ISO 10238:1999

INTERNATIONAL ISO
STANDARD 10238
First edition
1999-12-15
Carbonaceous materials used in the
production of aluminium — Pitch for
electrodes — Determination of sulfur
content by an instrumental method
Produits carbonés utilisés pour la production de l'aluminium — Brai pour
électrodes — Dosage du soufre par une méthode instrumentale
Reference number
©
ISO 1999
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ii © ISO 1999 – All rights reserved

Foreword
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member bodies). The work of preparing International Standards is normally carried out through ISO technical
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patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 10238 was prepared by Technical Committee ISO/TC 47, Chemistry, Subcommittee
SC 7, Aluminium oxide, cryolite, aluminium fluoride, sodium fluoride, carbonaceous products for the aluminium
industry.
© ISO 1999 – All rights reserved iii

INTERNATIONAL STANDARD ISO 10238:1999(E)
Carbonaceous materials used in the production of aluminium —
Pitch for electrodes — Determination of sulfur content by an
instrumental method
1 Scope
This International Standard describes a method for determining the sulfur content of pitch used in the production of
aluminium. The method is applicable to pitches of both coal tar and petroleum origin, provided that they contain
between 0,1 % and 4,0 % by mass of sulfur.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 565, Test sieves — Metal wire cloth, perforated metal plate and electroformed sheet — Nominal sizes of
openings.
ISO 3696, Water for analytical laboratory use — Specification and test methods.
ISO 4793, Laboratory sintered (fritted) filters — Porosity grading, classification and designation.
ISO 6257, Carbonaceous materials used in the production of aluminium — Pitch for electrodes — Sampling.
3 Principle
A known mass of the sample is burned in a stream of oxygen at a temperature of 1 350 °C. The oxides of sulfur
formed, together with any chlorine present, are absorbed in neutral hydrogen peroxide and determined
volumetrically. A correction is made to take account of the chlorine content of the sample. Aluminium oxide is added
to the sample to prevent the retention of sulfur in the ash.
4 Reagents
Unless otherwise specified, use reagents of analytical reagent grade and water conforming to grade 3 of ISO 3696.
4.1 Disodium tetraborate solution, c(½Na B O ·10H O) = 0,025 mol/l.
2 4 7 2
4.2 Sulfuric acid solution, c(½H SO ) = 0,025 mol/l.
2 4
4.3 Hydrogen peroxide solution, consisting of 3 % by volume of H 0 and 97 % by volume of water, neutralized
2 2
with the disodium tetraborate solution (4.1) to the screened indicator (4.4).
© ISO 1999 – All rights reserved 1

4.4 Screened indicator, consisting of equal volumes of a) and b) prepared as follows and mixed immediately
before use:
a) 0,125 g of methyl red dissolved in 100 ml of 95 % by volume ethanol solution;
b) 0,083 g of methylene blue dissolved in 100 ml of 95 % by volume ethanol solution.
Store in a dark glass bottle.
4.5 Mercury(II) oxycyanide solution, consisting of approximately 100 ml of water saturated with mercury(II)
oxycyanide (3Hg(CN) ·HgO).
Agitate thoroughly, filter and neutralize the filtrate with the sulfuric acid solution (4.2) to the screened indicator. Store
the solution in a dark glass bottle. Do not keep longer than 4 days.
WARNING — This compound and its solution are toxic and should be handled with appropriate care.
4.6 Aluminium oxide, finely divided, particle size approximately 0,1 mm.
4.7 Oxygen.
4.8 Sodium hydroxide on an inert base, preferably of coarse grading, for example 1,7 mm to 1,2 mm, and
preferably of the self-indicating type.
5 Apparatus
Ordinary laboratory apparatus and the following.
5.1 Combustion furnace and absorption train, as shown in Figure 1, and consisting of the following.
5.1.1 Furnace, electrically heated, designed to carry a tube of 28,5 mm outside diameter and to heat it over a
length of about 125 mm to give a temperature of 1 350 °C at the centre of the hot zone and a temperature
distribution curve similar to that shown in Figure 2.
5.1.2 Combustion tube, of 22 mm internal diameter and 28,5 mm outside diameter and 0,65 m long, made of
refractory aluminous porcelain that is not permeable to gases at 1 400 °C.
5.1.3 Combustion boat, of iron-free unglazed porcelain, 70 mm long, 12,5 mm wide and 10 mm deep, that does
not blister, discolour or change in mass on heating at 1 350 °C in oxygen for 3 h.
5.1.4 Silica pusher, comprising a sealed tube or rod of silica, 6 mm in diameter and approximately 450 mm long,
flattened at one end to form a disc of 12 mm diameter for pushing the combustion boat into the furnace.
The pusher passes loosely through a glass or metal T-piece, one end of which fits into the rubber stopper that
closes the inlet end
...