1、Designation: D 6745 06An American National StandardStandard Test Method forLinear Thermal Expansion of Electrode Carbons1This standard is issued under the fixed designation D 6745; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、anodesand cathodes 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 1000C. The recommendedmaximum use temperature for product evaluation is 500C.1.3 This test method and p
4、rocedure is based on Test MethodE 228, 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 ch
5、anges when heated.1.5 The values stated in SI units are to be regarded asstandard.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 establish appro-priate safety and health practices and d
6、etermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod Dilatometer3. Terminology3.1 Definitions:3.1.1 linear thermal expansionthe change in length perunit length re
7、sulting from a temperature change. Linear ther-mal expansion is symbolically represented by DL/L0, where DLis the length change of the specimen (L1L0), L0and L1are thespecimens lengths at reference temperature T0and test tem-perature T1, respectively. Linear thermal expansion is oftenexpressed as a
8、percentage or in parts per million (such asm/m).3.1.2 mean coeffcient of linear thermal expansion (CTE)The linear thermal expansion per change in temperature; themean coefficient of linear thermal expansion is represented by:aT15DL/L0DT51L0DLDT51L0L12 L0T12 T0(1)3.1.2.1 This has to be accompanied by
9、 the values of the twotemperatures to be meaningful; the reference temperature (T0)is 20C, and the notation may then only contain a singlenumber, such as a200, meaning the mean coefficient of linearthermal expansion between 20 and 200C.3.2 Definitions of Terms Specific to This Standard:3.2.1 referen
10、ce specimena particularly identified or pedi-greed material sample, with well-characterized behavior andindependently documented performance.3.2.2 specimena representative piece of a larger body(anode, cathode, and so forth) that is considered to be fairlytypical of a portion or of the entire piece.
11、3.2.3 vitreous silica dilatometera 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 Method4.1 Arepresentative specimen is placed into a vitreous silica
12、dilatometer 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 data.5. Significance and Use5.1 Coefficients of linear thermal ex
13、pansion 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.6. Apparatus6.1 DilatometerThe dilatometer consists of the following:1This test method is under t
14、he jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.Current edition approved Jan. 1, 2006. Published February 2006. Originallyapproved in 2001. Last previous editio
15、n approved in 2001 as D 674501.2For 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 website.1Copyright ASTM International,
16、 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.1.1 Specimen Holder and Push-rod, both made of vitreoussilica. The design of the device shall ensure that the push-rodload on the specimen by itself is not causing deformation. Theuse of pressure distribution quar
17、tz plates on top of thespecimen is permissible.NOTE 1Dilatometers are usually constructed in horizontal or verticalconfigurations (1)3Vertical devices are preferred for very large samplesand when extensive shrinkage is expected. Horizontal configurationsusually afford better temperature uniformity o
18、ver the specimen, but aresubject to drooping when large specimens are employed. Horizontaldevices, when used with very large specimens, require special provisionsto reduce friction between the specimen and the dilatometer tube tominimize push-rod pressure required to keep the specimen in contact wit
19、hthe end plate. For this application, either configuration is acceptable.NOTE 2For basic construction details and fused silica annealingschedule, consult Test Method E 228.NOTE 3Multiple 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 o
22、f the specimen with an accuracy within 6 0.5C.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 beemp
23、loyed. 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 coldjun
24、ction 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 expan
25、sion 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 andtempera
26、ture 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 similarrestriction
27、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 above1000C. Temperature uniformity shall be at least 6 0.5C per50 mm of sample length. The temperatures shall be
28、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 suffici
29、ent 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 6 25 m, and a capacity to open to the lengthof the specimen plus 1 mm.7. Test Specimen7.1 Specimen
30、s shall be cylindrical, preferably with a 50 62 mm diameter. Slightly smaller or larger diameters can also beaccommodated without degradation of data. The length of thespecimens shall be between 50 and 130 mm in length and haveflat and parallel ends to within 6 25 m.7.2 It is permissible to stack up
31、 to five disks of smallerlengths to obtain a proper length specimen. The interfaces,however, must be flat and parallel within 6 25 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,each specime
32、n must be kept in an oven at 110 6 5C 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 by imposing a
33、 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 temperature sensors
34、separately 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 of at least
35、one 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 5SDLL0Dt2SDLL
36、0Dm(2)where:3Hidnert, P. and Krider, H.S., “Thermal Expansion Measurements,” Journal ofResearch, National Bureau of Standards, Vol 48, 1952, p. 209.D6745062m = measured expansion of the reference material, andt = true or certified expansion of the reference material.8.4 If the calibration specimen i
37、s 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 specimen into it.
38、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 calibration procedure descri
39、bed 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 NIST4, or a similarnational standards organization of another country.5,6NOTE 4These mater
40、ials 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-lished literature an
41、d 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 alsoserve well in compa
42、ring 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 available in the lit
43、erature; 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 reasonablymatched to use li
44、terature 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 well character-ized, the data is primarily self consistent. If such a material isfound to be very stable by independent tests, it m
45、ay be used inround-robin tests, but caution should be exercised when thedata is intended to arbitrate disputes or differences betweenfacilities. Typical use should be limited to that of an in-houseworking reference. Primary reason for use is having thermalcharacteristics closely resembling those of
46、actual test speci-mens.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 specimen in a
47、 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 materials.9.4 Ma
48、ke 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 tocome to equil
49、ibrium.9.6 Record the initial readings of the temperature sensors,T0, and the transducer, X0.9.7 Heat the furnace to 300 or 500 6 10C at a rate notexceeding 10C/min. 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 1C/min arenot permitted.9.8 Alternate to 9.7. Heat the furnace at rates up to 10C/min. Hold the furnace and specimen at a single or series ofconstant temperatures until the tr
