ISO 19618:2017

Fine ceramics (advanced ceramics, advanced technical ceramics) - Measurement method for normal spectral emissivity using blackbody reference with an FTIR spectrometer

ISO 19618:2017 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 utilisant un corps noir de référence avec un spectromètre FTIR

General Information

• Status: Published
• Publication Date: 13-Feb-2017
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: ISO/TC 206 - Fine ceramics
• Drafting Committee: ISO/TC 206/WG 7 - Monolithic ceramics/Physical and thermal properties
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 13-Jan-2025
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 19618:2025 - Fine ceramics (advanced ceramics, advanced technical ceramics) - Measurement method for normal spectral emissivity using blackbody reference with an FTIR spectrometer
• Effective Date: 04-Feb-2023

Overview

ISO 19618:2017 specifies a laboratory measurement method for determining normal spectral emissivity and normal quasi‑total emissivity of fine ceramics (advanced/technical ceramics), ceramic matrix composites, and continuous fibre‑reinforced ceramic matrix composites. The method uses a blackbody reference and a Fourier transform infrared (FTIR) spectrometer to measure infrared radiance at elevated temperatures. It applies to opaque, highly non‑reflective materials in the wavelength range 1.67 μm to 25 μm and an approximate temperature range of 350 K to 1 100 K.

Key topics and technical requirements

• Principle: Direct comparison of specimen radiance to an internationally traceable blackbody using FTIR; spectral data are Fourier‑transformed from interferograms and integrated to obtain quasi‑total emissivity.
• Apparatus: FTIR with an external optical path, specimen heating device, blackbody furnace (total emissivity > 0.95), temperature sensors (thermocouples per IEC 60584‑2 or RTDs per IEC 60751), and a high‑reflectance mirror for background measurement.
• Measurement conditions:
  • Wavelength coverage: 1.67 μm–25 μm.
  • Temperature control: specimen surface controlled to within ±3 K.
  • Spectral resolution: better than 16 cm⁻¹; acquisitions/integrations >100.
  • Measurement spot and blackbody aperture: aperture >3× measurement spot area.
• Preparation and validation:
  • Wavelength calibration using polystyrene film.
  • Linearity checks using multi‑temperature blackbody ratios and neutral density filters.
  • Stability verification: repeat blackbody measurements within 10 min must be within ±1%.
  • System validation against literature data for standard materials (e.g., alumina).
• Calculations: Use Planck’s blackbody radiation function to compute theoretical radiance and calculate spectral and quasi‑total emissivity.

Practical applications and users

ISO 19618:2017 is intended for:

• Materials researchers and laboratories measuring high‑temperature radiative properties of advanced ceramics.
• Quality control and R&D in ceramic manufacturers and composite fabricators.
• Thermal engineers and modelling teams needing accurate emissivity inputs for radiative heat transfer simulations.
• Aerospace, power generation, and high‑temperature industrial sectors where ceramic components’ thermal emissivity affects performance and safety.

Using this standard helps ensure traceable, repeatable emissivity data for thermal design, coating evaluation, life‑prediction studies, and energy balance calculations.

Related standards and references

• IEC 60584‑2 - Thermocouples (tolerances)
• IEC 60751 - Industrial platinum resistance thermometers (RTDs)
• Planck’s blackbody radiation function (used in Annex A)
• ISO/TC 206 (Technical Committee on Fine Ceramics) - committee responsible for the standard

ISO 19618:2017 provides a robust, ISO‑consistent procedure for obtaining reliable emissivity data of fine ceramics using FTIR and blackbody referencing - essential input for accurate thermal analysis and materials characterization.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 19618
First edition
2017-02
Fine ceramics (advanced ceramics,
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 utilisant un corps noir de référence avec un spectromètre FTIR
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 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 . 6
7.1 Position of a blackbody furnace and a specimen . 6
7.2 Wavelength calibration . 6
7.3 Verification of linearity . 6
7.4 Verification of stability . 6
7.5 Validation of measurement system . 6
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. 7
10.1 Normal spectral emissivity . 7
10.2 Normal quasi-total emissivity . 8
11 Test report . 9
Annex A (informative) Calculation of theoretical infrared radiance spectrum L(λ,T) using
Planck’s blackbody radiation function .10
Annex B (informative) Christiansen effect .11
Annex C (informative) Validity of normal quasi-total emissivity .12
Bibliography .13
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 on 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 the following URL: www . i so .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 19618:2017(E)
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, definitions and symbols
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
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 (λ, T)
s
emissivity (3.1) of a specimen at a defined wavelength λ and temperature T
3.4
normal spectral emissivity
ε (λ, T)
ns
emissivity (3.1) perpendicular to the specimen at a defined wavelength λ and temperature T
3.5
normal total emissivity
ε (T)
n
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 at the same temperature T
3.6
normal quasi-total emissivity
ε (λ , λ , T)
n 1 2
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
1 2 1 2
temperature T.
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.
Integrating the infrared radiance spectrum data in the specified wavelength range numerically, normal
quasi-total emissivity is calculated.
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.
5.2 Fourier transform infrared spectrometer (FTIR)
Infrared radiation from a specimen or a blackbody furnace is let into a Mickelson interferometer of
an FTIR through an external optical path. Thereby, an interferogram of infrared radiation is obtained.
The infrared radiance spectrum is obtained numerically by Fourier transformation processing from
the interferogram.
The optical system including a Mickelson interferometer of an FTIR shall be filled with dry N or dry air of
which the dew point is lower than 220 K to reduce the effect of H O and CO in air. Vacuum may be used.
2 2
The measurement spot area at the sample position and at the blackbody furnace positions shall be
measured preliminarily.
5.3 Specimen heating device
A specimen shall be heated using a heating device such as electrical resistance heating elements,
heat-pipes, heat-transfer media, etc. The specimen surface temperature shall be well controlled to
within ± 3 K.
An example of a specimen heating device is depicted in Figures 2 and 3.
2 © ISO 2017 – All rights reserved

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