1、Designation: D6745 11 (Reapproved 2015)Standard Test Method forLinear Thermal Expansion of Electrode Carbons1This standard is issued under the fixed designation D6745; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 determination of the coef-ficient of linear thermal expansion (CTE) for carbon anodesand cath
3、odes used in the aluminum industry, in baked form, byuse of a vitreous silica dilatometer.1.2 The applicable temperature range for this test methodfor research purposes is ambient to 1000 C. The recom-mended maximum use temperature for product evaluation is500 C.1.3 This test method and procedure is
4、 based on Test MethodE228, which is a generic all-encompassing method. Specificsdictated by the nature of electrode carbons and the purposes forwhich they are used are addressed by this procedure.1.4 Electrode carbons in the baked form will only exhibitprimarily reversible dimensional changes when h
5、eated.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 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 establis
6、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod Dilatometer3. Terminology3.1 Definitions:3.1.1 linear thermal
7、expansion, nthe change in length perunit length resulting from a temperature change. Linear ther-mal expansion is symbolically represented by L/L0, where Lis the length change of the specimen (L1L0), L0and L1arethe specimens lengths at reference temperature T0and testtemperature T1, respectively. Li
8、near thermal expansion is oftenexpressed as a percentage or in parts per million (such asm/m).3.1.1.1 mean coeffcient of linear thermal expansion (CTE),nThe linear thermal expansion per change in temperature;the mean coefficient of linear thermal expansion is representedby:T15L/L0T51L0LT51L0L12 L0T1
9、2 T0(1)3.1.1.1 DiscussionThis has to be accompanied by thevalues of the two temperatures to be meaningful; the referencetemperature (T0) is 20 C, and the notation may then onlycontain a single number, such as 200, meaning the meancoefficient of linear thermal expansion between 20 C and200 C.3.2 Defi
10、nitions of Terms Specific to This Standard:3.2.1 reference specimen, na particularly identified orpedigreed material sample, with well-characterized behaviorand independently documented performance.3.2.2 specimen, na representative piece of a larger body(anode, cathode, and so forth) that is conside
11、red to be fairlytypical of a portion or of the entire piece.3.2.3 vitreous silica dilatometer, na device used to deter-mine linear thermal expansion, by measuring the difference inlinear thermal expansion between a test specimen and thevitreous silica parts of the dilatometer.4. Summary of Test Meth
12、od4.1 Arepresentative specimen is placed into a vitreous silicadilatometer and heated, while its linear expansion is continu-ously recorded. The change of the specimen length is recordedas a function of temperature. The coefficient of linear thermalexpansion is then calculated from these recorded da
13、ta.5. Significance and Use5.1 Coefficients of linear thermal expansion are used fordesign and quality control purposes and to determine dimen-sional changes of parts and components (such as carbonanodes, cathodes, and so forth) when subjected to varyingtemperatures.1This test method is under the jur
14、isdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.Current edition approved Oct. 1, 2015. Published December 2015. Originallyapproved in 2001. Last previo
15、us edition approved in 2011 as D6745 11. DOI:10.1520/D6745-11R15.2For referenced ASTM standards, 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 webs
16、ite.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Apparatus6.1 DilatometerThe dilatometer consists of the following:6.1.1 Specimen Holder and Push-rod, both made of vitreoussilica. The design of the device shall ensure that the p
17、ush-rodload on the specimen by itself is not causing deformation. Theuse of pressure distribution quartz plates on top of thespecimen is permissible.NOTE 1Dilatometers are usually constructed in horizontal or verticalconfigurations.3Vertical devices are preferred for very large samples andwhen exten
18、sive shrinkage is expected. Horizontal configurations usuallyafford better temperature uniformity over the specimen, but are subject todrooping when large specimens are employed. Horizontal devices, whenused with very large specimens, require special provisions to reducefriction between the specimen
19、 and the dilatometer tube to minimizepush-rod pressure required to keep the specimen in contact with the endplate. For this application, either configuration is acceptable.NOTE 2Multiple rods supporting a platform in place of large diametertubes have been also used successfully in the vertical confi
20、guration.6.1.2 Transducer or Indicator, for measuring the differencein length between the specimen and the dilatometer with anaccuracy within 6 2 m. The transducer shall translate thesemovements into an electrical signal suitable for displaying orrecording. The non-linearity of this conversion must
21、be lessthan 0.25 % of the full scale value of the output. The transducershall be protected or mounted so that the maximum tempera-ture change observed in the transducer during a test will affectthe transducer readings by less than 1 m.6.1.3 Temperature Sensors, for determining the mean tem-perature
22、of the specimen with an accuracy within 6 0.5 C.When a thermocouple is used, it shall be referenced (coldjunction compensated) to the ice point with an ice-water bathor an equivalent system.6.1.3.1 Due to the large size of the specimen, a minimum ofone thermocouple per 40 mm specimen length must be
23、em-ployed. It is permissible to read the output of each thermo-couple independently and average the readings or to connectthem in series and divide the single reading by the number ofthermocouples to obtain the average. In the latter case, inter-connections must be made at or beyond the point of col
24、djunction compensation.6.1.3.2 The temperature sensors shall be in close proximityto the specimen, preferably in between the quartz dilatometertube and the specimen. The temperature sensors shall not bedirectly exposed to the furnace walls.6.2 Readout or Recording of Data:6.2.1 Manual recording of e
25、xpansion and temperature val-ues indicated at selected temperature points may be made if thetransducer is equipped with or connected to a suitable displayand the thermocouples outputs are determined with a potenti-ometer or millivolt meter.6.2.2 Chart or data logger recording of the expansion andtem
26、perature signals may be accomplished using a devicewhose resolution is at least 1000 times higher than the expectedmaximum output signal. All calculations and corrections (seeSection 10) must be done externally based on the recordedvalues.6.2.3 Computerized recording may be used with similarrestrict
27、ion to 6.2.2. Calculations and corrections may be doneusing suitable software.6.3 FurnaceThe furnace is used for uniformly heating thespecimen over the temperature range of interest, but not above1000 C. Temperature uniformity shall be at least 6 0.5 C per50 mm of sample length. The temperatures sha
28、ll be controlledas a function of time. The furnace may have a muffle (quartz,mullite, alumina, inconel, monel, or stainless steel are mostcommon) or other provisions to provide a protective atmo-sphere for the specimen. The furnace shall have provisions forcontinuous purging with an inert gas at a s
29、ufficient rate, andexclude air from the specimen while a purge is maintained.6.4 CaliperThe caliper (micrometer or Vernier type) is formeasuring the initial length of the specimen, L0, with anaccuracy within 625 m, and a capacity to open to the lengthof the specimen plus 1 mm.7. Test Specimen7.1 Spe
30、cimens shall be cylindrical, preferably with a 50 mm6 2 mm diameter. Slightly smaller or larger diameters can alsobe accommodated without degradation of data. The length ofthe specimens shall be between 50 mm and 130 mm in lengthand have flat and parallel ends to within 625 m.7.2 It is permissible t
31、o stack up to five disks of smallerlengths to obtain a proper length specimen. The interfaces,however, must be flat and parallel within 625 m to preventrocking.7.3 The dimensions of the specimens should be ordinarilymeasured as received.7.4 If water was used in conjunction with their preparation,eac
32、h specimen must be kept in an oven at 110 C 6 5 C for atleast 6 h and allowed to cool down thereafter, prior to testing.If any heat or mechanical treatment is applied to the specimenprior to testing, this treatment should be noted in the report.8. Calibration8.1 The transducer should be calibrated b
33、y imposing a seriesof known displacements with a precision screw micrometer,gage blocks, or equally accurate device. For absolute transduc-ers (such as digital encoders, and so forth), this procedure isomitted and periodic verification is sufficient.8.2 Verification of the calibration of the tempera
34、ture sensorsseparately from the dilatometer is to be performed periodicallyor when contamination of the junction is suspected.8.3 Regardless of independent calibrations of the transducerand the thermocouples, the dilatometer, as a total system, shallbe calibrated by determining the thermal expansion
35、 of at leastone reference material of known thermal expansion. Recom-mended reference materials are listed in Annex A1.8.3.1 The calibration should be done using approximatelythe same thermal cycle as that used for testing (see 9.7 and9.8).8.3.2 The calibration constant may be derived as follows:A 5
36、SLL0Dt2SLL0Dm(2)3Hidnert, P. and Krider, H.S., “Thermal Expansion Measurements,” Journal ofResearch, National Bureau of Standards, Vol 48, 1952, p. 209.D6745 11 (2015)2where:m = measured expansion of the reference material, andt = true or certified expansion of the reference material.8.4 If the cali
37、bration specimen is considerably smaller in thecross section than the specimen, it is necessary to provide athermal jacket around it to prevent errors caused by convectivecurrents. A thermal jacket may be produced by drilling a holein the axis of a carbon specimen and loosely fitting thecalibration
38、specimen into it. The carbon jacket must be about 1mm shorter than the calibration specimen.8.5 The use of published values of thermal expansion forquartz may not be used to compute a correction factor.Accounting for the expansion of the dilatometer parts throughcalculations in place of a calibratio
39、n procedure described aboveis not permitted.8.6 Materials usable for calibration or verification of opera-tion fall into four categories.8.6.1 Standard Reference MaterialsThese are actualspecimens supplied with a certificate by NIST,4or a similarnational standards organization of another country.5,6
40、NOTE 3These materials are very few and NIST supplies have beenexhausted in some cases. To determine the absolute accuracy of a device,materials in this category are the most preferred.8.6.2 Traceable Reference MaterialsThese are exten-sively investigated materials, substantially described in pub-lis
41、hed literature and considered stable. Often they are generi-cally identical to Standard Reference Materials. Specific lotswhen tested in a systematic fashion using a dilatometercalibrated with a certified Standard Reference Material can bereferred to as Traceable Reference Materials. They may alsose
42、rve well in comparing equipment or test procedures atdifferent laboratories and to arbitrate disputes and differences.8.6.3 Reference MaterialsThese are widely investigated,well-characterized materials that were found to be stable withtime and temperature exposure and performance data arereadily ava
43、ilable in the literature; for example, platinum. Thesematerials are well suited for round-robin, day-to-day verifica-tion (working reference) of equipment performance and peri-odic verification programs. Purity and physical parameters(density, electrical resistivity, and so forth) must be reasonably
44、matched to use literature data.8.6.4 Characterized Private Stock MaterialsThese aresubstances that are mainly used for in-house verifications.Even though they may be thought of as being wellcharacterized, the data is primarily self consistent. If such amaterial is found to be very stable by independ
45、ent tests, it maybe used in round-robin tests, but caution should be exercisedwhen the data is intended to arbitrate disputes or differencesbetween facilities. Typical use should be limited to that of anin-house working reference. Primary reason for use is havingthermal characteristics closely resem
46、bling those of actual testspecimens.9. Procedure9.1 Measure the initial (room temperature) length of thespecimen, and record it as L0.9.2 Place the specimen into the dilatometer after makingcertain that all contacting surfaces are free of foreign material.It is important to have good seating of the
47、specimen in a stableposition. (WarningAlkali contamination will adversely af-fect fused silica parts. Avoid touching them with hands.)9.3 Ensure that the temperature sensors shall not restrictmovement of the specimen in the dilatometer. Do not allow anexposed junction to contact any carbonaceous mat
48、erials.9.4 Make certain that the push-rod is in stable contact withthe specimen.Apressure distribution plate made of fused silicamay be used between the push-rod and the specimen.9.5 Insert the loaded dilatometer into the furnace (at ambi-ent temperature) and allow the temperature of the specimen to
49、come to equilibrium.9.6 Record the initial readings of the temperature sensors,T0, and the transducer, X0.9.7 Heat the furnace to 300 C or 500 C 6 10 C at a ratenot exceeding 10 Cmin. Allow the furnace and specimen tostabilize at that temperature for 60 min. Record readings of thetemperature sensors, T1, and the transducer, X1. If data obtainedduring ramping is to be used, heating rates above 1 Cmin arenot permitted.9.8 Alternate to 9.7. Heat the furnace at rates up to10 Cmin. Hold the furnace and specimen at a single or serie
