1、Designation: C 714 05e1An American National StandardStandard Test Method forThermal Diffusivity of Carbon and Graphite by ThermalPulse Method1This standard is issued under the fixed designation C 714; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the 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.e1NOTEEditorial corrections were made to the end of 4.3 and 7.1 in January 2006.1. Scope1.1 This te
3、st method covers the determination of the thermaldiffusivity of carbons and graphite to 65 % at temperatures upto 500C. It requires only a small easily fabricated specimen.Thermal diffusivity values in the range from 0.04 to 2.0 cm2/sare readily measurable by this test method; however, for thereason
4、 outlined in Section 5, for materials outside this rangethis test method may require 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
5、 practices and determine the applica-bility of regulatory limitations prior to use.2. Summary of Test Method2.1 A high-intensity short-duration thermal pulse from aflash lamp is absorbed on the front surface of a specimen; andthe rear surface temperature change as a function of time isobserved on an
6、 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 cryostat. Thermal diffusivity iscalculated from the specimen thickness and the time requiredfor the temperature of th
7、e back surface to rise to one half of itsmaximum value (1).22.2 The critical factors in this test method are:2.2.1 t/t12 must be 0.02 or less. t is the pulse time as definedin Fig. 1 and t12 is the time for the rear surface temperature torise to one half of its maximum value (see Fig. 2).2.2.2 Heat
8、losses from the specimen via radiation, convec-tion, or conduction to the specimen holder must be small.Whether or not this condition is violated can be determinedexperimentally from the oscilloscope trace, an example ofwhich is shown in Fig. 2.IfD T (10 t12 )/D T (t12 ) 1.98, theheat losses are ass
9、umed to be zero.2.2.3 The oscilloscope trace must be such that DTmax, D T(10 t12 ), and t12 can be determined to 62%.2.2.4 The other conditions are less critical, and the experi-menter is left to his discretion.3. Significance and Use3.1 Thermal diffusivity is an important property required forsuch
10、purposes as design applications under transient heat flowconditions, determination of safe operating temperature, pro-cess control, and quality assurance.3.2 The flash method is used to measure values of thermaldiffusivity (a) of a wide range of solid materials. It isparticularly advantageous becaus
11、e of the simple specimengeometry, small specimen size requirements, rapidity of mea-surement, and ease of handling materials having a wide rangeof thermal diffusivity values over a large temperature rangewith a single apparatus. The short measurement times involvedreduce the chances of contamination
12、 and change of specimenproperties due to exposure to high temperature environments.3.3 Thermal diffusivity results in many cases can be com-bined with values for specific heat (Cp) and density (r) andused to derive thermal conductivity (l) from the relation l =aCpr.3.4 This test method can be used t
13、o characterize graphite fordesign purposes.4. Apparatus4.1 The essential features of the apparatus are shown in Fig.3. The 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 of
14、the sample.4.2 Thermocouple, used to monitor the transient tempera-ture response of the rear surface of the specimen. The wire endsshould be prepared to minimize heat losses from the specimento the thermocouple wires (that is, by grinding to points or1This test method is under the jurisdiction of AS
15、TM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Nov. 1, 2005. Published November 2005. Originallyapproved in 1972. Last previous edition approved in 2000 as C 71485(2000)
16、.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.clipping) and attached in a manner that prevents penetrationinto the specimen. They a
17、re separated by about 1 mm so thatthe electrical circuit of the thermocouple is completed throughthe specimen.4.3 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
18、range from 0.06 to 10 kHz to be perfectlyinsensitive to frequency in the range of interest described inSection 5. A minimum vertical deflection sensitivity of 1 C/cmis recommended. The cathode-ray tube should have a usableviewing area of at least 40 by 100 mm. A camera is used toFIG. 1 Flash Tube Re
19、sponseFIG. 2 Example of Oscilloscope Trace Showing Parameters Used to Calculate Thermal DiffusivityC71405e12photograph the oscilloscope trace. Alternatively, a digitaloscilloscope connected to a digital recording device may beused.4.4 Flash TubeThe experimenter has considerable lati-tude in his choi
20、ce of flash tube. A typical 1000-J unit raises thespecimen temperature from 1 to 3C. The power supply forsuch a unit might consist of a 125-F capacitor bank charged to4000 V; discharge time would be about 1 ms. Either an externaltrigger device or a delayed trigger pulse from the oscilloscopemay be u
21、sed to fire the flash tube.5. Test Specimen5.1 The specimen shall be a circular disk, 2 to 4 mm thickand 6 to 12 mm in diameter; however, several things must beconsidered in choosing specimen dimensions. The diameter isfairly arbitrary except that it must not be too large relative tothe flash source
22、 because the front surface of the specimen mustbe illuminated uniformly and, therefore, heated uniformly.Specimen thickness must be selected so that t/t12 1.98 and sufficiently small pulse width (t/t12 0.139.8.2 Where heat losses from the sample are significant orwhere the duration of the thermal pu
23、lse is not sufficiently short,techniques have been developed for applying the necessarycorrections (2,3,4,5).9. Report9.1 The report shall include the following:9.1.1 Thermal pulse source,9.1.2 Method of calculation,9.1.3 Identification and previous history of the test speci-men,9.1.4 Ambient temper
24、ature of the specimen,9.1.5 Calculated value of thermal diffusivity, and9.1.6 Density of the specimen.10. Keywords10.1 carbon; graphite; thermal conductivity; thermal diffu-sivityFIG. 3 Schematic Diagram of ApparatusC71405e13REFERENCES(1) Parker, W. J., Jenkins, R. J., Butler, C. P., and Abbott, G.
25、L., “FlashMethod of Determining Thermal Diffusivity, Heat Capacity, 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.
26、(3) Cowan, R. D., “Pulse Method of Measuring Thermal Diffusivity 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, 196
27、3, p. 1909.(5) Larson, K. B. and Koyama, K., “Correction for Finite-Pulse TimeEffects in Very Thin Samples Using the Flash Method of MeasuringThermal Diffusivity,” Journal of Applied Physics, Vol 38, 1967, p. 465.ASTM International takes no position respecting the validity of any patent rights asser
28、ted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by
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30、e careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM Intern
31、ational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).C71405e14
