ASTM D2797/D2797M-21a

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of the standard as published by ASTM is to be considered the official document.
Designation: D2797/D2797M − 21 D2797/D2797M − 21a
Standard Practice for
Preparing Coal Samples for Microscopical Analysis by
Reflected Light
This standard is issued under the fixed designation D2797/D2797M; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers laboratory procedures for the preparation of granular samples of bituminous coal and anthracite samples
for examination with a microscope using reflected light illumination. It does not apply to the preparation of oriented blocks of coal.
1.2 Units—The values stated in either SI units or non-SI units are to be regarded separately as standard. The values stated in each
system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D2013 Practice for Preparing Coal Samples for Analysis
D2234/D2234M Practice for Collection of a Gross Sample of Coal
D2798 Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal
D2799 Test Method for Microscopical Determination of the Maceral Composition of Coal
D4596 Practice for Collection of Channel Samples of Coal in a Mine
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
3. Summary of Practice
3.1 A representative sample is crushed to a specified particle size, air-dried, mixed with a binder, and formed into a briquet. The
briquet is then polished to a flat, scratch-free surface for examination by vertical illumination.
4. Significance and Use
4.1 Briquets of granular bituminous coals and anthracite prepared in accordance with the laboratory procedures of this practice
This practice is under the jurisdiction of ASTM Committee D05 on Coal and Coke and is the direct responsibility of Subcommittee D05.28 on Petrographic Analysis
of Coal and Coke.
Current edition approved May 15, 2021Sept. 1, 2021. Published May 2021September 2021. Originally approved in 1969. Last previous edition approved in 20202021 as
D2797/D2797M – 20a.D2797/D2797M – 21. DOI: 10.1520/D2797_D2797M-21.10.1520/D2797_D2797M-21A.
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 Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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D2797/D2797M − 21a
will have flat, scratch-free surfaces suitable for examination with a microscope using reflected light illumination. The polished
surfaces of briquettes prepared by this practice will contain particles representative of the original gross sample.
4.2 Samples prepared by this practice are used for microscopical determination of the reflectance of the organic components in
a polished specimen of coal (Test Method D2798) and for microscopical determination of the volume percent of physical
components of coal (Test Method D2799).
5. Apparatus
5.1 Grinder, Pulverizer, or Mill, for final crushing of the sample to pass a 850 μm [No. 20] U.S. Standard Sieve. Mortar and pestle
or other equipment suitable for reducing the particle size of a 250 g sample that already passes a 4.75 mm [No. 4] U.S. Standard
Sieve until all of it passes a 850 μm [No. 20] U.S. Standard Sieve (see 6.5).
5.2 Coarse Riffle Sampler—A riffle with at least twelve divisions of not less than 12.7 mm [ ⁄2 in.] and not greater than 19.1 mm
[ ⁄4 in.].
1 1
5.3 Fine Riffle Sampler—A riffle with at least twelve divisions of not less than 3.2 mm [ ⁄8 in.] and not greater than 6.4 mm [ ⁄4
in.].
5.4 Sieves—A 4.75 mm [No. 4] and a 850 μm [No. 20] U.S. Standard Sieve (Specification E11).
5.5 Molds—Containers to hold the coal binder mixture while the binder hardens.
5.5.1 The mold shall be capable of withstanding pressures up to 70 MPa [10 000 psi], and shall be made of separable parts so that
the briquet can be ejected after it has hardened.
5.5.2 The mold shall be large enough to provide a plane area of 4 cm or more on one side of the briquet. (Designs of suitable
25 mm [1 in.] and 32 mm [1 ⁄4 in.] inside-diameter molds are shown in Fig. 1.)
NOTE 1—Material: cold rolled or stainless steel. Dimensions a and b (inside diameters) are nominally 32 mm [1 ⁄4 in.] and 25 mm [1 in.]. If an
automatic polishing attachment is to be used, these dimensions should be specified to yield a briquet fitting snugly in the briquet holder.
FIG. 1 Molds Suitable for Briquetting Coal Samples
D2797/D2797M − 21a
5.6 Mounting Press—A manual or automated press that is capable of producing a pressure up to 35 MPa [5000 psi] on the briquet,
and has an attachment to eject the briquet after solidification of the binder. A heat-setting automated press shall be used with an
appropriate thermoset binder.
5.7 Grinding and Polishing Equipment—One or several laps on which the coal briquet can be ground and polished to a flat,
scratch-free surface. Laps may be made of aluminum, iron, brass, bronze, lead, glass, wax, or wood. Equipment that has 203 mm
[8 in.] diameter disk laps, gear-driven at 160 r ⁄min to 170 r ⁄min, and that has an automatic sample holder attachment is suitable.
For notes on grinding and polishing practices, see Appendix X1.
5.8 Sample Cleaner—Some equipment is essential for cleaning coal briquets between the different grinding or polishing stages.
This may be a simple stream of water or an air jet, but an ultrasonic cleaner is recommended.
5.9 Containers—If samples are to be transported or stored before briquets are prepared, glass jars, bottles, or metal cans having
tight-fitting closures shall be used. Metal cans shall have plastic liners.
6. Materials
6.1 Binder—Any binding material fulfilling the following requirements may be used for preparing the coal briquet:
6.1.1 The binder shall hold all coal particles securely during grinding, polishing, and observing the sample.
6.1.2 The binder and the hardening process used shall not react with the coal or the atmosphere or expose the coal to thermal
oxidation.
6.1.3 Under the microscope, the binder shall contrast markedly with constituents being measured when immersed in oil having
an index of refraction of about 1.518.
6.1.4 The binder shall be such that a substantially flat and scratch-free surface can be obtained as a result of the grinding and
polishing procedure.
6.1.4.1 Relief, or difference in level, particularly between the coal and the binder, is undesirable for reflectance determination.
Although relief depends to a great extent on the polishing technique, use of a binder with a hardness comparable to that of the coal
is very helpful.
6.1.4.2 Various types of epoxy resins and heat-setting powders are suitable as a binder.
6.2 Release Agent—Any preparation that does not damage the molds or adversely affect the coal or mounting medium may be used
to coat the inside of the mold and facilitate ejection of the briquet.
6.3 Grinding Abrasives—Water-resistant, adhesive-backed or magnetic-backed silicon carbide papers of grit Nos. 240, 320, 400,
and 600. coarse grit. Two or three of these are used according to a plan such as one of those listed in Table 1.
TABLE 1 Suggested Abrasive Sequences for Polishing of Briquets
Grinding with Silicon Carbide Paper Polishing with Alumina on Fabric Support
Step Coarse Intermediate Fine Fine Fine Fine
-6 -6
1 53.5 μm 23.6 μm 16 μm 3 μm [118.11 * 10 in.] 0.05 μm [1.968 x 10 in.] on -
[240 grit] [400 grit] [600 grit] on non-woven napless one or two layers of silk
textile cloth over chemotextile
-6 -6
2 23.6 μm 16 μm - 3 μm [118.11 * 10 in.] 0.05 μm [1.968 x 10 in.] on -
[400 grit] [600 grit] on chemotextile silk cloth alone or over
chemotextile
-6 -6
3 53.5 μm 23.6 μm - 3 μm [118.11 * 10 in.] 0.05 μm [1.968 x 10 in.] on -
[240 grit] [400 grit] on chemotextile cotton cloth over
chemotextile
-6 -6 -6
4 23.6 μm 16 μm - 1 μm [39.37 * 10 in.] 0.3 μm [11.8 x 10 in.] on 0.05 μm [1.968 x 10 in.] on
[400 grit] [600 grit] on two layers of cotton three layers of cotton silk cloth over two layers of
cloth cloth cotton cloth
D2797/D2797M − 21a
6.4 Polishing Abrasives—Aluminum oxide powders of 3 μm, 1 μm, 0.3 μm, and 0.05 μm decreasing sizes. Two or three of these
are used according to a plan such as one of those listed in Table 1.
6.5 Lap Coverings—Nap-free cloths of cotton and silk, and chemotextile material backed with water-resistant adhesive.
6.6 Detergent—Any nonoxidizing detergent may be used for cleaning briquets after each grinding or polishing stage.
7. Sampling
7.1 Obtain samples of coal in accordance w
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