Pitch-coke graphite

Pitch Coke. The manufacture of pitch coke provides a large toimage oudet for coke-oven pitch in Japan, the CIS and, until more recently, Germany (75,76). Pitch coke is used either alone or mixed with petroleum coke as the carbon component of electrodes, carbon bmshes, and shaped carbon and graphite articles. 

Graphitization. Graphitization is an electrical heat treatment of the product to ca 3000°C. The purpose of this step is to cause the carbon atoms in the petroleum coke filler and pitch coke binder to orient into the graphite lattice configuration. This ordering process produces graphite with intermetaHic properties that make it useful in many appHcations. 

Coke materials are generally made by heat-treatment of petroleum pitch or coal-tar pitch in an N2 atmosphere. Coke made from petroleum is called "petroleum coke" and that from coal is called "pitch coke". These materials have the closest-packed hexagonal structures. The crystallinity of coke materials is not so high as that of graphite. The crystallite size of coke along the c-axis (Lc) is small (about 10-20 A) and the interlayer distance (d value about 3.38-3.80 A) is large. 

A carbon rod is used as a current collector for the positive electrode in dry cells. It is made by heating an extruded mixture of carbon (petroleum coke, graphite) and pitch which serves as a binder. A heat treatment at temperatures of about 1100 °C is used to carbonize the pitch and to produce a solid structure with low resistance. For example, Takahashi [23] reported that heat treatment reduced the specific resistance from 1 Q cm to 3.6xlO"1Qcm and the density increased from 1.7 to 2.02 gem- 1. Fischer and Wissler [24] derived an experimental relationship [Eq. (1)] between the electrical conductivity, compaction pressure, and properties of graphite powder ... 

Cokes with binder pitches Polycrystalline graphite blocks Various densities, various degrees of orientation... 

The electrochemical production of aluminum utilizes pre-baked or Soderberg anodes. Pre-baked anodes are manufactured by mixing petroleum or pitch coke with around 20% of electrode binder (see Chapter 13.1.2), followed by molding, as is also usual for the production of graphite electrodes. The green electrodes are baked in a ring furnace at a temperature of 1200 °C. 

Figure 80a-c. Graphite found among various filler materials, unetched, POL. (a) natural graphite, (b) graphite from petroleum coke, (c) Graphite from pitch coke. Pores are dark in the images. 

The mechanism of graphitization of pyrolytic graphite is essentially the same as that of pitch coke, described in Ch. 4, Sec. 3.3.f l... 

Not all carbon materials are suitable for the solvent-catalyst transformation. For instance, while graphitized pitch cokes form diamond readily, no transformation is observed with turbostratic carbon.i °i... 

Coal-derived pitch coke, although it exhibits a pre-graphitic microstructure, has often a lower graphitizability than petroleum coke. Fractions of coal tar pitches (obtained by extraction or filtration) may form cokes with needle-like structures and have an improved graphitizability. The usually lower grcg>hitizability compared to petroleum coke is due to an inhibition ofmesophase growth because of chemical and physical differences of the cokes. See coal tar pitches, coke, petroleum coke... 

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