ISO/TS 23690:2023

TECHNICAL ISO/TS
SPECIFICATION 23690
First edition
2023-07
Nanotechnologies — Multiwall
carbon nanotubes — Determination
of carbon impurity content by
thermogravimetric analysis
Nanotechnologies – Nanotubes de carbone multicouches –
Détermination de la teneur en impureté de carbone par analyse
thermogravimetrique
Reference number
© ISO 2023
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
3.3 Abbreviated terms . 2
4 Principle . 2
5 Sample preparation .3
6 Measurement .3
6.1 Apparatus . 3
6.1.1 Thermogravimetric analyser . 3
6.1.2 Drying furnace . 3
6.1.3 Analytical balance . . 3
6.1.4 Desiccator . 3
6.2 Reagents . 3
6.2.1 Inert gas . 3
6.2.2 Carbon dioxide . 3
6.3 Measurement procedures . 3
7 Data analysis and interpretation of results . 4
8 Measurement uncertainty .5
8.1 Type A uncertainty . 5
8.2 Type B uncertainty . 5
9 Test report . 5
Annex A (informative) Repeatability test: Case study . 7
Annex B (informative) Reproducibility test: Case study.15
Annex C (informative) Detailed procedures for the analysis of the TG curve .19
Bibliography .21
iii
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 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) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at  www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
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 229, Nanotechnologies.
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
Introduction
Multiwall carbon nanotubes (MWCNTs) are quasi-one-dimensional tubular carbon nanomaterials
rolled up or coaxial nested by three or more graphene sheets. The production of carbon nanotubes
(CNT) generally results in significant amounts of carbon impurities (carbon material content not in
the form of CNT, including amorphous carbon and trace amounts of other types of structured carbon),
which influence the physical and chemical properties of the nanomaterial. Therefore, the measurement
of carbon impurities content in MWCNT samples is highly desirable for the determination of their
purity.
Several methods have been reported to characterize carbon impurities in MWCNT samples,
including transmission electron microscopy (TEM), temperature programmed oxidation (TPO) and
[1][2][3][4]
thermogravimetric analysis (TGA), etc., among which TGA can provide quantitative results.
[5][6]
This technique makes use of the fact that MWCNTs are more stable than the majority of carbon
impurities, so carbon impurities less stable than MWCNTs will react firstly with carbon dioxide in
carbon dioxide atmosphere. The oxidation of carbon impurities with carbon dioxide is an endothermal
process, which prevents overheating in certain areas and restrains the reaction of MWCNTs at the same
time. Therefore, the separation between the oxidation of carbon impurities and those of MWCNTs is
[7][8][9][10]
enhanced, allowing the amount of carbon impurities less stable than MWCNTs to be calculated
from the mass loss in thermogravimetric analysis.
v
TECHNICAL SPECIFICATION ISO/TS 23690:2023(E)
Nanotechnologies — Multiwall carbon nanotubes
— Determination of carbon impurity content by
thermogravimetric analysis
1 Scope
This document specifies a mild oxidation method to determine the content of carbon impurities (carbon
material content not in the form of CNT, including amorphous carbon and trace amountd of other types
of structured carbon) less stable than multiwall carbon nanotubes (MWCNTs) by thermogravimetric
analysis (TGA) under carbon dioxide atmosphere.
This document is applicable to the characterization of carbon impurities content in MWCNT samples
prepared by chemical vapour deposition (CVD). Measurement of carbon impurities in MWCNT samples
prepared by other methods can refer to this document. This method is not applicable to functionalized
MWCNT samples or MWCNT samples with encapsulant species.
NOTE This method is applicable for the case of TG curves with a single-stage.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
multiwall carbon nanotube
MWCNT
multi-walled carbon nanotube
carbon nanotube composed of nested, concentric or near-concentric graphene layers with interlayer
distances similar to those of graphite
Note 1 to entry: The structure is normally considered to be many single-walled carbon nanotubes nesting each
other and would be cylindrical for small diameters but tends to have a polygonal cross-section as the diameter
increases.
[11]
[SOURCE: ISO/TS 80004-3:2020, 3.3.6 ]
3.1.2
amorphous carbon
carbon material without long-range crystalline order
[12]
[SOURCE: IUPAC, Compendium of Chemical Terminology ]
3.2 Symbols
T temperature of the peak on DTG curve (°C)
o
w mass percentage (%) of the sample at 300 °C
w mass percentage (%) of the sample at temperature T
e e
ΔH is the enthalpy change
3.3 Abbreviated terms
CO carbon dioxide
CVD chemical vapour deposition
DTG derivative thermogravimetric
MWCNT multiwall carbon nanotube
TG thermogravimetric
TGA thermogravimetric analysis
4 Principle
Thermogravimetric analysis measures the change in mass of a material as a function of temperature. In
order to accomplish this, TGA requires the precise measurements of mass, temperature and temperature
change. The change in mass of a material relates to change in composition and structure of the material.
Observed mass changes with temperature increases may result from the removal of absorbed moisture,
solvent residues, chemically bound moieties and/or the thermal or oxidative decomposition of product.
[13]
The experiments are carried out in an inert or oxidising atmosphere. The recorded mass change
as a function of temperature is a thermogravimetric (TG) curve. Mass change and the extent of these
[14]
changes of a material in a TG curve are indicators of the thermal stability of the material. Derivative
thermogravimetric (DTG) curve is a display of the first derivative of thermogravimetry data with
[15]
respect to temperature or time .
The method specified in this document is based on different reactivity of MWCNTs and carbon impurities
under carbon dioxide (CO ) atmosphere during heating. Carbon dioxide works as a mild oxidant to first
oxidize carbon impurities less stable than MWCNTs. Moreover, the reaction between carbon impurities
[7][8][9]
and CO absorbs heat from environment, which prevents local overheating, and thus enhances
the separation of carbon impurities and MWCNTs. The amount of carbon impurities in MWCNT samples
can be calculated from the mass loss in thermogravimetric analyser. See the reaction formula below.
C + CO → 2 CO ; ΔH > 0
(s) 2(g) (g)
where
C is the carbon impurities in solid state;
(s)
CO is the carbon dioxide in gaseous state;
2(g)
CO is the carbon monoxide in gaseous state;
(g)
ΔH is the enthalpy change.
5 Sample preparation
MWCNT sample should be of good quality. MWCNT sample is first placed in a thermostatic vacuum
[16]
drying furnace for 2 h at 150 °C to remove unwanted volatile components. Then the sample is
transferred to a desiccator to cool down to room temperature and it is stored there until used.
6 Measurement
6.1 Apparatus
6.1.1 Thermogravimetric analyser
Thermogravimetric analyser should consist of a furnace, which is capable of heating from room
temperature to 1 000 °C or above. Heating rate during experiment should be controlled by temperature
[14]
programme set in software .
−1 −1
The linear heating rate should be controllable in the range from 1 °C min to 50 °C min . The balance
sensitivity should be at least 1 μg, and the temperature controller sensitivity less than or equal to
0,01 °C.
A crucible should be used as a sample container. The crucible is generally made of alumina, platinum,
quartz or other materials, which does not change or react under the measurement conditions.
6.1.2 Drying furnace
A drying furnace capable of controlled heating to at least 150 °C is used.
6.1.3 Analytical balance
An analytical balance capable of weighing 0,1 mg or lower is used.
6.1.4 Desiccator
A dessicator containing a desiccant such as dried silica gel impregnated with cobalt chloride is used.
The drying agent shall not react with MWCNT samples.
6.2 Reagents
6.2.1 Inert gas
Dry, commercially available inert gas, such as nitrogen gas or argon gas, with minimum volume fraction
of 99,999 % should be used in the measurement.
6.2.2 Carbon dioxide
Dry, commercially available carbon dioxide gas with minimum volume fraction of 99,999 % should be
used in the measurement.
6.3 Measurement procedures
The thermogravimetric analyser should be calibrated according to the manufacturer’s protocol to
ensure proper temperature and mass measurement.
a) Turn on the thermogravimetric analyser and wait until equilibrium is reached. Then inert gas and
carbon dioxide gas are introduced.
b) Obtain a baseline correction file using empty crucibles at the same experiment conditions to be
used for the MWCNT sample. Specifically, set the flow rate of gas to the furnace according to the
−1 −1
instrument type. The recommended inert gas flow is 10 ml min to 20 ml min and carbon dioxide
−1 −1 −1
gas flow is 20 ml min to 40 ml min ; set the heating rate as 10 °C min within the temperature
range from room temperature to 1 000 °C.
c) Weigh an appropriate amount of MWCNT sample (3 mg to 5 mg) using an analytical balance and
transfer the sample into the crucible.
d) Before starting the measurement, keep the MWCNT sample in a closed thermogravimetric analyser
under a gas flow for at least 15 min and wait until the signal (mass, temperature, gas flow) is stable.
e) Test the sample under
...