1、Designation: D8075 16 An American National StandardStandard Guide forCategorization of Microstructural and Microtextural FeaturesObserved in Optical Micrographs of Graphite1This standard is issued under the fixed designation D8075; the number immediately following the designation indicates the year
2、oforiginal adoption or, in the case of revision, the year of last 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 guide covers the identification and the assignmentof
3、 microstructural and microtextural features observed inoptical micrographs of graphite. The objective of this guide isto establish a consistent approach to the categorization of suchfeatures to aid unambiguous discussion of optical micrographsin the scientific literature. It also provides guidance o
4、n speci-men preparation and the compilation of micrographs.1.2 The values stated in SI units are to be regarded as thestandard.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 a
5、ppro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D7219 Specification for Isotropic and Near-isotropicNuclear Graphites3. Terminology3.1 The definitions listed below cover terms used in thisguide
6、 and apply specifically to the optical microscopy ofgraphite. Properties and features not apparent under the opticalmicroscope are avoided where possible. Definitions may notexactly match those adopted in general scientific usage butshould not be at variance. General terms have not beenredefined wit
7、h graphite-specific meanings or opticalmicroscopy-specific meanings. As with the identification offeatures in micrographs, some definitions have become unclearto differences in usage and this guide provides the basis for amore consistent approach.3.2 Definitions:3.2.1 accommodation cracks, n(also re
8、ferred to asMrozowski-like cracks) cracks and voids formed betweenbasal planes and at domain interfaces throughout the graphitemicrostructure from thermal contraction of the graphite duringcarbonization/graphitization (sometimes referred to as calcina-tion cracks), from chemical decomposition of the
9、 liquid crystalhydrocarbon precursor in graphite manufacture (also referredto as calcination cracks) and following cooling after graphiti-zation (manufacture). In irradiated graphite, they also comprisecracks arising from anisotropic responses to irradiation.3.2.2 agglomerate, nin manufactured carbo
10、n and graph-ite product technology, composite particle containing a numberof grains.3.2.3 binder, nsubstance such as coal tar pitch or petro-leum pitch, used to bond the coke or other filler material priorto baking.3.2.4 crystallite, nin manufactured carbon and graphiteproduct technology, a region o
11、f regular crystalline structurehaving parallel basal planes.3.2.5 filler, nin manufactured carbon and graphite prod-uct technology, particles that comprise the base aggregate in anunbaked green-mix formulation (also referred to as cokeparticles, grist particles, or filler grains).3.2.6 filler-binder
12、 phase, nin manufactured carbon andgraphite product technology, mix of finely ground filler (flour)and binder comprising the matrix in which the filler is bound.3.2.7 grain, nin manufactured carbon and graphite, par-ticle of filler material (usually coke or graphite) in the startingmix formulation.
13、Also referred to as granular material, fillerparticle, or aggregate material. The term is also used todescribe the general texture of a carbon or graphite body, as inthe descriptions listed below:3.2.7.1 coarse grained, adjcontaining grains in the start-ing mix that are substantially greater than 4
14、mm in size.3.2.7.2 medium coarse grained, adjcontaining grains inthe starting mix that are generally less than 4 mm in size.3.2.7.3 medium grained, adjcontaining grains in the start-ing mix that are generally less than 2 mm in size.1This guide is under the jurisdiction of ASTM Committee D02 on Petro
15、leumProducts, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-mittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Dec. 15, 2016. Published February 2017. DOI:10.1520/D8075-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
16、 orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis internationa
17、l standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
18、13.2.7.4 medium fine grained, adjcontaining grains in thestarting mix that are generally less than 1 mm in size.3.2.7.5 fine grained, adjcontaining grains in the startingmix that are less than 100 m in size.3.2.7.6 superfine grained, adjcontaining grains in thestarting mix that are less than 50 m in
19、 size.3.2.7.7 ultrafine grained, adjcontaining grains in the start-ing mix that are less than 10 m in size.3.2.7.8 microfine grained, adjcontaining grains in thestarting mix that are less than 2 m in size.3.2.7.9 DiscussionAll of the above descriptions relate tothe generally accepted practice of mea
20、suring the sizing frac-tions with a criterion that 90 % of the grains will pass throughthe stated sieve screen size in a standard particle sizing test.3.2.8 highly oriented region, nan area of uniform colorunder polarized light associated with a relatively crystallineunidirectional (at the observed
21、magnification) orientation.3.2.9 isotropic nuclear graphite, ngraphite in which theisotropy ratio based on the coefficient of thermal expansion(25 C to 500 C) is 1.00 to 1.10.3.2.10 mesophase, nfluid phase (discotic nematic liquidcrystal phase) converted to graphite during pyrolysis.3.2.11 mosaics,
22、nterm used to describe texture consistingof a grouping of isochromatic domains, often subdivided bygrain size. The following terms may be encountered relating tothese microtextural features:3.2.11.1 mosaic cluster, nan identifiable grouping ofsimilar-sized mosaic texture.3.2.11.2 mosaic ribbon, nan
23、identifiable ribbon-shaped orstrand grouping of mosaic texture.3.2.11.3 supra mosaic, naligned region of coarse mosaicsexhibiting a largely acicular shape.3.2.12 Mrozowski cracks, na subset of accommodationcracks formed between basal planes within coke particlecrystallites and the filler-binder phas
24、e from mismatches inthermal contraction of the graphite following cooling aftergraphitization (manufacture). These may also occur betweencrystallites if crystallite binding energies allow.3.2.13 optical domain, nthe smallest region of local pre-ferred orientation with relatively small misorientation
25、 anglesappearing isochromatic under polarized light with a sensitivetint plate.3.2.14 optical texture, nfine structure in an optic arraygiving rise to color variations under polarized light, attributedto variations in the optic axis of domains.3.2.15 pore, nsee void.3.2.16 porosity, nfraction of the
26、 total volume of a materialoccupied by both open and closed pores and cracks.3.2.17 void, nunfilled space enclosed within an apparentlysolid carbon or graphite body.4. Significance and Use4.1 The purpose of this guide is to provide a framework forconsistent description of microstructural and microte
27、xturalfeatures visible in optical micrographs of graphite. It alsoprovides some guidance on sample preparation and imageprocessing.5. Optical Microscopy Methods5.1 Three different methods of illumination are generallyemployed in optical microscopy: optical or bright field (BF),fluorescence under UV
28、light, and polarized light. While brightfield and polarized light methods can be undertaken directly ona prepared graphite surface, fluorescence requires the sample tobe impregnated with a resin incorporating a fluorescent dyeprior to preparation of the graphite surface. It is common for allthree me
29、thods of illumination to be used in the characterizationof graphite microstructure and texture so that resin impregna-tion is a standard procedure in sample preparation. It shouldalso be noted that resin impregnation stabilizes the graphitematrix and protects porosity from dust intrusion during poli
30、sh-ing of the surface being prepared for examination.5.2 If the sample requires impregnation, a low-viscosityresin is used to impregnate and encapsulate the sample. Theresin can have a small amount of fluorescent dye added forobservation under ultraviolet (UV) light. Once impregnatedwith resin and c
31、ured, the encapsulated sample is ready forpreparation of an examination face.5.3 The selected face of the sample is prepared for micro-scopic examination by grinding it using progressively finersilicon carbide (SiC) papers to 2500 grit (8.4 m 6 0.5 m).The face is then further polished with a diamond
32、 suspension toa 1 m finish. The same procedure is employed for bothuntreated and impregnated graphite samples. At this stage, theprepared face of the sample is ready for optical examination.5.4 With BF illumination, the sample is observed usingwhite light at normal incidence. Within the constraints
33、of theoptical resolution, this method of illumination allows micro-structural features in the sample to be seen.5.5 With fluorescence microscopy, incident UV light causesthe dye in the resin to fluoresce, thus showing the extent ofresin penetration into the sample and an indication of areas ofopen p
34、orosity. This method requires full impregnation of theaccessible porosity by the resin, which can be influenced by theviscosity of the resin and extent of evacuation. The method isless revealing in terms of characterizing microstructure infine-grained material because of incomplete penetration of th
35、eporosity by the resin.5.6 Illumination with polarized light merits a more detailedexplanation. The random variations in a light beam are indirections normal to the direction of propagating light. If thelight beam is passed through an optically active crystallinematerial (a plane polarizer), some di
36、rections of vibrations willbe suppressed and others rotated. The net result is that specificdirections of vibrations are favored on passing through thepolarizer. If the transmitted plane-polarized light is examinedafter passing through a second optically active material, andthis second optically act
37、ive material is at right angles to thepolarizer, then the light will be cut off completely. When thetwo optically active materials are in this position they are saidto be crossed. The second optically active material is termedD8075 162the analyzer. Polarization will occur on reflection from mostcrys
38、talline materials, even when they are isotropic. Examina-tion with crossed polarizers allows the polarization caused byinteraction with the specimen surface to be studied. The degreeof polarization will depend on the angle between the incidentlight and specific crystal planes in the material. Also,
39、qualita-tive analysis of the specimens surface relative crystallographyand degree of crystallinity can be made.5.6.1 If a sensitive tint plate is placed between the polarizerand analyzer, orientations of isotropic materials can be distin-guished. A 1 plate is most commonly used but12 platesmay also
40、be employed. A sensitive tint plate consists of a sliceof some birefringent (birefringence is the difference betweenthe highest and lowest refractive indices for anisotropic crys-tals) material that is cut parallel to the optic axis of the crystal.If plane-polarized light is transmitted through the
41、sensitive tintplate, then the emergent ordinary and extraordinary rays willhave a path difference of exactly one wavelength for light ofone particular wavelength. In this case, the wavelength ofgreen light is used, such that the transmitted light is white lightminus the green wavelength, which is ma
42、genta in color.5.6.2 A feature that appears dark with crossed polarizerswill appear magenta with a sensitive tint plate in its 45position. Other features with differing orientations and differ-ing polarization characteristics will suppress other wavelengthsand appear as a characteristic color (white
43、 light minus thesuppressed wavelength). In this way, different orientations willproduce different colors in cross-polarization optical micros-copy. The strength of the colors observed will indicate thedegree of long-range order and crystallinity within any onefeature.5.7 The specification for optica
44、l microscopy equipment willbe determined by the resolution required to observe micro-structural features of interest. Typically, low magnificationimages are taken with a 5 objective lens. The total magnifi-cation of the image will depend upon the strength of the ocularlens and the image capture arra
45、ngement. For more detailedimages, objective lenses may range up to 100, although imagequality can be challenging at this level of magnification.Determination of optical texture can be influenced by themagnification employed, and the user should be aware thatmagnification requirements may differ depe
46、nding upon thenature of the graphite under investigation.5.8 To correctly determine the size of optical objects or tomeasure distances on optical microscope images, or both, aspatial calibration must be performed. There are two basicways to perform spatial calibrations: either by using knownspatial
47、references in the image, or through estimations based oncamera and lens optical characteristics.5.8.1 Calibrations based on known spatial references aremore accurate, and should be used whenever trustful spatialreferences are available and can be imaged in identical opticalconditions as the area of
48、interest on the graphite specimen.When possible, a commercially available graduated reticleshould be used as spatial reference. Using the tools availablewith modern microscopy image acquisition software, calibra-tion should be done by repeatedly measuring linear segmentsdrawn between known reference
49、 points on the reticle andsaving the results along with the spatial distance values inappropriate units. If a graduated scale is not available, then anyother object whose size can be accurately measured can serveas a spatial reference.5.8.2 Fig. 1 shows an example of a graduated reticle. Ontop, a low magnification image shows a segment about 7 mmlong of the graduated scale, with marks at every 1 mm (left),0.1 mm (center) and 0.01 mm (right). The image is composedof 21 by 3 individual images stitched together. This image isuseful for calib
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