ASTM D4616-95 (R2018) pdf free download.Standard Test Method forMicroscopical Analysis by Reflected Light and Determination of Mesophase in a Pitch.
1.1 This test method covers laboratory pr(x:edures for the preparation of granular and melted samples for microscopic analysis using reflected light to identify and estimate the amount and size of the mesophase.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
3. Terminology
3. 1 Definitions of Terms Specific to This Standard:
3. 1.1 cenosoheres—usually a minor component of coal tar pitch. They are formed by the rapid pyrolysis of unconfined coal particles that are carried over trorn the coke oven to the tar. Microscopically, they appear like hollow spheres or segments thereof (see Fig.1), and are typically sized from about 10 um to 500 um. In polarized light (crossed polarizers), a cenosphere may be optically active. The size of the anisotropic pattern or mosaic depends upon the rank of the coal carbonlied. Cenospheres are harder than the continuous phase and polish in relief (see Fig. I).
3.1.2 coke-oven-coke—usually a minor component of coal tar pitch. It originates in carry-over from the coke oven to the tar side. It difFers from cenospheres only in terms of its shape and porosity. Coke-oven-coke is angular and less porous.
3.1.3 isotropic phase—usually the j)redorniflaflt. and continuous, phase. It is a complex mixture of organic aromatic compounds composed mainly of carbon and hydrogen. At room temperature. the isotropic phase is a glass-like solid. It is optically inactive in polarized light (see Fig.1 and Fig. 2).
3. 1 .4 mesophase—an optically anisotropic liquid crystal carbonaceous phase that forms from the parent liquor when molecular size, shape. and distribution arc favorable. in the early stages of its development. mesophase usually appears as spheroids. The planar molecules are lined up equatorially as shown schematically in Fig. 3. This equatorial arrangement may be distinguished in crossed polarized light. Under crossed polarizers, the distinctive mesophase spheroids. with their complex extinction patterns shown in Fig. 2. can he readily seen.ASTM D4616 pdf download.