SIST EN ISO 22007-2:2022

Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient plane heat source (hot disc) method (ISO 22007-2:2022)

This document specifies a method for the determination of the thermal conductivity and thermal diffusivity, and hence the specific heat capacity per unit volume of plastics. The experimental arrangement can be designed to match different specimen sizes. Measurements can be made in gaseous and vacuum environments at a range of temperatures and pressures.
This method gives guidelines for testing homogeneous and isotropic materials, as well as anisotropic materials with a uniaxial structure. The homogeneity of the material extends throughout the specimen and no thermal barriers (except those next to the probe) are present within a range defined by the probing depth(s) (see 3.1).
The method is suitable for materials having values of thermal conductivity, λ, in the approximate range 0,010 W∙m−1∙K−1 < λ < 500 W∙m−1∙K−1, values of thermal diffusivity, α, in the range 5 × 10−8 m2∙s−1 < α < 10−4 m2∙s−1, and for temperatures, T, in the approximate range 50 K < T < 1 000 K.
NOTE 1   The specific heat capacity per unit volume, C, C = ρ ∙ cp, where ρ is the density and cp is the specific heat per unit mass and at constant pressure, can be obtained by dividing the thermal conductivity, λ, by the thermal diffusivity, α, i.e. C = λ/α, and is in the approximate range 0,005 MJ∙m−3∙K−1 < C < 5 MJ∙m−3∙K−1. It is also referred to as the volumetric heat capacity.
NOTE 2   If the intention is to determine the thermal resistance or the apparent thermal conductivity in the through-thickness direction of an inhomogeneous product (for instance a fabricated panel) or an inhomogeneous slab of a material, reference is made to ISO 8301, ISO 8302 and ISO 472.
The thermal-transport properties of liquids can also be determined, provided care is taken to minimize thermal convection.

Kunststoffe - Bestimmung der Wärmeleitfähigkeit und der Temperaturleitfähigkeit - Teil 2: Transientes ebenes Wärmequellenverfahren (Hot‑Disc‑Verfahren) (ISO 22007‑2:2022)

Dieses Dokument legt ein Verfahren zur Bestimmung der Wärmeleitfähigkeit und Temperaturleitfähigkeit und somit der spezifischen Wärmekapazität je Volumeneinheit von Kunststoffen fest. Die experimentelle Anordnung kann so ausgeführt werden, dass Messungen an Probekörpern verschiedener Größe möglich sind. Die Messungen können in gasförmigen Umgebungen und unter Vakuum bei verschiedenen Temperaturen und verschiedenem Druck durchgeführt werden.
Dieses Verfahren liefert Leitlinien für die Prüfung von homogenen und isotropen Werkstoffen sowie von anisotropen Werkstoffen mit einer einachsigen Struktur. Die Homogenität des Werkstoffs erstreckt sich über den gesamten Probekörper, und innerhalb des durch die Messtiefe(n) (siehe 3.1) festgelegten Bereichs liegen keine Wärmebarrieren vor (außer in der Nähe der Sonde).
Das Verfahren ist für Werkstoffe geeignet, die Wärmeleitfähigkeitswerte λ im annähernden Bereich 0,010 W∙m−1∙K−1 < λ < 500 W∙m−1∙K−1, Temperaturleitfähigkeitswerte α im Bereich 5 × 10−8 m2∙s−1 < α < 10−4 m2∙s−1 aufweisen, sowie für Temperaturen T im annähernden Bereich 50 K < T < 1 000 K.
ANMERKUNG 1   Die spezifische Wärmekapazität je Volumeneinheit C, C = ρ ∙ cp, wobei ρ die Dichte und cp die spezifische Wärme je Masseeinheit und bei konstantem Druck ist, kann erhalten werden, indem die Wärmeleitfähigkeit λ durch die Temperaturleitfähigkeit α dividiert wird, d. h. C = λ/α, und liegt im annähernden Bereich von 0,005 MJ∙m−3∙K−1 < C < 5 MJ∙m−3∙K−1. Diese wird auch als volumetrische Wärmekapazität bezeichnet.
ANMERKUNG 2   Wenn die Absicht besteht, den Wärmewiderstand oder die scheinbare Wärmeleitfähigkeit in Dickenrichtung eines inhomogenen Produktes (zum Beispiel einer gefertigten Tafel) oder einer Platte aus einem inhomogenen Werkstoff zu bestimmen, wird auf ISO 8301, ISO 8302 und ISO 472 hingewiesen.
Die Wärmetransporteigenschaften von Flüssigkeiten können ebenfalls bestimmt werden, vorausgesetzt, dass die Wärmekonvektion auf ein Mindestmaß reduziert wird.

Plastiques - Détermination de la conductivité thermique et de la diffusivité thermique - Partie 2: Méthode de la source plane transitoire (disque chaud) (ISO 22007-2:2022)

Le présent document spécifie une méthode pour déterminer la conductivité thermique et la diffusivité thermique, et de ce fait la capacité calorifique spécifique par unité de volume, des plastiques. Le dispositif expérimental peut être conçu pour s’accorder à différentes tailles d’éprouvette. Les mesurages peuvent être effectués dans des environnements gazeux et sous vide sur une plage de températures et de pressions.
Cette méthode donne des lignes directrices pour les essais de solides homogènes, isotropes et anisotropes, ayant une structure uniaxiale. L’homogénéité du matériau s’étend au travers de l’éprouvette et aucune barrière thermique (excepté celle à côté de la sonde) n’est présente dans une plage définie par la(les) profondeur(s) de vérification (voir 3.1).
Cette méthode est appropriée pour les matériaux ayant des valeurs de conductivité thermique, λ, comprises approximativement dans la plage 0,010 W∙m−1∙K−1 < λ < 500 W∙m−1∙K−1, des valeurs de diffusivité thermique, α, comprises dans la plage 5 × 10−8 m2∙s−1 < α < 10−4 m2∙s−1 et des températures, T, comprises approximativement dans la plage 50 K < T < 1 000 K.
NOTE 1   La capacité calorifique spécifique par unité de volume, C (C = ρ ∙ cp, où ρ est la masse volumique et cp est la chaleur massique par unité de masse et à pression constante), peut être obtenue en divisant la conductivité thermique, λ, par la diffusivité thermique, α, c’est-à-dire C = λ/α, et se situe approximativement dans la plage 0,005 MJ∙m−3∙K−1 < C < 5 MJ∙m−3∙K−1. Elle est également appelée chaleur volumique.
NOTE 2   Si l’objectif est de déterminer la résistance thermique ou la conductivité thermique apparente dans la direction de l’épaisseur d’un produit non homogène (par exemple un panneau fabriqué) ou d’une plaque non homogène de matière, on se réfère à l’ISO 8301, l’ISO 8302 et l’ISO 472.
Les propriétés de transmission thermique des liquides peuvent être déterminées à condition que des précautions soient prises pour minimiser la convection thermique.

Polimerni materiali - Ugotavljanje toplotne prevodnosti in toplotne razprševalnosti - 2. del: Metoda s tranzientnim ploskovnim toplotnim virom (vroči disk) (ISO 22007-2:2022)

Ta dokument določa metodo za ugotavljanje toplotne prevodnosti in toplotne razprševalnosti ter posledično posebno toplotno kapaciteto polimernih materialov na enoto prostornine. Eksperimentalna ureditev je lahko oblikovana tako, da ustreza različnim velikostim vzorca. Meritve je mogoče opravljati v plinskem in vakuumskem okolju pri različni temperaturi oziroma tlaku. Ta metoda podaja smernice za preskušanje homogenih in izotropnih materialov ter anizotropnih materialov z enoosno strukturo. Homogenost materiala se razteza po celotnem vzorcu in ni prisotnih toplotnih pregrad (razen poleg sonde) v območju, opredeljenem z globino sondiranja (glej 3.1). Metoda je primerna za materiale z vrednostmi toplotne prevodnosti (λ) v približnem območju 0,010 W∙m−1∙K−1 < λ < 500 W∙m−1∙K−1, vrednostmi toplotne razprševalnosti (α) v območju 5 × 10−8 m2∙s−1 < α < 10−4 m2∙s−1 in temperatur (T) v približnem območju 50 K < T < 1000 K. OPOMBA 1: Specifična toplotna kapaciteta na enoto prostornine (C) C = ρ ∙ cp, pri čemer je ρ gostota in cp specifična toplota na enoto mase pri konstantnem tlaku, je mogoče pridobiti z deljenjem toplotne prevodnosti (λ) s toplotno razprševalnostjo (α), torej C = λ/α, in je v približnem obsegu 0,005 MJ∙m−3∙K−1 < C < 5 MJ∙m−3∙K−1. Za to se uporablja tudi izraz prostorninska toplotna kapaciteta. OPOMBA 2: Če je namen ugotavljanje toplotne upornosti ali dejanske toplotne prevodnosti nehomogenega izdelka v smeri skozi debelino (na primer izdelane plošče) ali nehomogene plošče iz enega materiala, je treba upoštevati standarde ISO 8301, ISO 8302 in ISO 472. Ugotoviti je mogoče tudi lastnosti toplotnega prenosa za tekočine, vendar je treba posebej paziti na zmanjšanje toplotne konvekcije.

General Information

• Status: Published
• Public Enquiry End Date: 31-Aug-2021
• Publication Date: 11-Jul-2022
• ICS: 83.080.01 - Plastics in general
• Technical Committee: IPMA - Polimer materials and products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 07-Jul-2022
• Due Date: 11-Sep-2022
• Completion Date: 12-Jul-2022
• Ref Project: EN ISO 22007-2:2022 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient plane heat source (hot disc) method (ISO 22007-2:2022)

Relations

• Replaces: SIST EN ISO 22007-2:2015 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient plane heat source (hot disc) method (ISO 22007-2:2015)
• Effective Date: 06-Jul-2022
• Revised: SIST EN ISO 22007-2:2015 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient plane heat source (hot disc) method (ISO 22007-2:2015)
• Effective Date: 07-Oct-2020

Overview

EN ISO 22007-2:2022 - "Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient plane heat source (hot disc) method" (ISO 22007-2:2022) is a CEN-adopted international standard that specifies the hot disc (transient plane heat source) technique for measuring the thermal-transport properties of plastics. The method determines thermal conductivity (λ) and thermal diffusivity (α) and therefore the volumetric heat capacity (C = ρ·cp = λ/α). It is applicable across a wide temperature range (approx. 50 K to 1 000 K) and supports testing in gaseous or vacuum environments and at different pressures.

Key topics and technical requirements

• Measurement technique: Transient plane heat source (hot disc) method - a transient measurement using a plane heat source (hot disc) that acts as both heater and temperature sensor.
• Material scope:
  • Homogeneous, isotropic plastics
  • Anisotropic plastics with uniaxial structure
  • Liquids (with precautions to minimize convection)
• Specimen types: Bulk specimens, anisotropic bulk, slabs and thin films - apparatus and test arrangement can be adapted to specimen size.
• Validated property ranges:
  • Thermal conductivity λ ≈ 0.010 to 500 W·m−1·K−1
  • Thermal diffusivity α ≈ 5×10−8 to 1×10−4 m2·s−1
  • Volumetric heat capacity C ≈ 0.005 to 5 MJ·m−3·K−1 (C = λ/α)
• Test control and data analysis:
  • Procedure for test execution, data fitting and property calculation for bulk, anisotropic, slab and thin-film specimens
  • Consideration of probing depth and elimination/minimization of thermal contact resistance
• Quality assurance:
  • Calibration and verification procedures for apparatus
  • Sections on precision, bias and required test reporting

Practical applications

• Material characterization for thermal management in electronics, automotive, aerospace and insulation applications
• R&D and quality control of polymers, composites and thermal interface materials
• Comparative testing of formulations, additives and processing effects on thermal performance
• Measurement of liquid thermal-transport properties where convection is controlled

Who uses this standard

• Polymer scientists and material engineers
• Thermal metrology and characterization laboratories
• Manufacturers of plastics, composites and thermal interface materials
• Test houses, certification bodies and researchers requiring standardized thermal property data

Related standards

• ISO 22007-1 - Plastics: General principles for thermal conductivity/diffusivity measurement
• ISO 8301, ISO 8302, ISO 472 - referenced for through-thickness resistance or apparent conductivity of inhomogeneous products

EN ISO 22007-2:2022 is the current (2022) edition, superseding the 2015 version, and is widely used where accurate, repeatable bulk thermal property data for plastics are required.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2022
Nadomešča:
SIST EN ISO 22007-2:2015
Polimerni materiali - Ugotavljanje toplotne prevodnosti in toplotne razprševalnosti
- 2. del: Metoda s tranzientnim ploskovnim toplotnim virom (vroči disk) (ISO 22007-
2:2022)
Plastics - Determination of thermal conductivity and thermal diffusivity - Part 2: Transient
plane heat source (hot disc) method (ISO 22007-2:2022)
Kunststoffe - Bestimmung der Wärmeleitfähigkeit und der Temperaturleitfähigkeit - Teil 2:
Transientes ebenes Wärmequellenverfahren (Hot‑Disc‑Verfahren) (ISO
22007‑2:2022)
Plastiques - Détermination de la conductivité thermique et de la diffusivité thermique -
Partie 2: Méthode de la source plane transitoire (disque chaud) (ISO 22007-2:2022)
Ta slovenski standard je istoveten z: EN ISO 22007-2:2022
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 22007-2
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2022
EUROPÄISCHE NORM
ICS 83.080.01 Supersedes EN ISO 22007-2:2015
English Version
Plastics - Determination of thermal conductivity and
thermal diffusivity - Part 2: Transient plane heat source
(hot disc) method (ISO 22007-2:2022)
Plastiques - Détermination de la conductivité Kunststoffe - Bestimmung der Wärmeleitfähigkeit und
thermique et de la diffusivité thermique - Partie 2: der Temperaturleitfähigkeit - Teil 2: Transientes
Méthode de la source plane transitoire (disque chaud) ebenes Wärmequellenverfahren (Hot-Disc-Verfahren)
(ISO 22007-2:2022) (ISO 22007-2:2022)
This European Standard was approved by CEN on 7 June 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 22007-2:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 22007-2:2022) has been prepared by Technical Committee ISO/TC 61 "Plastics"
in collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by
NBN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2022, and conflicting national standards
shall be withdrawn at the latest by December 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 22007-2:2015.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 22007-2:2022 has been approved by CEN as EN ISO 22007-2:2022 without any
modification.
INTERNATIONAL ISO
STANDARD 22007-2
Third edition
2022-06
Plastics — Determination of thermal
conductivity and thermal diffusivity —
Part 2:
Transient plane heat source (hot disc)
method
Plastiques — Détermination de la conductivité thermique et de la
diffusivité thermique —
Partie 2: Méthode de la source plane transitoire (disque chaud)
Reference number
ISO 22007-2:2022(E)
ISO 22007-2:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 22007-2:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 3
6 Test specimens . 5
6.1 Bulk specimens . 5
6.2 Anisotropic bulk specimens . 6
6.3 Slab specimens . 6
6.4 Thin-film specimens . 7
7 Procedure .7
8 Calculation of thermal properties . 9
8.1 Bulk specimens . 9
8.2 Anisotropic bulk specimens . 12
8.3 Slab specimens . 13
8.4 Thin-film specimens . 14
8.5 Low thermally conducting specimens . 15
8.5.1 Introductory remarks .15
8.5.2 Low thermally conducting bulk specimens . 15
8.5.3 Low thermally conducting anisotropic bulk specimens . 17
8.5.4 Low thermally conducting thin–film specimen . 17
9 Calibration and verification . .17
9.1 Calibration of apparatus . 17
9.2 Verification of apparatus . 18
10 Precision and bias .18
11 Test report .19
Bibliography .20
iii
ISO 22007-2:2022(E)
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 document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between
ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 22007-2:2015), which has been
technically revised.
The main changes are as follows:
— Figure 2 has been corrected;
— the term "penetration depth" (former 3.1) has been deleted;
— several Notes have been changed to body text;
— reference has been made in the main text to the theory of sensitivity coefficients.
A list of all parts in the ISO 22007 series can be found on the ISO website.
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
ISO 22007-2:2022(E)
Introduction
A significant increase in the development and application of new and improved materials for broad
ranges of physical, chemical, biological, and medical applications has necessitated better performance
data from methods of measurement of thermal-transport properties. The introduction of alternative
methods that are relatively simple, fast, and of good precision would be of great benefit to the scientific
[1]
and engineering communities .
A number of measurement techniques described as transient methods have been developed of which
several have been commercialized. These are being widely used and are suitable for testing many
types of materials. In some cases, they can be used to measure several properties separately or
[2],[3]
simultaneously .
A further advantage of some of these methods is that it has become possible to measure the true
bulk properties of a material. This feature stems from the possibility of eliminating the influence of
the thermal contact resistance (see 8.1.1) that is present at the interface between the probe and the
[1],[3],[4],[5],[6]
specimen surfaces .
v
INTERNATIONAL STANDARD ISO 22007-2:2022(E)
Plastics — Determination of thermal conductivity and
thermal diffusivity —
Part 2:
Transient plane heat source (hot disc) method
1 Scope
This document specifies a method for the determination of the thermal conductivity and thermal
diffusivity, and hence the specific heat capacity per unit volume of plastics. The experimental
arrangement can be designed to match different specimen sizes. Measurements can be made in gaseous
and vacuum environments at a range of temperatures and pressures.
This method gives guidelines for testing homogeneous and isotropic materials, as well as anisotropic
materials with a uniaxial structure. The homogeneity of the material extends throughout the specimen
and no thermal barriers (except those next to the probe) are present within a range defined by the
probing depth(s) (see 3.1).
The method is suitable for materials having values of thermal conductivity, λ, in the approximate
−1 −1 −1 −1
range 0,010 W∙m ∙K < λ < 500 W∙m ∙K , values of thermal diffusivity, α, in the range
−8 2 −1 −4 2 −1
5 × 10 m ∙s < α < 10 m ∙s , and for temperatures, T, in the approximate range 50 K < T < 1 000 K.
NOTE 1 The specific heat capacity per unit volume, C, C = ρ ∙ c , where ρ is the density and c is the specific heat
p p
per unit mass and at constant pressure, can be obtained by dividing the thermal conductivity, λ, by the thermal
−3 −1 −3 −1
diffusivity, α, i.e. C = λ/α, and is in the approximate range 0,005 MJ∙m ∙K < C < 5 MJ∙m ∙K . It is also referred to
as the volumetric heat capacity.
NOTE 2 If the intention is to determine the thermal resistance or the apparent thermal conductivity in the
through-thickness direction of an inhomogeneous product (for instance a fabricated panel) or an inhomogeneous
slab of a material, reference is made to ISO 8301, ISO 8302 and ISO 472.
The thermal-transport properties of liquids can also be determined, provided care is taken to minimize
thermal convection.
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 22007-1, Plastics — Determination of thermal conductivity and thermal diffusivity — Part 1: General
principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 22007-1 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/
ISO 22007-2:2022(E)
3.1
probing depth
d
p
measure of how far into the specimen, in the direction of heat flow, a heat wave has travelled during the
time window used for calculation
Note 1 to entry: The probing depth is given by:
dt=⋅κα
pmax
where
t is the maximum time of the time window used for calculating the thermal-transport prop-
max
erties;
α is the thermal diffusivity of the specimen material;
κ is a constant dependent on the sensitivity of the temperature recordings.
Note 2 to entry: It is expressed in metres (m).
Note 3 to entry: A typical value in hot disc measurements is κ = 2, which is assumed throughout this document.
3.2
sensitivity coefficient
β
Ψ
coefficient defined by the formula
∂ ΔTt()
[]
β =Ψ
Ψ
∂Ψ
where
Ψ is the thermal conductivity, λ, the thermal diffusivity, α, or the volumetric specific heat
capacity, C;
ΔT(t) is the mean temperature increase of the probe.
Note 1 to entry: Different sensitivity coefficients are defined for thermal conductivity, thermal diffusivity, and
[7]
specific heat per unit volume .
Note 2 to entry: To define the time window that is used to determine both the thermal conductivity and diffusivity
from one single experiment, the theory of sensitivity coefficients is used. Through this theory, which deals with a
large number of experiments and considers the constants, Ψ, as variables, it has been established that
03,/01<⋅trα < ,0
max
where r is the mean radius of the outermost spiral of the probe.
Assuming κ = 2, this expression can be rewritten as:
1,1r < d < 2,0r.
p
4 Principle
A specimen containing an embedded hot disc probe of negligible heat capacity shall be equilibrated at a
given temperature. A heat pulse in the form of a stepwise function is produced by an electrical current
through the probe to generate a dynamic temperature field within the specimen. The increase in the
temperature of the probe is measured as a function of time. The probe operates as a temperature sensor
ISO 22007-2:2022(E)
unified with a heat source (i.e. a self-heated sensor). The response is then analysed in accordance with
the model developed for the specific probe and the assumed boundary conditions.
5 Apparatus
5.1 A schematic diagram of the apparatus is shown in Figure 1.
Key
1 specimen with probe 5 bridge circuit
2 chamber 6 voltmeter
3 vacuum pump 7 voltage source
4 thermostat 8 computer
Figure 1 — Basic layout of the apparatus
5.2 A typical hot disc probe is shown in Figure 2. Convenient probes can be designed with diameters
from 2 mm to 200 mm, depending on the specimen size and the thermal-transport properties
of the material to be tested. The probe is constructed as a bifilar spiral etched out of a (10 ± 2) µm
thick metal foil and covered on both sides by thin (from 7 µm to 100 µm) insulating film. Nickel or
molybdenum should be used as the heater/temperature-sensing metal foil due to their relatively high
temperature coefficient of electrical resistivity and stability over a wide temperature range. Polyimide,
mica, aluminium nitride, or aluminium oxide should be used as the insulating film, depending on the
ultimate temperature of use. The arms of the bifilar spiral forming an essentially circular probe shall
have a width of (0,20 ± 0,03) mm for probes with an overall diameter of 15 mm or less and a width of
(0,35 ± 0,05) mm for probes of larger diameter. The distance between the edges of the arms shall be the
same as the width of the arms.
ISO 22007-2:2022(E)
Key
D sensor diameter
H, h, L, l dimensions of sensor details
The distances indicated in this figure shall be measured in any but the same unit of length, when used to calculate
the heat loss through the electrical leads according to 8.5.2.
Figure 2 — Hot disc probe with bifilar spiral as heating/sensing element
5.3 An electrical bridge shall be used to record the transient increase in resistance of the probe.
Through the bridge, which is initially balanced, the increase in resistance of the probe shall be
followed by recording the imbalance of the bridge with a sensitive voltmeter (see Figure 3). With this
arrangement, the probe is placed in series with a resistor which shall be designed in such a way that its
resistance is kept strictly constant throughout the transient. These two components are combined with
a precision potentiometer, the resistance of which shall be about 100 times larger than the sum of the
resistances of the probe and the series resistor. The bridge shall be connected to a power supply which
can supply 20 V and a current of up to 1 A. The digital voltmeter by which the difference voltages are
recorded shall have a resolution corresponding to 6,5 digits at an integration time of 1 power line cycle.
ISO 22007-2:2022(E)
The resistance of the series resistor, R , shall be close to the initial resistance of the probe with its leads,
S
R + R , in order to keep the power output of the probe as constant as possible during the measurement.
0 L
Key
1 potentiometer R total resistance of the probe leads
L
2 probe R series resistance
S
3 probe leads R initial resistance of the probe before initiating the
transient heating
ΔR increase in resistance of the probe during the
transient heating
ΔU voltage imbalance created by the increase in the
resistance of the probe
NOTE This experimental arrangement allows the determination of temperature deviations from the iterated
straight line (see treatment of experimental data in 8.1) down to or better than 50 µK.
Figure 3 — Diagram of electrical bridge for recording the resistance increase of the probe
5.4 A constant-temperature environment controlled to ±0,1 K or better for the duration of a
measurement shall be established (see Figure 1). The chamber need only be evacuated when working
with slab specimens (see 6.3).
6 Test specimens
6.1 Bulk specimens
6.1.1 For bulk specimens, the requirement for specimen thickness depends on the thermal properties
of the material from which the specimen is made. The expression for the probing depth contains the
diffusivity, which is not known prior to the measurement. This means that the probing depth shall be
calculated after an initial experiment has been completed. If, with this new information, the probing
depth is found to be outside the limits given in 8.1.3, the test shall be repeated, with an adjusted total
measurement time, until the required conditions are fulfilled.
The shape of the specimen can be cylindrical, square, or rectangular. Machining to a certain shape is
not necessary, as long as a flat surface (see 6.1.4) on each of the two specimen halves faces the sensor
and the requirements regarding sensor size given in 8.1.3 are fulfilled.
6.1.2 The measurement shall be conducted in such a way that the probing depth into the specimen
shall be at least 20 times the characteristic length of the components making up the material or of any
inhomogeneity in the material, such as the average diameter of the particles if the specimen is a powder.
ISO 22007-2:2022(E)
6.1.3 The specimen dimensions shall be chosen to minimize the effect that its outer surfaces will
have on the measurement. The specimen size shall be such that the distance from any part of the bifilar
spiral of the hot disc probe to any part of the outside boundary of the specimen is larger than the overall
mean radius of the bifilar spiral (see 5.2). An increase in this distance beyond the size of the diameter of
the spiral does not improve the accuracy of the results.
6.1.4 Specimen surfaces which are in contact with the sensor shall be plane and smooth. The
specimen halves shall be clamped on to both sides of the hot disc probe.
Heat sink contact paste shall not be used since:
a) it is difficult to obtain a sufficiently thin layer of paste which will actually improve the thermal
contact;
b) the paste obviously increases the heat capacity of the insulating layer and delays the development
of the constant temperature difference between the sensing material and the specimen surface;
c) it is difficult to obtain exactly the same thickness of paste on both sides of the probe and achieve a
strictly symmetrical flow of heat from the heating/sensing material through the insulation into the
two specimen halves.
6.1.5 For liquids, suitable containment vessels with adequate seals are necessary and air bubbles and
evaporation shall be avoided.
Storage and conditioning of the liquid can affect its properties, for example, by absorption of water or
gas. It can be necessary to pre-treat the specimen prior to testing, for example by degassing. However,
pre-treatment procedures shall not be used when they can detrimentally affect the material to be
tested, for example through degradation.
6.1.6 For materials prone to significant dimensional changes whether instigated by measurements
over large temperature ranges, thermal expansion, change of state, phase transition, or other causes,
care shall be taken to ensure that when placing the hot disc probe in contact with the specimen, the
applied load does not affect the properties of the specimen.
With soft materials, the clamping pressure shall not compress the specimen and thus change its
thermal-transport properties.
6.1.7 The specimen shall be conditioned in accordance with the standard specification which applies
to the type of material and its particular use.
6.2 Anisotropic bulk specimens
6.2.1 If a material is anisotropic, specimens shall be cut (or otherwise prepared) so that the probe can
be oriented in the main directions (e.g. the fibre directions in reinforced plastics, the main directions
[4],[8]
in layered structures or the principal axes in crystals) . The hot disc method is limited to materials
in which the thermal properties along two of the orthogonal and principal axes are the same, but are
different from those along the third axis.
6.2.2 The size of anisotropic specimens shall be chosen so that the requirements of 8.1.3 are fulfilled
along the principal axes.
6.3 Slab specimens
The so-called slab method is used with sheet-formed specimens extending in two dimensions, but with a
[9]
limited and well-defined thickness in a range from 1 mm to 10 mm . The slab specimen thickness shall
be known to an accuracy of 0,01 mm. When two equally thick slabs of a material are clamped around a
probe and thermally insulated on the outer sides, it is possible to measure the thermal conductivity and
ISO 22007-2:2022(E)
diffusivity of such specimens. The condition related to the probing depth shall be fulfilled in the plane
of the probe but not in the through-thickness direction. This method is particularly suited to studies
−1 −1
of materials having thermal conductivities higher than 10 W⋅m ⋅K but can also be used for materials
−1 −1
with thermal conductivities as low as 1 W⋅m ⋅K , provided good thermal insulation of the slabs can be
arranged (for instance by performing the measurements in a vacuum).
6.4 Thin-film specimens
The so-called thin-film method is used with specimens such as paper, textiles, polymer films or
deposited thin-film layers (such as ceramic coatings) with thicknesses ranging from 0,05 mm to about
[10]
5,0 mm . The thickness of thin-film specimens (placed on both sides of the probe) shall be known to
an accuracy of ±1 µm.
NOTE 1 When making a measurement on a material with a high thermal conductivity, the temperature
undergoes a rapid increase at the very beginning of the transient followed by a much more gradual increase. The
insulating layer, between which the sensing spiral is sandwiched, causes this rapid increase. It has been shown
both experimentally and in computer simulations that the temperature difference across the insulating layer
becomes constant within a very short time and remains constant throughout the measurement. The reason is
that the total power output, the area of the sensing material and the thickness of the insulating layer are constant
in the test.
If thin films of a material are placed between the probe and a high-conductivity background material
(in the form of an “infinite” solid), it is possible to measure the apparent thermal conductivity of the
film material, provided that the apparent thermal conductivity of the insulating layer with which the
[10]
probe is covered has been determined in a separate experiment .
NOTE 2 It can be necessary to make measurements on films of different thicknesses and the same properties
or with different clamping pressures to eliminate mathematically the influence of thermal contact resistances.
The thermal
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