Date: 2025-07-21

ISO/DIS 6376:2025(en)

ISO/TC 226/SC /WG 1

Secretariat: SNV

Carbonaceous materials for the production of aluminium — Pitch for electrodes — Determination of content of toluene-insoluble material

Élément introductif — Élément central — Élément complémentaire

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Contents Page

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 1

5 Reagents and materials 1

5.1 Toulene 1

5.2 Acetone 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

Foreword

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This document was prepared by Technical Committee ISO/TC 226, Materials for the production of primary aluminium .

This third edition cancels and replaces the second edition (ISO 6376:1980 (R2014)), which has been technically revised.

The main changes compared to the previous edition are as follows:

— added analysis procedure details to help run the analysis

— corrected text to formal SI formatting

— updated test report description

Introduction

The content of toluene-insoluble material for pitch is a vital step in analysis and testing of this material. The coking toluene insoluble content can give important information about the quality and likely performnance of the material. Such importance is recognised in this International Standard which specifies the most fundamental method of test for grades of pitch used in the electrolytic production of aluminium.

Carbonaceous materials for the production of aluminium — Pitch for electrodes — Determination of content of toluene-insoluble material

This document specifies a gravimetric method for the determination of the content of toluene- insoluble material in pitch used for the production of aluminium.

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 6257, Carbonaceous materials used in the production of aluminium — Pitch for electrodes — Sampling

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 https://www.electropedia.org/

— ISO Online browsing platform: available at https://www.iso.org/obp

Determination by weighing of the fraction of a test portion of pitch which is insoluble in toluene after boiling for a specified period.

During the analysis, use only reagents of recognized analytical grade.

WARNING — Highly flammable. Harmful by inhalation. Keep away from sources of ignition. Used toluene shall be disposed of safely and responsibly. Take precautionary measures against static discharges.

WARNING — Highly flammable. Harmful by inhalation. Keep away from sources of ignition. Used Acetone shall be disposed of safely and responsibly. Take precautionary measures against static discharges.

Ordinary laboratory apparatus and:

6.1 Conical flask, of capacity 500 ml, of borosilicate glass, fitted with a ground glass socket.

6.2 Reflux condenser, effective length 300 mm, having a ground glass cone at its lower end, by means of which it can be fitted to the socket of the conical flask (5.1).

6.3 Filter crucible, of glass, of capacity about 30 ml, fitted with a sintered glass disc of porosity grade P16 (pore size index 10 µm to 16 µm) and having the following approximate principal dimensions:

— disc diameter: 30 mm;

— height (disc to upper rim): 35 mm.

6.4 Hartley funnel, or equivalent, having a disc diameter of 70 mm (a suitable type is shown in the Figure 1).

6.5 Electric oven, capable of being controlled at a temperature between 105 °C and 110 °C.

See ISO 6257 for sampling procedure.

In the case of hard pitches, crush and grind the sample to pass a 212 µm aperture mesh sieve.

In the case of soft pitches, use the sample as received.

WARNING — Toluene is toxic and highly flammable. Carry out all operations involving its use in an efficiently ventilated fume cupboard.

Weigh, to the nearest 0,001 g, approximately 1 g of the sample (see clause 7).

Prepare the filter crucible (6.3) for the determination by heating it for about 1 h in the oven (6.5) controlled at a temperature between 105 °C and 110 °C, allowing it to cool to ambient temperature in a desiccator and weighing it to the nearest 0,001 g.

Place the test portion (8.1) in the conical flask (6.1). Add 100 ml ± 2 ml of toluene (5.1) at ambient temperature and swirl the contents of the flask to disperse the test portion.

NOTE Dissolution before boiling of soft pitches that are liquid on transfer to the flask is particularly necessary to prevent the formation of droplets of pitch which are subsequently not readily soluble in the boiling toluene.

Fit the condenser (6.2) to the flask and start the water circulation. With occasional gentle and careful swirling, bring the contents of the flask to a steady boil. Continue boiling under reflux, with gentle swirling at approximately 5 minutes intervals, for 30 minutes ± 2 minutes.

Stop the heating and remove the condenser. Using gentle suction, immediately filter the contents of the flask through the dried and weighed filter crucible (6.3), fitted to the Hartley funnel (6.4) . Rinse the flask (6.1) with approximately 10 ml of toluene (5.1) at ambient temperature and filter the washings through the filter crucible (6.3). When the filtration is complete, repeat the rinsing and filtering operations with further approximately 10 ml portions of ambient temperature toluene until all residue in the flask is transferred to the filter crucible and the filtrate is colourless. Wash the filter crucible and it’s contents with approximately 10 ml portions of acetone (5.2) and, when filtration is complete, repeat the operation with three further approximately 10 ml portions of the acetone (5.2).

Treat the filter crucible and its contents as follows:

Heat for approximately 1 h in the oven (6.5), maintained at a temperature between 105 °C and 110 °C, allow to cool to ambient temperature in a desiccator and weigh to the nearest 0,001 g.

The quantity of toluene-insoluble material, expressed as a percentage by mass, is given by the formula

where

is the mass, in grams, of the test portion (7.1);

is the mass, in grams, of the crucible containing the insoluble material;

is the mass, in grams, of the empty crucible.

Repeatability : 0,5 %

Reproducibility : 1,0 %

The test report shall include the following information:

a) an identification of the sample;

b) reference to International Standard ISO 6376 (include year of publication);

c) the date of the test;

d) the result with reference to clause 9.1 which explains how the result was calculated;

e) any deviations from the procedure;

f) any unusual features observed.

Key

A 4 terry spring clips or similar fastenings

B 68 holes, each 1 mm diameter

Material aluminium or other suitable metal

Finish fine machine all over polished bores and mating surfaces, i.e. flanges

Figure 1 — Details of Hartley funnel