1、Designation: E 1461 07Standard Test Method forThermal Diffusivity by the Flash Method1This standard is issued under the fixed designation E 1461; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n 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 thermaldiffusivity of primarily homogeneous isotropic solid materials.Thermal diffusivity val
3、ues ranging from 10-7to 10-3m2/s aremeasurable by this test method from about 75 to 2800 K.1.2 This test method is a more detailed form of Test MethodC 714, having applicability to much wider ranges of materials,applications, and temperatures, with improved accuracy ofmeasurements.1.3 This test meth
4、od is intended to allow a wide variety ofapparatus designs. It is not practical in a test method of thistype to establish details of construction and procedures to coverall contingencies that might offer difficulties to a personwithout pertinent technical knowledge, or to stop or restrictresearch an
5、d development for improvements in the basictechnique.1.4 This test method is applicable to the measurementsperformed on essentially fully dense (preferably, but lowporosity would be acceptable), homogeneeous, and isotropicsolid materials that are opaque to the specimen of appliedenergy pulse. Experi
6、ence has shown, however, that somedeviation from these strict guidelines can be accommodatedwith care and proper experimental design, substantially broad-ening the usefulness of the method.1.5 This test method can be considered an absolute (orprimary) method of measurement, since no reference standa
7、rdsare required. It is advisable to use reference materials to verifythe performance of the instrument used.1.6 The values stated in SI units are to be regarded as thestandard.1.7 For systems employing lasers as power sources, it isimperative that the safety requirement be fully met1.8 This standard
8、 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.2. Referenced Documents2.1 ASTM
9、Standards:2C 714 Test Method for Thermal Diffusivity of Carbon andGraphite by Thermal Pulse MethodE 228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod Dilatometer3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 thermal conductivity, l, of a solid mat
10、erialthe timerate of steady heat flow through unit thickness of an infiniteslab of a homogeneous material in a direction perpendicular tothe surface, induced by unit temperature difference. Theproperty must be identified with a specific mean temperature,since it varies with temperature.3.1.2 thermal
11、 diffusivity, a, of a solid materialthe prop-erty given by the thermal conductivity divided by the productof the density and heat capacity per unit mass.3.2 Description of Symbols and Units Specific to ThisStandard:3.2.1 Ddiameter, meters.3.2.2 Cpspecific heat capacity, J/(kgK).3.2.3 kconstant depen
12、ding on percent rise.3.2.4 Kcorrection factors.3.2.5 K1,K2constants depending on b.3.2.6 Lspecimen thickness, m.3.2.7 tresponse time, s.3.2.8 t12 half-rise time or time required for the rear facetemperature rise to reach one half of its maximum value, s.3.2.9 t*dimensionless time (t*=4ast/DT2).3.2.1
13、0 Ttemperature, K.3.2.11 athermal diffusivity, m2/s.3.2.12 bfraction of pulse duration required to reachmaximum intensity.3.2.13 rdensity, kg/m3.3.2.14 lthermal conductivity, W/mK.3.2.15 Dt5T (5t12 )/T (t12 ).3.2.16 Dt10T (10t12 )/T (t12 ).1This test method is under the jurisdiction ofASTM Committee
14、 E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.05 on Thermo-physical Properties.Current edition approved Nov. 1, 2007. Published January 2008. Originallyapproved in 1992. Last previous edition approved in 2001 as E 1461 01.2For referenced ASTM standards, visit the A
15、STM 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, PA 19428-2959, Uni
16、ted States.3.2.17 DTmaxtemperature difference between baseline andmaximum rise, K.3.3 Description of Subscripts Specific to This Standard:3.3.1 oambient.3.3.2 sspecimen.3.3.3 Tthermocouple.3.3.4 xpercent rise.3.3.5 CCowan.3.3.6 Rratio.3.3.7 mmaximum.3.3.8 ttime.4. Summary of Test Method4.1 A small,
17、thin disc specimen is subjected to a high-intensity short duration radiant energy pulse (Fig. 1). Theenergy of the pulse is absorbed on the front surface of thespecimen and the resulting rear face temperature rise (thermo-gram) is recorded. The thermal diffusivity value is calculatedfrom the specime
18、n thickness and the time required for the rearface temperature rise to reach certain percentages of itsmaximum value (Fig. 2). When the thermal diffusivity of thesample is to be determined over a temperature range, themeasurement must be repeated at each temperature of interest.This test method is d
19、escribed in detail in a number ofpublications (1, 2)3and review articles (3, 4, 5).Asummary ofthe theory can be found in Appendix X1.5. Significance and Use5.1 Thermal diffusivity is an important property, requiredfor such purposes under transient heat flow conditions, such asdesign applications, de
20、termination of safe operating tempera-ture, process control, and quality assurance.5.2 The flash method is used to measure values of thermaldiffusivity, a, of a wide range of solid materials. It isparticularly advantageous because of simple specimen geom-etry, small specimen size requirements, rapid
21、ity of measure-ment and ease of handling5.3 Under certain strict conditions, specific heat capacity ofa homogeneous isotropic opaque solid sample can be deter-mined when the method is used in a quantitative fashion (seeAppendix X2).5.4 Thermal diffusivity results, together with related valuesof spec
22、ific heat capacity (Cp) and density (r) values, can beused in many cases to derive thermal conductivity (l), accord-ing to the relationship:l5aCpr. (1)6. Interferences6.1 In principle, the thermal diffusivity is obtained from thethickness of the sample and from a characteristic time functiondescribi
23、ng the propagation of heat from the front surface of thesample to its back surface. The sources of uncertainties in themeasurement are associated with the sample itself, the tem-perature measurements, the performance of the detector and ofthe data acquisition system, the data analysis and morespecif
24、ically the finite pulse time effect, the nonuniform heatingof the specimen and the heat losses (radiative and conductive.These sources of uncertainty can be considered systematic, andshould be carefully considered for each experiment. Errorsrandom in nature (noise, for example) can be best estimated
25、 byperforming a large number of repeat experiments. The relativestandard deviation of the obtained results is a good represen-tation of the random component of the uncertainty associatedwith the measurement. Guidelines in performing a rigorousevaluation of these factors are given in (31).7. Apparatu
26、sThe essential components of the apparatus are shown in Fig.3. These are the flash source, specimen holder, environmentalenclosure (optional), temperature response detector and record-ing device.7.1 The flash source may be a pulse laser, a flash lamp, orother device capable to generate a short durat
27、ion pulse ofsubstantial energy. The duration of the pulse should be lessthan 2 % of the time required for the rear face temperature riseto reach one half of its maximum value (see Fig. 2), to keep theerror due to finite pulse width less than 0.5 %, if pulse widthcorrection (17, 18, 19) is not applie
28、d.7.1.1 The energy of the pulse hitting the specimens surfacemust be spatially uniform in intensity.7.2 An environmental control chamber is required for mea-surements above and below room temperature.7.3 The detector can be a thermocouple, infrared detector,optical pyrometer, or any other sensor tha
29、t can provide a linearelectrical output proportional to a small temperature rise. Itshall be capable of detecting 0.05 K change above thespecimens initial temperature. The detector and its associatedamplifier must have a response time not more than 2 % of thehalf-rise time value.3The boldface number
30、s given in parentheses refer to a list of references at theend of the text.FIG. 1 Schematic of the Flash MethodFIG. 2 Characteristic Thermogram for the Flash MethodE14610727.4 The signal conditioner includes the electronic circuit tobias out the ambient temperature reading, spike filters, ampli-fier
31、s, and analog-to-digital converters.7.5 Data Recording7.5.1 The data acquisition system must be of an adequatespeed to ensure that time resolution in determining half of themaximum temperature rise on the thermogram is at least 1 %,for the fastest thermogram for which the system is qualified.7.6 Mea
32、surement of specimens temperature is to be doneby accepted means, such as calibrated thermocouple, opticalpyrometer, platinum RTD, etc. whichever is appropriate for thetemperature range. In all cases, such a device must be inintimate contact with or trained on the sample holder, in closeproximity of
33、 the specimen. Touching the specimen withthermocouples is not recommended. Embedding thermo-couples into the sample is not acceptable.7.7 The temperature controller and/or programmer are tobring the specimen to the temperatures of interest.8. Test Specimen8.1 The usual specimen is a thin circular di
34、sc with a frontsurface area less than that of the energy beam. Typically,specimens are 10 to 12.5 mm in diamete (in special cases, assmall as 6 mm diameter and as large as 30 mm diameter havebeen reported as used successfully). The optimum thicknessdepends upon the magnitude of the estimated thermal
35、 diffusiv-ity, and should be chosen so that the time to reach half of themaximum temperature falls within the 10 to 1000 ms range.Thinner specimens are desired at higher temperatures tominimize heat loss corrections; however, specimens shouldalways be thick enough to be representative of the test ma
36、terial.Typically, thicknesses are in the 1 to 6 mm range.8.2 Specimens must be prepared with faces flat and parallelwithin 0.5 % of their thickness, in order to keep the error inthermal diffusivity due to the measurement average thickness,to less than 1 %. Non-uniformity of iether surface (craters,s
37、cratches, markings) of significant depth compared to thespecimen thickness should be avoided8.3 Specimen Surface PreparationIt is a good practice toapply a very thin, uniform graphite or other high emissivitycoating on both faces of the specimen to be tested, prior toperforming the measurements. The
38、 coating may be applied byspraying, painting, sputtering, etc. This will improve thecapability of the specimen to absorb the energy applied,especially in case of highly reflective materials. For transparentmaterials, a layer of gold, silver, or other opaque materialsmust be deposited first, followed
39、 by graphite coating. For someopaque reflective materials, grit blasting of the surface canprovide sufficient pulse absorption and emissivity, especially athigher temperatures, where coatings may not be stable or mayreact with the material.9. Calibration and Verification9.1 Calibrate the micrometer
40、used to measure the specimenthickness, so that the thickness measurements are accurate towithin 0.2 %.9.2 The Flash Method is an absolute (primary) method byitself, therefore it requires no calibration. However, actualexecution of the measurement itself is subject to random andsystematic errors. It
41、is therefore important to periodicallyverify the performance of a device, to establish the extent theseerrors may affect the data generated. This can be accomplishedby testing one or several materials whose thermal diffusivity iswell known. While most materials used are not true certifiedstandards,
42、they are generally accepted industry-wide with thebest available literature data (see Appendix X3).9.2.1 It must be emphasized that the use of referencematerials to establish validity of the data on unknown materialshas often led to unwarranted statements on accuracy. The useof references is only va
43、lid when the properties of the reference(including half-rise times and thermal diffusivity values) areclosely similar to those of the unknown and the temperature-rise curves are determined in an identical manner for thereference and unknown.9.2.2 One important check of the validity of data (inadditi
44、on to the comparison of the rise curve with the theoreticalmodel), when corrections have been applied, is to vary thespecimen thickness. Since the half times vary as L2, decreasingthe specimen thickness by one-half should decrease the halftime to one-fourth of its original value. Thus, if one obtain
45、s thesame thermal diffusivity value (appropriate heat loss correc-tions being applied) with representative specimens from thesame material of significantly different thicknesses, the resultscan be assumed valid.10. Procedure10.1 For commercially produced systems, follow manufac-turers instructions.1
46、0.2 The testing procedure must contain the followingfunctions:10.2.1 Determine and record the specimen thickness.FIG. 3 Block Diagram of a Flash SystemE146107310.2.2 Mount the specimen in its holder.10.2.3 Establish vacuum or inert gas environment in thechamber if necessary.10.2.4 Determine specimen
47、 temperature unless the systemwill do it automatically.10.2.5 Especially at low temperatures, use the lowest levelof power for the energy pulse able to generate a measurabletemperature rise, in order to ensure that the detector functionswithin its linear range.10.2.6 After the pulse delivery, monito
48、r the raw or pro-cessed thermogram to establish in-range performance. In caseof multiple sample testing, it is advisable (for time economy) tosequentially test samples at the same temperature (includingreplicate tests) before proceeding to the next test temperature.10.2.7 In all cases, the temperatu
49、re stability (base line) priorand during a test must be verified either manually or automati-cally to be less than 4 % of the maximum temperature rise.Testing on a ramp is not recommended.10.2.8 Determine the specimen ambient temperature andcollect the base line, transient-rise and cooling data, andanalyze the results according to Section 11.10.2.9 Change or program the specimen temperature asdesired and repeat the data collection process to obtainmeasurements at each temperature.10.2.10 If required, repeat the measurements at each tem-perature
