SIST EN ISO 21068-2:2024
(Main)Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-nitride, silicon-oxynitride and sialon - Part 2: Determination of volatile components, total carbon, free carbon, silicon carbide, total and free silicon, free and surface silica (ISO 21068-2:2024)
Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-nitride, silicon-oxynitride and sialon - Part 2: Determination of volatile components, total carbon, free carbon, silicon carbide, total and free silicon, free and surface silica (ISO 21068-2:2024)
This document specifies analytical techniques for the determination of volatile components by thermal treatment at specified temperatures, and methods for the determination of the total carbon, free carbon, silicon carbide, total and free silicon and free and surface silica content of silicon-carbide, silicon-nitride and silicon-oxynitride containing raw materials and refractory products.
Chemische Analyse von Rohstoffen und feuerfesten Erzeugnissen, die Siliciumcarbid, Siliciumnitrid, Siliciumoxinitrid und Sialon enthalten - Teil2: Bestimmung des Gehaltes an flüchtigen Bestandteilen, Gesamtkohlenstoff, freiem Kohlenstoff, Siliziumcarbid, gesamtem und freiem Silizium, freiem und anhaltendem Siliziumdioxid (ISO 21068-2:2024)
Dieses Dokument legt Analysenverfahren für die Bestimmung flüchtiger Bestandteile durch Wärmebehandlung bei festgelegten Temperaturen, sowie Verfahren für die Bestimmung des Gehaltes an Gesamtkohlenstoff, freiem Kohlenstoff, Siliciumcarbid, gesamtem und freiem Silicium sowie des Gehaltes an freiem und anhaftendem Siliciumdioxid von Siliciumcarbid, Siliciumnitrid und Siliciumoxinitrid enthaltenden Rohstoffen und feuerfesten Erzeugnissen fest.
Analyse chimique des matières premières et des produits réfractaires contenant du carbure de silicium, du nitrure de silicium, de l’oxynitrure de silicium et du sialon - Partie 2: Dosage des composés volatils, du carbone total, du carbone libre, du carbure de silicium, du silicium total et libre et de la silice libre et superficielle (ISO 21068-2:2024)
Ce document spécifie des techniques d’analyse permettant de doser les composés volatils par un traitement thermique à des températures spécifiées ainsi que des méthodes permettant de déterminer les teneurs en carbone total, en carbone libre, en carbure de silicium, en silicium total et libre et en silice libre et superficielle des matières premières et des produits réfractaires contenant du carbure de silicium, du nitrure de silicium et de l’oxynitrure de silicium.
Kemijska analiza surovin in ognjevzdržnih izdelkov, ki vsebujejo silicijev karbid, silicijev nitrid, silicijev oksinitrid in sialon - 2. del: Določevanje hlapnih sestavin, celotnega ogljika, prostega ogljika, silicijevega karbida, celotnega in prostega silicija, prostega in površinskega silicija (ISO 21068-2:2024)
Ta del standarda ISO 21068 določa analitske tehnike za določevanje hlapnih sestavin s toplotno obdelavo pri določenih temperaturah ter metode za določevanje vsebnosti celotnega ogljika, prostega ogljika, silicijevega karbida, celotnega in prostega silicija ter prostega in površinskega silicija v surovinah in ognjevzdržnih izdelkih, ki vsebujejo silicijev karbid, silicijev nitrid, silicijev oksinitrid in sialon.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2024
Kemijska analiza surovin in ognjevzdržnih izdelkov, ki vsebujejo silicijev karbid,
silicijev nitrid, silicijev oksinitrid in sialon - 2. del: Določevanje hlapnih sestavin,
celotnega ogljika, prostega ogljika, silicijevega karbida, celotnega in prostega
silicija, prostega in površinskega silicija (ISO 21068-2:2024)
Chemical analysis of raw materials and refractory products containing silicon-carbide,
silicon-nitride, silicon-oxynitride and sialon - Part 2: Determination of volatile
components, total carbon, free carbon, silicon carbide, total and free silicon, free and
surface silica (ISO 21068-2:2024)
Chemische Analyse von Rohstoffen und feuerfesten Erzeugnissen, die Siliciumcarbid,
Siliciumnitrid, Siliciumoxinitrid und Sialon enthalten - Teil2: Bestimmung des Gehaltes an
flüchtigen Bestandteilen, Gesamtkohlenstoff, freiem Kohlenstoff, Siliziumcarbid,
gesamtem und freiem Silizium, freiem und anhaltendem Siliziumdioxid (ISO 21068-
2:2024)
Analyse chimique des matières premières et des produits réfractaires contenant du
carbure de silicium, du nitrure de silicium, de l’oxynitrure de silicium et du sialon - Partie
2: Dosage des composés volatils, du carbone total, du carbone libre, du carbure de
silicium, du silicium total et libre et de la silice libre et superficielle (ISO 21068-2:2024)
Ta slovenski standard je istoveten z: EN ISO 21068-2:2024
ICS:
71.040.40 Kemijska analiza Chemical analysis
81.080 Ognjevzdržni materiali Refractories
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 21068-2
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2024
EUROPÄISCHE NORM
ICS 81.080 Supersedes EN ISO 21068-2:2008
English Version
Chemical analysis of raw materials and refractory
products containing silicon-carbide, silicon-nitride, silicon-
oxynitride and sialon - Part 2: Determination of volatile
components, total carbon, free carbon, silicon carbide,
total and free silicon, free and surface silica (ISO 21068-
2:2024)
Analyse chimique des matières premières et des Chemische Analyse von Rohstoffen und feuerfesten
produits réfractaires contenant du carbure de silicium, Erzeugnissen, die Siliciumcarbid, Siliciumnitrid,
du nitrure de silicium, de l'oxynitrure de silicium et du Siliciumoxinitrid und Sialon enthalten - Teil2:
SiAlON - Partie 2: Dosage des composés volatils, du Bestimmung des Gehaltes an flüchtigen Bestandteilen,
carbone total, du carbone libre, du carbure de silicium, Gesamtkohlenstoff, freiem Kohlenstoff, Siliziumcarbid,
du silicium total et libre et de la silice libre et gesamtem und freiem Silizium, freiem und
superficielle (ISO 21068-2:2024) anhaltendem Siliziumdioxid (ISO 21068-2:2024)
This European Standard was approved by CEN on 24 May 2024.
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, Türkiye 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
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21068-2:2024 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 21068-2:2024) has been prepared by Technical Committee ISO/TC 33
"Refractories" in collaboration with Technical Committee CEN/TC 187 “Refractory products and
materials” the secretariat of which is held by BSI.
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 2024, and conflicting national standards
shall be withdrawn at the latest by December 2024.
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 21068-2:2008.
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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 21068-2:2024 has been approved by CEN as EN ISO 21068-2:2024 without any
modification.
International
Standard
ISO 21068-2
Second edition
Chemical analysis of raw materials
2024-06
and refractory products containing
silicon-carbide, silicon-nitride,
silicon-oxynitride and sialon —
Part 2:
Determination of volatile
components, total carbon, free
carbon, silicon carbide, total and
free silicon, free and surface silica
Analyse chimique des matières premières et des produits
réfractaires contenant du carbure de silicium, du nitrure de
silicium, de l’oxynitrure de silicium et du SiAlON —
Partie 2: Dosage des composés volatils, du carbone total, du
carbone libre, du carbure de silicium, du silicium total et libre et
de la silice libre et superficielle
Reference number
ISO 21068-2:2024(en) © ISO 2024
ISO 21068-2:2024(en)
© ISO 2024
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
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Published in Switzerland
ii
ISO 21068-2:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Determination of volatile components by gravimetric methods . 1
4.1 General .1
4.2 Determination of the loss on drying at 250 °C (w ) .2
LOD250
4.2.1 Principle .2
4.2.2 Apparatus .2
4.2.3 Procedure .2
4.2.4 Calculation .2
4.3 Determination of the loss on ignition in argon (w ) .2
LOIAr
4.3.1 Principle .2
4.3.2 Apparatus .3
4.3.3 Test assembly .3
4.3.4 Reagents .3
4.3.5 Procedure .4
4.3.6 Calculation .4
5 Determination of the total carbon content . 5
5.1 Scope . .5
5.2 Combustion techniques .5
5.2.1 Combustion in a resistance furnace with lead borate or tin as decomposing agent .5
5.2.2 Combustion in an induction furnace (IF) with metallic powder as decomposing
agent .6
5.3 Detection techniques .7
5.3.1 Coulometry .7
5.3.2 Detection of the released carbon dioxide, CO , by infrared absorption (IR) .7
5.3.3 Thermal conductivity (TC) method .8
5.4 Expression of results . .8
6 Determination of free carbon content . 8
6.1 General .8
6.1.1 Direct methods .8
6.1.2 Indirect methods . 13
7 Determination of silicon carbide content.16
7.1 General .16
7.2 Determination of silicon carbide, SiC, by indirect method .16
7.2.1 Principle .16
7.2.2 Calculation .16
7.2.3 Precision .17
7.3 Determination of silicon carbide, SiC, by combustion methods .17
7.3.1 Procedure .17
7.3.2 Calculation .17
7.4 Determination of silicon carbide, SiC, by combustion at 750 °C .17
7.4.1 Principle .17
7.4.2 Residue production .17
7.4.3 Determination of the total carbon content of the residue .18
7.4.4 Calculation .18
8 Determination of total silicon content . 19
9 Determination of free silicon content . 19
9.1 Principle .19
iii
ISO 21068-2:2024(en)
9.2 Pretreatment with hydrochloric acid .19
9.3 Determination of free silicon by hydrogen evolution .19
9.3.1 Reagents .19
9.3.2 Apparatus . 20
9.3.3 Mass of test portion . 20
9.3.4 Procedure .21
9.3.5 Blank test . 22
9.3.6 Calculation . 22
10 Determination of free silica content .23
10.1 Principle . 23
10.2 Reagents . 23
10.3 Apparatus . 23
10.4 Sample preparation .24
10.5 Procedure .24
10.5.1 Determination . 25
10.5.2 Calculation and expression of SiO content . 25
11 Determination of surface silica content . .25
12 Expression of results .26
13 Test report .26
Annex A (informative) Precision data .27
Annex B (informative) Examples of certified reference materials for calibration of carbon
analyser .33
Annex C (normative) Correction of the free carbon content in case of oxidation of SiC .34
Bibliography .35
iv
ISO 21068-2:2024(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 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 33, Refractories, in collaboration with the
European Committee for Standardization (CEN) Technical Committee CEN/TC 187, Refractory products
and materials, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO 21068-2:2008), which has been technically
revised.
The main changes are as follows:
— methods described in ISO 12698-1:2007 for the determination of free carbon, silicon carbide and free
silica have been included in this document;
— methods that are no longer used in practice have been removed;
— normative references and bibliography have been updated;
— document has been editorially revised.
A list of all parts in the ISO 21068 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.
v
ISO 21068-2:2024(en)
Introduction
[1]
The ISO 21068 series has been developed from the combination of EN 12698-1:2007 and EN 12698-
[2] [3] [4] [5]
2:2007 and ISO 21068-1:2008, ISO 21068-2:2008 and ISO 21068-3:2008. The last three standards
[6]
have been originally developed from the combination of Japanese standard JIS R 2011:2007 and work items
developed within CEN. Because there is a wide variety of laboratory equipment in use, the most commonly
used methods are described.
[2]
ISO 21068-4 is derived from EN 12698-2:2007 describing XRD methods for the determination of
mineralogical phases typically apparent in nitride and oxy-nitride bonded silicon carbide refractory
products using a Bragg-Brentano diffractometer.
[7]
The ISO 21068 series is applicable to the analysis of all refractory products as classified in ISO 10081-1,
[8] [9] [10] [11]
ISO 10081-2, ISO 10081-3 and ISO 10081-4 (shaped) and ISO 1927-1 (unshaped) and for raw
materials containing carbon and/or silicon carbide. Therefore, the ISO 21068 series covers the full range of
analysis from pure silicon carbide to oxide refractory composition with low-content silicon carbide and/or
nitrides. Primarily, the ISO 21068 series provides methods to distinguish between different carbon bound
types like total carbon (C ) and free carbon (C ) and derives from these two the silicon carbide content.
total free
ISO 21068-4 includes details of sample preparation and general principles for qualitative and quantitative
analysis of mineralogical phase composition. Quantitative determination of α-Si N , β-Si N , Si ON , AlN,
3 4 3 4 2 2
and sialon are described.
If free carbon is present, ISO 21068-2 includes different temperature treatments to determine the mass
changes gravimetrically. Frequently, the resulting residue is used for other determinations.
The determination of other groups of analytes described in the ISO 21068 series are free metals, free silicon
(Si ), free aluminium (Al ), free magnesium (Mg ), free iron (Fe ) and the group of oxides from main
free free free free
to trace components.
The ISO 21068 series also describes the determination of silicon dioxide, total silicon, oxygen and nitrogen
and other oxide bound metals that typically occur in the materials.
It represents a listing of analytical methods which is generally structured according to material composition.
However, it is still the user who should prove the applicability of the method depending on the material and
analytical requirements.
The most broadly used analytical techniques such as X-ray fluorescence spectroscopy (XRF) and inductively
coupled plasma-optical emission spectrometry (ICP-OES) suffer from the disadvantage that the analytical
results are chemical species independent. For carbon-containing ceramic raw materials and compositions,
the ISO 21068 series provides analytical methods for the determination of free carbon, and SiC in the
presence of oxide compounds in particular SiO .
Due to the diversity of laboratory equipment, the ISO 21068 series summarizes broadly used analytical
techniques which lead to equivalent results. For example, the determination of carbon is based on all
described methods on the reaction of carbon with oxygen at elevated temperatures to CO . Thus, carbon is
analysed as CO .
As well as carbon and carbide compounds, metallic silicon, aluminium and magnesium are considered. While
metallic silicon is mainly a precursor material which remains after the production process of SiC in the raw
material, metallic aluminium is added as an antioxidant in carbon-containing refractory formulations.
Mostly oxide bound components, such as Al O , CaO, MgO, TiO , Cr O , ZrO and alkalis, can be determined
2 3 2 2 3 2
[13] [23] [20] [21]
by XRF, ICP-OES or wet chemical methods (see ISO 12677 , ISO 26845 , ISO 21587-1 , ISO 21587-2
[22]
and ISO 21587-3 ). These results can be corrected by formulae provided by the ISO 21068 series, in
consideration of the values obtained by the determination of carbon, SiC, and metallic components.
The ISO 21068 series also provides methods for qualitative and quantitative determinations of the nitrogen
content and the determination of oxygen. Thereby only the total content of nitrogen and oxygen is given; a
precise determination of non-carbide components (oxides and nitrides) is not possible in this way.
vi
ISO 21068-2:2024(en)
The ISO 21068 series also provides methods to distinguish quantitatively between different varieties of
nitrides like silicon nitride, silicon oxy-nitride and sialon.
vii
International Standard ISO 21068-2:2024(en)
Chemical analysis of raw materials and refractory products
containing silicon-carbide, silicon-nitride, silicon-oxynitride
and sialon —
Part 2:
Determination of volatile components, total carbon, free carbon,
silicon carbide, total and free silicon, free and surface silica
1 Scope
This document specifies analytical techniques for the determination of volatile components by thermal
treatment at specified temperatures, and methods for the determination of the total carbon, free carbon,
silicon carbide, total and free silicon and free and surface silica content of silicon-carbide, silicon-nitride and
silicon-oxynitride containing raw materials and refractory products.
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 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 9286:2021, Abrasive grains and crude — Chemical analysis of silicon carbide
ISO 21068-1, Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-
nitride, silicon-oxynitride and sialon — Part 1: General information, terminology and sample preparation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21068-1 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/
4 Determination of volatile components by gravimetric methods
4.1 General
The determination of volatile components is defined as change in mass caused by heat treatment of the
sample at a defined temperature. The change in mass is measured by weighing.
Table 1 gives an overview of methods for determination of volatile components.
ISO 21068-2:2024(en)
Table 1 — Methods for determination of volatile components
Title of method Temperature Subclause Application
Attached water and chemically combined water are
Loss on drying (w ) 250 °C 4.2 removed, for example, in clay containing plastic for-
LOD250
mulations.
Loss on ignition in argon All volatile compounds from pitch- or resin-bonded
750 °C 4.3
(w ) formulations are removed.
LOIAr
4.2 Determination of the loss on drying at 250 °C (w )
LOD250
4.2.1 Principle
The test sample is heated at 250 °C ± 10 °C and the change in mass is determined gravimetrically.
4.2.2 Apparatus
4.2.2.1 Heat-resistant container, for example, with dimensions 200 mm × 150 mm × 30 mm and made
from stainless steel.
4.2.2.2 Analytical balance, capable of measuring to the nearest 0,01 g.
4.2.3 Procedure
Heat the heat-resistant container at 250 °C ± 10 °C for 30 min. Cool in a desiccator, weigh and record its
empty mass, m , to the nearest 0,01 g.
Transfer 100 g to 600 g of the sample into the container and spread it out evenly. Then weigh and record the
mass, m , of the container and sample to the nearest 0,01 g.
Place the container without a lid in air and heat it at 250 °C ± 10 °C for 16 h. Allow to cool in a desiccator.
Weigh and record the mass, m , of the container plus the dried sample to the nearest 0,01 g.
4.2.4 Calculation
Calculate the loss on drying at 250 °C, w , as a percentage by mass, using Formula (1).
LOD250
mm−
w = ×100 (1)
LOD250
mm−
where
w is the loss on drying at 250 °C, in mass percent;
LOD250
m is the mass of the empty container, in grams;
m is the mass of the container plus the sample before heating, in grams;
m is the mass of the container plus the sample after heating, in grams.
4.3 Determination of the loss on ignition in argon (w )
LOIAr
4.3.1 Principle
The sample is heated in an argon atmosphere at 750 °C to remove volatile matter. The change in mass is
determined gravimetrically.
NOTE The residue can be used for determination of C , SiC and C in organic matter containing materials.
total free
ISO 21068-2:2024(en)
The change in mass during heating in argon must be considered for the calculation of C , SiC and C .
total free
4.3.2 Apparatus
Ordinary laboratory apparatus and the following.
4.3.2.1 Analytical balance, capable of measuring to the nearest 0,001 g.
4.3.2.2 U-tube, with ground stoppers and filled with magnesium perchlorate.
4.3.2.3 Resistance furnace, capable of reaching (750 ± 25) °C, in the centre of the heating zone.
4.3.2.4 Thermocouple with display, registering up to 1 200 °C.
4.3.2.5 Ceramic tube, with cones or other gastight connector, of suitable diameter, made from porcelain,
sillimanite, quartz or other suitable material.
4.3.2.6 Open combustion boats, of unglazed ceramic material, the length of which matches the oven's
zone of constant temperature. The boats shall be broad enough to accommodate the amount of sample
required for the determination.
4.3.2.7 Gas flowmeter, with an upper scale reading of around 20 l/h.
The argon-conducting parts, such as tubes and connections, must be made of material proofed against
oxygen diffusion. Preferable materials are glass and copper. Silicone is unsuitable.
4.3.3 Test assembly
The test assembly is set up as shown in Figure 1.
Key
1 valve for pressure control 5 argon cylinder 9 combustion boat
2 cold zone B 6 glass wool 10 gas flowmeter
3 cold zone A 7 magnesium perchlorate
4 ceramic tube 8 resistance furnace
Figure 1 — Apparatus set-up for determination of loss on calcination in argon
4.3.4 Reagents
4.3.4.1 Argon, 99,997 %.
ISO 21068-2:2024(en)
4.3.5 Procedure
4.3.5.1 Check of test assembly, blank value determination
To check a newly set up test assembly or to carry out routine checks, at least two samples of known volatile-
matter content shall be calcined as described in 4.3.5.2 before determining the analytical sample.
The difference between the result found in accordance with 4.3.5.2 and the known volatile-matter content
shall be considered as the blank value.
4.3.5.2 Determination
Carry out at least two determinations.
Before use, flush the apparatus for at least 15 min with argon (4.3.4.1).
Weigh the empty combustion boat that has previously been heated at (750 ± 25) °C and cooled down to room
temperature and record the mass m . Weigh approximately 2 g of the sample to the nearest 0,001 g into the
combustion boat and record the mass m .
Place the combustion boat and sample in cold zone A of the apparatus at 200 °C. Pass argon through it at a
rate that ensures at least five changes of gas in the tube within 15 min.
NOTE 1 The required argon flow rate can be estimated according to Formula (2):
π××Dl
F = (2)
Ar
200 000
where
F is the argon flow rate, in litres per hour;
Ar
D is the tube inner diameter, in millimetres;
l is the tube length, in millimetres.
Place the sample in the centre of the heating zone and heat for 20 min at (750 ± 25) °C, without interruption
of the argon stream.
Move the combustion boat into cold zone B and cool in the argon stream at 200 °C.
NOTE 2 A period of 20 min is usually required to cool the sample.
Allow the boat to cool to room temperature in a desiccator, weigh to the nearest 0,001 g and record the final
mass, m .
Repeat the calcination in the argon stream at (750 ± 25) °C until constant mass is obtained, that means,
when two measurements taken at an interval of 30 min do not differ by more than 5 mg.
If the residue is required for the determination of other components, homogenize it and keep it in a closed
weighing bottle in a desiccator.
4.3.6 Calculation
Calculate the loss on ignition in argon at 750 °C, w , as a percentage by mass, using Formula (3).
LOIAr
mm−
1 2
w = ×100 (3)
LOIAr
mm−
ISO 21068-2:2024(en)
where
w is the loss on ignition in argon at 750 °C, in mass percent;
LOIAr
m is the mass of the empty combustion boat, in grams;
m is the mass of the combustion boat plus the sample before heating, in grams;
m is the mass of the combustion boat plus the sample after heating, in grams.
5 Determination of the total carbon content
5.1 Scope
This clause describes a quantitative analysis of the total carbon content by combustion in a resistance or
an induction furnace. In both cases the sample is combusted in an oxygen stream whereby CO and CO are
formed. Remaining CO is catalytically oxidised to CO prior to the measurement. Thereafter, CO is measured
2 2
by coulometric, infrared absorption or thermal conductivity methods.
5.2 Combustion techniques
For sample combustion with oxygen, one of the listed techniques shall be used:
— a resistance furnace (RF) with lead borate or tin fusion as accelerator/decomposition agent,
— an induction furnace (IF) with metal fusion as accelerator.
5.2.1 Combustion in a resistance furnace with lead borate or tin as decomposing agent
5.2.1.1 Principle
The sample is heated together with lead borate or tin in a stream of oxygen in a resistance tube furnace to
convert the carbon to carbon dioxide by combustion. The sample mass and the details of the combustion
depend on the method of determination used.
5.2.1.2 Reagents
Use only reagents of analytical grade.
5.2.1.2.1 Oxygen, 99,99 %.
5.2.1.2.2 Lead borate, 2 PbO·B O .
2 3
If not commercially available, prepare lead borate by melting 45 g of analytical grade lead oxide, PbO,
together with 7 g of analytical grade boron trioxide, B2O3, for 10 min at (950 °C ± 25) °C, cooling the melt by
pouring it onto a clean aluminium plate and then pulverizing it.
5.2.1.2.3 Tin powder, grain size < 100 µm.
5.2.1.3 Apparatus
Ordinary laboratory apparatus and the following.
5.2.1.3.1 Analytical balance, capable of measuring to the nearest 0,000 01 g (0,01 mg).
5.2.1.3.2 Resistance furnace with ceramic tube, capable of being maintained at a temperature of
(1 050 ± 25) °C if lead borate is used as the accelerator or (1 350 ± 25) °C if tin is used as the accelerator
ISO 21068-2:2024(en)
in the centre of the heating zone. The furnace shall be fitted with a thermocouple connected to a device
permitting measurement of the furnace temperature.
5.2.1.3.3 Open combustion boats of unglazed ceramic material, the length of which is selected to
match the heating zone of the furnace, and which are broad enough to accommodate the amount of sample
required for the determination. Before use, the boats shall be heated in a laboratory furnace at 1 000 °C for
1 h and stored in a desiccator after cooling.
5.2.1.4 Setting up of test assembly
Set up the test assembly in accordance with the manufacturer’s instructions.
5.2.1.5 Procedure for RF combustion with lead borate or tin
Adjust the oxygen (5.2.1.2.1) flow rate to prevent the risk of air being sucked in from the outside. Preheat the
furnace to a temperature of (1 050 ± 25) °C if lead borate is used as the accelerator or (1 350 ± 25) °C if tin is
used as the accelerator.
Weigh the required sample mass to the nearest 0,000 01 g into the combustion boat and spread it uniformly
in the combustion boat. Cover the sample with 1,5 g of lead borate (5.2.1.2.2) or, alternatively, 2,0 g of tin
powder (5.2.1.2.3) and place the combustion boat in the centre of the heating zone.
NOTE Combustion is usually complete after 5 min.
The carbon dioxide gas formed is supplied by the oxygen carrier gas to the detection unit (5.3).
5.2.1.6 Precision
Precision data for the determination of total carbon by combustion in a resistance furnace with tin as
decomposing agent and detection by infrared absorption is given in A.1.2.
5.2.2 Combustion in an induction furnace (IF) with metallic powder as decomposing agent
5.2.2.1 Principle
The sample is heated together with a metal additive in a stream of oxygen using a high-frequency induction
furnace. The carbon dioxide released is transferred by carrier gas to the detection unit.
5.2.2.2 Reagents
Use only reagents of at least analytical grade.
5.2.2.2.1 Granulated iron accelerator, for example as supplied by the supplier of the furnace.
5.2.2.2.2 Granulated tungsten accelerator, for example as supplied by the supplier of the furnace.
5.2.2.2.3 Granulated copper accelerator, for example as supplied by the supplier of the furnace.
5.2.2.2.4 Oxygen, 99,99 %
5.2.2.3 Apparatus
5.2.2.3.1 Analytical balance, capable of measuring to the nearest 0,000 01 g (0,01 mg).
ISO 21068-2:2024(en)
5.2.2.3.2 Combustion crucibles, of ceramic material with covers and holders as recommended by the
apparatus provider.
Before use, the combustion crucibles and covers should be fired at a minimum temperature of 1 000 °C.
5.2.2.4 Proce
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