ASTM C714-85(2000)
(Test Method)Standard Test Method for Thermal Diffusivity of Carbon and Graphite by a Thermal Pulse Method
Standard Test Method for Thermal Diffusivity of Carbon and Graphite by a Thermal Pulse Method
SCOPE
1.1 This test method covers the determination of the thermal diffusivity of carbons and graphite to +5% at temperatures up to 500°C. It requires only a small easily fabricated specimen. Thermal diffusivity values in the range from 0.04 to 2.0 cm /s are readily measurable by this test method; however, for the reason outlined in Section 5, for materials outside this range this test method may require modification.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation:C 714–85(Reapproved2000)
Standard Test Method for
Thermal Diffusivity of Carbon and Graphite by a Thermal
Pulse Method
This standard is issued under the fixed designation C 714; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2.3 The oscilloscope trace must be such that DT , D T
max
1 1
(10 t ⁄2), and t ⁄2 can be determined to 62%.
1.1 Thistestmethodcoversthedeterminationofthethermal
2.2.4 The other conditions are less critical, and the experi-
diffusivity of carbons and graphite to 65 % at temperatures up
menter is left to his discretion.
to 500°C. It requires only a small easily fabricated specimen.
Thermal diffusivity values in the range from 0.04 to 2.0 cm /s
3. Significance and Use
are readily measurable by this test method; however, for the
3.1 Sulfur, even in very low concentrations, is of concern in
reason outlined in Section 5, for materials outside this range
a nuclear reactor because of potential corrosion of metallic
this test method may require modification.
components. This test method has the sensitivity to analyze
1.2 This standard does not purport to address all of the
very low sulfur contents in graphite using very small samples.
safety concerns, if any, associated with its use. It is the
3.2 This test method can be used to characterize graphite for
responsibility of the user of this standard to establish appro-
design purposes.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4. Apparatus
2. Summary of Test Method 4.1 The essential features of the apparatus are shown in Fig.
3. The window may be any material that is transparent to the
2.1 A high-intensity short-duration thermal pulse from a
flash source.The specimen holder should be a ceramic or other
flash lamp is absorbed on the front surface of a specimen; and
material whose thermal conductivity is low relative to that of
the rear surface temperature change as a function of time is
the sample.
observed on an oscilloscope. The pulse raises the average
4.2 Thermocouple, used to monitor the transient tempera-
temperature of the specimen only a few degrees above its
tureresponseoftherearsurfaceofthespecimen.Thewireends
initial value. The ambient temperature of the specimen is
should be prepared to minimize heat losses from the specimen
controlled by a furnace or cryostat. Thermal diffusivity is
to the thermocouple wires (that is, by grinding to points or
calculated from the specimen thickness and the time required
clipping) and attached in a manner that prevents penetration
for the temperature of the back surface to rise to one half of its
2 into the specimen. They are separated by about 1 mm so that
maximum value (1).
the electrical circuit of the thermocouple is completed through
2.2 The critical factors in this test method are:
the specimen.
2.2.1 t/t ⁄2 must be 0.02 or less. t is the pulse time as defined
4.3 Oscilloscope, with calibrated sweep speeds that can be
in Fig. 1 and t ⁄2 is the time for the rear surface temperature to
varied from 0.1 ms/cm to 0.5 s/cm or more. The vertical
rise to one half of its maximum value (see Fig. 2).
amplifier section of the oscilloscope should have a frequency
2.2.2 Heat losses from the specimen via radiation, convec-
response in the range from 0.06 to 10 kHz to be perfectly
tion, or conduction to the specimen holder must be small.
insensitive to frequency in the range of interest described in
Whether or not this condition is violated can be determined
Section 5.Aminimum vertical deflection sensitivity of 1 C/cm
experimentally from the oscilloscope trace, an example of
is recommended. The cathode-ray tube should have a usable
1 1
which is shown in Fig. 2. If D T (10 t ⁄2)/D T (t ⁄2) > 1.98, the
viewing area of at least 40 by 100 mm. A camera is used to
heat losses are assumed to be zero.
photograph the oscilloscope trace.
4.4 Flash Tube—The experimenter has considerable lati-
This test method is under the jurisdiction of ASTM Committee D02 on tude in his choice of flash tube.Atypical 1000-J unit raises the
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
specimen temperature from 1 to 3°C. The power supply for
D02.F on Manufactured Carbon and Graphite Products .
suchaunitmightconsistofa125-µFcapacitorbankchargedto
Current edition approved July 26, 1985. Published September 1985. Originally
4000V;dischargetimewouldbeabout1ms.Eitheranexternal
published as C 714 – 72. Last previous edition C 714 – 72.
The boldface numbers in parentheses refer to the list of references at the end of
this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 714
FIG. 1 Flash Tube Response
FIG. 2 Example of Oscilloscope Trace Showing Parameters Used to Calculate Thermal Diffusivity
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