Optical texture increase

This characteristic pattern is termed the optical texture of the coke Optical texture increases in size with increasing fluidity (decreasing plasticity) of the mesophase Mesophase viscosity can be affected by parameters of carbonization such as heating rate, HTT and soak time but the single most important factor is chemical reactivity (13) If reactivities are too high, early polymerisation leads to the formation of isotropic carbon because of randomly aligned interactions Low reactivities give rise to a low viscosity mesophase which flows and coalesces easily Hence the size and type of optical texture is predominantly a function of the parent material carbonized and may be used to characterise the coke It is therefore necessary to define precisely the different types of optical texture seen in cokes A standard... 

In situ X-ray examination of crystallizing polyethylene, at high temperature and pressure, then confirmed this proposal in detail, showing that the wide-angle diffraction pattern changed abruptly with the optical texture [ 10]. That corresponding to the spherulitic texture was of the usual orthorhombic form while the new intermediate phase had two-dimensional hexagonal symmetry, with an increased cross-sectional area per chain, but without... 

As the pyrolysis of model, polynuclear hydrocarbon compounds represents, possibly, the ultimate in ability to form the largest and most stable of mesophase molecules leading to the domains (Table 1) of optical texture in cokes, then smaller sizes of optical texture can be explained by processes which restrict or inhibit polymerization to larger molecule sizes. Conversely, it may be possible to increase the size of the optical texture of coke by suitable ameliorative treatments to a pitch. 

Pressure of Carbonization. The effect of a pressurized carbonization is to create a closed system preventing loss of volatile materials. Hence, carbon yields increase. Further, the material normally lost as volatiles in open systems is now retained and the effect of this, by reducing turbulence and bubble formation, is to enhance the size of resultant optical textures. Hiittinger and Rosenblatt (54) report such effects when gas pressures up to 15 MPa pressure (150 bar) were applied to the carbonization of a coal-tar pitch. If higher pressures are used, the pressure being applied hydraulically to the carbonization system, then the effect of pressures at, say, 300 MPa, is to enhance the viscosity of the total system and this prevents coalescence of the mesophase. The resultant appearance of the carbon has been described as botryoidal (55, 56) and an example is Figure 8. 

The review of Marsh and Walker (22) places emphasis upon the relationships between molecular structure and size of resultant optical texture. Certainly, the presence of reactive groups attached to aromatic nuclei, e.g. phenolic, carboxylic and the presence of heteroatoms, all lead to decreased size of optical texture, A principal conclusion of such studies is the difficulty of precise prediction of optical texture for a given carbonizing system. This is because it is difficult to quantify, precisely, for such many and diverse systems being carbonized, the critical balance which has to be maintained between the rate of carbonization, controlled by the reactivity of components of carbonizing systems (to increase the average size of constituent molecules), and the viscosity of the resultant pitch necessary for the movement and orientation of these... 

This influences the structural features of the mesophase which remains more disordered, a point made by Cranmer et al. (43). Stadelhofer (107) found that the presence of QI did not change rates of formation of mesophase. Romovacek et al. (108) consider that pyrolytic particles in pitch (primary QI) retard the development of mesophase and suppress coalescence. Decrease in size of optical texture, as brought about by mechanical modification as distinct from chemical modification of pitch properties can increase both the strength and reactivity to oxidising gases of the resultant coke, as recently put forward by Markovic et al. (109). ... 

Breeze Additives. Optical microscopy of the Six Bells (CR 301a), Cortonwood (CR 401) and Maltby (CR 502) cokes with the A170 pitch coke breeze additives shows that the breeze additives with predominantly flow domain anisotropy optical texture are easily distinguishable from the surrounding coal coke of predominantly fine-grained mosaics. The effect of carbonization to 1200 K upon the petroleum coke breeze is to increase progressively the number and size of fissures within the breeze particles. 

Thirdly, when A200 is blended with prime coking and medium volatile caking coals (CR 301-501) the resultant coke shows an increase in size of optical texture compared to that of the coal coke when carbonized singly. This new optical texture is intermediate in size between that of the coal coke and pitch coke. 

The widest columnar mesophase temperature ranges were obtained for the bis-[l,3-di-(substi-tuted-phenyl)-/3-diketonate] metal complexes bearing ten and twelve chains ((55) R = H or OC H2 +i). The ten-chain copper, palladium, and oxovanadium(IV) complexes ((55) M = Cu, Pd, VO R = H, = 6, 8, 10, 12, 14) were all mesomorphic and the enantiotropic mesophases were identified by optical texture and variable-temperature X-ray diffraction as columnar phases (Table 34). The copper and palladium complexes displayed a Coh phase for short chain length ( = 6, 8 for M = Cu = 6, 8, 10 for M = Pd), which transformed to a Coin phase as the chain length was increased. Surprisingly, no direct Cok-to-Colh phase transition was observed within the same compound, but weakly first-order Cok-to-Cok and Colh-to-Colh phase transitions were found for compounds with intermediate chain lengths. In contrast, the vanadyl complexes exhibited only one Coh mesophase. Infrared studies indicated that the VO complexes possessed a linear V=0—V=0 linear polymeric chain structure in the crystal phase, while no... 

In the substrate configuration the stainless steel carrier is coated with a Ag-ZnO bilayer in order to enhance the back reflection of the back contact see Figure 73 [11]. An increase in 7sc of about 50% was achieved by Banerjee and Guha [589] by using a textured Ag-ZnO bilayer, which further enhances the optical path length and consequently the absorption. As at this stage no [Pg.172]

---