. Resistance Measurements A single fiber was prepared for in situ resistance measurements by attaching the fiber by silver conductive paint to platinum wires wound around a

Hat.

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20 (1983)D QElsevier Science Publishing Co.,

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64 The substrate was inserted into a pyrex tube and the ceramic substrate. platinum wires were spot-welded to nickel wires extending through the glass Freshly distilled alkali metal was then introduced at