Filler coke

In this context, a review is presented of the complex chain of events affecting anode performance, ranging from the properties of precursors for filler cokes and binder pitches, through production of these raw materials and their fabrication into anode carbon, and concluding with anode performance evaluation in full-size prebake and Soderberg cells of different designs. 

When pitch binder is pyrolyzed during the carbon bake operation, it is converted from an isotropic liquid, with no structural order, to a liquid-crystal (called mesophase) having a layered structure which is finally converted to layers of carbon atoms in a hexagonal lattice of graphite crystallites. These crystallites of binder coke become more disordered and crosslinked into a more-isotropic coke as the pitch QI content increases. Such moderately-isotropic coke, in contrast to highly-anisotropic microstructure (10), is preferred binder coke because it forms both physical and chemical bonds between filler coke particles which are stronger and more oxidation-resistant (8,9). 

Coke is produced when organic matter is heated to 400-600°C, essentially in the absence of air. The organic matter used for anode binder coke has come primarily from coal tar, with minor amounts from petroleum residues. In contrast, filler coke is produced almost entirely from petroleum, with minor amounts from coal-tar pitch. Also in recent years, solvent-refined coal (SRC) filler coke has been found to produce high quality anode carbon. 

Filler coke is formed by the same general mechanism as that already described for binder coke. However, the feedstocks used are various petroleum residual fractions, instead of coal tar. Temperatures of 400-500°C convert these resids into green coke within a day. A complex series of endothermic pyrolysis reactions produce liquid-crystal mesophase which is transformed to a carbon polymer of generally graphitic structure. However, there are varying amounts of... 

For example, with filler coke blends, maximum incompatibility has been found for blends of flaky, low-modulus, oxidation-resistant, anisotropic (ordered) delayed coke, and round, high-modulus, oxidation-sensitive, relatively-isotropic (disordered) fluid coke. 

In this case, anode carbon using such a filler-coke blend exhibited 15% higher carbon consumption than that carbon made with the anisotropic filler alone. 

Carbon mix is a mixture of filler coke, for example grains and/or powders of solid carbon materials, and a carbonaceous binder and selected additives, prepared in heated mixers at temperatures in the range of 410K-445K as a preliminary step for the formation of shaped green bodies. 

Filler coke is the main constituent of a carbon artifact, introduced as solid component (predominantly in the form of particulate carbon) into the carbon mix from which polygranular carbon and graphite materials are obtained by heat treatment. 

Filler coke is not necessarily the only, but it is commonly the most important filler material used in a carbon mix which consists 0/filler and binder. 

Fluid coke consists of spherulitic grains with a spherical layer structure and is generally less graphitizable than delayed coke. Therrfore, it is not suitable as filler coke for poly-granular graphite products and is also less suitable for polycrystalline carbon products. Due to its isotropy it is less suitable to produce an anisotropic synthetic graphite. All cokes contain a fraction of matter that can be released as volatiles during heat treatment. This mass fraction, the so-called volatile matter, is in the case fluid coke about 6 wt%. 

See coke, delayed coke, filler coke, polygranular graphite polycrystalline carbon, synthetic graphite... 

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