ASTM D4616-95(2008)
(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.
1.3 This 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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Designation:D4616 −95(Reapproved 2008)
Standard Test Method for
Microscopical Analysis by Reflected Light and
Determination of Mesophase in a Pitch
This standard is issued under the fixed designation D4616; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) 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 Thevaluesstatedininch-poundunitsaretoberegarded
cenospheremaybeopticallyactive.Thesizeoftheanisotropic
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 isotropic phase—usually the predominant, and
continuous, phase. It is a complex mixture of organic aromatic
2. Referenced Documents
compounds composed mainly of carbon and hydrogen. At
2.1 ASTM Standards:
room temperature, the isotropic phase is a glass-like solid. It is
D329Specification for Acetone
optically inactive in polarized light (see Fig. 1 and Fig. 2).
D1160TestMethodforDistillationofPetroleumProductsat
3.1.4 mesophase—an optically anisotropic liquid crystal
Reduced Pressure
carbonaceous phase that forms from the parent liquor when
D2318Test Method for Quinoline-Insoluble (QI) Content of
molecular size, shape, and distribution are favorable. In the
Tar and Pitch
early stages of its development, mesophase usually appears as
D3104Test Method for Softening Point of Pitches (Mettler
spheroids. The planar molecules are lined up equatorially as
Softening Point Method)
shown schematically in Fig. 3. This equatorial arrangement
D4296Practice for Sampling Pitch
may be distinguished in crossed polarized light. Under crossed
E11Specification forWovenWireTest Sieve Cloth andTest
polarizers, the distinctive mesophase spheroids, with their
Sieves
complex extinction patterns shown in Fig. 2, can be readily
E562Test Method for Determining Volume Fraction by
seen.
Systematic Manual Point Count
3.1.4.1 spheroids—Atmagnificationsof400×and500×,the
3. Terminology
minimumspheroidsizewhichcanberesolvedwithconfidence
is 4 µm in diameter. At magnifications of 1000 to 1800×, the
3.1 Definitions of Terms Specific to This Standard:
minimumspheroidsizethatcanberesolvedwithconfidenceis
about 2µm in diameter. Typically, the upper size may be 100
This test method is under the jurisdiction of ASTM Committee D02 on
µm. Mesophase spheroids are relatively soft and do not form
PetroleumProductsandLubricantsandisthedirectresponsibilityofSubcommittee
reliefstructures(seeFig.4).Quinolineinsolubleparticlesoften
D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.
aggregate at the interface between the continuous isotropic
Current edition approved Dec. 1, 2008. Published February 2009. Originally
approved in 1986. Last previous edition approved in 2005 as D4616–95(2005).
phase and mesophase.
DOI: 10.1520/D4616-95R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM AmorecompletediscussionwillbefoundinapaperbyHonda,H.,Kimura,H.,
Standards volume information, refer to the standard’s Document Summary page on andSanada,Y.,“ChangesofPleochroismandExtinctionContoursinCarbonaceous
the ASTM website. Mesophase ,” Carbon, 9, 1971, pp. 695–697.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4616−95 (2008)
FIG. 1 Photomicrographs of a Coal Tar Pitch at 500× Magnification in Polarized Light (Crossed Polarizers) and Bright Light Showing
the Isotropic Phase, Natural Quinoline Insolubles, and a Cenosphere.
FIG. 2 Photomicrographs of a Heat-Treated Coal Tar Pitch at 500× Magnification in Polarized Light (Crossed Polarizers) Showing Natu-
ral Quinoline Insolubles and Mesophase Spheroids
3.1.4.2 isotropicphase—Theisotropicphaseismoresoluble etching is achieved by soaking the polished surface in toluene
than the mesophase in solvents such as toluene. Solvent for a few seconds, rinsing the surface with cold flowing water,
D4616−95 (2008)
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
quinolineinsolubletestisnotnecessarilyatruemeasureofthe
solid constituents of pitch.
Normal QI with radial symmetry is produced by oxy-
cracking during the early portion of the coking cycle when
partially oxidizing conditions can exist, and is referred to as
combustion black (see Fig. 5a). Normal QI with concentric
symmetry is produced by thermal cracking later in the
cokingcycleunderreducingconditions,andisreferredtoas
thermal black (see Fig. 5b). These two symmetries can only
4,5
bedifferentiatedusingelectronmicroscopy. Thequinoline
insolubles content determined by Test Method D2318 is
sometimes greater than that anticipated on the basis of the
concentration of the quinoline insolubles during distillation
FIG. 3 Structure of Mesophase Spheroid
orheattreatmenttoproducethefinalpitch.Thedifferenceis
known as the “secondary” quinoline insolubles content, and
is traditionally regarded as the mesophase content. This
and drying in a current of hot air. Etching produces sharply
equivalence of secondary quinoline insolubles and mesoph-
defined mesophase spheroids (see Fig. 4).
ase is erroneous because the mesophase may be partially
3.1.5 mineral matter—formed when minute particles of the
soluble in quinoline.
cokeovenchargearecarriedoverintothecokeovencollecting
3.1.7 pyrolytic carbon—acarbonthatoriginatesasadeposit
main during the charging operation.The tiny coal particles are
on the upper walls, tunnel head, and standpipes of a coke oven
digested in the collecting main tar, resulting in a residue that is
due to thermal cracking. It is usually a minor phase in coal tar
rich in mineral matter. This mineral matter is identified under
pitch, highly variable in shape and porosity, and may be sized
bright field illumination by its high reflectivity, in the case of
up to 500 µm. It is usually optically active under crossed
pyrite, and its low reflectance in the case of clay, quartz, and
polarizers.Thefinesizeddomainsarecommonlyreferredtoas
carbonates. The association of mineral matter with insoluble
spherulitic, while the coarser anisotropic domains are called
organic matter from coal aids in its identification.
pyrolytic. Spherulitic and pyrolytic carbons are highly
3.1.6 normal quinoline insolubles—(sometimes termed
reflecting,relativelyhardmaterialsandstandoutinrelieffrom
“true,” natural or “primary” quinoline insolubles)—a carbon
the softer isotropic phase.
black-like solid phase in coal tar pitch that is produced by
3.1.8 reactorcoke—amaterialthatoriginatesonthewallsof
thermal cracking of organic compounds in the tunnel head
the pipestill reactor used in the distillation or heat treatment to
above the coal charge in a by-product coke oven. The indi-
produce pitch from either coal tars or petroleum oils. It is
vidual spherically-shaped particles are usually less than 2 µm
thermally more advanced than reactor mesophase. It is usually
in diameter. A typical coal tar pitch may contain from about
a minor component of pitch and may be sized up to 200 µm. It
1% to about 20% (by weight) of normal quinoline insolubles.
may be angular or rounded, and it may be relatively porous
The normal quinoline insolubles are relatively hard. They are
with a coarse appearance under crossed polarizers. It is
outlinedinbrightincidentlightbecausetheystandoutinrelief
distinguished from the reactor mesophase mentioned in 3.1.9
from the softer isotropic phase (see Fig. 1).
by its relative hardness, which causes it to show up in relief in
3.1.6.1 Discussion—SometimesthetermprimaryQIisused bright field illumination.
to describe all quinoline insoluble materials that are carried
3.1.9 reactor mesophase—a material that originates on the
overduringthecokingoperation(cenospheres,mineralmatter,
walls of the pipestill or reactor used in the distillation or heat
normal, QI, and so forth).
treatment to produce pitch from either coal tars or petroleum
3.1.6.2 normal quinoline insoluble material—Observed un-
oils.Itisusuallyaminorcomponentofpitchandmaybesized
der crossed polarizers, the normal quinoline insoluble material
up to 200 µm. It may be angular or rounded, and it may be
displays a Brewster cross pattern (see Fig. 1 and Fig. 2). This
relatively porous. Under crossed polarizers reactor mesophase
interference figure remains stationary when the specimen is
rotated through 360°. The onionskin arrangement can be
observedinparticleswithaminimumdiameterof2µmathigh
Bertau, B.L., and Souffrey, B., “Composition of Tar and Pitches as a Result of
magnification (1000 to 2000×) under cross polarizers.
theSpecificAspectsoftheCokingPlant,” Coke Making International,Vol2,1990,
pp.61–63.
3.1.6.3 Discussion—The quinoline insolubles content is de-
Lafdi, K., Bonnamy, S., and Oberlin, A., “TEM Studies of Coal Tars—Crude
termined by Test Method D2318 and represents the total Tar and its Insoluble Fractions,” Carbon, Vol 28, No. 1, 1990, pp. 57–63.
D4616−95 (2008)
FIG. 4 Photomicrographs of a Heat Treated Coal Tar Pitch at 500× Magnification in Bright Field Showing the Effectiveness of Etching
With Toluene to Accentuate the Interface Between Mesophase Spheroids and the Isotropic Phase
poured into a mold, or a representative crushed sample is
meltedandpouredintoamold.IftheMettlersofteningpointis
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,
sampleisgroundandpolishedtoaflatsurfaceforexamination
in reflected light.
4.2 The mesophase spheroid content of a representative
sampleisidentifiedandtheproportiondeterminedonavolume
basis by observing a statistically adequate number of points.
Only the area proportion is determined on a surface section of
a sample; however, the area and volume proportion are the
same when the components are randomly distributed through-
out the sample.
FIG. 5 The Structure of a Normal Quinoline Insoluble Particles
5. Significance and Use
has a coarse mosaic appearance. In contradistinction to the
5.1 Sometimes coal tar and petroleum pitches are heat
reactor coke mentioned in 3.1.8, reactor mesophase is com-
paratively soft and shows no relief in bright field illumination. treated thereby forming mesophase spheroids. The mesophase
may be partially soluble in quinoline and cannot be estimated
3.1.10 refractory—usually a minor component that origi-
by the quinoline insoluble test (Test Method D2318). This test
natesfromthecokeovenwalls,doors,andpatchesduetowear
method provides for the identification, quantitative estimation,
and degeneration; another component is charge hole sealant. It
and size determination of mesophase spheroids.
can be recognized under the microscope through optical
properties, hardness, shape, and associated minerals. 5.2 The mesophase initially forms as spheroids that may
coalesce to form a variety of asymmetrical shapes. The
4. Summary of Test Method
smallest mesophase particle that can be detected with certainty
4.1 Arepresentativesamplewithasofteningpointofatleast at 400× or 500× magnification is 4 µm in diameter; mesophase
212°F (100°C), as measured by Test Method D3104 (Mettler particles sizes less than 4 µm should be ignored. If mesophase
method), is crushed to a specific particle size and encapsulated material less than 4 µm in size is of interest, then magnifica-
in resin.Alternatively, a representative molten pitch sample is tions of 1000 to 1800× shall be used and the results should be
D4616−95 (2008)
appropriately identified. This method is limited to determining is used, incremental steps in one direction across the specimen
minor levels of mesophase, that is, ≤20% mesophase. may be actuated by the counter switches. One eyepiece of the
microscope should be fitted with a graticule or cross-hair. If
6. Apparatus
other than cross-hairs are used, the eyepiece disk shall contain
a Whipple graticule or one of such design that four or
6.1 Grinder, Pulverizer, or Mill , for crushing the represen-
twenty-five points are visible, lying at the corners of a square
tativesampleandmortarandpestleorotherequipmentsuitable
covering most of the field of view.
for reducing the particle size of a 100-g sample to less than 8
mesh (2.4 mm).
6.10 Sample Leveling Process—Aconventionalmanuallev-
eling device may be employed to level the polished specimens
6.2 Sieves—U. S. sieve No. 8. See Specification E11.
when they are mounted on microscope slides with clay for
6.3 Vacuum DistillationApparatus ,suchasthatspecifiedin
observations with an upright microscope.
Test Method D1160.
6.11 Counter—The counter shall be capable of recording
6.4 Vacuum Chamber, equipped with an observation win-
counts for two or more components.
dow.
6.5 Hotplate or Laboratory Oven , possibly fitted to receive
7. Reagents and Materials
inert gas.
8 ,10
7.1
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