ISO/TR 9686:2017

TECHNICAL ISO/TR
REPORT 9686
First edition
2017-05
Direct reduced iron — Determination
of carbon and/or sulfur — High-
frequency combustion method with
infrared measurement
Minerais de fer préréduits — Dosage du carbone et/ou du soufre —
Méthode par combustion haute fréquence et mesurage par infrarouge
Reference number
ISO/TR 9686:2017(E)
©
ISO 2017

---------------------- Page: 1 ----------------------
ISO/TR 9686:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TR 9686:2017(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Sampling and samples . 3
7.1 Laboratory sample . 3
7.2 Preparation of predried test samples . 3
8 Procedure. 3
8.1 General operating instructions . 3
8.2 Test portion . 3
8.3 Blank test . 3
8.4 Calibration . 4
8.4.1 Crucible preparation . 4
8.4.2 Combustion . 5
8.5 Determination . 5
9 Expression of results . 5
9.1 Calculation of mass fraction of carbon or sulfur . 5
9.2 General treatment of results . 5
9.2.1 Repeatability and permissible tolerance . 5
9.2.2 Determination of analytical result . 6
9.2.3 Between-laboratories precision . 6
9.2.4 Check for trueness . 7
9.2.5 Calculation of final result . 8
10 Test report . 8
Annex A (informative) Crucible loading sequence . 9
Annex B (informative) Flowsheet of the procedure for the acceptance of analytical values
for test samples .10
Annex C (informative) Features of commercial HF combustion/infrared sulfur analysers .11
Annex D (informative) Derivation of repeatability and permissible tolerance formulae .12
Annex E (informative) Precision data obtained by international analytical trials .13
Bibliography .15
© ISO 2017 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TR 9686:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 2, Chemical analysis.
This first edition Technical Report cancels and replaces the second edition International Standard
(ISO 9686:2006), which has been technically revised and has been converted to a Technical Report
because it is not suitable for determination of carbon or sulfur as a referee method.
iv © ISO 2017 – All rights reserved

---------------------- Page: 4 ----------------------
TECHNICAL REPORT ISO/TR 9686:2017(E)
Direct reduced iron — Determination of carbon and/or
sulfur — High-frequency combustion method with infrared
measurement
WARNING — This document may involve hazardous materials, operations and equipment. This
document does not purport to address all of the safety problems associated with its use. It is the
responsibility of the user of this document to establish appropriate health and safety practices.
1 Scope
This document specifies a method for the determination of the mass fraction of carbon and/or sulfur in
direct reduced iron by infrared measurement after high-frequency combustion.
This method is applicable to mass fractions of carbon between 0,05 % and 2,5 %, and/or mass fractions
of sulfur between 0,001 % and 0,05 % in direct reduced iron.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Principle
The test portion is combusted in a refractory crucible in a flow of oxygen in the presence of an
accelerator, the crucible being inserted in the combustion tube of a high-frequency (HF) furnace.
The carbon present is converted into carbon dioxide and the sulfur into sulfur dioxide. Each gas is
measured by infrared absorption, with calibration using barium carbonate and potassium sulfate.
5 Reagents
During analysis, use only reagents of recognized analytical grade and only distilled water or water of
equivalent purity.
5.1 Oxygen, minimum purity 99,5 % (mass fraction).
The pressure in the furnace should be controlled by a pressure regulator designed especially for the
purpose and complying with the manufacturer’s specification.
5.2 Magnesium perchlorate, grain size 0,7 mm to 1,2 mm.
© ISO 2017 – All rights reserved 1

---------------------- Page: 5 ----------------------
ISO/TR 9686:2017(E)

5.3 Accelerator, tungsten (granular form) with known low mass fractions of carbon (<0,002 %) and
sulfur (<0,000 5 %).
5.4 Pure iron, or iron of known low mass fractions of carbon and sulfur, as in 5.3.
5.5 Tin capsules, of capacity 0,3 ml, diameter 5 mm, length 17 mm.
5.6 Barium carbonate (BaCO ), fine powder.
3
Dry at 105 °C for 3 h and cool in a desiccator.
5.7 Sulfur standard solutions.
Dry potassium sulfate (K SO ) at 105 °C for 1 h and cool in a desiccator.
2 4
Weigh, to the nearest 0,000 2 g, the amounts of potassium sulfate specified in Table 1.
Transfer to five 100 ml one-mark volumetric flasks, dissolve with 50 ml of water, dilute to volume and mix.
5.8 Ascarite, used only for carbon determination.
Table 1 — Sulfur standard solutions
Sulfur standard solution Mass of K SO Sulfur concentration
2 4
g mg/ml
SS 1 0,217 4 0,4
SS 2 0,434 8 0,8
SS 3 0,652 2 1,2
SS 4 0,869 6 1,6
SS 5 2,174 0 4,0
6 Apparatus
Ordinary laboratory apparatus, including micropipettes and one-mark volumetric flasks complying
with the specifications of ISO 7550 and ISO 1042, respectively, and the following.
6.1 Commercial carbon/sulfur apparatus
The apparatus required for HF combustion of the samples and the subsequent infrared absorption
measurement of evolved carbon dioxide and/or sulfur dioxide may be obtained commercially from a
number of manufacturers. Common features of such systems are discussed in Annex C.
The manufacturer’s instruction for the operation of their equipment should be followed.
6.2 Ceramic combustion crucibles, required for containing the sample and any additions that may
be necessary for the subsequent combustion.
The crucibles should be of precise dimensions for the system, and should adapt to the supporting
pedestal post, so that the sample in the crucible will be positioned at the correct height within the
induction coil when it is in the raised position.
These crucibles should be pre-ignited in an oxygen flow, in a furnace, for not less than 2 h at 1 350 °C (or at
1 100 °C if only sulfur is to be determined), and then stored in a desiccator or closed container before use.
For pre-ignition, a resistance furnace may be used.
2 © ISO 2017 – All rights reserved

---------------------- Page: 6 ----------------------
ISO/TR 9686:2017(E)

6.3 Micropipette, of capacity 50 µl.
7 Sampling and samples
7.1 Laboratory sample
For analysis, use a laboratory sample of minus 160 µm particle size, which has been taken and prepared
in accordance with ISO 10835.
7.2 Preparation of predried test samples
Thoroughly mix the laboratory sample using non-magnetic materials. Taking multiple increments with
a non-magnetic spatula, extract a test sample in such a manner that it is representative of the whole
contents of the container.
Dry the test sample at 105 °C ± 2 °C as specified in ISO 7764. (This is the predried test sample.)
8 Procedure
WARNING — The risks related to combustion analysis are mainly hand burns when pre-igniting
the ceramic crucibles, and in the subsequent combustion. Normal precautions for handling
oxygen cylinders should be taken. Oxygen from the combustion process should be removed
effectively from the apparatus and room, since a too high concentration of oxygen in a confined
space may present a fire hazard. HF screening should be effective to avoid radiation hazards.
8.1 General operating instructions
Purify the oxygen supply using tubes packed with ascarite (5.8) and magnesium perchlorate (5.2) and
maintain a quiescent flow rate of about 0,5 l/min whilst on standby.
Maintain a glass-wool filter between the furnace chamber and the analyser and change as necessary. The
furnace chamber, pedestal post and filter trap should be cleaned frequently to remove oxide build-up.
The oxygen flow rate may vary from one instrument to another, but is usually about 2,0 l/min during
the combustion period, according to the nature of the material
...