ISO 19618:2025
(Main)Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement method for normal spectral emissivity using blackbody reference with an FTIR spectrometer
Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement method for normal spectral emissivity using blackbody reference with an FTIR spectrometer
This document specifies a method used for the determination of normal spectral emissivity and normal quasi-total emissivity of fine ceramics using blackbody reference with a Fourier transform infrared spectrometer (FTIR) at elevated temperatures. This method is applicable to fine ceramics, ceramic matrix composites, and continuous fibre-reinforced ceramic matrix composites which are opaque and highly non-reflective at wavelengths between 1,67 μm and 25 μm. The applicable temperature range is approximately 350 K to 1 100 K.
Céramiques techniques — Méthode de mesure de l’émissivité spectrale normale au moyen d’un corps noir de référence par spectrométrie infrarouge à transformée de Fourier (IRTF)
General Information
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Standards Content (Sample)
International
Standard
ISO 19618
Second edition
Fine ceramics (advanced ceramics,
2025-01
advanced technical ceramics) —
Measurement method for
normal spectral emissivity using
blackbody reference with an FTIR
spectrometer
Céramiques techniques — Méthode de mesure de l’émissivité
spectrale normale au moyen d’un corps noir de référence par
spectrométrie infrarouge à transformée de Fourier (IRTF)
Reference number
© ISO 2025
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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 Principle . 2
5 Apparatus . 2
5.1 Measurement system .2
5.2 Fourier transform infrared spectrometer (FTIR) .2
5.3 Specimen heating device .2
5.4 Blackbody furnace .4
5.5 Temperature measuring devices and thermometer .4
5.6 Mirror .4
6 Test specimens . 4
7 Measurement preparation . 5
7.1 Position of a blackbody furnace and a specimen .5
7.2 Wavelength calibration .6
7.3 Verification of linearity .6
7.4 Verification of stability . .7
7.5 Validation of measurement system .7
8 Test condition . 7
9 Test procedure . 7
9.1 Background infrared radiance spectrum measurement .7
9.2 Specimen installation .7
9.3 Infrared radiance spectrum measurement .7
10 Calculations . 8
10.1 Normal spectral emissivity .8
10.2 Normal quasi-total emissivity .8
11 Test report . 9
Annex A (informative) Calculation of theoretical infrared radiance spectrum L using Planck’s
λ,T
blackbody radiation function . 10
Annex B (informative) Christiansen effect .11
Annex C (informative) Validity of normal quasi-total emissivity .12
Bibliography .13
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 19618:2017), which has been technically
revised.
The main changes are as follows:
— correction of the procedure for the linearity verification of the FTIR system in 7.3;
— addition of the thermal history of the specimen to the items to be reported in Clauses 6 and 11;
— correction of the terms to be used for the calculations in Clause 10.
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 19618:2025(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Measurement method for normal spectral
emissivity using blackbody reference with an FTIR
spectrometer
1 Scope
This document specifies a method used for the determination of normal spectral emissivity and normal
quasi-total emissivity of fine ceramics using blackbody reference with a Fourier transform infrared
spectrometer (FTIR) at elevated temperatures. This method is applicable to fine ceramics, ceramic matrix
composites, and continuous fibre-reinforced ceramic matrix composites which are opaque and highly non-
reflective at wavelengths between 1,67 μm and 25 μm. The applicable temperature range is approximately
350 K to 1 100 K.
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.
IEC 60584-2, Thermocouples — Part 2: Tolerances
IEC 60751, Industrial platinum resistance thermometers and platinum temperature sensors
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
emissivity
ε
ratio of the radiant emittance of a substance (specimen) to the radiant emittance of a blackbody (3.2) at the
same temperature
3.2
blackbody
ideal thermal radiator that absorbs all incident radiation completely, whatever the wavelength, direction of
incidence or polarization
3.3
spectral emissivity
ε
s,λ,T
emissivity (3.1) of a specimen at a defined wavelength λ and temperature T
3.4
normal spectral emissivity
ε
ns,λ,T
emissivity (3.1) perpendicular to the specimen at a defined wavelength λ and temperature T
3.5
normal total emissivity
ε
n,T
ratio of the normal component of the total emissive power of a specimen surface to the normal component of
the total emissive power of a blackbody (3.2) at the same temperature T
3.6
normal quasi-total emissivity
ε
n,λλ,, T
normal emissivity between λ and λ at temperature T
1 2
Note 1 to entry: Calculated as the ratio of the normal component of the emissive intensity of a specimen between λ
and λ to the normal component of the emissive intensity of a blackbody between λ and λ at the same temperature T.
2 1 2
4 Principle
The infrared radiance spectrum data from a specimen surface and from a blackbody furnace are measured
using an FTIR spectrometer. The normal spectrum emissivity of a specimen is determined by direct
comparison to a blackbody reference data at the same temperature.
The normal quasi-total emissivity is calculated by integrating the infrared radiance spectrum data in the
specified wavelength range numerically.
5 Apparatus
5.1 Measurement system
The measurement system consists of a Fourier transform infrared spectrometer (FTIR), specimen heating
device, blackbody furnace, and temperature measuring devices as shown in Figure 1. Other optical
arrangements than the one presented in Figure 1 can also be used, such as the blackbody and then the
specimen heating device travelling linearly in front of the FTIR spectrometer.
5.2 Fourier transform infrared spectrometer (FTIR)
Infrared radiation from a specimen or a blackbody furnace is let into a Michelson interferometer of an FTIR
through an external optical path. Thereby, an interferogram of infrared radiation is obtained. The infrared
radiance spectrum is obtained
...
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