1、Designation: C714 17 An American National StandardStandard Test Method forThermal Diffusivity of Carbon and Graphite by ThermalPulse Method1This standard is issued under the fixed designation C714; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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. Scope*1.1 This test method covers the determination of the thermaldiffusivity of carbons and graphit
3、e at temperatures up to500 C. It requires only a small easily fabricated specimen.Thermal diffusivity values in the range from 0.04 cm2/s to2.0 cm2/s are readily measurable by this test method; however,for the reason outlined in Section 7, for materials outside thisrange this test method may require
4、 modification.1.2 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 determine the applica-bility of regulatory limitations prior to use.1
5、.3 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to
6、Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C781 Practice for Testing Graphite and Boronated GraphiteMaterials for High-Temperature Gas-Cooled Nuclear Re-actor ComponentsD7775 Guide for Measurements on Small Graphite Speci-mensE1461 Test Method for Thermal Diffusivity by the Fla
7、shMethod3. Terminology3.1 Definitions:3.1.1 thermal conductivity, nthe rate at which heat passesthrough a material, expressed as the amount of heat that flowsper unit time through a unit area with a temperature gradient ofone degree per unit distance.3.1.2 thermal diffusivity, na measure of the abil
8、ity of amaterial to conduct thermal energy relative to its ability to storethermal energy; it is equal to the thermal conductivity dividedby density and specific heat capacity at constant pressure.4. Summary of Test Method4.1 A high-intensity short-duration thermal pulse from aflash lamp is absorbed
9、 on the front surface of a specimen; andthe rear surface temperature change as a function of time isobserved on an oscilloscope. The pulse raises the averagetemperature of the specimen only a few degrees above itsinitial value. The ambient temperature of the specimen iscontrolled by a furnace or cry
10、ostat. Thermal diffusivity iscalculated from the specimen thickness and the time requiredfor the temperature of the back surface to rise to one half of itsmaximum value (1).34.2 The critical factors in this test method are:4.2.1 /t12 must be 0.02 or less. is the pulse time as definedin Fig. 1 and t1
11、2 is the time for the rear surface temperature torise to one half of its maximum value (see Fig. 2).4.2.2 Heat losses from the specimen via radiation,convection, or conduction to the specimen holder must besmall. Whether or not this condition is violated can bedetermined experimentally from the osci
12、lloscope trace, anexample of which is shown in Fig. 2.If T(10 t12 )/ T(t12 )1.98, the heat losses are assumed to be zero.4.2.3 The oscilloscope trace must be such that Tmax, T(10 t12 ), and t12 can be determined to 62%.4.2.4 The other conditions are less critical, and the experi-menter is left to hi
13、s discretion.5. Significance and Use5.1 Thermal diffusivity is an important property required forsuch purposes as design applications under transient heat flow1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct respon
14、sibility ofSubcommittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved May 1, 2017. Published May 2017. Originallyapproved in 1972. Last previous edition approved in 2015 as C714 05 (2015).DOI: 10.1520/C0714-17.2For referenced ASTM standards, visit the ASTM website, www
15、.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 in parentheses refer to the list of references at the end ofthis test method.*A Summary of Changes
16、 section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decisi
17、on on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.131 conditions, determination of safe operating temperature, pro-cess control, and quality assurance.5.2 The flash method is u
18、sed to measure values of thermaldiffusivity () of a wide range of solid materials. It isparticularly advantageous because of the simple specimengeometry, small specimen size requirements, rapidity ofmeasurement, and ease of handling materials having a widerange of thermal diffusivity values over a l
19、arge temperatureFIG. 1 Flash Tube ResponseFIG. 2 Example of Oscilloscope Trace Showing Parameters Used to Calculate Thermal DiffusivityC714 17231 range with a single apparatus. The short measurement timesinvolved reduce the chances of contamination and change ofspecimen properties due to exposure to
20、 high temperatureenvironments.5.3 Thermal diffusivity results in many cases can be com-bined with values for specific heat (Cp) and density ()toderive thermal conductivity () from the relation = Cp. Forguidance on converting thermal diffusivity to thermalconductivity, refer to Practice C781.5.4 This
21、 test method can be used to characterize graphite fordesign purposes.5.5 Test Method E1461 is a more detailed form of this testmethod and has applicability to much wider ranges ofmaterials, applications, and temperatures.6. Apparatus6.1 The essential features of the apparatus are shown in Fig.3. The
22、 window may be any material that is transparent to theflash source. The specimen holder should be a ceramic or othermaterial whose thermal conductivity is low relative to that ofthe sample.6.2 Thermocouple, used to monitor the transient tempera-ture response of the rear surface of the specimen. The
23、wire endsshould be prepared to minimize heat losses from the specimento the thermocouple wires (that is, by grinding to points orclipping) and attached in a manner that prevents penetrationinto the specimen. They are separated by about 1 mm so thatthe electrical circuit of the thermocouple is comple
24、ted throughthe specimen.6.3 Oscilloscope, with calibrated sweep speeds that can bevaried from 0.1 ms cm to 0.5 s cm or more. The verticalamplifier section of the oscilloscope should have a frequencyresponse in the range from 0.06 kHz to 10 kHz to be perfectlyinsensitive to frequency in the range of
25、interest described inSection 7. A minimum vertical deflection sensitivity of 1 C cmis recommended. The cathode-ray tube should have a usableviewing area of at least 40 mm by 100 mm. A camera is usedto photograph the oscilloscope trace. Alternatively, a digitaloscilloscope connected to a digital reco
26、rding device may beused.6.4 Flash TubeThe experimenter has considerable latitudein his choice of flash tube. A typical 1000 J unit raises thespecimen temperature from 1 C to 3 C. The power supply forsuch a unit might consist of a 125 F capacitor bank charged to4000 V; discharge time would be about 1
27、 ms. Either an externaltrigger device or a delayed trigger pulse from the oscilloscopemay be used to fire the flash tube.7. Test Specimen7.1 The specimen shall be a circular disk, 2 mm to 4 mmthick and 6 mm to 12 mm in diameter; however, several thingsmust be considered in choosing specimen dimensio
28、ns. Thediameter is fairly arbitrary except that it must not be too largerelative to the flash source because the front surface of thespecimen must be illuminated uniformly and, therefore, heateduniformly. Specimen thickness must be selected so that /t12 1.98 and sufficiently small pulse width (/t12
29、0.139.10.2 Where heat losses from the sample are significant orwhere the duration of the thermal pulse is not sufficiently short,techniques have been developed for applying the necessarycorrections (2,3,4,5).11. Report11.1 The report shall include the following:11.1.1 Thermal pulse source,11.1.2 Met
30、hod of calculation,11.1.3 Identification and previous history of the testspecimen,11.1.4 Temperature of the specimen,11.1.5 Calculated value of thermal diffusivity,11.1.6 Any change in mass of the specimen, and11.1.7 Operational validation of the instrument, that is, acomparison of a reference mater
31、ial diffusivity measurement inthe temperature range of interest to published data.12. Keywords12.1 carbon; graphite; thermal conductivity; thermal diffu-sivityREFERENCES(1) Parker, W. J., Jenkins, R. J., Butler, C. P., and Abbott, G. L., “FlashMethod of Determining Thermal Diffusivity, Heat Capacity
32、, andThermal Conductivity,” Journal of Applied Physics, JAPIA, Vol 32 ,1961, p. 1679.(2) Taylor, R. E. and Cape, J. A., “Finite Pulse-Time Effects in the FlashDiffusivity Technique,” Applied Physics Letters, Vol 5, No. 10, 1964,p. 212.(3) Cowan, R. D., “Pulse Method of Measuring Thermal Diffusivity
33、atHigh Temperatures,” Journal of Applied Physics, Vol 34, 1963, p. 926.(4) Cape, J. A. and Lehman, G. W., “Temperature and Pulse-Time Effectsin the Flash Method for Measuring Thermal Diffusivity,” Journal ofApplied Physics, Vol 34, 1963, p. 1909.(5) Larson, K. B. and Koyama, K., “Correction for Fini
34、te-Pulse TimeEffects in Very Thin Samples Using the Flash Method of MeasuringThermal Diffusivity,” Journal of Applied Physics, Vol 38, 1967, p.465.SUMMARY OF CHANGESSubcommittee D02.F0 has identified the location of selected changes to this standard since the last issue(C714 00 (2015) that may impac
35、t the use of this standard. (Approved May 1, 2017.)(1) Added new Sections 2, Referenced Documents, and 3,Terminology.(2) Added new subsections 5.5, 7.3, and 11.1.7.(3) Revised subsection 5.3.C714 17431 ASTM International takes no position respecting the validity of any patent rights asserted in conn
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