EN ISO 21068-3:2008

SLOVENSKI STANDARD
01-december-2008
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Chemical analysis of silicon-carbide-containing raw materials and refractory products -
Part 3: Determination of nitrogen, oxygen and metallic and oxidic constituents (ISO21068
-3:2008)
Chemische Analyse von Siliciumcarbid enthaltenden Rohstoffen und feuerfesten
Erzeugnissen - Teil 3: Bestimmung des Gehaltes an Stickstoff, Sauerstoff sowie
metallenen und oxidischen Bestandteilen (ISO 21068-3:2008)
Analyse chimique des matières premières et des produits réfractaires contenant du
carbure de silicium - Partie 3: Dosage de l'azote, de l'oxygène et des constituants
métalliques et oxydés (ISO 21068-3:2008)
Ta slovenski standard je istoveten z: EN ISO 21068-3:2008
ICS:
81.080 Ognjevzdržni materiali Refractories
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 21068-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2008
ICS 81.080
English Version
Chemical analysis of silicon-carbide-containing raw materials
and refractory products - Part 3: Determination of nitrogen,
oxygen and metallic and oxidic constituents (ISO 21068-3:2008)
Analyse chimique des matières premières et des produits Chemische Analyse von Siliciumcarbid enthaltenden
réfractaires contenant du carbure de silicium - Partie 3: Rohstoffen und feuerfesten Erzeugnissen - Teil 3:
Dosage de l'azote, de l'oxygène et des constituants Bestimmung des Gehaltes an Stickstoff, Sauerstoff sowie
métalliques et oxydés (ISO 21068-3:2008) metallischen und oxidischen Bestandteilen (ISO 21068-
3:2008)
This European Standard was approved by CEN on 11 July 2008.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21068-3:2008: E
worldwide for CEN national Members.

Contents Page
Foreword.3

Foreword
This document (EN ISO 21068-3:2008) 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 February 2009, and conflicting national standards shall be withdrawn
at the latest by February 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 21068-3:2008 has been approved by CEN as a EN ISO 21068-3:2008 without any
modification.
INTERNATIONAL ISO
STANDARD 21068-3
First edition
2008-08-01
Chemical analysis of silicon-carbide-
containing raw materials and refractory
products —
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 —
Partie 3: Dosage de l'azote, de l'oxygène et des constituants
métalliques et oxydés
Reference number
ISO 21068-3:2008(E)
©
ISO 2008
ISO 21068-3:2008(E)
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© ISO 2008
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Published in Switzerland
ii © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
Contents Page
Foreword .iv
Introduction.v
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 (CR) and infrared absorption (IR) detection.2
5 Determination of nitrogen calculated as Si N .4
3 4
5.1 General .4
5.2 Acid decomposition — Titration method.5
5.3 Acid decomposition — Photometry method .9
5.4 Inert-gas fusion — Thermal conductivity method .12
5.5 Determination of total nitrogen.17
6 Determination of free Iron by Inductively Coupled Plasma Atomic Emission Spectrometry
(ICP-AES).17
6.1 General .17
6.2 Copper sulfate method .18
6.3 Bromine/methanol method.19
7 Determination of free aluminium and free magnesium.22
7.1 General .22
7.2 Acid decomposition — Inductively coupled plasma atomic emission spectroscopy
(ICP-AES).22
7.3 Acid decomposition — Flame Atomic Absorption Spectrometry (FAAS).24
7.4 Hydrogen generating method .25
8 Analysis of oxides .26
8.1 General .26
8.2 Wet methods .26
8.3 Flame atomic absorption and/or inductively coupled plasma atomic emission
spectrometer.26
8.4 XRF fusion method after ignition of the sample .27
8.5 Determination of silicon(IV) oxide, aluminium oxide, iron(III) oxide, titanium(IV) oxide,
calcium oxide, magnesium oxide, sodium oxide, potassium oxide, chromium(III) oxide,
zirconium oxide, and boron oxide .29
9 Expression of results.31
10 Test report.31
Annex A (informative) Statistical results obtained with analysis of refractories containing carbon
and/or silicon carbide .32
Bibliography.37

ISO 21068-3:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 21068-3 was prepared by Technical Committee ISO/TC 33, Refractories.
ISO 21068 consists of the following parts, under the general title Chemical analysis of silicon-carbide-
containing raw materials and refractory products:
⎯ Part 1: General information and sample preparation
⎯ Part 2: Determination of loss on ignition, total carbon, free carbon and silicon carbide, total and free silica
and total and free silicon
⎯ Part 3: Determination of nitrogen, oxygen and metallic and oxidic constituents
iv © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
Introduction
[8]
ISO 21068, Parts 1 to 3, have been developed from the combination of a Japanese standard JIS 2011 and
work items originally developed within CEN. Because there is a wide variety of laboratory equipment in use,
the most commonly used methods are described.
This part of ISO 21068 is applicable to the analysis of all refractory products as classified in
[3], [4], [5], [6] [1]
ISO 10081 (all parts) (shaped) and ISO 1927 (unshaped) and raw materials containing carbon
and/or silicon carbide. Therefore, this part of ISO 21068 covers the full range of analysis from pure silicon
carbide to oxidic refractory composition with a low content of silicon carbide and/or nitrides. Primarily, this part
of ISO 21068 provides methods to distinguish between different carbon bound types like total carbon (C )
total
and free carbon (C ) and derives from these two the silicon carbide content.
free
If free carbon is present, this part of ISO 21068 includes different types of temperature treatment in order to
determine the mass changes gravimetrically. Frequently, the resulting residue is used for other determinations.
The determination of other groups of analytes described in this part of ISO 21068 are free metals, free silicon
(Si ), free aluminum (Al ), free magnesium (Mg ), free iron (Fe ) and the group of oxides from main to
free free free free
trace components.
This part of ISO 21068 also describes the chemical analysis of SiO , total Si, oxygen and nitrogen and other
oxidic bound metals which typically occur in the materials.
This part of ISO 21068 represents a listing of analytical methods which is approximately 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.

INTERNATIONAL STANDARD ISO 21068-3:2008(E)

Chemical analysis of silicon-carbide-containing raw materials
and refractory products —
Part 3:
Determination of nitrogen, oxygen and metallic and oxidic
constituents
1 Scope
This part of ISO 21068 specifies methods for the determination of total nitrogen and nitrogen calculated as
silicon nitride, total oxygen, and free metallic and oxidic components in silicon carbide raw materials and
refractory products.
It applies only to silicon carbide materials that are not bonded with nitrogen. Nitride-bonded silicon carbide
refractories are covered in EN 12698-1.
2 Normative references
The following referenced documents are indispensable for the application 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 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 spectrometry (FAAS) and inductively coupled
plasma emission spectrometry (ICP-AES)
ISO 12677, Chemical analysis of refractory products by XRF — Fused cast bead method
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 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 emission spectrometry (ICP-AES)
ISO 21068-1:2008, Chemical analysis of silicon-carbide-containing raw materials and refractory products —
Part 1: General information and sample preparation
ISO 21068-3:2008(E)
ISO 21068-2:2008, Chemical analysis of silicon-carbide-containing raw materials and refractory products —
Part 2: Determination of loss on ignition, total carbon, free carbon and silicon carbide, total and free silica and
total and free silicon
ISO 21079-1, Chemical analysis of refractories containing alumina, zirconia and silica — Refractories
containing 5 % to 45 % of ZrO (alternative to the X-ray fluorescence method) — Part 1: Apparatus, reagents
and dissolution
ISO 21079-2, Chemical analysis of refractories containing alumina, zirconia and silica — Refractories
containing 5 % to 45 % of ZrO (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 % to 45 % of ZrO (alternative to the X-ray fluorescence method) — Part 3: Flame atomic
absorption spectrometry (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
ISO 26845, Chemical analysis of refractories — General requirements for wet chemical analysis, atomic
absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES)
methods
EN 12698-1:2007, Chemical analysis of nitride bonded silicon carbide refractories — Part 1: Chemical
methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21068-1 apply.
4 Determination of nitrogen and oxygen
4.1 General
For oxygen only, the IR detection method is given; for nitrogen, several different methods are described,
calculated nominally as Si N .
3 4
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 (CR) and infrared absorption (IR) detection
4.2.1 Principle
The method uses inert-gas fusion analysis. A preweighed sample is placed in a graphite crucible positioned
between the electrodes of an impulse furnace. 5 kW of power (typically) is passed through the crucible
generating a temperature of approximately 2 800 °C.
NOTE 1 Furnace temperatures can be varied by increasing and decreasing current/voltage.
2 © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
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 rare-earth copper catalyst, which converts
carbon monoxide to carbon dioxide, and then to an infrared 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 or other suitable analyser to quantify the nitrogen.
[7]
NOTE 2 A method for the determination of oxygen contents less than 3 % is given in EN 725-3 .
Because the sample will invariably be in the form of a powder, it should be enclosed in a small nickel capsule
before placing it in the graphite crucible to prevent any loss of sample during analysis.
When materials with dissociation temperatures higher than 2 400 °C ± 25 °C are being analysed, it is
recommended that a fluxing agent is also included with the sample. A suitable agent would be a nickel wire
basket.
4.2.2 Reagents
4.2.2.1 Nickel or tin capsule, of suitable dimensions and oxygen and nitrogen free.
4.2.2.2 Nickel basket, of suitable dimensions and oxygen and nitrogen free.
4.2.2.3 Carbon dioxide, 99,998 % pure.
4.2.2.4 Nitrogen, 99,998 % pure.
4.2.2.5 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.
4.2.4 Calibration
Referring to the instrument operation manual, the calibration can be achieved by two methods:
a) using certified reference materials (preferably primary);
b) by injection of known volumes of pure carbon dioxide and nitrogen into the detection system.
If b) is used, it is recommended that a standard reference material be analysed to verify the performance of
the electrode furnace, associated chemicals and detection system.
For both methods, a minimum of three calibration points and a zero shall be used to establish the calibration.
4.2.5 Procedure
4.2.5.1 General
Operate the instrument in accordance with the instrument operation manual.
ISO 21068-3:2008(E)
4.2.5.2 Determination
Dry and grind the sample (see Clause 4 of ISO 21068-1:2008). Weigh it, to the nearest 0,1 mg, into the nickel
capsule and seal it, taking care to expel any air present.
NOTE A typical sample mass is approximately 50 mg ± 1 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.
Put the nickel capsule into the loading-mechanism analyser.
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, for a period of
time sufficient to allow any entrapped oxygen and nitrogen to be expelled;
b) drop the sample into the graphite crucible and perform the analysis.
Because of the sample masses involved, report results as the mean of at least three determinations.
4.2.5.3 Blank determinations
Although any oxygen and nitrogen present in the graphite crucible is removed prior to the analysis being
carried out [see 4.2.5.2 a)], there may still be oxygen and nitrogen present in the tin capsule and nickel basket.
Make blank determinations and subtract them from subsequent analyses. The blank shall be the mean of at
least three determinations.
Prepare a solution containing approximately 75 ml of acetic acid, 25 ml of nitric acid and 1,5 ml of hydrochloric
acid. In a well-ventilated fume cupboard, heat the solution to a temperature of 55 °C ± 5 °C, immerse the
nickel basket in the heated solution for 30 s to 60 s, remove the nickel basket from the solution and rinse
immediately in running water. Immerse the nickel basket in chemically pure acetone, dry thoroughly and place
the cleaned nickel basket in a desiccator.
4.2.5.4 Calculation
Calculate the mass fraction of nitrogen or oxygen, w , expressed as a percentage, using Equation (1).
a
wwb=− (1)
am
where
w is the mass fraction of nitrogen or oxygen, respectively, measured in the sample, expressed as a
m
percentage;
b is the average blank determination of nitrogen or oxygen respectively, expressed as a percentage by
mass.
Report the results as the mean of three determinations.
5 Determination of nitrogen calculated as Si N
3 4
5.1 General
The nitrogen determined is calculated as silicon nitride. The determination of silicon nitride is carried out using
one of the following methods:
a) acid decomposition with pressurization/separation by the steam distillation/neutralization titration method;
4 © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
b) acid decomposition with pressurization/separation by steam distillation/indophenol blue absorption
spectroscopy; this method should be used for samples containing silicon nitride whose percentage is less
than 2 % by mass;
c) inert-gas fusion-thermal conductivity method.
The calculation of Si N by using the measured nitrogen content is only justified and expedient if nitrogen is
3 4
chemically bonded as silicon nitride quantitatively. The methods described in Clause 4 are, in principle,
applicable for the determination of total nitrogen. When method 5.2 or 5.3 is used for determining total
nitrogen, the obtained result should be verified by a method as described in Clause 4 or 5.4. This is because
of the high chemical resistance of nitrides, particularly with regard to unknown nitrides, besides Si N ,
3 4
contained in the sample.
5.2 Acid decomposition — Titration method
5.2.1 Principle
A sample is decomposed with sulfuric acid and hydrofluoric acid in a pressurization container, so that silicon
nitride changes to ammonium salt, and boric acid is then added to it. The resulting solution is transferred into
a distillation flask. Sodium hydroxide is added to the flask and steam distillation is carried out, and the
ammonia distillate is absorbed into an appropriate amidosulfonic acid. The remaining amidosulfonic acid is
titrated with sodium hydroxide.
5.2.2 Reagents
Solutions 5.2.2.1, 5.2.2.2 and 5.2.2.7 shall be stored in plastics bottles.
5.2.2.1 Hydrofluoric acid.
5.2.2.2 Sulfuric acid (1+1).
5.2.2.3 Boric acid.
5.2.2.4 Sodium hydroxide (500 g/l).
5.2.2.5 Ammonium sulfate, purity more than 99,9 % by mass. Heat at 110 °C ± 10 °C for 3 h and cool in
a desiccator.
5.2.2.6 Amidosulfuric acid solution, 0,1 mol/l.
Weigh 10,0 g, to the nearest 0,1 mg, of amidosulfuric acid (reference material for volumetric analysis, or high-
purity reagent above 99,99 % by mass). Dissolve in water, transfer to a 1 000 ml volumetric flask, and dilute to
the mark with water.
Calculate the factor, F, for the 0,1 mol/l amidosulfuric acid solution using Equation (2).
mP×
a
F = (2)
9,709 5 ×100
where
m is the mass of amidosulfuric acid, in grams;
a
P is the purity of amidosulfuric acid, expressed as a percentage by mass.
ISO 21068-3:2008(E)
5.2.2.7 Sodium hydroxide solution, 1 mol/l.
Weigh 165 g of sodium hydroxide in a 500 ml polyethylene airtight container, add 150 ml of carbon-dioxide-
free water to dissolve it, and allow it to stand for 4 to 5 days with shielding from carbon dioxide. Take 54 ml of
its supernatant liquid in a 1 l polyethylene airtight container, add carbon-dioxide-free water to it to make a total
1 l, mix well, and store it with a soda-lime tube attachment.
5.2.2.8 Sodium hydroxide solution, 0,1 mol/l.
Pipette 100 ml of 1 mol/l sodium hydroxide solution into a 1 000 ml volumetric flask, dilute with carbon-dioxide-
free water to 1 000 ml, mix well, put it in an airtight polyethylene container, and store it with a soda-lime tube
attachment.
Transfer precisely 50 ml of 0,1 mol/l amidosulfuric acid solution (5.2.2.6) to a 200 ml beaker, dilute to about
100 ml with water, and titrate with 0,1 mol/l sodium hydroxide solution using a pH meter equipped with a
glassy electrode. Determine the titration volume of 0,1 mol/l sodium hydroxide solution at the end point of
which the pH is 5,5.
Calculate the factor, F′, of this 0,1 mol/l sodium hydroxide solution using Equation (3).
F × 50,00
′
F = (3)
V
where,
F is the factor of 0,1 mol/l amidosulfuric acid solution;
V is the volume of titration of 0,1 mol/l sodium hydroxide, in millilitres.
5.2.3 Apparatus
5.2.3.1 Pressurization vessel, for decomposition; the inner cap and the vessel are made of ethylene
4-fluoride resin and outer cap and pressure-resistant container are made of stainless steel.
To avoid cross-contamination by nitrogen from other uses of the vessel, reserve pressure vessels solely for
the determination of silicon nitride.
5.2.3.2 Steam distillation apparatus, consisting of the elements listed in 5.2.3.2.1 to 5.2.3.2.6.
NOTE An example of the steam distillation apparatus is given in Figure 1. Each component is made of borosilicate
glass and they are connected with common ground-glass joints and fixed with springs or clamps.
6 © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
Dimensions in millimetres
Key
1 funnel 5 rubber tube 9 connection of rubber tube with pinchcock
2 ball joint 6 13 to15 coils 10 jack
3 Dumet wire 7 small holes
4 funnel with stopcock 8 electric heater
a c e
Flask (2,5 l) for generation of steam. Sphere and tube. Graham condenser.
b d f
Trap (500 ml). Distillation flask (750 ml). Collecting vessel.
Figure 1 — Example of the steam distillation apparatus
ISO 21068-3:2008(E)
5.2.3.2.1 Flask, 2,5 l, for generation of steam, attached to a funnel with a stopcock and an outlet tube for
the steam, and an electric heater (using 1 kW Nichrome wire).
5.2.3.2.2 Trap, having a rubber tube with pinchcock connected to the bottom tube on the sphere. The
nozzle of the inner tube for steam has several small holes.
5.2.3.2.3 Sphere and tube, with an inlet tube for steam, a funnel with a stopcock and a trap guarding
against splashing. The inlet tube from the trap (see Figure 1, footnote b) is cut to size and connected by a
rubber tube to the lower inlet tube inside of the distillation flask (see Figure 1, footnote d). This allows rapid
changing over of the lower inlet tube which dips into the NaOH solution. Replace both the inlet and rubber
tubes when they show signs of being attacked.
5.2.3.2.4 Distillation flask, 750 ml.
5.2.3.2.5 Graham condenser.
5.2.3.2.6 Collecting vessel, 300 ml tall beaker.
5.2.4 Mass of test portion
The mass of test portion depends on the silicon nitride content, as shown in Table 1.
Table 1 — Mass of test portion
Silicon nitride content Mass of test portion
% by mass g
below 10 1,0
10 to 20 0,5
above 20 0,3
5.2.5 Procedure
Weigh the sample into a platinum crucible (No. 20), put it in a resin vessel, add 5 ml of sulfuric acid (1+1) and
10 ml of hydrofluoric acid. Put the vessel into a pressure-resistant container with an inner cap, fasten an inner
cap tightly, and heat at 160 °C ± 5 °C in an air bath for about 16 h.
After cooling, remove the outer and inner caps, pick up the platinum crucible using a pair of plastic tweezers,
and transfer the solution into a 100 ml plastic beaker. Wash the platinum crucible, the tweezers, the inner cap,
and the resin vessel with a small amount of water, add the washings to the beaker, add 5 g of boric acid and
dissolve.
Transfer the solution into a distillation flask. Set up the distillation apparatus, add 50 ml of 0,1 mol/l
amidosulfonic acid to a collecting vessel and immerse the end of the Graham condenser in the solution in the
collecting vessel. Pour in 50 ml of sodium hydroxide solution (500 g/l) from the funnel of the distillation flask,
wash the funnel with water until there is a total of about 150 ml of liquid and then close the stopcock to the
funnel.
When a new distillation apparatus is used or when a distillation apparatus has not been used for a long period,
the apparatus should be washed in advance by distillation without cooling water at the Graham condenser.
Commence steam distillation. When the liquid volume in the collecting vessel reaches 170 ml, lower the
collecting vessel so that it is level with the top of the Graham condenser rather than the surface of liquid, and
continue the steam distillation until 200 ml of the liquid volume is collected.
8 © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
Open the pinchcock on the bottom tube of the trap when steam starts to be generated, and close it when the
steam flow maintains 4,5 to 5,0 ml per minute after adjustment of the heater.
Wash the ends of the outer and inner sides of the Graham condenser, and the inner side of the ball joint
attached to it, with a small amount of water.
Titrate the distillate with 0,1 mol/l sodium hydroxide solution, using a pH meter equipped with a glassy
electrode until pH 5,5 as end point and calculate the volume of 0,1 mol/l sodium hydroxide solution used.
5.2.6 Measurement of recovery rate
Weigh 0,280 g of ammonium sulfate (5.2.2.5), to the nearest 0,1 mg, into a platinum crucible (No. 20), and
carry out the procedure given in 5.2.5.
Calculate the recovery, R, as a percentage using Equation (4).
′
(50,00×−FV×F )× 0,001400 7
R=×100 (4)
m × 0,212 0
s
where
F is the factor of 0,1 mol/l amidosulfonic acid solution;
V is the used volume of 0,1 mol/l sodium hydroxide solution, in millilitres;
F′ is the factor of 0,1 mol/l sodium hydroxide solution;
m is the mass of ammonium sulfate weighed, in grams.
s
5.2.7 Calculation
Calculate the mass fraction of silicon nitride, w , expressed as a percentage, using Equation (5).
Si N
3 4
′
(50,00×−FV×F )× 0,003 507 2 100
w=××100 (5)
Si N
mR
where
F is the factor of 0,1 mol/l amidosulfonic acid solution;
V is the volume of 0,1 mol/l sodium hydroxide solution used (see 5.2.2.8), in millilitres;
F′ is the factor of 0,1 mol/l sodium hydroxide solution;
R is the recovery rate in 5.2.6, in percent;
m is the mass of test portion weighed, in grams.
5.3 Acid decomposition — Photometry method
5.3.1 Principle
A sample is decomposed with sulfuric acid and hydrofluoric acid in a pressurization container, so that silicon
nitride changes to ammonium salt, and boric acid is added to it. The resulting solution is transferred into a
distillation flask. Sodium hydroxide is added to the flask, steam distillation is carried out and the ammonia
distillate is absorbed into sulfuric acid. Sodium hypochlorite and sodium phenolate are added to a portion of
the absorbed solution and the absorbance of the developed indo-phenol blue is measured.
ISO 21068-3:2008(E)
5.3.2 Reagents
5.3.2.1 Sulfuric acid, 0,05 mol/l.
5.3.2.2 Sodium hydroxide solution, 200 g/l.
Dissolve 20 g of sodium hydroxide in water and dilute to 100 ml with water. The reagent should be prepared
freshly as required.
5.3.2.3 Sodium phenolate solution.
Dissolve 25 g of phenol in 55 ml of sodium hydroxide solution (200 g/l), cool to room temperature, add 6ml of
acetone, and dilute to 200 ml with water. The reagent should be freshly prepared on each occasion.
5.3.2.4 Sodium thiosulfate solution, 0,1 mol/l.
Transfer 26 g of sodium thiosulfate pentahydrate and 0,2 g of sodium carbonate into a 1 l volumetric flask, add
1 l of oxygen-free water to dissolve it, and store in an airtight container. Allow to stand for 2 days before use.
Heat the required amount of potassium iodate (reference material for volumetric analysis or high-purity
reagent above 99,99 % by mass) at 130 °C for a minimum of 2 h, and cool in a desiccator. Weigh 0,9 g to
1,1 g of potassium iodate and transfer, to the nearest 0,1 mg, into a 250 ml volumetric flask. Add the minimum
amount of water required to dissolve it, and further dilute with water to 250 ml. Pipette 25 ml from the
volumetric flask into a 200 ml interchangeable ground Erlenmeyer flask. Add 2 g of potassium iodide and 2 ml
of sulfuric acid (1+1) to the Erlenmeyer flask. After immediately stoppering, shake it gently, and allow to stand
for 5 min in a dark place. As an indicator, add starch solution, and titrate it with the 0,1 mol/l sodium thiosulfate
solution. Then add about 0,5 ml of starch solution when the colour of the solution fades to a faint yellow which
shows the end point is near. The end point is when the blue colour of the solution has just disappeared.
Separately, transfer 25 ml of water and 2 g of potassium iodide into a 200 ml interchangeable ground
Erlenmeyer flask. Add 2 ml of sulfuric acid (1+1). After immediately stoppering, shake gently until completely
disolved, and allow to stand for 5 min in a dark place. Carry out the blank test under the same conditions as
above, and correct the volume needed for titration.
Calculate the factor, F, of the 0,1 mol/l sodium thiosulfate solution using Equation (6).
m ×
p
A
F=⋅ (6)
0,003 566 7 ×V 100
where
m is the mass of potassium iodate weighed out, in grams;
p
A is the purity of potassium iodate, expressed as a percentage by mass;
0,003 566 7 is the mass of potassium iodate equivalent to 1 ml of 0,1 mol/l sodium thiosulfate solution, in
grams;
V is the volume of 0,1 mol/l sodium thiosulfate solution needed for titration, in millilitres.
5.3.2.5 Sodium hypochlorite solution, effective chlorine 10 g/l.
Determine the effective chlorine of the sodium hypochlorite solution (effective chlorine 5 % to 12 %) and dilute
to 10 g/l of effective chlorine with water. The reagent should be prepared freshly as required.
Determine the effective chlorine of the sodium hypochlorite solution as follows.
10 © ISO 2008 – All rights reserved

ISO 21068-3:2008(E)
Transfer 10 ml of sodium hypochlorite solution to a 200 ml volumetric flask and dilute to the mark with water.
Transfer precisely 10 ml to a 300 ml Erlenmeyer flask with stopper and dilute to 100 ml with water. Add 1 g to
2 g of potassium iodide and 6 ml of acetic acid (1+1) to it, stopper, shake well, keep it in the dark for 5 min,
and titrate with 0,1 mol/l sodium thiosulfate solution. When the yellow colour of the solution becomes fainter,
add 2 ml of starch solution as an indicator and titrate until the resulting blue colour of iodostarch disappears.
Separately, as a blank test, transfer 10 ml of water, carry out the same procedures as described above, and
adjust the titration value using this blank test result.
Calculate the effective chlorine of the sodium hypochlorite solution, N, in grams per litre, using Equation (7).
200 1
NV=×F× × × 0,000 546×1000 (7)
t
10 V
where
V is the titration volume of 0,1 mol/l sodium thiosulfate solution, in millilitres;
t
F is the factor of 0,1 mol/l sodium thiosulfate solution;
V is the volume of sodium hypochlorite solution, in millilitres.
4+
5.3.2.6 Ammonium ion standard solution, 1 mg NH /ml.
Keep ammonium sulfate in a desiccator overnight. Weigh 3,66 g of ammonium sulfate, dissolve in water,
transfer to a 1 000 ml volumetric flask, and dilute to the mark with water.
5.3.3 Apparatus
Use the same pressurization apparatus as described in 5.2.3.1.
5.3.4 Mass of test portion
Weigh 0,5 g of the sample.
5.3.5 Procedure
Carry out the procedure in 5.2.5, but adding 50 ml of sulfuric acid (0,05 mol/l) to the gathering vessel instead
of 0,1 mol/l amidosulfonic acid solution.
Transfer the distillate into a 250 ml volumetric flask and dilute to the mark with water. Transfer an aliquot of
this solution to a 50 ml volumetric flask and dilute to about 25 ml with water.
NOTE The volume of the aliquot portion of the stock solution depends on the content of silicon nitride (percent), as
shown in Table 2.
Table 2 — Aliquot portion of stock solution
Silicon nitride content Aliquot of stock solution
% by mass ml
below 0,5 10
0,5 to 1 5
above 1 2
ISO 21068-3:2008(E)
Add 10 ml of sodium phenolate solution to a 50 ml volumetric flask and shake it, add 5 ml of sodium
hypochlorite solution (effective chlorine 10 g/l), dilute to the mark with water, allow to stand at 25 °C ± 2,5 °C
for about 30 min.
Transfer a portion of the solution to a 10 mm cell and measure the absorbance at a wave-length around
630 nm against water as a reference.
5.3.6 Blank test
Carry out the procedure in accordance with 5.3.5 without the sample.
5.3.7 Plotting of calibration graph
Dilute the ammonium ion standard solution precisely 2 000 times with water, transfer a range from 0 ml to
25 ml (0,0 mg to 0,125 mg as ammonium ion) of the diluted solution to several 50 ml volumetric flasks, dilute
to about 25 ml with water. Carry out the procedure described in 5.3.5 and plot the relation between the
absorbance and mass of ammonium ion, and prepare the calibration graph by adjusting the curve so that it
passes through the point of origin.
5.3.8 Calculation
Calculate the mass fraction of silicon nitride, w , expressed as a percentage, in the sample using
Si N
3 4
Equation (8), with the amount of ammonium ion obtained from the absorbances obtained in 5.3.5 and 5.3.6,
and the calibration graph plotted in 5.3.7.
()AA−
w =××1,944
...