ASTM D4616-95(2005)
(Test Method)Standard Test Method for Microscopical Analysis by Reflected Light and Determination of Mesophase in a Pitch
Standard Test Method for Microscopical Analysis by Reflected Light and Determination of Mesophase in a Pitch
SIGNIFICANCE AND USE
Sometimes coal tar and petroleum pitches are heat treated thereby forming mesophase spheroids. The mesophase may be partially soluble in quinoline and cannot be estimated by the quinoline insoluble test (Test Method D 2318). This test method provides for the identification, quantitative estimation, and size determination of mesophase spheroids.
The mesophase initially forms as spheroids that may coalesce to form a variety of asymmetrical shapes. The smallest mesophase particle that can be detected with certainty at 400× or 500× magnification is 4 μm in diameter; mesophase particles sizes less than 4 μm should be ignored. If mesophase material less than 4 μm in size is of interest, then magnifications of 1000 to 1800× shall be used and the results should be appropriately identified. This method is limited to determining minor levels of mesophase, that is, ≤20 % mesophase.
SCOPE
1.1 This test method covers laboratory procedures 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.
1.3This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation: D 4616 – 95 (Reapproved 2005)
Standard Test Method for
Microscopical Analysis by Reflected Light and
Determination of Mesophase in a Pitch
This standard is issued under the fixed designation D 4616; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 cenospheres—usually a minor component of coal tar
pitch. They are formed by the rapid pyrolysis of unconfined
1.1 This test method covers laboratory procedures for the
coal particles that are carried over from the coke oven to the
preparation of granular and melted samples for microscopic
tar. Microscopically, they appear like hollow spheres or seg-
analysis using reflected light to identify and estimate the
ments thereof (see Fig. 1), and are typically sized from about
amount and size of the mesophase.
10 to 500 µm. In polarized light (crossed polarizers), a
1.2 The values stated in inch-pound units are to be regarded
cenosphere may be optically active.The size of the anisotropic
as standard. The values given in parentheses are mathematical
pattern or mosaic depends upon the rank of the coal carbon-
conversions to SI units that are provided for information only
ized. Cenospheres are harder than the continuous phase and
and are not considered standard.
polish in relief (see Fig. 1).
1.3 This standard does not purport to address all of the
3.1.2 coke-oven-coke—usually a minor component of coal
safety concerns, if any, associated with its use. It is the
tar pitch. It originates in carry-over from the coke oven to the
responsibility of the user of this standard to establish appro-
tar side. It differs from cenospheres only in terms of its shape
priate safety and health practices and determine the applica-
and porosity. Coke-oven-coke is angular and less porous.
bility of regulatory limitations prior to use.
3.1.3 mineral matter—formed when minute particles of the
2. Referenced Documents cokeovenchargearecarriedoverintothecokeovencollecting
main during the charging operation. The tiny coal particles are
2.1 ASTM Standards:
digested in the collecting main tar, resulting in a residue that is
D 329 Specification for Acetone
rich in mineral matter. This mineral matter is identified under
D 1160 Test Method for Distillation of Petroleum Products
bright field illumination by its high reflectivity, in the case of
at Reduced Pressures
pyrite, and its low reflectance in the case of clay, quartz, and
D 2318 Test Method for Quinoline-Insoluble (QI) Content
carbonates. The association of mineral matter with insoluble
of Tar and Pitch
organic matter from coal aids in its identification.
D 3104 Test Method for Softening Point of Pitches (Mettler
3.1.4 refractory—usuallyaminorcomponentthatoriginates
Softening Point Method)
from the coke oven walls, doors, and patches due to wear and
D 4296 Practice for Sampling Pitch
degeneration; another component is charge hole sealant. It can
E11 Specification for Wire-Cloth Sieves for Testing Pur-
berecognizedunderthemicroscopethroughopticalproperties,
poses
hardness, shape, and associated minerals.
E 562 Test Method for Determining Volume Fraction by
3.1.5 isotropic phase—usually the predominant, and con-
Systematic Manual Point Count
tinuous, phase. It is a complex mixture of organic aromatic
3. Terminology
compounds composed mainly of carbon and hydrogen. At
room temperature, the isotropic phase is a glass-like solid. It is
3.1 Definitions of Terms Specific to This Standard:
optically inactive in polarized light (see Fig. 1 and Fig. 2).
3.1.6 mesophase—an optically anisotropic liquid crystal
This test method is under the jurisdiction of ASTM Committee D02 on
carbonaceous phase that forms from the parent liquor when
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
molecular size, shape, and distribution are favorable. In the
D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.
early stages of its development, mesophase usually appears as
Current edition approved May 1, 2005. Published May 2005. Originally
approved in 1986. Last previous edition approved in 2000 as D 4616 – 95 (2000).
spheroids. The planar molecules are lined up equatorially as
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
shown schematically in Fig. 3. This equatorial arrangement
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
may be distinguished in crossed polarized light. Under crossed
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4616 – 95 (2005)
The normal quinoline insolubles are relatively hard. They are
outlined in bright incident light because they stand out in relief
from the softer isotropic phase (see Fig. 1).
NOTE 1—Sometimes the term primary QI is used to describe all
quinoline insoluble materials that are carried over during the coking
operation (cenospheres, mineral matter, normal, QI, and so forth).
3.1.7.1 Observed under crossed polarizers, the normal
quinoline insoluble material displays a Brewster cross pattern
(see Fig. 1 and Fig. 2). This interference figure remains
stationary when the specimen is rotated through 360°. The
onionskin arrangement can be observed in particles with a
minimum diameter of 2 µm at high magnification (1000 to
20003) under cross polarizers.
NOTE 2—The quinoline insolubles content is determined by Test
Method D 2318 and represents the total amount of natural quinoline
insolubles, cenospheres, coke-oven-coke, pyrolytic carbon, refractory,
reactor coke, and free ash in a pitch.Additionally, the quinoline insolubles
will contain any insoluble species from the isotropic phase and the
insoluble portion of the mesophase. Hence, the quinoline soluble fraction
is composed of the bulk of the isotropic phase and the soluble fraction of
the mesophase. However, the quinoline insoluble test is not necessarily a
true measure of the solid constituents of pitch.
NormalQIwithradialsymmetryisproducedbyoxycracking
during the early portion of the coking cycle when partially
FIG. 1 Photomicrographs of a Coal Tar Pitch at 5003
oxidizing conditions can exist, and is referred to as combustion
Magnification in Polarized Light (Crossed Polarizers) and Bright
black (see Fig. 5a). Normal QI with concentric symmetry is
Light Showing the Isotropic Phase, Natural Quinoline Insolubles,
and a Cenosphere.
produced by thermal cracking later in the coking cycle under
reducing conditions, and is referred to as thermal black (see
Fig. 5b). These two symmetries can only be differentiated
polarizers, the distinctive mesophase spheroids, with their
4,5
using electron microscopy. The quinoline insolubles content
complex extinction patterns shown in Fig. 2, can be readily
determined by Test Method D 2318 is sometimes greater than
seen.
that anticipated on the basis of the concentration of the
3.1.6.1 At magnifications of 4003 and 5003, the minimum
quinoline insolubles during distillation or heat treatment to
spheroid size which can be resolved with confidence is 4 µm in
produce the final pitch. The difference is known as the
diameter. At magnifications of 1000 to 18003, the minimum
“secondary” quinoline insolubles content, and is traditionally
spheroid size that can be resolved with confidence is about 2
regarded as the mesophase content. This equivalence of sec-
µm in diameter. Typically, the upper size may be 100 µm.
ondary quinoline insolubles and mesophase is erroneous be-
Mesophase spheroids are relatively soft and do not form relief
cause the mesophase may be partially soluble in quinoline.
structures (see Fig. 4). Quinoline insoluble particles often
3.1.8 pyrolytic carbon—acarbonthatoriginatesasadeposit
aggregate at the interface between the continuous isotropic
on the upper walls, tunnel head, and standpipes of a coke oven
phase and mesophase.
due to thermal cracking. It is usually a minor phase in coal tar
3.1.6.2 The isotropic phase is more soluble than the me-
pitch, highly variable in shape and porosity, and may be sized
sophase in solvents such as toluene. Solvent etching is
up to 500 µm. It is usually optically active under crossed
achieved by soaking the polished surface in toluene for a few
polarizers.The fine sized domains are commonly referred to as
seconds, rinsing the surface with cold flowing water, and
spherulitic, while the coarser anisotropic domains are called
drying in a current of hot air. Etching produces sharply defined
pyrolytic. Spherulitic and pyrolytic carbons are highly reflect-
mesophase spheroids (see Fig. 4).
ing, relatively hard materials and stand out in relief from the
3.1.7 normal quinoline insolubles (sometimes termed
softer isotropic phase.
“true,” natural or “primary” quinoline insolubles)—a carbon
3.1.9 reactor coke—a material that originates on the walls
black-like solid phase in coal tar pitch that is produced by
of the pipestill reactor used in the distillation or heat treatment
thermal cracking of organic compounds in the tunnel head
to produce pitch from either coal tars or petroleum oils. It is
above the coal charge in a by-product coke oven. The indi-
thermally more advanced than reactor mesophase. It is usually
vidual spherically-shaped particles are usually less than 2 µm
in diameter. A typical coal tar pitch may contain from about
1 % to about 20 % (by weight) of normal quinoline insolubles.
Bertau, B.L., and Souffrey, B., “Composition of Tar and Pitches as a Result of
the SpecificAspects of the Coking Plant,” Coke Making International, Vol 2, 1990,
AmorecompletediscussionwillbefoundinapaperbyHonda,H.,Kimura,H., pp. 61–63.
and Sanada,Y., “Changes of Pleochroism and Extinction Contours in Carbonaceous Lafdi, K., Bonnamy, S., and Oberlin, A., “TEM Studies of Coal Tars—Crude
Mesophase,” CARBON, 9, 1971, pp 695–697. Tar and its Insoluble Fractions,” Carbon, Vol 28, No. 1, 1990, pp. 57–63.
D 4616 – 95 (2005)
FIG. 2 Photomicrographs of a Heat-Treated Coal Tar Pitch at 5003 Magnification in Polarized Light
(Crossed Polarizers) Showing Natural Quinoline Insolubles and Mesophase Spheroids
3.1.10 reactor mesophase—a material that originates on the
walls of the pipestill or reactor used in the distillation or heat
treatment to produce pitch from either coal tars or petroleum
oils. It is usually a minor component of pitch and may be sized
up to 200 µm. It may be angular or rounded, and it may be
relatively porous. Under crossed polarizers reactor mesophase
has a coarse mosaic appearance. In contradistinction to the
reactor coke mentioned in 3.8, reactor mesophase is compara-
tively soft and shows no relief in bright field illumination.
4. Summary of Test Method
4.1 Arepresentativesamplewithasofteningpointofatleast
212°F (100°C), as measured by Test Method D 3104 (Mettler
method), is crushed to a specific particle size and encapsulated
in resin. Alternatively, a representative molten pitch sample is
poured into a mold, or a representative crushed sample is
melted and poured into a mold. If the Mettler softening point is
less than 212°F (100°C), it is raised to 212 to 248°F (100 to
120°C) by vacuum distillation. The encapsulated, or molded,
FIG. 3 Structure of Mesophase Spheroid
sample is ground and polished to a flat surface for examination
in reflected light.
4.2 The mesophase spheroid content of a representative
a minor component of pitch and may be sized up to 200 µm. It
sampleisidentifiedandtheproportiondeterminedonavolume
may be angular or rounded, and it may be relatively porous
basis by observing a statistically adequate number of points.
with a coarse appearance under crossed polarizers. It is
Only the area proportion is determined on a surface section of
distinguished from the reactor mesophase mentioned in 3.1.10 a sample; however, the area and volume proportion are the
by its relative hardness, which causes it to show up in relief in
same when the components are randomly distributed through-
bright field illumination. out the sample.
D 4616 – 95 (2005)
FIG. 4 Photomicrographs of a Heat Treated Coal Tar Pitch at 5003 Magnification in Bright Field Showing the Effectiveness of Etching
With Toluene to Accentuate the Interface Between Mesophase Spheroids and the Isotropic Phase
should be appropriately identified. This method is limited to
determining minor levels of mesophase, that is,#20 % me-
sophase.
6. Apparatus
6.1 Grinder, Pulverizer, or Mill, for crushing the represen-
tativesampleandmortarandpestleorotherequipmentsuitable
for reducing the particle size of a 100-g sample to less than 8
mesh (2.4 mm).
6.2 Sieves—U. S. sieve No. 8. See SpecificationE11.
6.3 Vacuum Distillation Apparatus, such as that specified in
Test Method D 1160.
6.4 Vacuum Chamber, equipped with an observation win-
FIG. 5 The Structure of a Normal Quinoline Insoluble Particles
dow.
6.5 Hotplate or Laboratory Oven, possibly fitted to receive
5. Significance and Use
inert gas.
5.1 Sometimes coal tar and petroleum pitches are heat
6.6 Bakelite Rings , 1 in. (25 mm) or 1 ⁄4 in. (32 mm) in
treated thereby forming mesophase spheroids. The mesophase
diameter.
may be partially soluble in quinoline and cannot be estimated
by the quinoline insoluble test (Test Method D 2318). This test
method provides for the identification, quantitative estimation,
Bakelite, a trademark of the Union Carbide Corporation, Old Ridgebury Road,
and size determination of mesophase spheroids. Danbury, CT, 06817, has been found satisfactory for this purpose. If you are aware
of alternative suppliers, please provide this information to ASTM International
5.2 The mesophase initially forms as spheroids that may
Headquarters.Your comments will receive careful consideration at a meeting of the
coalesce to form a variety of asymmetrical shapes. The
responsible technical committee , which you may attend.
smallest mesophase particle that can be detected with certainty
Rings supplied by Buehler Ltd., 41 Waukegan Road, Lake Bluff, IL, and Leco
Corporation, 3000 Lakeview Ave., St. Joseph, MI, 49085, have been found
at 4003 or 5003 magnification is 4 µm in diameter; me-
satisfactoryforthispurpose.Ifyouareawareofalternativesuppliers,pleaseprovide
sophase particles sizes less than 4 µm should be ignored. If
this information to ASTM International Headquarters. Your comments will receive
mesophase material le
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