1、Designation: D2798 11aStandard Test Method forMicroscopical Determination of the Vitrinite Reflectance ofCoal1This standard is issued under the fixed designation D2798; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the microscopical determinationof both the mean maximum and mean random reflectancesmeasured in
3、oil of polished surfaces of vitrinite and othermacerals present in coals ranging in rank from lignite toanthracite. This test method can be used to determine thereflectance of other macerals.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included i
4、n thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
5、2. Referenced Documents2.1 ASTM Standards:2D121 Terminology of Coal and CokeD388 Classification of Coals by RankD2797 Practice for Preparing Coal Samples for Microscopi-cal Analysis by Reflected Light3. Terminology3.1 DefinitionsFor definitions of terms, refer to Terminol-ogy D121.3.2 Abbreviations:
6、3.2.1 Romaxmean maximum reflectance measured in oil.3.2.2 Roranmean random reflectance measured in oil.3.2.2.1 DiscussionOther organizations may use other ab-breviations for mean maximum and mean random reflectance.4. Summary of Test Method4.1 The reflectance of the maceral vitrinite or other macera
7、lsis determined in this test method by illuminating a polishedsurface of a section of coal in immersion oil using a micro-scopic system that photometrically measures the amount oflight reflected from the surface. The reflected light is recordedin percent reflectance after calibration of photometric
8、equip-ment by measuring the reflected light from standards ofreflectance as calculated from their refractive indices.5. Significance and Use5.1 The mean maximum reflectance of the vitrinite compo-nent in coal as determined by this test method is often used asan indicator of rank as presented in Clas
9、sification D388,independent of petrographic composition, and in the charac-terization of coal as feedstock for carbonization, gasification,liquefaction, and combustion processes.5.2 This test method is for use in scientific and industrialresearch.6. Apparatus6.1 MicroscopeAny microscope equipped for
10、 reflectedlight microscopy (such as a metallurgical or opaque-ore mi-croscope) can be used, provided the lens combination ofobjective and eyepieces permits examination of the specimenat a magnification between 400 and 3 750, such that particlesof 1 m can be resolved. The objectives shall be construc
11、ted sothat samples can be examined in oil with plane-polarized lightand have the highest quality of antireflection coatings. Themicroscope shall be able to project an image at similarmagnification to a photomultiplier tube and to support thephotomultiplier tube housing. Means shall be provided topos
12、ition the tube housing laterally to obtain maximum re-sponse. The microscope shall have a circular stage that iscapable of rotating a specimen through 360. The mechanicalstage attached to the microscope stage shall enable the analyst1This test method is under the jurisdiction of ASTM Committee D05 o
13、n Coaland Coke and is the direct responsibility of Subcommittee D05.28 on PetrographicAnalysis of Coal and Coke.Current edition approved June 1, 2011. Published July 2011. Originally approvedin 1969. Last previous edition approved in 2011 as D2798 11. DOI: 10.1520/D2798-11A.2For referenced ASTM stan
14、dards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
15、PA 19428-2959, United States.to move the specimen accurately (within 0.1 mm) to a givenfield location. A combination of objective and circular stageshall permit centering. The viewing eyepiece shall be suppliedwith a crosshair or grid to be used as a reference to locateprecisely the area sampled by
16、the phototube. During measure-ment, no light shall be permitted to enter the observers end ofthe viewing eyepiece.6.2 Polarizer and IlluminatorThe light incident on thevertical illuminator of the microscope shall be plane-polarizedby a prism or sheet polarizer. The vertical illuminator cancontain a
17、Berek prism, a Smith illuminator, or high-qualityglass plate. The polarizer shall be oriented at 45 when using aBerek prism or at 0 when using a Smith illuminator or glassplate.6.3 Photomultiplier TubeIn combination with the micro-scope optical system, light source, and filter used, the photo-multip
18、lier photometer shall be capable of detecting the mini-mum light reflected from the limited portion of the coal sample(see 6.8). The high voltage supplied to the photomultiplier tubemust be within the prescribed range to obtain linearity ofresponse. This is usually from 300 to 1100 V for side-window
19、tubes and from 1000 to 1500 V for end-window tubes.Photodiode arrays, channeltrons, or other light-measuring de-vices are acceptable alternatives providing that sufficient graylevels obtainable will enable reliable differentiation of signalequivalent to 0.01 % reflectance and that the system is line
20、ar inthe range of the reflectance measured.6.4 Photometer AmplifierThe signal from the photomul-tiplier tube shall be amplified and displayed by a galvanometer,digital meter, or recorder. When adjusted for operation, theamplifier and meter shall be capable of reliably distinguishingdifferences in si
21、gnal equivalent to 0.01 % reflectance and shallbe linear in the range of reflectance measured.6.5 Recorder or MeterThe recorder or meter used shallhave a response time at full scale of no more than1stodetectthe maximum reflectance level during rotation of the micro-scope stage.6.6 Light SourceThe li
22、ght source shall have a regulatedpower supply to provide for stable output. Some photometersand recorders require supplemental voltage-stabilizing trans-formers if the line voltage fluctuates.6.7 FiltersThe light shall be made approximately mono-chromatic green by passage through an interference fil
23、ter orcombination of filters with peak transmittance of 546 6 5nmand a half-peak transmittance bandwidth of less than 20 nm.Insert the filter into the light path after the sample and beforethe photomultiplier tube.6.8 Limiting ApertureA limiting aperture made of nonre-flecting and opaque material sh
24、all be placed approximately inthe focal plane of the eyepiece at its central axis to restrict lightto the photomultiplier tube window so that only a small area ofthe reflectance standard or sample is sensed. The diameter ofthe aperture shall be selected to provide an effective field ofmeasurement (s
25、ensed spot) of about 5 m diameter or about20-m2area.6.9 Calibration StandardsPrisms constructed of high-index glasses or synthetic minerals shall be used as standardsto calibrate the photometer for reflectance measurement. Thesestandards must be durable, isotropic, resistant to corrosion, freefrom i
26、nternal flaws or fractures, and have negligible lightabsorption.Aprism with sides that form a 30-60-90 triangle isthe most effective shape, with the side between the 30 and 90angles highly polished and used as the reflectance-measuringsurface. The prisms shall be enclosed, except for the polishedsur
27、face, in a durable, lightabsorbent, water- and oil-resistantmount; polyester or epoxy resin, made light absorbent with adye or filler, serves adequately. It is desirable to have a numberof different standards with reflectances near those of thevitrinite studied; these also serve to check the linear
28、responseof the photometer. The reflectance of each standard shall becalculated to the nearest 0.001 % by means of the followingequation:Rs5 100ng2 1.5180!2/ng1 1.5180!2(1)where:Rs= standard reflectance in oil of the glass, % andng= refractive index of the glass at 546-nm wavelength, tothe nearest 0.
29、0001 index value.NOTE 1Most coal laboratories in North America use the followingBausch and Lomb Co. or Schott Co. optical glasses (the reportedrefractive index at 546 nm and the calculated standard reflectance in oilare given in parentheses):Bausch and Lomb Schott689 309 (1.6935; 0.299 %) SF8-689-31
30、2 (1.6945; 0.303 %)751 278 (1.7566; 0.532 %) SF13-714-276 (1.7477; 0.496 %)827 250 (1.8351; 0.895 %) LaF12-836-423 (1.8400; 0.921 %)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 %)980 222 (1.9907; 1.817 %) LaSF6-961-249 (1.9670; 1.66
31、2 %)Other standards available that can be used include the following:Leucosapphire (1.77; 0.59 %)Yttrium aluminum garnet, YAG (1.84; 0.92 %)Gadolinium gallium garnet, 3G (1.98; 1.73 %)Silicon carbide (2.663; 7.52 %)6.10 Immersion OilThe oil shall be a nondrying, noncor-rosive type that will not reac
32、t with coal, does not containcarcinogens, and has a refractive index within the range from1.515 to 1.519 at 546 nm and 25C. Within the specified range,the refractive index of the oil is not critical provided thespecified value of 1.5180 is used in calculating reflectance ofstandards as specified in
33、6.9. Periodic checking of the refrac-tive index of the oil is discretionary.6.11 Sample-Leveling PressA conventional manual level-ing device can be used to level sample briquettes and glassstandards when they are mounted on microscope slides withmodeling clay.7. Test Specimen7.1 Prepare the sample b
34、riquette in accordance with PracticeD2797.8. Setting Up and Calibrating the Apparatus8.1 Turn on the photometer and light source and allowequipment to warm up for at least12 h.8.2 Mount the glass standards and a polished briquettecontaining the sample on slides using modeling clay and aleveling pres
35、s or use a leveling briquette holder.D2798 11a28.3 Place the mounted briquette on the stage, apply immer-sion oil, and verify leveling of the mount and stage by checkingthat there is no systematic focus change when the briquette ismoved laterally on the stage. Use Khler illumination. Tominimize glar
36、e, restrict the illuminated field by means of thefield diaphragm so that the diameter is about one third or lessthan the size of the full field.Adjust any other provisions of theilluminator to reduce scattered light in the system.8.4 Verify the position of the limiting aperture of thephotometer with
37、 respect to the field of view. This can be doneby moving a small bright object of the sample across theposition of the crosshair or reticle that marks the photometer-sensed spot, ascertaining that readings are highest when thebright object is within the sensed area or by using back-litillumination o
38、f the measuring aperture if so equipped.8.5 Using a small, distinctive feature of the sample as aguide, adjust the microscope so that the axis of rotation of thestage is coincident with the photometer-sensed spot. This isaccomplished by adjusting the centering screws of the objec-tive or stage. The
39、purpose is to eliminate movement of theobject grain or area from the sensed spot when the stage isrotated.8.6 Adjust the polarizer to a 45 position when using aBerek prism or 0 when using a Smith illuminator or glassplate. Place a glass standard covered with clean immersion oilon the microscope stag
40、e and focus on the polished surface.8.7 With no light reflected from the standard to the photo-tube, adjust the photometer zero setting or dark current.8.8 Place on the microscope stage a briquette of opaqueresin that has a hole 5 mm in diameter and 5 mm deep whichis filled with immersion oil. Measu
41、re the reflectance of the holeto ensure that a reflectance of 0.00 6 0.03 % is obtainedthereby ensuring that parasitic reflectances of the objective areminimal. If the reflectance of the hole exceeds the stated limits,then another objective having a higher quality anti-reflectioncoating shall be use
42、d.8.9 Then allow the reflected light to impinge on the tube.Adjust the photometer amplifier or the illumination to obtain ameter or recorder scale setting that conveniently represents thecalculated reflectance of the glass standard (see Appendix X1).8.10 Without changing the settings, measure the re
43、flectanceof one or more additional standards to check that the photom-eter system measures correctly in the range to be studied.8.10.1 Because the photometric system cannot give a linearresponse to a wide range of light flux, standards with reflec-tance values close to that of the coal being measure
44、d should beused. At least two standards having reflectances that span therange of the coal being measured should be used.8.11 Make all standardization measurements under the sameconditions used in measuring vitrinite reflectance. When mea-suring mean maximum reflectance of vitrinite, rotate the stag
45、ethrough 360 and note the maximum reflectance value of theglass reflectance standard. If values change during rotationmore than 0.03 %, then the system alignment shall be checked.8.12 Measure the same areas of the glass reflectance stan-dards each time the calibration is made.8.13 Glass standards sh
46、ould be cleaned at least once amonth to avoid oxidation and changes in reflectances.9. Procedure for Measuring Maximum Reflectance of aSample9.1 Immediately after calibrating the system, place a pol-ished briquette of the sample on the microscope stage andapply immersion oil.9.2 Adopt a systematic s
47、cheme of transection of the bri-quette for selection of areas to be measured. Transect intervalsshall be such that the entire surface of the briquette orbriquettes will be sampled for the component being measured.The transect spacing shall be suitable for a total of 100measurements.9.3 Using the pro
48、cedure specified in 9.2, select the locationto be measured. Slight adjustments to the maceral position maybe made to obtain a scratch-free area of uniform appearance.Rotate the circular stage slowly (approximately 4 r/min)through 360. Reflectance will vary progressively from amaximum value to a mini
49、mum value as the stage is rotated.Observe and record the maximum value. If the effective field ofmeasurement does not remain on the component being mea-sured when the stage is rotated, then recenter the objective orstage as described in 8.5. Avoid taking measurements of areasthat are near highly reflecting grains such as pyrite. Becausesome relief and nonplanarity may develop during polishing,avoid edges of particles and particles near the edge of thebriquette.9.4 Move the stage to the next area to be measured andrepeat 9.3. Continue the location se
