1、Designation: C714 05 (Reapproved 2015)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 oforigina
2、l adoption 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. Scope Scope*1.1 This test method covers the determination of the thermal di
3、ffusivity of carbons and graphite to 65 % at temperatures up to500 C. It requires only a small easily fabricated specimen. Thermal diffusivity values in the range from 0.04 cm2/s to 2.0 cm2/sare readily measurable by this test method; however, for the reason outlined in Section 57, for materials out
4、side this range this testmethod may require modification.1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicabilit
5、y of regulatorylimitations prior to use.1.3 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Tra
6、de Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C781 Practice for Testing Graphite and Boronated Graphite Materials for High-Temperature Gas-Cooled Nuclear ReactorComponentsD7775 Guide for Measurements on Small Graphite SpecimensE1461 Test Metho
7、d for Thermal Diffusivity by the Flash Method3. Terminology3.1 Definitions:3.1.1 thermal conductivity, nthe rate at which heat passes through a material, expressed as the amount of heat that flows perunit time through a unit area with a temperature gradient of one degree per unit distance.3.1.2 ther
8、mal diffusivity, na measure of the ability of a material to conduct thermal energy relative to its ability to store thermalenergy; it is equal to the thermal conductivity divided by density and specific heat capacity at constant pressure.4. Summary of Test Method4.1 A high-intensity short-duration t
9、hermal pulse from a flash lamp is absorbed on the front surface of a specimen; and the rearsurface temperature change as a function of time is observed on an oscilloscope. The pulse raises the average temperature of thespecimen only a few degrees above its initial value. The ambient temperature of t
10、he specimen is controlled by a furnace or cryostat.Thermal diffusivity is calculated from the specimen thickness and the time required for the temperature of the back surface to riseto one half of its maximum value (1).34.2 The critical factors in this test method are:4.2.1 /t12 must be 0.02 or less
11、. is the pulse time as defined in Fig. 1 and t12 is the time for the rear surface temperature to riseto one half of its maximum value (see Fig. 2).1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
12、 SubcommitteeD02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Oct. 1, 2015May 1, 2017. Published December 2015May 2017. Originally approved in 1972. Last previous edition approved in 20102015 asC714 05 (2010).(2015). DOI: 10.1520/C0714-05R15.10.1520/C0714-17.2 For referen
13、cedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The boldface numbers in parentheses refer to the list of references at t
14、he end of this test method.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends t
15、hat users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
16、 Conshohocken, PA 19428-2959. United States14.2.2 Heat losses from the specimen via radiation, convection, or conduction to the specimen holder must be small. Whetheror not this condition is violated can be determined experimentally from the oscilloscope trace, an example of which is shown inFig. 2.
17、 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 t12can be determined to 62 %.4.2.4 The other conditions are less critical, and the experimenter is left to his discretion.FIG. 1 Flash Tube ResponseFIG. 2 Example of
18、 Oscilloscope Trace Showing Parameters Used to Calculate Thermal DiffusivityC714 1725. Significance and Use5.1 Thermal diffusivity is an important property required for such purposes as design applications under transient heat flowconditions, determination of safe operating temperature, process cont
19、rol, and quality assurance.5.2 The flash method is used to measure values of thermal diffusivity () of a wide range of solid materials. It is particularlyadvantageous because of the simple specimen geometry, small specimen size requirements, rapidity of measurement, and ease ofhandling materials hav
20、ing a wide range of thermal diffusivity values over a large temperature range with a single apparatus. Theshort measurement times involved reduce the chances of contamination and change of specimen properties due to exposure to hightemperature environments.5.3 Thermal diffusivity results in many cas
21、es can be combined with values for specific heat (Cp) and density () and used toderive thermal conductivity () from the relation = Cp. For guidance on converting thermal diffusivity to thermal conductivity,refer to Practice C781.5.4 This test method can be used to characterize graphite for design pu
22、rposes.5.5 Test Method E1461 is a more detailed form of this test method and has applicability to much wider ranges of materials,applications, and temperatures.6. Apparatus6.1 The essential features of the apparatus are shown in Fig. 3. The window may be any material that is transparent to the flash
23、source. The specimen holder should be a ceramic or other material whose thermal conductivity is low relative to that of the sample.6.2 Thermocouple, used to monitor the transient temperature response of the rear surface of the specimen. The wire ends shouldbe prepared to minimize heat losses from th
24、e specimen to the thermocouple wires (that is, by grinding to points or clipping) andattached in a manner that prevents penetration into the specimen. They are separated by about 1 mm so that the electrical circuitof the thermocouple is completed through the specimen.6.3 Oscilloscope, with calibrate
25、d sweep speeds that can be varied from 0.1 mscm to 0.5 scm or more. The vertical amplifiersection of the oscilloscope should have a frequency response in the range from 0.06 kHz to 10 kHz to be perfectly insensitive tofrequency in the range of interest described in Section 57. A minimum vertical def
26、lection sensitivity of 1 Ccm is recommended.The cathode-ray tube should have a usable viewing area of at least 40 mm by 100 mm. A camera is used to photograph theoscilloscope trace. Alternatively, a digital oscilloscope connected to a digital recording device may be used.6.4 Flash TubeThe experiment
27、er has considerable latitude in his choice of flash tube.Atypical 1000 J unit raises the specimentemperature from 1 C to 3 C. The power supply for such a unit might consist of a 125 F capacitor bank charged to 4000 V;discharge time would be about 1 ms. Either an external trigger device or a delayed
28、trigger pulse from the oscilloscope may be usedto fire the flash tube.7. Test Specimen7.1 The specimen shall be a circular disk, 2 mm to 4 mm thick and 6 mm to 12 mm in diameter; however, several things mustbe considered in choosing specimen dimensions. The diameter is fairly arbitrary except that i
29、t must not be too large relative to theflash source because the front surface of the specimen must be illuminated uniformly and, therefore, heated uniformly. Specimenthickness must be selected so that /t12 1.98 and sufficiently small pulse width (/t12 0.139.10.2 Where heat losses from the sample are
30、 significant or where the duration of the thermal pulse is not sufficiently short,techniques have been developed for applying the necessary corrections (2,3,4,5).11. Report11.1 The report shall include the following:11.1.1 Thermal pulse source,11.1.2 Method of calculation,11.1.3 Identification and p
31、revious history of the test specimen,11.1.4 Ambient temperature Temperature of the specimen,11.1.5 Calculated value of thermal diffusivity, and11.1.6 Any change in mass of the specimen, and11.1.7 Density of the specimen.Operational validation of the instrument, that is, a comparison of a reference m
32、aterial diffusivitymeasurement in the temperature range of interest to published data.12. Keywords12.1 carbon; graphite; thermal conductivity; thermal diffusivityC714 174REFERENCES(1) Parker, W. J., Jenkins, R. J., Butler, C. P., and Abbott, G. L., “Flash Method of Determining Thermal Diffusivity, H
33、eat Capacity, and ThermalConductivity,” Journal of Applied Physics, JAPIA, Vol 32 , 1961, p. 1679.(2) Taylor, R. E. and Cape, J. A., “Finite Pulse-Time Effects in the Flash Diffusivity Technique,” Applied Physics Letters, Vol 5, No. 10, 1964, p. 212.(3) Cowan, R. D., “Pulse Method of Measuring Therm
34、al Diffusivity at High Temperatures,” Journal of Applied Physics, Vol 34, 1963, p. 926.(4) Cape, J. A. and Lehman, G. W., “Temperature and Pulse-Time Effects in the Flash Method for Measuring Thermal Diffusivity,” Journal of AppliedPhysics, Vol 34, 1963, p. 1909.(5) Larson, K. B. and Koyama, K., “Co
35、rrection for Finite-Pulse Time Effects in Very Thin Samples Using the Flash Method of Measuring ThermalDiffusivity,” 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 (2
36、015) that may impact 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.ASTM International takes no position respecting the validity of any patent rights asserte
37、d 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 th
38、e responsible technical 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 c
39、areful 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 Internati
40、onal, 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). 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:/ 175
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