Polycrystalline coke

The coke formed on the alonized Incoloy 800 surface was amorphous, and it could be scraped from the surface rather easily. Amorphous coke, as defined here, is sometimes referred to as polycrystalline coke. Other examples of amorphous coke are shown in Figure 6. 

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

Fig. 38. Ratio of D, ujD as a function of the amount of coke deposited for three HZSM-5 specimens (crystal type, as shown in Fig. 42, with mean equivalent diameters of 8.5 /Am (A), 14 /im ( ), and 28 /iw (v) and an HZSM-5 polycrystalline grain (O cf. Fig. 43) (131-133).

The self-diffusivity of propane in the coked polycrystalline grains unveils details of coke formation in polycrystalline particles. Figure 44 shows that coking reduces the translational mobility inside the grains. The effect of intracrystalline coke deposition on the translational mobility of propane is indicated in Fig. 43. After a coking time of 1 h, only a slight increase of Di ,ra with increasing observation times occurs. After 12 h, a decrease is ob-... 

Fig. 44. Self-diffusivity of propane (10 CjHg per u.c., 293 K) as a function of the observation time t of self-difTiision for the polycrystalline grains shown in Fig. 43 after different coking times by n-hexane cracking (732) O, starting ZSM-5 Cl h, 3.6 wt% C , 12 h, 4.3 wt% C.

Figure 9 Self-diffusion coefficients of propane (loading ca 2.5 molecules per channel intersection) in polycrystalline grains of fresh H ZSM-5 and after 1 h (corresponding to 3.6 mass X coke) and 12 h (corresponding to 4.3 mass % coke) on n-hsxane stream for different observation times h at 296 K (Reproduced with permission from Ref. 33. Copyright 1987 Elsevier)...

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... 

Finally a number of EPR papers have been reported describing various surface aspects of Ti02, including the role of surface coke residues in Ti02 photocatalysis, single crystals of Ti02, porous Ti02, mixed polycrystalline... 

Nuclear graphite is an artihcially produced polycrystalline material with around 20% porosity [12]. The raw materials and manufacture route used to produce nuclear graphite are basically the same as those used to manufacture graphite electrodes and graphite components used in the electronic industry. The raw materials used are a graphitizable pitch or petroleum coke along with a pitch-based binder and pitch-based impregnating medium. 

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