Optical texture mosaics

Figure 3. Optical micrograph of a coke surface showing an optical texture of fine-grained mosaics <1.5 ym diameter, OTI = 1.

System B pyrolysis of coal-pitch blend with good modification of coal by pitch to give coke with coarse-grained mosaics, <10 pm diameter System C pyrolysis of pitch to give coke with optical texture of domains >60 pm diameter, (See Ref, 44). 

Chemical Modifications to Pitch. The earlier attempts to improve the commercial value of pitch residues must have been essentially exploratory research. Sanada et al, (71) in 1973 methylated the hydroxyl groups of 3,5-dimethyl phenol formaldehyde resin and noted, on carbonization, the formation of spheres of mesophase, the original resin giving an optical texture of mosaics in resultant carbons. Mochida et al. (72) carbonized naphthalene, anthracene and pyrene with aluminium chloride, sodium and potassium and examined the structure of the resultant carbons by optical microscopy and high resolution, fringe-imaging transmission electron microscopy (TEM),... 

Miyazawa et al. (92) related rates of decrease of aliphatic hydrogen protons during pyrolysis of ethylene tar pitch to formation of mesophase. Yokono et al, (93) used the model compound anthracene to monitor the availability of transferable hydrogen. Co-carboniza-tions of pitches with anthracene suggested that extents of formation of 9,10-dihydroanthracene could be correlated with size of optical texture. The method was then applied to the carbonization behaviour of hydrogenated ethylene tar pitch (94). This pitch, hydrogenated at 573 K, had a pronounced proton donor ability and produced, on carbonization, a coke of flow-type anisotropy compared with the coarse-grained mosaics (<10 ym dia) of coke from untreated pitch. 

Obara et al. (95) co-carbonized a petroleum pitch which gave a coke of mosaic size of optical texture with the strong Lewis acid catalyst, aluminium chloride,which promoted the size of the optical texture and extents of hydrogen transfer to added anthracene. A correlation was established between size of optical texture of the resultant cokes and extents of formation of 9,10-dihydroanthracene plus evolved hydrogen gas. 

Under the polarized optical microscope, the liquid crystal films show colorful patterns, i.e., the optical textures. Each liquid crystal phase shows its typical texture which provides the means to identify the phase of the liquid crystals. The typical textures are the Schlieren, threadlike, homeotropic, homogeneous, marble, finger-print, focal-conic, Dupin cyclide, fan-shape, sanded, mosaic, and so on. They are the integrations of many typical defects mentioned above. Demus Richter (1978) were the first to review... 

Fissure propagation through the pore wall material of coke is also dependent on the size and orientation of anisotropic components present fissures propagate easily through large optical textures (>60 ym) while mosaic textures (1 to 10 ym) tend to act as fissure stops. Experimental verification of this aspect of fissure generation and propagation will be discussed below ... 

Gasification and Heat Treatment. Examination under the optical microscope showed the Spencer works and Clyde Ironworks cokes to have optical textures mainly consisting of fine- and medium-grained mosaics with some coarse flow anisotropy and isotropic inert material. Of particular interest are the fissures which develop in different types of optical texture and those occurring at the anisotropic-inert interface. SEM examination of these polished surfaces before experimentation shows all of them to be flat and featureless. 

Figure 4 shows the same area examined by SEM after heat treatment. Once again, comparison shows fissures of the same size and orientation as the optical texture (predominantly medium-grained mosaics) to have developed (Position D ). These fissures appear... 

Differences in coke behaviour in the blast furnace (not detectable by cold testing prior to the charging of the blast furnace) may be attributable to differences in the mode of gasification of the coke as a result of combined effects of thermal and gasification fissuring. These results indicate that mosaic optical textures are preferable to flow anisotropy in terms of fissure containment and also show that inert particles can act as centres of fissure generation. 

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. 

Fourthly, A200 pitch when co-carbonized with high volatile caking coals (CR 601-701) almost completely modifies the isotropic texture of the coal coke to give an optical texture predominantly of medium-grained mosaics. Again, the optical texture is uniform rather than having two phases. 

Figure 3. Typical optical textures ofa lamellar phase (a) mosaic oily streaks, (b) Maltese crosses.

Figure 2.10. Optical micrograph of polished surfaces of an anisotropic carbon of small optical texture composed of mosaics, sizes of <5 p,m. The size of the image of the micrograph is 30 X 60 pm.

The optically anisotropic textures of mesophase from the samples heat-treated at the early stages of carbonization are classified into five types corresponding to isotropic, fine mosaic, coarse mosaic, fibrous, and domain. 

These different contrast mechanisms can all be used to reveal the scale of liquid crystalline polymer microstructures. In specimens that exhibit a mosaic texture, and in those that contain predominantly planar defects, domain size is easily defined in terms of areas that uniformly show extinction between crossed polars. However, if the defects are predominantly linear, as in specimens that exhibit schlieren textures, such simple characterization of microstructural scale is no longer possible. Here it is more convenient to look at the length of disclination line per unit volume, which is equivalent to the number of lines intersecting unit area, and analogous to the dislocation density as defined for crystalline solids. Good contrast is essential in order to obtain an accurate count. Technologically, microstructural scale is of growing interest because of its relevance to processability, mechanical properties and optical transparency. 

By studying paramorphotic patterns and the way that they appear in focal-conics, phase identification can be accomplished and information on mesophase structure can be obtained. However, the problems of phase identification are greatly cased when the focal-conic texture is accompanied by a homeotropically oriented texture. For example, the smectic A phase can exhibit the unbroken focal-conic and optically extinct homeotropic textures together, whereas the smectic C phase exhibits broken focal-conic and schlieren textures, and the E phase exhibits banded focal-conic and mosaic textures. Thus, the... 

Mosaics can be observed for a number of phases, for example, smectics F and hexatic B, and crystals B, E, G, J, K, and H, all exhibit mosaics of one form or another (see Figure 10). It is very difficult to identify these phases from their mosaic textures as they all look very similar. Two exceptions are worthy of note the E phase, because it is biaxial, has a very characteristic mosaic pattern where the domains tend to overlap to give a ghost-like appearance and the B phases, where the mosaic texture is often accompanied by a homeotropic texture that remains optically extinct on rotation of the microscope stage. Figure 11 shows a variety of mosaic textures where the molecules are either tilted or perpendicular with respect to the layer planes. 

Figure 8). The enthalpy and entropy changes associated with these transitions are summarized in Table 4. Presently we do not know the degree of crystallinity of these polyethers. However, the fact that the enthalpy and entropy changes of all transitions are larger than those of melting seems to indicate that the polyethers exhibit multiple smectic mesophases. Additional support for smectic type mesophases are provided by their high viscosity and by the optical polarizing micrographs which exhibit mosaic textures, typical of higher ordered smectic phases, or batonnets textures,...

The smectic G and H phases are three-dimensional monoclinic crystals whose molecules are tilted with respect to the layers. The Sq phase is more symmetric than the 5h phase since it has a face-centered lattice. Optically, three-dimensional phases often show the so-called mosaic textures. 

The blue phases BP I and BP II, which appear in a narrow temperature range between the cholesteric and isotropic phase, are not birefringent but optically active. In the transmitted light of a polarizing microscope they look like a blue isotropic liquid. Sometimes small single crystals of the blue phase with distinct habit are seen. The polycrystalline blue phase platelet texture resembles the mosaic texture of the smectic B phase. 

An opposed diamond anvil cell was used as a high pressure optical cell. For getting good textures a 0.1 mm thick gasket made of hardened steel was used. A Sm-N transition is identified by a change from the Schlieren to the focal conic texture with ellipses. The monotropic SmB phase shows a mosaic texture. 

---