ISO 18755:2022

INTERNATIONAL ISO
STANDARD 18755
Second edition
2022-12
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Determination of thermal diffusivity
of monolithic ceramics by flash
method
Céramiques techniques — Détermination de la diffusivité thermique
des céramiques monolithiques par la méthode flash
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Apparatus . 3
4.1 General . 3
4.2 Specimen holder . 4
4.3 Flash source . 4
4.4 Thermometer for measuring steady-state temperature of the specimen . 5
4.5 Detector for measuring transient temperature rise of rear face of the specimen . 5
4.6 Environment for measurements . . 5
4.7 Temperature control unit . 5
4.8 Data acquisition unit . 5
5 Specimen . 5
5.1 Shape and dimension of specimens . 5
5.2 Density of the specimen . 6
5.3 Coating on the specimen . 6
5.4 Reference specimen . 6
6 Measurement procedure . 6
6.1 Measurement of specimen thickness . 6
6.2 Surface treatment . 6
6.3 Determination of the flash time of the laser or light pulse and the chronological
profile of the laser or light pulse . . 7
6.4 Temperature and atmosphere control . 7
6.5 Stability of specimen temperature . 7
6.6 Energy of pulse heating . 7
6.7 Measurement temperature . 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 . 8
8 Measurement report .10
Annex A (informative) Principle of flash thermal diffusivity measurements .13
Annex B (normative) Correction for non-ideal initial and boundary conditions .14
Annex C (informative) Data analysis algorithms to calculate thermal diffusivity
from observed transient temperature curve under non-ideal initial and
boundary conditions .21
Annex D (informative) Other error factors .23
Annex E (informative) Procedure to determine intrinsic thermal diffusivity.29
Annex F (informative) Reference data and reference materials of thermal diffusivity .32
Annex G (informative) Evaluation of specific heat capacity and thermal conductivity .34
Annex H (informative) Example data including precision and uncertainty up to high
temperature .36
Bibliography .39
iii
Foreword
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electrotechnical standardization.
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 18755:2005), which has been technically
revised.
The main changes are as follows:
— a change of title and scope to enable the use of flash lamps to generate the energy pulse;
— the addition of three new informative annexes: one dealing with the determination of the intrinsic
thermal diffusivity; the second with the determination of specific heat and thermal conductivity of
the samples tested; and the third providing precision data for the method on the basis of an inter-
laboratory study carried out by seven European laboratories in 2020-2021 in the framework of the
project Hi-TRACE;
— an additional normative reference to provide clear instructions on the determination of the density
of the materials to be analysed;
— relevant specifications added concerning the size and the density of the specimen;
— improvement of Annex F, with an updated list of potential reference material and incorporation of a
validation method.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 18755:2022(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Determination of thermal diffusivity of
monolithic ceramics by flash method
1 Scope
This document specifies the test method for the determination of thermal diffusivity from room
temperature to at least 1 700 K by the flash method for homogeneous monolithic ceramics with porosity
less than 10 %.
Flash methods, like laser flash, are applicable to homogeneous isotropic materials with thermal
2 -1
diffusivity values ranging from 0,1 to 1 000 mm s within the temperature range from approximately
100 K to 2 300 K.
The method described in Annex G describes how to estimate, on the basis of the thermal diffusivity
test, the specific heat capacity and the thermal conductivity of homogeneous monolithic ceramics with
porosity less than 10 %.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3611, Geometrical product specifications (GPS) — Dimensional measuring equipment: Micrometers for
external measurements — Design and metrological characteristics
ISO 18754, Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of density
and apparent porosity
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
thermal diffusivity
thermal conductivity divided by the product of specific heat 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
τ
p
full width at half maximum (FWHM), which is the time duration when the laser or light pulse intensity
is larger than half of its maximum value on time basis
3.5
centroid of laser pulse
chronological centroid of laser light energy
3.6
centroid of light pulse
chronological centroid of light energy
3.7
spatial energy distribution of pulse laser beam
energy density of the laser beam or light flash incident at each point on the front face of the specimen
3.8
transient temperature curve
transient
...