oSIST prEN ISO 19629:2026

• Abstract:

  This document describes the flash method for the determination of thermal diffusivity of ceramic matrix composites with continuous fibre reinforcement.; In order to conform with the unidimensional heat transfer hypothesis, the experimental conditions are defined such that the material behaves in a homogeneous manner. This involves performing tests in one symmetry axis of the composite.; The method is applicable to materials which are physically and chemically stable during the measurement, and covers the range of temperature from 100 K to 2 800 K. It is suitable for the measurement of thermal diffusivity values in the range 10−4 m2∙s−1 to 10−7 m2∙s−1.

• Status: Not Published
• Public Enquiry End Date: 09-Sep-2026
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 14-Jul-2026
• Due Date: 01-Dec-2026
• Ref Project: prEN ISO 19629 - Fine ceramics (advanced ceramics, advanced technical ceramics) - Thermophysical properties of ceramic composites - Determination of unidimensional thermal diffusivity by flash method (ISO/DIS 19629:2026)

• Revises: SIST EN ISO 19629:2022 - Fine ceramics (advanced ceramics, advanced technical ceramics) - Thermophysical properties of ceramic composites - Determination of unidimensional thermal diffusivity by flash method (ISO 19629:2018)
• Effective Date: 16-Oct-2024

SLOVENSKI STANDARD
01-september-2026
Fina keramika (sodobna keramika, sodobna tehnična keramika) - Termofizikalne
lastnosti keramičnih kompozitov - Ugotavljanje enodimenzionalne toplotne
difuzivnosti z bliskovno metodo (ISO/DIS 19629:2026)
Fine ceramics (advanced ceramics, advanced technical ceramics) - Thermophysical
properties of ceramic composites - Determination of unidimensional thermal diffusivity by
flash method (ISO/DIS 19629:2026)
Hochleistungskeramik - Thermophysikalische Eigenschaften keramischer
Verbundwerkstoffe - Bestimmung der eindimensionalen Temperaturleitfähigkeit mittels
Flashverfahren (ISO/DIS 19629:2026)
Céramiques techniques - Propriétés thermophysiques des composites céramiques -
Détermination de la diffusivité thermique unidimensionnelle par la méthode flash
(ISO/DIS 19629:2026)
Ta slovenski standard je istoveten z: prEN ISO 19629
ICS:
81.060.30 Sodobna keramika Advanced ceramics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 19629
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
Thermophysical properties
2026-06-24
of ceramic composites —
Voting terminates on:
Determination of unidimensional
2026-09-16
thermal diffusivity by flash method
Céramiques techniques — Propriétés thermophysiques des
composites céramiques — Détermination de la diffusivité
thermique unidimensionnelle par la méthode flash
ICS: 81.060.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
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This document is circulated as received from the committee secretariat.
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PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 19629:2026(en)
DRAFT
ISO/DIS 19629:2026(en)
International
Standard
ISO/DIS 19629
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
Thermophysical properties
of ceramic composites —
Voting terminates on:
Determination of unidimensional
thermal diffusivity by flash method
Céramiques techniques — Propriétés thermophysiques des
composites céramiques — Détermination de la diffusivité
thermique unidimensionnelle par la méthode flash
ICS: 81.060.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
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WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
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NOTIFICATION OF ANY RELEVANT PATENT
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Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 19629:2026(en)
ii
ISO/DIS 19629:2026(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 3
5.1 Heat pulse source .3
5.2 Test chamber .3
5.3 Specimen holder .4
5.4 Thermometer for measuring steady-state temperature of the specimen .5
5.5 Detector for measuring transient temperature rise of the back face of the specimen .5
5.6 Data acquisition .5
5.7 Thickness measurement device .6
6 Test specimens . 6
7 Test specimen preparation . 6
7.1 Machining and preparation .6
7.2 Number of test specimens .6
8 Procedure . 6
8.1 Calibration of apparatus .6
8.2 Verification of apparatus .7
8.3 Measurement procedure .7
9 Data analysis . 8
9.1 Determination of the thermal diffusivity .8
9.2 Sources of uncertainties .9
10 Test report . 9
Annex A (informative) Unidimensional thermal model .11
Annex B (informative) Determination of the intrinsic thermal diffusivity .13
Annex C (informative) Correction for finite pulse duration . 14
Annex D (informative) Precision .15
Bibliography . 17

iii
ISO/DIS 19629:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards 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 take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility 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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
This second edition cancels and replaces the first edition (ISO 19269:2018), which has been technically
revised.
The main changes are as follows:
— change of the scope to extend the maximum temperature of use of the flash method to 3300 K;
— addition of terms and definitions in clause 3;
— specifications added concerning the components of apparatus (clause 5) and the test specimens (clauses 6
and 7);
— introduction of important steps in clause 8 about procedures of calibration and verification of the
apparatus, as well as measurement procedure;
— improvement of the data analysis and the identification of the uncertainty sources in clause 9;
— addition of annexes B and C describing corrections for non-ideal initial and boundary conditions;
— addition of annex D related to precision;
— updated list of references in the Bibliography.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
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
DRAFT International Standard ISO/DIS 19629:2026(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Thermophysical properties of ceramic
composites — Determination of unidimensional thermal
diffusivity by flash method
1 Scope
This document specifies the use of the flash method for the determination of thermal diffusivity of ceramic
matrix composites with continuous fibre reinforcement.
In order to conform with the unidimensional heat transfer hypothesis, the experimental conditions are
defined such that the material behaves in a homogeneous manner. This involves performing tests in one
symmetry axis of the composite.
The method is applicable to materials which are physically and chemically stable during the measurement,
and covers the range of temperature from 100 K to 3 300 K. It is suitable for the measurement of thermal
−4 2 −1 −7 2 −1
diffusivity values in the range 10 m ∙s to 10 m ∙s .
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 — Design and
metrological characteristics of micrometers for external measurements
ISO 20507, Fine ceramics (advanced ceramics, advanced technical ceramics) — Vocabulary
EN 60584-1, Thermocouples — Part 1: Reference tables (IEC 60584‑1:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20507 and the following apply.
ISO and IEC maintain terminological 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
a
ratio of the thermal conductivity to the product of the bulk density and the specific heat capacity
2 -1
Note 1 to entry: It is expressed in square metres per second (m ∙s ).

ISO/DIS 19629:2026(en)
3.2
time origin
t
start of the light pulse
Note 1 to entry: It is expressed in seconds (s).
3.3
maximum temperature rise
ΔT
max
difference between the maximum temperature reached by the rear face of the specimen after the pulse
heating and its steady temperature before the pulse.
Note 1 to entry: It is expressed in kelvin (K).
3.4
half-rise time
t
1/2
time from the initiation of the pulse until the increase of the temperature on the back face of the test
specimen reaches one half of the maximum temperature increase ΔT
max
Note 1 to entry: It is expressed in second (s).
3.5
pulse width
t
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
Note 1 to entry: It is expressed in second (s).
3.6
thickness
h
dimension of the test specimen in the direction of heat transfer measurement
Note 1 to entry: It is expressed in meter (m).
3.7
Thermogram (transient temperature curve)
temperature versus time curve for the back face of the specimen (see Figure 1)
Note 1 to entry: If a radiation thermometer or a radiation detector is used to observe the transient temperature of the
back face of the specimen, then the observed transient curve is proportional to the change of the spectral radiance
rather than the change of temperature.
4 Principle
One side of a plane- and parallel-face specimen is exposed to a uniformly distributed energy pulse that is of
very short duration compared with the transient half time (see clause 6).
The transient temperature rise (ΔT) on the opposite face (back face) or a quantity directly proportional to
ΔT is recorded as a function of time (t) (see Figure 1).
The thermal diffusivity is obtained by comparing the experimental thermogram with a theoretical model,
which is a unidimensional analytical thermal model, with two parameters, as described in Annex A. If other
models are used, they are to be specified in the test report.
[1]
NOTE The principle of the flash method has been proposed originally by Parker .

ISO/DIS 19629:2026(en)
5 Apparatus
The apparatus shall be designed to obtain the thermal diffusivity as described in Clause 4 and shall consist
of the following main components as shown in Figure 2. These are the heat pulse source (e.g. laser), the pulse
detector (e.g. photodiode), the test chamber with a specimen holder and temperature measurement device
(e.g. thermocouple), the transient detector (e.g. IR detector) and the control, data acquisition and analysis
unit.
Key
X time
Y temperature rise
a baseline
b transient-rise period
c cooling period
t pulse triggering at t = 0
Figure 1 — Schematic representation of the temperature rise of the back face of the specimen
5.1 Heat pulse source
The heat pulse source may be a flash tube or a pulse laser capable of generating a pulse with a duration
shorter than 1 ms in full width at half maximum (FWHM).
The pulse energy shall be as uniform as possible over the front face of the specimen.
A photodiode can be used to determine the duration and form of the pulse and the time origin.
5.2 Test chamber
The test chamber shall be either a furnace or a cryostat, capable of operation within the temperature range
required.
The design of the test chamber shall meet the following requirements:
a) it shall contain a working area in which the spatial temperature gradient is sufficiently low (≤5 K over
working area width) to result in a homogeneous temperature on the specimen;

ISO/DIS 19629:2026(en)
b) in steady state conditions, the drift in temperature shall be less than 0,01 K/s;
c) the test chamber shall be fitted with two windows, one shall be transparent to the pulse
radiation and the other shall be transparent to the working wavelength range of the IR detector;
Key
1 heat pulse source
2 pulse detector
3 test chamber
4 windows
5 specimen
6 specimen holder
7 thermometer
8 transient detector
9 control, data acquisition and analysis unit
Figure 2 — Schematic diagram of laser flash apparatus
d) the environment in the test chamber shall be a vacuum or an inert gas atmosphere to avoid oxidative
degradation during heating and testing of the test specimen. For temperature below 280 K care
should be taken to avoid water condensation on the windows. For high temperature measurements, it
is recommended to work with a high purity inert gas (argon or helium up to 2 300 K, and preferably
[2]
helium above 2 300 K) in order to avoid sublimation phenomena of the tested specimens .
When the test is performed under gas, the specimen should be in a horizontal position in order to reduce
convection effects of the gas on the specimen.
5.3 Specimen holder
The specimen holder shall be designed to minimize thermal contact with the specimen and to suppress stray
light transmitted from the light beam to the IR detector.
For high temperature measurements, the specimen holder should be made of either compatible refractory
metallic materials (if the tested material is a pure metal or a metallic alloy) or graphite to limit chemical
[2]
interactions between the holder and the specimen .

ISO/DIS 19629:2026(en)
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 placed close to the back face of the
specimen.
5.4 Thermometer for measuring steady-state temperature of the specimen
The steady-state temperature of the specimen before pulse heating shall be measured either with a
thermocouple (in accordance with EN 60584-1) or with radiation thermometers (or pyrometers).
Thermocouples and radiation thermometers shall be periodically calibrated in their operating temperature
ranges as they can be subjected to drift over time.
Thermocouples may be calibrated by measurement either at a series of fixed-point temperatures (e.g.
melting/freezing points) or by comparison with reference thermometers in thermally stabilised baths or
furnaces.
[3]
NOTE Guidelines on the Calibration of Thermocouples are available at the following address: https:// www
.euramet .org/ publications -media -centre/ calibration -guidelines/ .
Pyrometers are usually calibrated in radiance temperature using reference blackbodies. In addition to these
calibrations performed outside the flash apparatus, it is recommended to perform in-situ calibrations of the
[4]
pyrometers by using fixed-point temperatures .
5.5 Detector for measuring transient temperature rise of the back face of the specimen
The detector shall be either a quantum radiation detector, a thermocouple or any other means that does not
disturb the measurement of the transient response of the specimen. Non-contact measurement techniques
are recommended to avoid heat losses and to measure the variation of the mean temperature of the specimen
back-face. However, thermocouples should sometimes be used for low temperature thermal diffusivity
measurements (below 280 K).
The detector shall be capable of detecting changes of 0,01 K in the temperature of the specimen back-
face, with a linear response over the range of temperature change less than or equal to 5 K. The frequency
response of the detector and its associated electronics (amplifiers, analogue/digital converters, filters, etc.)
shall be faster than 10 kHz.
The infrared detector, when used, shall be of a type appropriate to the minimum specimen temperature, for
example:
a) HgCdTe or PbSnTe cells, liquid nitrogen cooled, for test specimen temperatures within the range 280 K
to 1 000 K;
b) PbS or InSb cells for test specimen temperatures from 500 K to 1 500 K.
c) InGaAs or Si cells for test specimen temperatures above 1 300 K.
Care shall be taken that the signal comes only from the specimen back face.
When used, thermocouples shall be of the separated junction type, the hot junction being the back face of
the specimen. They shall be in accordance with EN 60584-1. Electrically non-conductive material shall be
coated on the front face and on the back face, with a thin coating of high thermal conductivity material in
order to ensure accurate measurement of surface temperatures.
In order to minimize heat losses, the use of the thermocouples with wires of the smallest possible diameter
is recommended.
5.6 Data acquisition
The signal delivered by the transient detector shall be recorded continuously over the duration of the test
(before, during and after the pulse). The data acquisition system, which may be analogue or digital shall be

ISO/DIS 19629:2026(en)
able to sample more than 1 000 data points on the thermogram with a sampling frequency higher than 100/
−5
t . The accuracy of the time base shall be better than ±1 × 10 s.
1/2
5.7 Thickness measurement device
The specimen thickness shall be measured with an accuracy of ±5 µm using a calibrated thickness
measurement device having a resolution of ±1 µm.
6 Test specimens
The size of the test specimens shall be chosen to meet the requirements for application of the chosen thermal
model (for example like the one described in Annex A). Generally a disc of a diameter between 5 mm to
20 mm is used.
The specimen thickness shall be selected such that the pulse width is less than 0,01 of the half-rise time t .
1/2
Typically, the thickness is between 1 mm and 3 mm. The ratio of the diameter to the thickness shall be larger
than 3:1 in order that 2D effects are negligible.
In addition, the thickness of the specimen shall be sufficient in order to avoid influence of potential material
inhomogeneity. This shall be ensured by performing tests on two series of test specimens with a thickness
ratio of about 2. Homogeneous material behaviour can be assumed when the mean values of the thermal
diffusivity determined from each series do not differ by more than 10 %.
7 Test specimen preparation
7.1 Machining and preparation
The test specimen shall be representative of the material being examined and shall be prepared and handled
with care. Test specimens shall be cut with their longitudinal axis coinciding with one of the principal
directions of the reinforcement. The faces perpendicular to the measurement face shall be flat and parallel.
The parallelism error of the two faces shall be less than 0,05 mm.
If the test specimen is transparent to the infrared radiation at the considered wavelength
...