1、 Reference number ISO 18755:2005(E) ISO 2005INTERNATIONAL STANDARD ISO 18755 First edition 2005-03-15 Fine ceramics (advanced ceramics, advanced technical ceramics) Determination of thermal diffusivity of monolithic ceramics by laser flash method Cramiques techniques Dtermination de la diffusivit th
2、ermique des cramiques monolithiques par la mthode flash laser ISO 18755:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to
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6、n in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2005 All rights reservedI
7、SO 18755:2005(E) ISO 2005 All rights reserved iiiContents Page Foreword iv 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Apparatus. 3 4.1 Specimen holder . 4 4.2 Pulse laser . 4 4.3 Thermometer for measuring steady-state temperature of the specimen . 5 4.4 Detector for measuring
8、transient temperature rise of rear face of the specimen 5 4.5 Environment for measurements 5 4.6 Temperature control unit 5 4.7 Data acquisition unit. 5 5 Specimen . 5 5.1 Shape and dimension of specimens. 5 5.2 Coating on the specimen . 6 5.3 Reference specimen . 6 6 Measurement procedure 6 6.1 Mea
9、surement of specimen thickness . 6 6.2 Surface treatment 6 6.3 Determination of flash time of the laser pulse and the chronological profile of the laser pulse. 6 6.4 Temperature and atmosphere control 6 6.5 Stability of specimen temperature 6 6.6 Energy of pulse heating . 7 6.7 Measurement temperatu
10、re . 7 6.8 Record 7 7 Data analysis . 7 7.1 Calculation based on the half-rise-time method 7 7.2 Criteria for applicability of the half-rise-time method . 7 8 Measurement report 10 Annex A (informative) Principle of laser flash thermal diffusivity measurements 12 Annex B (informative) Correction for
11、 non-ideal initial and boundary conditions 13 Annex C (informative) Data analysis algorithms to calculate thermal diffusivity from observed temperature history curve under non-ideal initial and boundary conditions 19 Annex D (informative) Other error factors . 22 Annex E (informative) Reference data
12、 and reference materials of thermal diffusivity 28 Bibliography . 29 ISO 18755:2005(E) iv ISO 2005 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Stan
13、dards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also t
14、ake part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees
15、is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibil
16、ity that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 18755 was prepared by Technical Committee ISO/TC 206, Fine ceramics. INTERNATIONAL STANDARD ISO 18755:2005(E) ISO 2005 All rights r
17、eserved 1Fine ceramics (advanced ceramics, advanced technical ceramics) Determination of thermal diffusivity of monolithic ceramics by laser flash method 1 Scope This International Standard specifies the test method for the determination of thermal diffusivity from room temperature to 1700 K by the
18、laser flash method for homogeneous monolithic ceramics with porosity less than 10 %. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of t
19、he referenced document (including any amendments) applies. ISO 3611, Micrometer callipers for external measurement 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 thermal diffusivity thermal conductivity divided by the product of specific hea
20、t capacity and density 3.2 thermal conductivity density of heat flow rate divided by temperature gradient under steady state condition 3.3 specific heat capacity heat capacity per unit mass 3.4 pulse width pfull width of half maximum (FWHM) which is the time duration when the laser pulse intensity i
21、s larger than the half of its maximum value on time basis 3.5 centroid of laser pulse chronological centroid of laser light energy 3.6 spatial energy distribution of pulse heating energy density of the laser beam incident at each point on the front face of the specimen ISO 18755:2005(E) 2 ISO 2005 A
22、ll rights reserved3.7 transient temperature curve transient temperature change of the rear face of the specimen after the light pulse heating 3.8 transient radiance curve transient change of the spectral radiance from the rear face of the specimen after the light pulse heating NOTE It should be note
23、d that the observed transient curve is proportional to the change of the spectral radiance rather than the change of temperature when a radiation thermometer or a radiation detector is used to observe the transient temperature rise of the specimen after the light pulse heating. 3.9 maximum temperatu
24、re rise T maxdifference between the steady temperature before the pulse heating and the maximum temperature of the rear face of the specimen after the pulse heating NOTE See Figure 1. 3.10 half rise-time t l/2time until T max /2 is attained from the pulse heating 3.11 characteristic time of heat los
25、s ctime of heat loss determined when the cooling region is fitted with an exponential function, T 0 exp( - t/ C ) NOTE See Figure 1. ISO 18755:2005(E) ISO 2005 All rights reserved 3Key X: time Y: temperature rise 1 exponential function () 0 exp / c Tt 2 initial noise Figure 1 Transient temperature c
26、urve of the rear face of the specimen after a light pulse heating onto the front face of the specimen 3.12 extrapolated temperature rise T 0temperature rise determined when the cooling region is fitted with an exponential function, T 0exp( - t/ C ) 3.13 initial noise superimposed on transient temper
27、ature curve initial spike and/or hump superimposed on the initial part of the transient temperature curve, due to transmitted and/or scattered light from the heating laser pulse and/or electrically induced noise associated with the laser pulse discharge 3.14 homogeneity of specimen degree of homogen
28、eity of local thermal diffusivity over the specimen 4 Apparatus The apparatus shall be designed for obtaining the thermal diffusivity from the transient temperature curve of the rear face of a specimen after the laser pulse is irradiated onto the front face of the specimen, and shall consist of the
29、following principal components as shown in Figure 2. ISO 18755:2005(E) 4 ISO 2005 All rights reserved4.1 Specimen holder The specimen holder shall hold the specimen stable, with minimum thermal contact, and shall be designed to suppress stray lights from the laser beam being transmitted to the trans
30、ient detector. A diaphragm with aperture diameter slightly larger than the specimen diameter should be placed close to the front face of the specimen, and another diaphragm with aperture diameter smaller than the specimen diameter and larger than the target size of radiative detection should be plac
31、ed close to the rear face of the specimen. Key 1 pulsed laser 2 data analysis 3 detector 4 specimen holder 5 power supply 6 heater aTrigger signal. bTransient temperature response. Figure 2 Block diagram of laser flash apparatus for measuring thermal diffusivity 4.2 Pulse laser The pulse laser shall
32、 be capable of emitting the light pulse with pulse duration preferably shorter than 1,0 ms in full width at half maximum (FWHM). The specimen should be irradiated uniformly by the light pulse. When a pulse laser is used for the light pulse, the direct beam profile is often irregular because of multi
33、-mode oscillation. In this case, the beam should be converted to a uniform beam using beam-homogenizing optics. ISO 18755:2005(E) ISO 2005 All rights reserved 54.3 Thermometer for measuring steady-state temperature of the specimen The steady-state temperature of the specimen before pulse heating sho
34、uld be measured by a thermocouple, or an equally or more reliable thermometer. The thermocouple shall be positioned such that it does not interrupt the light pulse heating onto the front face of the specimen, or the radiation from the rear face of the specimen. If the specimen does not react with th
35、e thermocouple, a thin thermocouple should be contacted with the specimen to measure the specimen temperature with minimal uncertainty. If the thermocouple junction cannot be allowed to contact the specimen because of chemical reaction with the specimen, or because it interrupts the setting of the s
36、pecimen, or because of the system design, the tip should be placed as close as practical to the specimen in the same plane. 4.4 Detector for measuring transient temperature rise of rear face of the specimen The transient temperature rise curve on the rear face of the specimen shall be observed with
37、a non-contact radiation thermometer or a radiation detector. The frequency response of the detector and its associated electronics should be faster than 10 kHz. The target diameter of the radiation detector should be smaller than 50 % of the diameter for disk specimens, or 50 % of the shortest side-
38、length for square and rectangular specimens. 4.5 Environment for measurements Measurements may be performed under open air, under an inert gas atmosphere, or under vacuum at room temperature. For higher temperature measurements, an appropriate inert atmosphere or vacuum shall be used, when necessary
39、, to protect furnace parts and specimen holders from oxidation and to protect the specimen and its coating from structure/phase changes and compatibility problems. 4.6 Temperature control unit For higher temperature measurements, the specimen should be kept at a stable temperature by electric heater
40、s before pulse heating. Drift and fluctuation of the temperature should be less than 0,01 K/s. 4.7 Data acquisition unit The transient detector signal should be amplified and converted to the digital signal using a digital oscilloscope or an AD converter which is input to a personal computer for com
41、putation of the thermal diffusivity. The frequency response of the amplifier and the AD conversion should be faster than 10 kHz. The resolution of the AD conversion should be larger than 10 bits, more than 1000 data points should be sampled with the sampling time faster than 1 % of the half rise-tim
42、e “t 1/2 ”. 5 Specimen 5.1 Shape and dimension of specimens The specimen shall be a flat plate of circular, square or rectangular shape. The specimen diameter or side shall be between 5 mm and 15 mm. The specimen thickness shall be chosen to be as follows: a) thicker than 0,5 mm and thinner than 5 m
43、m; b) sufficiently thick that the t 1/2value is larger than 5 times the pulse width. The uniformity of the specimen thickness shall be smaller than 1,0 %. ISO 18755:2005(E) 6 ISO 2005 All rights reserved5.2 Coating on the specimen If the specimen does not have a high absorption coefficient for the h
44、eating laser beam or a high emissivity for radiative temperature detection, the surfaces of the specimen shall be coated with a thin, opaque, preferably black layer. The coating shall be dense enough to prevent penetration of the laser beam or thermal radiation at the observed wavelength, and should
45、 be resistive against laser pulse heating at high temperatures. Coating thickness should be a minimum commensurate with excluding directly transmitted laser pulse. NOTE Suitable coatings for many ceramic materials include evaporated, sputtered carbon or sprayed colloidal graphite. If the test specim
46、en reacts with carbon at high temperatures, a metal coating, such as platinum, gold or nickel may alternatively be used. The surface of the test specimen may, with advantage, be roughened to improve adhesion of the coating. The coating thickness dependence must be evaluated for the observed thermal
47、diffusivity, if the contribution of coatings is not negligible. 5.3 Reference specimen Reference specimens can be used to evaluate uncertainty of thermal diffusivity measurements by a laser flash apparatus. The uncertainty is obtained as the difference between the measured value and the reference va
48、lue of thermal diffusivity of the reference specimen. NOTE There are no certified reference materials for thermal diffusivity measurements authorized by national or international organizations yet, although several materials are used as such (see Annex E). Care should be taken in the use of these re
49、ferences to ensure that the half rise-time and the thermal diffusivity value are similar to those of the test materials. 6 Measurement procedure The specimen shall be measured under the following procedures. 6.1 Measurement of specimen thickness Measure the thickness of the specimen to an accuracy of 0,5 % or better, using a micrometer in accordance with ISO 3611. 6.2 Surface treatment Carry out the surface treatment in accordance with 5.2. 6.3 Determination of flash time of the laser pulse
