ISO/PRF 6376

• Abstract:

  Specifies a gravimetric method, the principle of which consists in weighing the fraction of a test portion of pitch which is insoluble in toluene after boiling for a specified period.

• Status: Not Published
• ICS: 71.100.10 - Materials for aluminium production
• Technical Committee: ISO/TC 226 - Materials for the production of primary aluminium
• Drafting Committee: ISO/TC 226/WG 1 - Carbonaceous binders, including pitch
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 11-Sep-2026
• Completion Date: 19-Sep-2026

• Revises: ISO 6376:1980 - Carbonaceous materials for the production of aluminium — Pitch for electrodes — Determination of content of toluene-insoluble material
• Effective Date: 04-Nov-2023

Overview

ISO/PRF 6376:2026 is an international standard developed by ISO for the aluminium industry, specifically addressing the determination of toluene-insoluble material content in pitch used for electrode production. This standard specifies a gravimetric method that involves weighing the portion of pitch that remains insoluble after boiling with toluene for a set period. The quality and performance of pitch used in aluminium smelting processes are significantly impacted by its toluene-insoluble content, making this method an essential analytical tool for producers and quality assurance laboratories within the aluminium sector.

Key Topics

• Purpose: Outlines the procedure for quantifying toluene-insoluble materials in pitch intended for electrodes in the electrolytic production of aluminium.
• Method Principle: The sample is treated with boiling toluene, and the fraction remaining insoluble is separated and weighed to determine its percentage by mass.
• Reagents and Safety: Only analytical grade reagents, including toluene and acetone, must be used. Both chemicals are highly flammable and hazardous, requiring proper handling, adequate ventilation, and responsible disposal.
• Required Equipment:
  • Borosilicate glass conical flask (500 ml)
  • Reflux condenser (300 mm)
  • Glass filter crucible (porosity grade P16)
  • Hartley funnel (or equivalent)
  • Controlled electric oven (105 °C - 110 °C)
• Sampling Guidelines: Sampling procedures refer to ISO 6257. Hard pitches should be ground; soft pitches are tested as received.
• Calculating Results: The toluene-insoluble content is calculated as a mass percentage using specific mass measurements before and after extraction.
• Precision: The method provides repeatability of 0.5% and reproducibility of 1.0%.

Applications

ISO/PRF 6376:2026 is essential in the following practical contexts:

• Quality Control in Aluminium Production: Ensures pitch materials meet the necessary quality standards for use in electrode manufacturing, directly affecting the efficiency and lifespan of anodes in electrolysis cells.
• Material Comparison and Specification: Facilitates accurate comparison of different batches or suppliers of pitch material by providing standardized test results for toluene-insoluble content.
• Process Optimization: Data obtained from this method can inform adjustments to pitch selection or production processes to enhance smelting performance and electrode durability.
• Regulatory Compliance and Reporting: The requirement to include relevant sample identification, test conditions, and calculation details ensures transparency and traceability, supporting regulatory and client reporting needs in the aluminium industry.

Related Standards

• ISO 6257: Carbonaceous materials used in the production of aluminium - Pitch for electrodes - Sampling. This standard provides the sampling procedures referenced in ISO 6376.
• ISO/TC 226: Technical committee overseeing standards for materials used in the primary production of aluminium.
• ISO Laboratory and Safety Standards: Referenced throughout to ensure safe and reliable operation of equipment and chemical handling during the test.

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By adhering to ISO/PRF 6376, organisations involved in aluminium production can ensure rigorous, reproducible determination of toluene-insoluble content in pitch, supporting quality management, process optimization, and compliance with international industry norms.

International
Standard
ISO 6376
Second edition
Carbonaceous materials for the
production of aluminium — Pitch
for electrodes — Determination
of content of toluene-insoluble
material
Produits carbonés utilisés pour la production de l'aluminium —
Brais pour électrodes — Détermination du taux des matières
insolubles dans le toluène
PROOF/ÉPREUVE
Reference number
ISO 6376:2026(en) © ISO 2026
ISO 6376:2026(en)
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 6376:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 1
7 Sampling . 3
8 Procedure . 4
8.1 Test portion .4
8.2 Determination .4
9 Expression of results . 4
9.1 Method of calculation .4
9.2 Precision . . .4
10 Test report . 5
PROOF/ÉPREUVE
iii
ISO 6376:2026(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 226, Materials for the primary production of
aluminium.
This second edition cancels and replaces the first edition (ISO 6376:1980), which has been technically
revised.
The main changes are as follows:
— added analysis procedure details to help run t
...

ISO/TC 226/SC /WG 1
Secretariat: SNV
Date: 2026-07-1709-11
Carbonaceous materials for the production of aluminium — Pitch
for electrodes — Determination of content of toluene-insoluble
material
Copyright notice
ThisProduits carbonés utilisés pour la production de l'aluminium — Brais pour électrodes — Détermination du
taux des matières insolubles dans le toluène
PROOF
© ISO document is a working draft2026
All rights reserved. Unless otherwise specified, or committee draft and is copyright-protected by ISO. While required in
the reproductioncontext of working drafts or committee drafts in any form for use by participants in the ISO standards
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ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
iii
ISO/WD 6376:2021(E)ISO/PRF 6376:2026(en)
Contents Page
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 1
7 Sampling . 3
8 Procedure . 4
8.1 Test portion . 4
8.2 Determination . 4
9 Expression of results . 4
9.1 Method of calculation . 4
9.2 Precision . 5
10 Test report . 5

1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sampling . 2
8 Procedure . 2
8.1 Test portion . 2
8.2 Determination . 2
9 Expression of results . 3
9.1 Method of calculation . 3
9.2 Precision . 3
10 Test report . 3

iv
iv
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 t
...