Standard Test Method for Thermal Diffusivity and Conductivity by the Flash Method
Thermal diffusivity is measured by laser flash. The sample size for the Laser Flash unit is a 0.500" (plus 0.000"/minus 0.005") diameter disk. Samples of 0.08", 0.12" and 0.16" thickness should be provided. Since sample configuration may be dependent on sample composition, inquire before machining samples for submittal. Thermal conductivity is calculated from the thermal diffusivity, heat capacity, and density. See ASTM E1269 for sample size requirements for determination of heat capacity. The diffusivity price schedule includes the heat capacity determination.
SIGNIFICANCE AND USE
Thermal diffusivity is an important property, required for such purposes under transient heat flow conditions, such as design applications, determination of safe operating temperature, process control, and quality assurance.
The flash method is used to measure values of thermal diffusivity, Î±, of a wide range of solid materials. It is particularly advantageous because of simple specimen geometry, small specimen size requirements, rapidity of measurement and ease of handling..
Under certain strict conditions, specific heat capacity of a homogeneous isotropic opaque solid specimen can be determined when the method is used in a quantitative fashion (see Appendix X2).
Thermal diffusivity results, together with related values of specific heat capacity (Cp) and density (Ï) values, can be used in many cases to derive thermal conductivity (Î»), according to the relationship:
1.1 This test method covers the determination of the thermal diffusivity of primarily homogeneous isotropic solid materials. Thermal diffusivity values ranging from 10-7 to 10-3 m2·s-1 are measurable by this test method from about 75 to 2800 K.
1.2 Practice E2585 is adjunct to this Test Method and contains detailed information regarding the use of the flash method. The two documents are complementing each other.
1.3 This test method is a more detailed form of Test Method C714, having applicability to much wider ranges of materials, applications, and temperatures, with improved accuracy of measurements.
1.4 This test method is intended to allow a wide variety of apparatus designs. It is not practical in a test method of this type to establish details of construction and procedures to cover all contingencies that might offer difficulties to a person without pertinent technical knowledge, or to stop or restrict research and development for improvements in the basic technique.
1.5 This test method is applicable to the measurements performed on essentially fully dense (preferably, but low porosity would be acceptable), homogeneeous, and isotropic solid materials that are opaque to the applied energy pulse. Experience has shown, however, that some deviation from these strict guidelines can be accommodated with care and proper experimental design, substantially broadening the usefulness of the method.
1.6 This test method can be considered an absolute (or primary) method of measurement, since no reference standards are required. It is advisable to use reference materials to verify the performance of the instrument used.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 For systems employing lasers as power sources, it is imperative that the safety requirement be fully met.
1.9 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.
Extracted, with permission, from ASTM E1461 Standard Test Method for Thermal Diffusivity by the Flash Method, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the standard may be purchased from ASTM International, phone 610-832-9555, e-mail: firstname.lastname@example.org, website:www.astm.org.
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