Electrical Resistivity of Graphite Materials

Other new tables include the Melting Curve of Mercury, Enthalpy of Hydration of Gases, and Electrical Resistivity of Graphite Materials. Several other tables have been updated with recently reported data. 

Electrical Conductivity of Water, 5-72 Electrical Resistivity of Graphite Materials,... 

Electrically, graphite can be considered as a semi-metai, that is a conductor in the basal plane and an insulator normal to the basal plane. Its atomic structure is such that the highest-filled valence band overlaps the lowest-empty conduction band by approximately 36 meV and the delocalized fourth-valence electrons form a partially-filled conduction band between the basal planes where they can moved readily in a wave pattern as they respond to electric fields.P°l Consequently, the electrical resistivity of graphite parallel to the basal planes (ab directions) is low and the material is a relatively good conductor of electricity. 

As mentioned above, the electronic structure of graphite is anisotropic, and this anisotropy is reflected in the differing electrical resistance of the material perpendicular and parallel to the carbon layers. Further, as a result of this... 

Jilai Xue, Jun Zhu, and Yunxia Song, Electrical Resistance of Graphitic and Graphitized Cathode Materials at Elevated Temperatures, Light Metals, (2010), 829-834. 

The coke for synthetic graphite is also calcined before further processing. It is calcined until a sample of —35 + 100 mesh material shows an electrical resistivity of less than 0.05 ohm-inch. The same type of calciners are used that are used to calcine coke for the aluminum industry (29). The calcined coke retains a major portion of the sulfur present in the green petroleum coke (1). Low-sulfur, green coke is preferred. 

Table IX, Comparison of Electrical Resistivity of Desulco with Various Graphite Materials...

For metal or resin impregnated carbon.graphite materials, the extent of polymerization, cure cycles, and degradation can be assessed by measuring electrical resistance of the resin [lOlj. For example, the internal viscosity of a polymer can be determined by monitoring the electrical resistivity as a function of temperature. Electrical and electromagnetic properties of composites as well as NDT techniques are described next. 

This kind of ohmic resistance is associated with that of the bus bars, the conductors of electricity between the rectifier and the cell and between the cells themselves, and that of the electrodes. It is also important to avoid contact resistances. The resistances of electrode materials are varied for example, copper has a low resistivity of 1.7 x 10" ohm-m, titanium s is 46 X 10 ohm-m, and graphite s is 700 x 10 ohm-m. Voltage losses for all solid conductors can be estimated from Ohm s law. 

Graphitization increases the resistance of the material to thermal shock and chemical attack. It also increases its thermal and electrical conductivities. 

The electrical resistivity of the graphite crystal was reviewed in Ch. 3, Sec. 5. The crystal has a high degree of electrical anisotropy with resistivity that is low in the ab directions and high in the c direction. Molded graphites (even the isostatically molded material where the crystallites are essentially random) have higher resistivity than the singie-crystal in the ab directions, but can stiii be considered electrical conductors. 

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