The Electrical Conductivity of Carbons

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The electrical resistivity of carbons was measured by the potential drop methods. When car-bons were used as powdered form, the measurement of resistivity (ρ) depended strikingly upon the compressive pressure (p), and their relation was illustrated as follows; ρ=a/p+b The extrapolated values of resistivity (ρ∞= b) were classified to next groups by their linear extensions of layer planes of crystallites (a); graphite 0.029Ωcm., a > 400Å, acethylene black 0.077Ωcm., -40Å, pitch cokes (calcinated at-1100°C) 0.083Ωcm., -40 Å, pitch cokes 0.26Ωcm., -20 A, carbon black 0.32Ωcm., 20Å - 30Å, charcoal-103Ωcm., -10Å. and the resistivity of pitch is 107Ωcm. The activation energy (Δ∈) calculated from the temperature dependency of resistivity is very small, for example Δ∈ of carbon black is the order of 10-2- 10-3 eV. While some sorts of graphites (carbon brush) have shown transition from semi-conduction to metallic conduction at a certain temperature, ranged from 400°C to 500°C.
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