1、Designation: E2585 09 (Reapproved 2015)Standard Practice forThermal Diffusivity by the Flash Method1This standard is issued under the fixed designation E2585; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. 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 practice covers practical details associated with thedetermination of the thermal diffusivity of primarily homoge-neous isotr
3、opic solid materials. Thermal diffusivity valuesranging from 10-7to 10-3m2/s are readily measurable by thisfrom about 75 to 2800 K.1.2 This practice is adjunct to Test Method E1461.1.3 This practice is applicable to the measurements per-formed on materials opaque to the spectrum of the energypulse,
4、but with special precautions can be used on fully orpartially transparent materials.1.4 This practice is intended to allow a wide variety ofapparatus designs. It is not practical in a document of this typeto establish details of construction and procedures to cover allcontingencies that might offer
5、difficulties to a person withoutpertinent technical knowledge, or to stop or restrict researchand development for improvements in the basic technique.This practice provides guidelines for the constructionprinciples, preferred embodiments and operating parametersfor this type of instruments.1.5 This
6、practice is applicable to the measurements per-formed on essentially fully dense materials; however, in somecases it has shown to produce acceptable results when usedwith porous specimens. Since the magnitude of porosity, poreshapes, and parameters of pore distribution influence thebehavior of the t
7、hermal diffusivity, extreme caution must beexercised when analyzing data. Special caution is advisedwhen other properties, such as thermal conductivity, arederived from thermal diffusivity obtained by this method.1.6 The flash can be considered an absolute (or primary)method of measurement, since no
8、 reference materials arerequired. It is advisable to use only reference materials toverify the performance of the instrument used.1.7 This method is applicable only for homogeneous solidmaterials, in the strictest sense; however, in some cases it hasbeen shown to produce data found to be useful in c
9、ertainapplications:1.7.1 Testing of Composite MaterialsWhen substantialnon-homogeneity and anisotropy is present in a material, thethermal diffusivity data obtained with this method may besubstantially in error. Nevertheless, such data, while usuallylacking absolute accuracy, may be useful in compar
10、ing mate-rials of similar structure. Extreme caution must be exercisedwhen related properties, such as thermal conductivity, arederived, as composite materials, for example, may have heatflow patterns substantially different than uniaxial. In caseswhere the particle size of the composite phases is s
11、mallcompared to the specimen thickness (on the order of 1 to 25 %of thickness) and where the transient thermal response of thespecimen appears homogenous when compared to the model,this method can produce accurate results for composite mate-rials. Anisotropic materials can be measured by varioustech
12、niques, as long as the directional thermal diffusivities (twodimensional or three dimensional) are mutually orthogonal andthe measurement and specimen preparation produce heat flowonly along one principle direction. Also, 2D and 3D modelsand either independent measurements in one or two directions,o
13、r simultaneous measurements of temperature response atdifferent locations on the surface of the specimen, can beutilized.1.7.2 Testing LiquidsThis method has found an especiallyuseful application in determining thermal diffusivity of moltenmaterials. For this technique, specially constructed specime
14、nenclosures must be used.1.7.3 Testing Layered MaterialsThis method has alsobeen extended to test certain layered structures made ofdissimilar materials, where the thermal properties of one of thelayers are considered unknown. In some cases, contact con-ductance of the interface may also be determin
15、ed.1This practice is under the jurisdiction of ASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.05 on Thermo-physical Properties.Current edition approved Sept. 1, 2015. Published September 2015. Originallyapproved in 2009. Last previous edition approved
16、in 2009 as E2585 09. DOI:10.1520/E2585-09R15.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.8 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.9 This standard
17、 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
18、Standards:2E228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE1461 Test Method for Thermal Diffusivity by the FlashMethod3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 thermal conductivity, , of a solid materialthe timerate of steady h
19、eat 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 diffusivity, , of a solid ma
20、terialthe propertygiven by the thermal conductivity divided by the product of thedensity and heat capacity per unit mass.3.2 Description of Symbols and Units Specific to ThisStandard:3.2.1 Cpspecific heat capacity, J/(kgK).3.2.2 Ddiameter, metres.3.2.3 kconstant depending on percent rise.3.2.4 Kcorr
21、ection factors.3.2.5 K1,K2constants depending on .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*=4st/DT2).3.2.10 Ttemperature, K.3.2.11 thermal d
22、iffusivity, m2/s.3.2.12 thermal conductivity, (W/mK).3.2.13 fraction of pulse duration required to reach maxi-mum intensity.3.2.14 density, kg/m3.3.2.15 t5T(5t12 )/T(t12 ).3.2.16 t10T(10t12 )/T(t12 ).3.2.17 Tmaxtemperature difference between baseline andmaximum rise, K.3.3 Description of Subscripts
23、Specific to This Standard:3.3.1 CCowan.3.3.2 mmaximum.3.3.3 oambient.3.3.4 Rratio.3.3.5 sspecimen.3.3.6 ttime.3.3.7 Tthermocouple.3.3.8 xpercent rise.4. Summary of Practice4.1 A small, thin disc specimen is subjected to a high-intensity short duration radiant energy pulse (Fig. 1). Theenergy of the
24、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 specimen thickness and the time required for the rearface temperature rise to reach certain percentages of itsmaximum valu
25、e. When the thermal diffusivity of the sample isto be determined over a temperature range, the measurementmust be repeated at each temperature of interest. This isdescribed in detail in a number of publications (1, 2)3andreview articles (3, 4, 5). A summary of the theory can be foundin Test Method E
26、1461, Appendix 1.5. Significance and Use5.1 Thermal diffusivity is an important property, requiredfor such purposes under transient heat flow conditions, such asdesign applications, determination of safe operatingtemperature, process control, and quality assurance.2For referenced ASTM standards, vis
27、it 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.3The boldface numbers given in parentheses refer to a list of references at theend of the text.F
28、IG. 1 Block Diagram of a Flash SystemE2585 09 (2015)25.2 The flash method is used to measure values of thermaldiffusivity, , of a wide range of solid materials. It is particu-larly advantageous because of simple specimen geometry,small specimen size requirements, rapidity of measurementand ease of h
29、andling.5.3 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 (seeTest Method E1461, Appendix 1).5.4 Thermal diffusivity results, together with related valuesof specific heat capa
30、city (Cp) and density () values, can beused in many cases to derive thermal conductivity (), accord-ing to the relationship: 5 Cp (1)6. Interferences6.1 In principle, the thermal diffusivity is obtained from thethickness of the sample and from a characteristic time functiondescribing the propagation
31、 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 morespecifically the finite
32、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 byperforming a l
33、arge 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 for performing a rigorousevaluation of these factors are given in (6).7. Apparatus7.1 The essentia
34、l components of the apparatus are shown inFig. 1. These are the flash source, specimen holder, environ-mental enclosure (optional), temperature response detector andrecording device.7.2 The flash source may be a pulse laser, a flash lamp, orother device capable to generate a short duration pulse ofs
35、ubstantial 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, to keep the error dueto finite pulse width less than 0.5 %, if pulse width correction(7, 8, 9) is not applied.7.2.1 The pulse hitting the
36、 specimens surface must bespatially uniform in intensity. Most pulse lasers exhibit hotspots and a substantially higher intensity in the center region ofthe beam than in the periphery. For this reason, systems usingunmodified beams directly from a pulse laser should use beamssomewhat larger in diame
37、ter than the largest diameter of thespecimens to be tested. The use of an optical fiber between thelaser and the specimen improves substantially the uniformity ofthe beam (up to 95 %). Since this method produces almost noedge effects, a larger portion of the energy can be directed tothe specimen tha
38、n from natural beam lasers.7.2.2 Most commonly used lasers are: ruby (visible red),Nd: glass, and Nd: YAG (near infrared); however, other typesof lasers may be used. In some instances, properly engineeredXenon flash sources can provide comparable performance forall but the shortest rise times. Xenon
39、 flash sources, whenproperly focused, provide a lower cost and lower maintenancealternative to lasers for many applications.7.3 An environmental control chamber is required for mea-surements above and below room temperature. This chambermust be gas or vacuum tight if operation in a protectiveatmosph
40、ere is desired. The enclosure shall be fitted with awindow, which has to be transparent to the flash source. Asecond window is required if optical detection of the rear facetemperature rise is used. In such cases it is recommended thatthe optical detector be shielded from direct exposure to theenerg
41、y beam with the use of appropriate filter(s).7.4 The furnace or cryostat should be loosely coupled(thermally) to the specimen support and shall be capable ofmaintaining the specimen temperature constant within4%ofthe maximum temperature rise over a time period equal to fivehalves of the maximum rise
42、 time. The furnace may behorizontal or vertical. The specimen support shall also beloosely coupled thermally to the specimen. Specimen supportsmay be constructed to house one specimen or several at a time,with the latter providing substantial improvements in data andtesting speed.7.5 The detector ca
43、n be a thermocouple (see Appendix X1),infrared detector, optical pyrometer, or any other means thatcan provide a linear electrical output proportional to a smalltemperature rise. It shall be capable of detecting 0.05 K changeabove the specimens initial temperature. The detector and itsassociated amp
44、lifier must have a response time substantiallysmaller than2%ofthehalf-rise time value. When intrinsicthermocouples are used, the same response requirements shallapply. Electronic filters, if used, shall be verified not to distortthe shape of the thermogram. Several precautions are requiredwhen using
45、 optical temperature sensing. The sensor must befocused on the center of the back surface of the specimen. Italso must be protected from the energy beam, to preventdamage or saturation. When the specimen is housed in afurnace, the energy beam may bounce or shine past the edgesand enter the detector.
46、 To avoid this, proper shielding isnecessary. For protection against lasers, dielectric spike filtersthat are opaque at the selected wavelength are very useful. Theviewing window and any focusing lenses must not absorbappreciably the radiation in the wavelength region of thedetector. This is particu
47、larly important for infrared detectors,and means should be provided to ensure that during hightemperature measurements all window surfaces are monitoredand kept free of deposits, which might lead to absorption ofenergy. Such build-ups can lead to loss of signal intensity andmay cause non-uniform spe
48、cimen heating from the energysource.7.6 The signal conditioner includes the electronic circuit tobias out the ambient temperature reading, spike filters, ampli-fiers and analog-to-digital converters.E2585 09 (2015)37.7 Data Recording:7.7.1 The data acquisition system must be of an adequatespeed to e
49、nsure 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.7.7.2 The recorded signal must contain information thatenables the precise definition of the starting time of the energypulse.7.7.2.1 If no other means are available, the inevitable spikecaused by the trigger pulse (for a laser of flash lamp) may beused. This, however, is considered marginal, as it uses thebeginning of the capacitor discharge as “time zer
