EN ISO 21068-3:2024
(Main)Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-nitride, silicon-oxynitride and sialon - Part 3: Determination of nitrogen, oxygen and metallic and oxidic constituents (ISO 21068‑3:2024)
Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-nitride, silicon-oxynitride and sialon - Part 3: Determination of nitrogen, oxygen and metallic and oxidic constituents (ISO 21068‑3:2024)
This document specifies analytical techniques for the determination of total nitrogen and nitrogen calculated as silicon nitride, total oxygen, and metallic and oxidic components in silicon carbide raw materials and refractory products.
Chemische Analyse von Rohstoffen und feuerfesten Erzeugnissen, die Siliciumcarbid, Siliciumnitrid, Siliciumoxynitrid und Sialon enthalten -Teil 3: Bestimmung des Gehaltes an Stickstoff, Sauerstoff sowie metallischen und oxidischen Bestandteilen (ISO 21068-3:2024)
Dieses Dokument legt Analysenverfahren für die Bestimmung von Gesamtstickstoff und als Siliciumnitrid berechnetem Stickstoff, Gesamtsauerstoff sowie metallischen und sauerstoffhaltigen Bestandteilen in Siliciumcarbid 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 3: Dosage de l'azote, de l'oxygène et des constituants métalliques et oxydés (ISO 21068‑3:2024)
Ce document spécifie des techniques analytiques permettant de doser l’azote total et l’azote calculés sous forme de nitrure de silicium, l’oxygène total et les composés métalliques et oxydés dans les matières premières et produits réfractaires de carbure de silicium.
Kemijska analiza surovin in ognjevzdržnih izdelkov, ki vsebujejo silicijev karbid, silicijev nitrid, silicijev oksinitrid in sialon - 3. del: Določevanje dušika, kisika ter kovinskih in oksidnih sestavin (ISO 21068-3:2024)
Ta del standarda ISO 21068 določa analitske tehnike za določevanje celotnega dušika in dušika, izračunanega kot silicijev nitrid, celotnega kisika ter kovinskih in oksidnih sestavin v surovinah in ognjevzdržnih izdelkih, ki vsebujejo silicijev karbid.
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 - 3. del: Določevanje dušika, kisika ter
kovinskih in oksidnih sestavin (ISO 21068-3:2024)
Chemical analysis of raw materials and refractory products containing silicon-carbide,
silicon-nitride, silicon-oxynitride and sialon - Part 3: Determination of nitrogen, oxygen
and metallic and oxidic constituents (ISO 21068-3:2024)
Chemische Analyse von Rohstoffen und feuerfesten Erzeugnissen, die Siliziumcarbid,
Siliziumnitrid, Siliziumoxynitrid und Sialon enthalten - Teil 3: Bestimmung des Gehaltes
an Stickstoff, Sauerstoff sowie metallischen und oxidischen Bestandteilen (ISO 21068-
3:2024)
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
3: Dosage de l'azote, de l'oxygène et des constituants métalliques et oxydés (ISO 21068
-3:2024)
Ta slovenski standard je istoveten z: EN ISO 21068-3:2024
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 21068-3
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2024
EUROPÄISCHE NORM
ICS 81.080 Supersedes EN ISO 21068-3:2008
English Version
Chemical analysis of raw materials and refractory
products containing silicon-carbide, silicon-nitride, silicon-
oxynitride and sialon - Part 3: Determination of nitrogen,
oxygen and metallic and oxidic constituents (ISO 21068-
3:2024)
Analyse chimique des matières premières et des Chemische Analyse von Rohstoffen und feuerfesten
produits réfractaires contenant du carbure de silicium, Erzeugnissen, die Siliziumcarbid, Siliziumnitrid,
du nitrure de silicium, de l'oxynitrure de silicium et du Siliziumoxynitrid und Sialon enthalten - Teil 3:
SiAlON - Partie 3: Dosage de l'azote, de l'oxygène et des Bestimmung des Gehaltes an Stickstoff, Sauerstoff
constituants métalliques et oxydés (ISO 21068-3:2024) sowie metallischen und oxidischen Bestandteilen (ISO
21068-3:2024)
This European Standard was approved by CEN on 25 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 21068-3:2024 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 21068-3:2024) 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 21068-3:2008.
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 21068-3:2024 has been approved by CEN as EN ISO 21068-3:2024 without any
modification.
International
Standard
ISO 21068-3
Second edition
Chemical analysis of raw materials
2024-06
and refractory products containing
silicon-carbide, silicon-nitride,
silicon-oxynitride and sialon —
Part 3:
Determination of nitrogen, oxygen
and metallic and oxidic constituents
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 3: Dosage de l'azote, de l'oxygène et des constituants
métalliques et oxydés
Reference number
ISO 21068-3:2024(en) © ISO 2024
ISO 21068-3:2024(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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Phone: +41 22 749 01 11
Email: copyright@iso.org
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Published in Switzerland
ii
ISO 21068-3:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Determination of nitrogen and oxygen. 2
4.1 General .2
4.2 Combined determination of nitrogen and oxygen by an analyser with thermal
conductivity (TC) and infrared (IR) absorption detection .2
4.2.1 Principle .2
4.2.2 Reagents .3
4.2.3 Apparatus .3
4.2.4 Nickel pre-treatment .3
4.2.5 Calibration . . .4
4.2.6 Procedure .4
4.2.7 Precision .5
4.3 Determination of total nitrogen content by fusion decomposition .5
4.3.1 General .5
4.3.2 Principle .5
4.3.3 Reagents .5
4.3.4 Apparatus .5
4.3.5 Sample preparation .6
4.3.6 Procedure .6
4.3.7 Calculation and expression of results.7
4.3.8 Precision .8
4.4 Determination of total nitrogen content by Kjeldahl distillation .8
4.4.1 Principle .8
4.4.2 Reagents .8
4.4.3 Apparatus .9
4.4.4 Sample preparation .9
4.4.5 Procedure .9
4.4.6 Calculation and expression of results.10
4.4.7 Precision .10
4.5 Calculation of Si N content using total nitrogen content .10
3 4
4.5.1 Calculation .10
5 Determination of soluble iron by extraction with hydrochloric acid followed by
inductively coupled plasma-optical emission spectrometry (ICP-OES) .10
5.1 General .10
5.2 Principle .11
5.3 Apparatus .11
5.4 Reagents .11
5.5 Sample preparation .11
5.6 Procedure .11
5.7 Measurement .11
5.8 Calculation . 12
6 Determination of metallic (free) aluminium by the hydrogen generating method .12
6.1 Principle . 12
6.2 Reagents . 12
6.3 Apparatus . 12
6.4 Sample preparation . 13
6.5 Procedure . 13
6.6 Calculation and expression of results . 13
iii
ISO 21068-3:2024(en)
7 Determination of acid soluble aluminium and magnesium . 14
7.1 General .14
7.2 Reagents .14
7.3 Procedure .14
7.4 Measurement .14
7.5 Precision . . .14
8 Determination of elemental impurities in SiC raw materials . 14
8.1 General . 15
8.1.1 Alkaline melt fusion . 15
8.1.2 Acid pressure decomposition.16
8.2 Determination of impurities by XRF (fused bead method) .18
8.3 Determination of impurities by DCArc-OES (direct solid sampling method) .18
9 Expression of results .18
10 Test report .18
Annex A (informative) Precision data . 19
Bibliography .24
iv
ISO 21068-3:2024(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 21068-3:2008), which has been technically
revised.
The main changes are as follows:
— methods described in ISO 12698-1:2007 for the dosage of free aluminium, total nitrogen and free alumina
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 21068-3:2024(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.
This document is also applicable to the analysis of SiC raw materials.
Except the XRD method specified in ISO 21068-4, all chemical methods specified in this document are
[7] [8]
only validated for SiC raw materials. For refractory products classified in ISO 10081-1 , ISO 10081-2 ,
[9] [10] [11]
ISO 10081-3 and ISO 10081-4 (shaped) and ISO 1927-1 (unshaped) and raw materials containing
carbon and/or silicon carbide this document applies after appropriate verification for any matrix
composition.
vi
International Standard ISO 21068-3:2024(en)
Chemical analysis of raw materials and refractory products
containing silicon-carbide, silicon-nitride, silicon-oxynitride
and sialon —
Part 3:
Determination of nitrogen, oxygen and metallic and oxidic
constituents
1 Scope
This document specifies analytical techniques for the determination of total nitrogen and nitrogen calculated
as silicon nitride, total oxygen, and metallic and oxidic components in silicon carbide 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 10058-1, Chemical analysis of magnesite and dolomite refractory products (alternative to the X-ray
fluorescence method) — Part 1: Apparatus, reagents, dissolution and determination of gravimetric silica
ISO 10058-2, Chemical analysis of magnesite and dolomite refractory products (alternative to the X-ray
fluorescence method) — Part 2: Wet chemical analysis
ISO 10058-3, Chemical analysis of magnesite and dolomite refractory products (alternative to the X-ray
fluorescence method) — Part 3: Flame atomic absorption spectrophotometry (FAAS) and inductively coupled
plasma atomic emission spectrometry (ICP-AES)
ISO 12677, Chemical analysis of refractory products by X-ray fluorescence (XRF) — Fused cast-bead method
ISO 16169, Preparation of silicon carbide and similar materials for analysis by ISO 12677
ISO 20565-1, Chemical analysis of chrome-bearing refractory products and chrome-bearing raw materials
(alternative to the X-ray fluorescence method) — Part 1: Apparatus, reagents, dissolution and determination of
gravimetric silica
ISO 20565-2, Chemical analysis of chrome-bearing refractory products and chrome-bearing raw materials
(alternative to the X-ray fluorescence method) — Part 2: Wet chemical analysis
ISO 20565-3, Chemical analysis of chrome-bearing refractory products and chrome-bearing raw materials
(alternative to the X-ray fluorescence method) — Part 3: Flame atomic absorption spectrometry (FAAS) and
inductively coupled plasma atomic emission spectrometry (ICP-AES)
ISO 21068-1, Chemical analysis of raw materials and refractory products containing silicon-carbide, silicon-
nitride, silicon-oxynitride and sialon — Part 1: General information and sample preparation
ISO 21079-1, Chemical analysis of refractories containing alumina, zirconia and silica — Refractories containing
5 percent to 45 percent of ZrO2 (alternative to the X-ray fluorescence method) — Part 1: Apparatus, reagents
and dissolution
ISO 21068-3:2024(en)
ISO 21079-2, Chemical analysis of refractories containing alumina, zirconia, and silica — Refractories containing
5 percent to 45 percent of ZrO2 (alternative to the X-ray fluorescence method) — Part 2: Wet chemical analysis
ISO 21079-3, Chemical analysis of refractories containing alumina, zirconia, and silica — Refractories containing
5 percent to 45 percent of ZrO2 (alternative to the X-ray fluorescence method) — Part 3: Flame atomic absorption
spectrophotometry (FAAS) and inductively coupled plasma emission spectrometry (ICP -AES)
ISO 21587-1, Chemical analysis of aluminosilicate refractory products (alternative to the X-ray fluorescence
method) — Part 1: Apparatus, reagents, dissolution and gravimetric silica
ISO 21587-2, Chemical analysis of aluminosilicate refractory products (alternative to the X-ray fluorescence
method) — Part 2: Wet chemical analysis
ISO 21587-3, Chemical analysis of aluminosilicate refractory products (alternative to the X-ray fluorescence
method) — Part 3: Inductively coupled plasma and atomic absorption spectrometry methods
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 nitrogen and oxygen
4.1 General
For oxygen only the inert-gas fusion method is given; for nitrogen, calculated usually as Si N several
3 4,
different methods are described.
NOTE The calculation of nitrogen as Si N is only applicable in the case where other nitride species are absent or
3 4
too low to detect by XRD, see ISO 21068-1. Otherwise, nitrogen is reported as total nitrogen.
4.2 Combined determination of nitrogen and oxygen by an analyser with thermal
conductivity (TC) and infrared (IR) absorption detection
4.2.1 Principle
The method uses inert-gas fusion analysis. A pre-weighed sample is placed in a graphite crucible positioned
between the electrodes of an impulse furnace. Typically, 5 kW of power is passed through the crucible
generating a temperature of approximately 2 800 °C.
NOTE Furnace temperatures can be varied by increasing and decreasing current/voltage.
The sample decomposes, releasing any oxygen and nitrogen present. The nitrogen released remains
as elemental nitrogen, while oxygen combines with the carbon of the graphite crucible to form carbon
monoxide. The sample gases are carried on a helium carrier gas either to a copper oxide catalyst, which
converts carbon monoxide to carbon dioxide, and then to an infrared absorption cell which measures the
carbon dioxide present or are measured directly without catalyst as carbon monoxide. The gas stream is
then passed through sodium hydroxide to remove carbon dioxide, and magnesium perchlorate to remove
any moisture present, and finally through a thermal conductivity cell to quantify the nitrogen.
Because the sample will invariably be in the form of a powder, it should be enclosed in a small tin capsule
before placing it in the graphite crucible to prevent any loss of sample during analysis.
ISO 21068-3:2024(en)
For materials difficult to decompose, a fluxing agent shall be added to the sample. A suitable agent is oxygen
free nickel capsule or nickel wire basket.
4.2.2 Reagents
Only chemicals with a known and sufficient analytical purity for the analytical purpose shall be used. Distilled
water or water which has been completely deionized by means of an ion exchange process shall be used.
WARNING — Concentrated acids used are to be handled with care, be aware of local safety regulations.
4.2.2.1 Tin capsule, of suitable dimensions and oxygen and nitrogen free.
4.2.2.2 High temperature graphite crucibles, of suitable size, recommended by the instrument producer.
4.2.2.3 Nickel capsules or basket, of suitable dimensions and oxygen and nitrogen free.
4.2.2.4 Acetic acid, 96 % mass fraction.
4.2.2.5 Nitric acid, 65 % mass fraction.
4.2.2.6 Hydrochloric acid, 32 % mass fraction.
4.2.2.7 Acetone.
4.2.2.8 Carbon dioxide, 99,998 % pure.
4.2.2.9 Nitrogen, 99,998 % pure.
4.2.2.10 Helium, 99,998 % pure.
4.2.3 Apparatus
Ordinary laboratory apparatus and the following.
4.2.3.1 Combined nitrogen/oxygen analyser, commercially available.
NOTE If no combined analyser for nitrogen and oxygen is available, a separate nitrogen and/or oxygen analyser
can be used.
4.2.3.2 Analytical balance, with a resolution of at least 0,01 mg.
4.2.4 Nickel pre-treatment
If nickel capsules or baskets are used, surface oxygen shall be removed by the following cleaning procedure.
Prepare a solution containing approximately 75 ml of acetic acid (4.2.2.4), 25 ml of nitric acid (4.2.2.5) and
1,5 ml of hydrochloric acid (4.2.2.6). In a well-ventilated fume cupboard, heat the solution to a temperature
of 55 °C ± 5 °C, immerse the nickel capsule or basket in the heated solution for 30 s to 60 s, remove the nickel
capsule or basket from the solution and rinse immediately in running water. Immerse the nickel capsule or
basket in chemically pure acetone (4.2.2.7), dry thoroughly and place the cleaned nickel capsules or basket
in a desiccator.
ISO 21068-3:2024(en)
4.2.5 Calibration
Referring to the instrument operation manual, the calibration can be achieved by two methods:
a) using primary standards or certified reference materials;
b) by injection of known volumes of pure carbon dioxide (4.2.2.8) and nitrogen (4.2.2.9) into the
detection system.
If b) is used, it is recommended to additionally analyse a certified reference material to verify the
performance of the electrode furnace, associated chemicals and detection system.
4.2.6 Procedure
4.2.6.1 General
Operate the instrument in accordance with the instrument operation manual.
4.2.6.2 Determination
Prepare and dry the sample as specified in ISO 21068-1. Weigh it, to the nearest 0,01 mg, into the capsule
(4.2.2.1) and seal it, taking care to expel any air present.
NOTE A typical sample mass is approximately 50 mg. However, in practice, the sample mass is determined by
a combination of the dynamic range of the analyser and the magnitude of the concentration of oxygen and nitrogen
present in the sample.
Place the tin capsule including the sample into the loading-mechanism of the analyser. If nickel is used, the
tin capsule is firstly put into the nickel capsule or basket.
Carry out the analysis in two stages:
a) heat the graphite crucible to a temperature at least as high as that used for the analysis, until any
entrapped oxygen and nitrogen is expelled;
b) drop the sample into the graphite crucible and perform the analysis.
At least three determinations per sample shall be carried out.
4.2.6.3 Blank determinations
Carry out the blank determination as described in 4.2.6.2, but without a sample. The blank shall be the mean
of at least three determinations.
4.2.6.4 Calculation
Calculate the mass fraction of nitrogen or oxygen, w , expressed as a percentage, using Formula (1).
a
ww=−b (1)
am
where
w is the content of nitrogen or oxygen in the sample, in mass percent;
a
w is the measured content of nitrogen or oxygen in the sample, in mass percent;
m
b is the measured blank of nitrogen or oxygen, in mass percent.
Report the results as the mean of three determinations.
ISO 21068-3:2024(en)
4.2.7 Precision
The precision data for the determination of total nitrogen and total oxygen in a silicon carbide powder
sample by inert-gas fusion is given in A.1.
4.3 Determination of total nitrogen content by fusion decomposition
4.3.1 General
This method is used to determine nitrogen in silicon nitride, Si N , and other compounds in the form of
3 4
nitrides and oxynitrides by fusion decomposition. Analogous methods may be used to determine nitrogen
in materials containing not less than 5 % by mass of nitrogen bound in the form of nitrides and oxynitrides.
4.3.2 Principle
The sample is fused with lithium hydroxide a 700 °C to convert the nitrogen into ammonia. A stream of inert
gas is used to transfer the ammonia to an absorption vessel containing boric acid solution. The amount of
absorbed ammonia is determined by titration with an acid of known concentration.
4.3.3 Reagents
Only chemicals with a known and sufficient analytical purity for the analytical purpose shall be used.
4.3.3.1 Water, distilled or fully demineralized by ion exchange.
4.3.3.2 Powdered lithium hydroxide, LiOH.
4.3.3.3 Sulfuric acid, ρ = 1,84 g/ml.
4.3.3.4 Titration acid, 0,1 mol/l hydrochloric or sulfuric acid of known standardization for titration.
4.3.3.5 Boric acid solution, prepared by dissolving 40 g of boric acid, H BO , in 1 l of hot water.
3 3
4.3.3.6 Inert gas, argon or nitrogen, with a purity of 99,99 %.
4.3.3.7 Sodium carbonate, Na CO , with a purity of at least 99,95 %.
2 3
4.3.3.8 Calcium chloride, CaCl , dried.
4.3.4 Apparatus
4.3.4.1 Analytical balance, with a resolution of at least 0,01 mg.
4.3.4.2 Measurement device, apparatus for releasing, carrying over and absorbing ammonia (see
Figure 1), comprised of:
a) flow meter;
b) gas washing bottles;
c) vitreous silica reaction tube with ground joints, stoppers and gas inlet;
d) unglazed porcelain boats;
e) tube furnace, e.g. heated by infrared radiation, capable of being heated to, and maintained at,
(700 ± 10) °C;
ISO 21068-3:2024(en)
f) vitreous silica wool;
g) gas inlet tube with ground joint and capillary tip or frit.
The inert gas from a pressurized gas cylinder passes through a gas washing bottle filled with sulfuric acid
(4.3.3.3), preceded and followed by an empty washing bottle for safety reasons.
NOTE No gas purification is necessary if the ammonia content of the inert gas does not exceed 0,005 % by volume.
The inert gas is then passed through a flow meter and into the vitreous silica reaction tube at the side gas
inlet. The ground joint through which the sample is inserted is also located at this point. The other end of
the reaction tube is connected by a ground joint to a gas inlet tube with capillary tip or frit which extends
almost to the bottom of a narrow absorption vessel.
The reaction tube shall be heated by a tubular furnace which can be maintained at (700 ± 10) °C. The still
hot part of the tube outside the tubular furnace and adjacent to the absorption vessel is packed with loose
vitreous silica wool which is capable of condensing any lithium hydroxide which evaporates.
Key
1 tubular furnace 5 gas inlet tube with capillary tip or frit 8 washing bottles
2 vitreous silica wool 6 sulfuric acid 9 boric acid solution
3 vitreous silica tube with 7 porcelain boat 10 absorption vessel
connections
4 inert gas (Ar or N )
Figure 1 — Nitrogen determination apparatus for fusion decomposition
4.3.4.3 Potentiometric titrator, with a metering volume of 50 ml and a maximum relative tolerance of 0,1 %.
4.3.5 Sample preparation
Prepare and dry the sample as specified in ISO 21068-1.
4.3.6 Procedure
4.3.6.1 Decomposition by fusion
The time for complete reaction should be established before the method is applied.
ISO 21068-3:2024(en)
Coat the entire inside of the porcelain boats with 500 mg of lithium hydroxide (4.3.3.2) at 600 °C and store
the boats in a desiccator. Weigh 100 mg of the sample to the nearest 0,01 mg, into a coated porcelain boat
and mix thoroughly with 1,5 g of lithium hydroxide. Flush the apparatus with inert gas (4.3.3.6) and pour
40 ml of boric acid solution (4.3.3.5) into the absorption vessel and immerse the gas inlet tube in it. Set
the inert gas flow to 70 ml/min to 100 ml/min, open the ground joint closure and push the porcelain boat
into the centre of the reaction tube to the point where the thermocouple is located. After closing the tube
again, slowly heat the tube furnace to (700 ± 10) °C in stages to prevent the melt from spattering. For tube
furnaces that heat up rapidly, the heating phase shall not be less than 15 min. After 30 min at (700 ± 10) °C,
the nitride nitrogen will have been quantitatively converted into ammonia. Ensure the furnace temperature
does not, under any circumstances exceed 730 °C, as lithium hydroxide will start to evaporate above that
temperature.
4.3.6.2 Standardization of titration acid
Dry the sodium carbonate (4.3.3.7) at 270 °C to 300 °C for 1 h, stirring occasionally, and store it in a desiccator
over calcium chloride (4.3.3.8).
Weigh 200 mg of dried sodium carbonate to the nearest 0,01 mg in a sealable weighing bottle.
Dissolve the sodium carbonate in 50 ml of water (4.3.3.1) and add the titration acid (4.3.3.4) to be standardized
using a potentiometric titrator (4.3.4.3) until the equivalent point in the pH range 4,6 ± 0,2 is reached. Take
the mean value of not less than three titrations. The coefficient of variation shall not exceed 0,001.
4.3.6.3 Titrating the absorption solution
When the reaction is complete, remove the gas inlet tube from the absorption vessel and rinse its inside and
outside with water. Titrate the amount of absorbed ammonia to the equivalence point which is generally a
pH value of 4,6 ± 0,2 with the standardized titration acid using the potentiometric titrator.
4.3.6.4 Blank value
Carry out a blank determination as described in 4.3.6.1 and 4.3.6.3, without a test sample.
4.3.7 Calculation and expression of results
4.3.7.1 General
When calculating the results, the titration correction factor (see 4.3.7.2) shall be included.
Report the result to the nearest 0,1 %.
4.3.7.2 Calculation of titration correction factor
Calculate the titration correction factor, t, of the acid using Formula (2):
m
Na
t = (2)
5,2994⋅V
where
t is the titration correction factor;
m is the sample mass of sodium carbonate, in milligrams;
Na
V is the volume used of the 0,1 mol/l acid to be standardized, in millilitres;
5,299 4 is the titrimetric factor, in milligrams per millilitres.
ISO 21068-3:2024(en)
4.3.7.3 Calculation of nitrogen content
Calculate the nitrogen content, M , as a percentage by mass using Formula (3):
N
()VV− ××t 1,4007×100
M = (3)
N
m
where
M is the total nitrogen of the sample, in mass percent;
N
V is the volume of titration acid used for the sample, in millilitres;
V is the volume of titration acid used for the blank value, in millilitres;
t is the titration correction factor of the acid;
m is the sample mass, in milligrams;
1,400 7 is the titrimetric factor, in milligrams per millilitres.
4.3.8 Precision
The precision data for the determination of total nitrogen in a silicon nitride powder sample by fusion
decomposition is given in A.2.
4.4 Determination of total nitrogen content by Kjeldahl distillation
4.4.1 Principle
The nitrogen in silicon nitride, Si N , and other compounds in the form of nitrides and oxynitrides are
3 4
determined using high pressure acid decomposition.
The sample is dissolved in hydrofluoric acid under pressure and the nitrogen is distilled over as ammonia
into an absorption vessel containing boric acid solution, using an ammonia distillation apparatus. The
amount of absorbed ammonia is determined by titration with an acid of known concentration.
4.4.2 Reagents
During the analysi
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