ASTM D2798-99(2004)
(Test Method)Standard Test Method for Microscopical Determination of the Reflectance of Vitrinite in a Polished Specimen of Coal
Standard Test Method for Microscopical Determination of the Reflectance of Vitrinite in a Polished Specimen of Coal
SCOPE
1.1 This test method covers the microscopical determination of both the mean maximum and mean random reflectances measured in oil of polished surfaces of vitrinite and other macerals present in coals ranging in rank from lignite to anthracite. This test method can be used to determine the reflectance of other macerals.
1.2 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: D 2798 – 99 (Reapproved 2004)
Standard Test Method for
Microscopical Determination of the Reflectance of Vitrinite
in a Polished Specimen of Coal
This standard is issued under the fixed designation D 2798; 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 in percent reflectance after calibration of photometric equip-
ment by measuring the reflected light from standards of
1.1 Thistestmethodcoversthemicroscopicaldetermination
reflectance as calculated from their refractive indices.
of both the mean maximum and mean random reflectances
measured in oil of polished surfaces of vitrinite and other
5. Significance and Use
macerals present in coals ranging in rank from lignite to
5.1 The mean maximum reflectance of the vitrinite compo-
anthracite. This test method can be used to determine the
nent in coal as determined by this test method is often used as
reflectance of other macerals.
an indicator of rank as presented in Classification D 388,
1.2 This standard does not purport to address all of the
independent of petrographic composition, and in the charac-
safety concerns, if any, associated with its use. It is the
terization of coal as feedstock for carbonization, gasification,
responsibility of the user of this standard to establish appro-
liquefaction, and combustion processes. If mean maximum
priate safety and health practices and determine the applica-
reflectance is used as a rank indicator, the types of vitrinites
bility of regulatory limitations prior to use.
measured shall be specified.
2. Referenced Documents 5.2 This test method is for use in scientific and industrial
research.
2.1 ASTM Standards:
D 121 Terminology of Coal and Coke
6. Apparatus
D 388 Classification of Coals by Rank
6.1 Microscope—Any microscope equipped for reflected
D 2797 Practice for Preparing Coal Samples for Micro-
light microscopy (such as a metallurgical or opaque-ore mi-
scopical Analysis by Reflected Light
croscope) can be used, provided the lens combination of
3. Terminology objective and eyepieces permits examination of the specimen
at a magnification between 400 and 3 750, such that particles
3.1 Definitions—For definitions of terms, refer to Terminol-
of 1 µm can be resolved.The objectives shall be constructed so
ogy D 121.
that samples can be examined in oil with plane-polarized light
3.2 Abbreviations:Abbreviations:
and have the highest quality of antireflection coatings. The
3.2.1 R —mean maximum reflectance measured in oil.
max
microscope shall be able to project an image at similar
3.2.2 R —mean random reflectance measured in oil.
m
magnification to a photomultiplier tube and to support the
4. Summary of Test Method
photomultiplier tube housing. Means shall be provided to
position the tube housing laterally to obtain maximum re-
4.1 Thereflectanceofthemaceralvitriniteorothermacerals
sponse. The microscope shall have a circular stage that is
is determined in this test method by illuminating a polished
capable of rotating a specimen through 360°. The mechanical
surface of a section of coal in immersion oil using a micro-
stage attached to the microscope stage shall enable the analyst
scopic system that photometrically measures the amount of
to move the specimen accurately (within 0.1 mm) to a given
light reflected from the surface. The reflected light is recorded
field location. A combination of objective and circular stage
shall permit centering. The viewing eyepiece shall be supplied
This test method is under the jurisdiction of ASTM Committee D05 on Coal
with a crosshair or grid to be used as a reference to locate
and Coke and is the direct responsibility of Subcommittee D05.28 on Petrographic
precisely the area sampled by the phototube. During measure-
Analysis of Coal and Coke.
ment, no light shall be permitted to enter the observer’s end of
Current edition approved Oct 1, 2004. Published October 2004. Originally
the viewing eyepiece.
approved in 1969. Last previous edition approved in 1999 as D 2798 – 99.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6.2 Polarizer and Illuminator—The light incident on the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
vertical illuminator of the microscope shall be plane-polarized
Standards volume information, refer to the standard’s Document Summary page on
by a prism or sheet polarizer. The vertical illuminator can
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2798 – 99 (2004)
contain a Berek prism, a Smith illuminator, or high-quality vitrinite studied; these also serve to check the linear response
glass plate. The polarizer shall be oriented at 45° when using a of the photometer. The reflectance of each standard shall be
Berek prism or at 0° when using a Smith illuminator or glass calculated to the nearest 0.001 % by means of the following
plate. equation:
2 2
R 5 100~n 2 1.5180! /~n 1 1.5180! (1)
NOTE 1—Photodiode arrays, channeltrons, or other light-measuring
s g g
devices are acceptable providing that sufficient gray levels obtainable will
where:
enable reliable differentiation of signal equivalent to 0.01 % reflectance
R = standard reflectance in oil of the glass, % and
and that the system is linear in the range of the reflectance measured.
s
n = refractive index of the glass at 546-nm wavelength, to
g
6.3 Photomultiplier Tube—In combination with the micro-
the nearest 0.0001 index value.
scope optical system, light source, and filter used, the photo-
NOTE 2—Most coal laboratories in North America use the following
multiplier photometer shall be capable of detecting the mini-
Bausch and Lomb Co. or Schott Co. optical glasses (the reported
mum light reflected from the limited portion of the coalsample
refractive index at 546 nm and the calculated standard reflectance in oil
(see 6.8).The high voltage supplied to the photomultiplier tube
are given in parentheses):
must be within the prescribed range to obtain linearity of
Bausch and Lomb Schott
response. This is usually from 300 to 1100 V for side-window
tubes and from 1000 to 1500 V for end-window tubes. 689 309 (1.6935; 0.299 %) SF8-689-312 (1.6945; 0.303 %)
751 278 (1.7566; 0.532 %) SF13-714-276 (1.7477; 0.496 %)
6.4 Photometer Amplifier—The signal from the photomul-
827 250 (1.8351; 0.895 %) LaF12-836-423 (1.8400; 0.921 %)
tipliertubeshallbeamplifiedanddisplayedbyagalvanometer,
850 324 (1.8543; 0.996 %) LaSF9-850-322 (1.8567; 1.009 %)
915 213 (1.9235; 1.390 %) LaSF18-913-325 (1.9273; 1.413 %)
digital meter, or recorder. When adjusted for operation, the
980 222 (1.9907; 1.817 %) LaSF6-961-249 (1.9670; 1.662 %)
amplifier and meter shall be capable of reliably distinguishing
Other standards available that can be used include the following:
differences in signal equivalent to 0.01 % reflectance and shall
Leucosapphire (1.77; 0.59 %)
be linear in the range of reflectance measured.
Yttrium aluminum garnet, YAG (1.84; 0.92 %)
6.5 Recorder or Meter—The recorder or meter used shall Gadolinium gallium garnet, 3G (1.98; 1.73 %)
Silicon carbide (2.663; 7.52 %)
have a response time at full scale of no more than1sto detect
6.10 Immersion Oil—The oil shall be a nondrying, noncor-
the maximum reflectance level during rotation of the micro-
rosive type that will not react with coal, does not contain
scope stage.
carcinogens, and has a refractive index within the range from
6.6 Light Source—The light source shall have a regulated
1.515 to 1.519 at 546 nm and 25°C.Within the specified range,
power supply to provide for stable output. Some photometers
the refractive index of the oil is not critical provided the
and recorders require supplemental voltage-stabilizing trans-
specified value of 1.5180 is used in calculating reflectance of
formers if the line voltage fluctuates.
standards as specified in 6.9. Periodic checking of the refrac-
6.7 Filters—The light shall be made approximately mono-
tive index of the oil is discretionary.
chromatic green by passage through an interference filter or
6.11 Sample-Leveling Press—Aconventional manual level-
combination of filters with peak transmittance of 546 65nm
ing device can be used to level sample briquettes and glass
and a half-peak transmittance bandwidth of less than 20 nm.
standards when they are mounted on microscope slides with
The filters can be inserted into the light path between the light
modeling clay.
source and photomultiplier tube at any convenient position in
the optical system.
7. Test Specimen
6.8 Limiting Aperture—A limiting aperture made of nonre-
flecting and opaque material shall be placed approximately in 7.1 PreparethesamplebriquetteinaccordancewithPractice
D 2797.
the focal plane of the eyepiece at its central axis to restrict light
to the photomultiplier tube window so that only a small area of 7.2 Place the sample briquettes in the desiccator at least 15
h before measuring the reflectance as stated in the Moisture
the reflectance standard or sample is sensed. The diameter of
Control section of Practice D 2797.
the aperture shall be selected to provide an effective field of
measurement (sensed spot) of about 5 µm diameter or about
8. Setting Up and Calibrating the Apparatus
20-µm area.
6.9 Calibration Standards—Prisms constructed of high- 8.1 Turn on the photometer and light source and allow
index glasses or synthetic minerals shall be used as standards equipment to warm up for at least ⁄2 h.
to calibrate the photometer for reflectance measurement.These 8.2 Mount the glass standards and a polished briquette
standardsmustbedurable,isotropic,resistanttocorrosion,free containing the sample on slides using modeling clay and a
from internal flaws or fractures, and have negligible light leveling press or use a leveling briquette holder.
absorption.Aprism with sides that form a 30-60-90° triangle is 8.3 Place the mounted briquette on the stage, apply immer-
the most effective shape, with the side between the 30 and 90° sionoil,andverifylevelingofthemountandstagebychecking
angles highly polished and used as the reflectance-measuring that there is no systematic focus change when the briquette is
surface. The prisms shall be enclosed, except for the polished moved laterally on the stage. Use Köhler illumination. To
surface, in a durable, lightabsorbent, water- and oil-resistant minimize glare, restrict the illuminated field by means of the
mount; polyester or epoxy resin, made light absorbent with a field diaphragm so that the diameter is about one third or less
dye or filler, serves adequately. It is desirable to have a number than the size of the full field.Adjust any other provisions of the
of different standards with reflectances near those of the illuminator to reduce scattered light in the system.
D 2798 – 99 (2004)
8.4 Verify the position of the limiting aperture of the briquettes will be sampled for the component being measured.
photometer with respect to the field of view. This can be done The transect spacing shall be suitable for a total of 100
by moving a small bright object of the sample across the measurements.
position of the crosshair or reticle that marks the photometer- 9.3 Using the procedure specified in 9.2, select the location
sensed spot, ascertaining that readings are highest when the tobemeasured.Slightadjustmentstothemaceralpositionmay
bright object is within the sensed area or by using back-lit be made to obtain a scratch-free area of uniform appearance.
illumination of the measuring aperture if so equipped. Rotate the circular stage slowly (approximately 4 r/min)
8.5 Using a small, distinctive feature of the sample as a through 360°. Reflectance will vary progressively from a
guide, adjust the microscope so that the axis of rotation of the maximum value to a minimum value as the stage is rotated.
stage is coincident with the photometer-sensed spot. This is Observeandrecordthemaximumvalue.Iftheeffectivefieldof
accomplished by adjusting the centering screws of the objec- measurement does not remain on the component being mea-
tive or stage. The purpose is to eliminate movement of the sured when the stage is rotated, then recenter the objective or
object grain or area from the sensed spot when the stage is stage as described in 8.5. Avoid taking measurements of areas
rotated. that are near highly reflecting grains such as pyrite. Because
8.6 Adjust the polarizer to a 45° position when using a some relief and nonplanarity may develop during polishing,
Berek prism or 0° when using a Smith illuminator or glass avoid edges of particles and particles near the edge of the
plate. Place a glass standard covered with clean immersion oil briquette.
on the microscope stage and focus on the polished surface. 9.4 Move the stage to the next area to be measured and
8.7 With no light reflected from the standard to the photo- repeat 9.3. Continue the location selecting and measuring
tube, adjust the photometer zero setting or dark current. Place procedure. After approximately ⁄2 h of operation, remove the
on the microscope stage a briquette of opaque resin that has a briquette and recheck the calibration of the glass standards. If
hole 5 mm in diameter and 5 mm deep which is filled with this value indicates a drift equivalent to more than 0.01 %
immersion oil. Measure the reflectance of the hole to ensure reflectance of the initial standard reflectance value, discard the
that a reflectance of 0.00 6 0.03 % is obtained thereby set of readings on the coal sample and rerun the measurements
ensuring that parasitic reflectances of the objective are mini- after recalibrating the system in accordance with 8.7.
mal.Ifthereflectanceoftheholeexceedsthestatedlimits,then 9.5 When determining the reflectance of vitrinite, continue
another objective having a higher quality antireflection coating the procedure until at least 100 measurements have been
shall be used. obtained. The number of measurements for any other maceral
8.8 Then allow the reflected light to impinge on the tube. will vary according to the application of the data.
Adjust the photometer amplifier or the illumination to obtain a 9.6 For blends that contain coals of different rank, 150
meter or recorder scale setting that conveniently represents the measurements are necessary to determine the mean maximum
calculated reflectance of the glass standard (seeAppendix X1). reflectance.
8.9 Without changing the settings, measure the reflectance
NOTE 4—Although the term “maximum reflectance” is used, the actua
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