ASTM C714-05(2010)
(Test Method)Standard Test Method for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse Method
Standard Test Method for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse Method
SIGNIFICANCE AND USE
3.1 Thermal diffusivity is an important property required for such purposes as design applications under transient heat flow conditions, determination of safe operating temperature, process control, and quality assurance.
3.2 The flash method is used to measure values of thermal diffusivity (α) of a wide range of solid materials. It is particularly advantageous because of the simple specimen geometry, small specimen size requirements, rapidity of measurement, and ease of handling materials having a wide range of thermal diffusivity values over a large temperature range with a single apparatus. The short measurement times involved reduce the chances of contamination and change of specimen properties due to exposure to high temperature environments.
3.3 Thermal diffusivity results in many cases can be combined with values for specific heat (Cp) and density (ρ) and used to derive thermal conductivity (λ) from the relation λ = αCpρ.
This test method can be used to characterize graphite for design purposes.
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 cm2/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 does not purport to address all of the safety concerns, if any, 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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Designation: C714 − 05(Reapproved 2010) An American National Standard
Standard Test Method for
Thermal Diffusivity of Carbon and Graphite by Thermal
Pulse Method
This standard is issued under the fixed designation C714; 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 (´) indicates an editorial change since the last revision or reapproval.
1 1
1. Scope example of which is shown in Fig. 2.If ∆ T(10 t ⁄2)/∆ T(t ⁄2)>
1.98, the heat losses are assumed to be zero.
1.1 Thistestmethodcoversthedeterminationofthethermal
2.2.3 The oscilloscope trace must be such that ∆T , ∆
max
diffusivity of carbons and graphite to 65 % at temperatures up
1 1
T(10 t ⁄2), and t ⁄2can be determined to 62%.
to 500°C. It requires only a small easily fabricated specimen.
2.2.4 The other conditions are less critical, and the experi-
Thermal diffusivity values in the range from 0.04 to 2.0 cm /s
menter is left to his discretion.
are readily measurable by this test method; however, for the
reason outlined in Section 5, for materials outside this range
3. Significance and Use
this test method may require modification.
1.2 This standard does not purport to address all of the
3.1 Thermal diffusivity is an important property required for
safety concerns, if any, associated with its use. It is the
such purposes as design applications under transient heat flow
responsibility of the user of this standard to establish appro-
conditions, determination of safe operating temperature, pro-
priate safety and health practices and determine the applica-
cess control, and quality assurance.
bility of regulatory limitations prior to use.
3.2 The flash method is used to measure values of thermal
diffusivity (α) of a wide range of solid materials. It is
2. Summary of Test Method
particularly advantageous because of the simple specimen
2.1 A high-intensity short-duration thermal pulse from a
geometry, small specimen size requirements, rapidity of
flash lamp is absorbed on the front surface of a specimen; and
measurement, and ease of handling materials having a wide
the rear surface temperature change as a function of time is
range of thermal diffusivity values over a large temperature
observed on an oscilloscope. The pulse raises the average
range with a single apparatus. The short measurement times
temperature of the specimen only a few degrees above its
involved reduce the chances of contamination and change of
initial value. The ambient temperature of the specimen is
specimen properties due to exposure to high temperature
controlled by a furnace or cryostat. Thermal diffusivity is
environments.
calculated from the specimen thickness and the time required
3.3 Thermal diffusivity results in many cases can be com-
for the temperature of the back surface to rise to one half of its
2 bined with values for specific heat (C ) and density (ρ) and
p
maximum value (1).
used to derive thermal conductivity (λ) from the relation λ =
2.2 The critical factors in this test method are:
αC ρ.
p
2.2.1 τ/t ⁄2 must be 0.02 or less.τ is the pulse time as defined
3.4 This test method can be used to characterize graphite for
in Fig. 1 and t ⁄2 is the time for the rear surface temperature to
design purposes.
rise to one half of its maximum value (see Fig. 2).
2.2.2 Heat losses from the specimen via radiation,
4. Apparatus
convection, or conduction to the specimen holder must be
small. Whether or not this condition is violated can be
4.1 The essential features of the apparatus are shown in Fig.
determined experimentally from the oscilloscope trace, an
3. The window may be any material that is transparent to the
flash source.The specimen holder should be a ceramic or other
material whose thermal conductivity is low relative to that of
This test method is under the jurisdiction of ASTM Committee D02 on the sample.
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
4.2 Thermocouple, used to monitor the transient tempera-
D02.F0 on Manufactured Carbon and Graphite Products.
Current edition approved May 1, 2010. Published May 2010. Originally
tureresponseoftherearsurfaceofthespecimen.Thewireends
approved in 1972. Last previous edition approved in 2005 as C714–05. DOI:
should be prepared to minimize heat losses from the specimen
10.1520/C0714-05R10.
to the thermocouple wires (that is, by grinding to points or
The boldface numbers in parentheses refer to the list of references at the end of
this test method. clipping) and attached in a manner that prevents penetration
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C714 − 05 (2010)
FIG. 1 Flash Tube Response
FIG. 2 Example of Oscilloscope Trace Showing Parameters Used to Calculate Thermal Diffusivity
into the specimen. They are separated by about 1 mm so that amplifier section of the oscilloscope should have a frequency
the electrical circuit of the thermocouple is completed through response in the range from 0.06 to 10 kHz to be perfectly
the specimen.
insensitive to frequency in the range of interest described in
Section 5.Aminimum vertical deflection sensitivity of 1 C⁄cm
4.3 Oscilloscope, with calibrated sweep speeds that can be
is recommended. The cathode-ray tube should have a usable
varied from 0.1 ms/cm to 0.5 s/cm or more. The vertical
C714 − 05 (2010)
FIG. 3 Schematic Diagram of Apparatus
viewing area of at least 40 by 100 mm. A camera is used to 7. Procedure
photograph the oscilloscope trace. Alternativel
...
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