Table I. Structural and electrical characteristics of graphite materials. most stable intercalation compounds. For all experiments, the metal chloride is intercalated in vapour phase at 7'>300 K in presence of chlorine gas (P~l to 5 atm). The kinetics are usually slow: the reaction lasts several days. In our investigation, we have used the following chemical dopants: CuCl2, A1C13, InCl3, GaCl3, FeCl3, SbCl5, CdCl2 and PdCl2. After intercalation the products are characterized by scanning electron microscopy, density determination on monofilaments (by a flotation method), Raman microprobe spectroscopy and X-ray diffraction. These methods combined with weight uptake measurements give the average composition and stage (number of carbon layers between two successive intercalated layers). 1. Electrical resistivity. The electrical resistivity was measured on monofilaments by a four-probe method. The main results are given in Table 3. Whereas the pristine fibres behave as semi-conductors, they become metallic after intercalation. The lowest resistivities are obtained with benzene-derived fibres. However, these fibres can be prepared only in small lengths (a few centimetres at most). Ex mesophase fibres from Union Carbide exhibit lower figures. Nevertheless the novel PX5 fibres give results very close to those of ex benzene fibres. Finally, the best intercalates investigated up to now are CuCl2, CdCl2 and PdCl2. To compare the conductivity increase observed in pyrographites [14] and in the different graphite fibres, we have plotted in Fig. 1 the conductivity enhancement factor at room temperature versus the electrical resistivity of the host material. We observe that this factor is scattered between 4 and 12 for pyrographites, depending upon the
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