1、Designation: C714 05 (Reapproved 2015) 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 adopt
2、ion or, in the case 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. Scope1.1 This test method covers the determination of the thermaldiffusivity of ca
3、rbons and graphite to 65 % at temperatures upto 500 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 5, for materials outside thisrange thi
4、s 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 practices and determine the applica-bility of regulatory l
5、imitations 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 oscilloscope. The pulse raises the averagetemperature of t
6、he 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 the back surface to rise to one half of itsmaximum value (1).
7、22.2 The critical factors in this test method are:2.2.1 /t12 must be 0.02 or less. 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 losses from the specimen via radiation,convection, or conducti
8、on to the specimen holder must besmall. Whether or not this condition is violated can bedetermined experimentally from the oscilloscope 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.2.2.3 The oscilloscope trace must be such that Tmax,
9、 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 purposes as design applications under transient heat flowconditions, de
10、termination of safe operating temperature, pro-cess control, and quality assurance.3.2 The flash method is used to measure values of thermaldiffusivity () of a wide range of solid materials. It isparticularly advantageous because of the simple specimengeometry, small specimen size requirements, rapi
11、dity ofmeasurement, and ease of handling materials having a widerange of thermal diffusivity values over a large temperaturerange with a single apparatus. The short measurement timesinvolved reduce the chances of contamination and change ofspecimen properties due to exposure to high temperatureenvir
12、onments.3.3 Thermal diffusivity results in many cases can be com-bined with values for specific heat (Cp) and density () andused to derive thermal conductivity () from the relation =Cp.3.4 This test method can be used to characterize graphite fordesign purposes.4. Apparatus4.1 The essential features
13、 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 ofthe sample.4.2 Thermocouple, used to monitor the transient tempera-ture response
14、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 orclipping) and attached in a manner that prevents penetration1This test method is under the jurisdiction of ASTM Committee D02 onPe
15、troleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Oct. 1, 2015. Published December 2015. Originallyapproved in 1972. Last previous edition approved in 2010 as C714 05 (2010).DOI:
16、 10.1520/C0714-05R15.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1into the specimen. They are separated by about 1 mm so thatthe ele
17、ctrical 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 range from 0.06 kHz to 10 kHz to be perfe
18、ctlyinsensitive 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 usableFIG. 1 Flash Tube ResponseFIG. 2 Example of Oscilloscope Trace Showing Parameters Used to Calculate Thermal Diffusi
19、vityC714 05 (2015)2viewing area of at least 40 mm by 100 mm. A camera is usedto photograph the oscilloscope trace. Alternatively, a digitaloscilloscope connected to a digital recording device may beused.4.4 Flash TubeThe experimenter has considerable latitudein his choice of flash tube. A typical 10
20、00 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 ms. Either an externaltrigger device or a delayed trigger pulse from the oscilloscopemay be used to fire the flash tube.
21、5. Test Specimen5.1 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 dimensions. Thediameter is fairly arbitrary except that it must not be too largerelative to the flash source because the front su
22、rface 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 0.139.8.2 Where heat losses from the sample are significant orwhere the duration of the thermal pulse is not sufficiently
23、 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 testspecimen,9.1.4 Ambient temperature of the specimen,9.1
24、.5 Calculated value of thermal diffusivity, and9.1.6 Density of the specimen.FIG. 3 Schematic Diagram of ApparatusC714 05 (2015)310. Keywords10.1 carbon; graphite; thermal conductivity; thermal diffu-sivityREFERENCES(1) Parker, W. J., Jenkins, R. J., Butler, C. P., and Abbott, G. L., “FlashMethod of
25、 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.(3) Cowan, R. D.,
26、“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, 1963, p. 1909.(5) Lar
27、son, 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 asserted in connection w
28、ith 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 the responsible tec
29、hnical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful considera
30、tion 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 International, 100 Barr H
31、arbor 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 05 (2015)4
