ISO 6257:2002

INTERNATIONAL ISO
STANDARD 6257
Second edition
2002-10-01
Carbonaceous materials used in the
production of aluminium — Pitch for
electrodes — Sampling
Produits carbonés utilisés pour la production de l'aluminium — Brais pour
électrodes — Échantillonnage
Reference number
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ii ISO 2002 – All rights reserved

Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General procedures and precautions . 3
5 Sampling of solid pitch . 5
6 Soft pitches . 9
7 Hot liquid pitch . 10
8 Sample size reduction . 17
9 Sample containers . 19
10 Sampling report . 19
Bibliography. 21
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ISO 2002 – All rights reserved iii

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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 6257 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.
This second edition cancels and replaces the first edition (ISO 6257:1980), which has been technically revised.
©
iv ISO 2002 – All rights reserved

Introduction
Sampling is a vital step in analysis and testing. Its importance is recognized in this International Standard which
specifies comprehensive methods of sampling the grades of pitch used for the electrolytic production of aluminium.
Such samples should be as representative as possible of the materials sampled (whether from the whole or part of a
batch or consignment) and in a form that facilitates the determination of the distribution of values of properties.
©
ISO 2002 – All rights reserved v

INTERNATIONAL STANDARD ISO 6257:2002(E)
Carbonaceous materials used in the production of aluminium —
Pitch for electrodes — Sampling
WARNING —This International Standard may involve the use of hazardous materials, operations and
equipment. This International Standard cannot address all the safety implications associated with its use. It
is the responsibility of the user of this International Standard to establish appropriate health and safety
practices and assess the applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies methods for sampling and preparing samples prior to testing of binder pitch
used in the manufacture of electrodes for the electrolytic production of aluminium.
These methods are applicable to grades of pitch in liquid or solid form, the latter having softening points higher than
◦
30 C (determined according to the method specified in ISO 5940), in bulk, or in a number of containers making up
one batch at sites of manufacture, storage, or delivery. Sampling methods and sampling plans for large
consignments, or lots, of pitch in liquid form during the loading and unloading of ships are included.
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 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 5940, Carbonaceous materials for the production of aluminium — Pitch for electrodes — Determination of
softening point by the ring-and-ball method
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
sampling unit
defined quantity of material having a boundary which may be physical, for example a container, or hypothetical, for
example a particular time or time interval in the case of a stream of material
NOTE 1 A number of sampling units may be gathered together, for example in a package or box.
NOTE 2 In French, the term “individu” is sometimes used, a synonym of “unité d'échantillonnage”. In English, the terms
“individual”, “unit” and “item” are sometimes used in practice as synonyms of “sampling unit”.
[ISO 6206]
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ISO 2002 – All rights reserved 1

3.2
sample
one or more sampling units taken from a larger number of sampling units, or one or more increments taken from a
sampling unit
[ISO 6206]
3.3
representative sample
sample assumed to have the same composition as the material sampled when the latter is considered as
homogeneous whole
[ISO 6206]
3.4
sampling plan
planned procedure of selection, withdrawal and preparation of a sample or samples from a lot (see 3.6) to yield the
required knowledge of the characteristic(s) from the final sample (see 3.10) so that a decision can be made
regarding the lot
NOTE Considerations of cost, effort and delay usually determine an acceptable sampling error.
[ISO 6206]
3.5
consignment
quantity of material covered by a particular consignment note or shipping document
[ISO 6206]
3.6
lot
total quantity of material to be sampled using a particular sampling plan
NOTE A lot may consist of consignments, batches or items.
[ISO 6206]
3.7
batch
definite quantity of material that may be one item or a number of items which belong together because of their
manufacture or production under conditions which are presumed to be uniform
[ISO 6206]
3.8
bulk sample
collected set of samples which do not maintain their individual identity
[ISO 6206]
3.9
incremental sample
one of a series of samples taken during the sampling process
NOTE Incremental samples may or may not retain their individual identity depending on the sampling instructions.
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2 ISO 2002 – All rights reserved

3.10
final sample
sample obtained or prepared under the sampling plan for possible subdivision into identical portions for testing
reference or storage
[ISO 6206]
3.11
laboratory sample
sample as prepared for sending to the laboratory and intended for inspection or testing
[ISO 6206]
3.12
reference sample
sample prepared at the same time as, and identical with, the laboratory sample, which is acceptable to the parties
concerned and retained for use as a laboratory sample if a disagreement occurs
[ISO 6206]
3.13
spot sample
sample of specified number or size taken from a specified place in the material or at a specified place and time in a
stream of material and representative of its own immediate or local environment
NOTE In English, the term “snap sample” is sometimes used as a synonym for “spot sample”.
[ISO 6206]
4 General procedures and precautions
4.1 Sampling methods
Manual and automated sample-taking are equally acceptable. Details of the methods employed shall be described in
the sampling report (see clause 10).
4.2 Contamination of sample or of pitch being sampled
The sampling procedure shall not cause contamination of the sample or of the pitch being sampled.
Sample containers, sampling apparatus and any ancillary gear shall be dry.
Sample containers, sampling apparatus, any ancillary gear, the hands and gloves and the protective clothing of the
sampler shall be clean.
Pitch undergoes slow surface oxidation in the presence of air. Finely divided products, because of their large surface
area per unit mass, may show a significant rise in softening point even if stored for only a short time. It is
recommended therefore that finely divided reference samples be prepared for storage by melting and resolidifying as
follows.
a) Place a sufficient amount of the powdered sample in a suitable container with a loose-fitting lid in an oven
◦
controlled at approximately 50C2 above the expected softening point of the pitch. Leave in the oven for h at this
temperature. After heating, the surface of the melt should be smooth, shiny and free of skin.
b) If the surface of the melt is covered with froth, suggesting the presence of water, discard it and prepare another
melt using a further portion of the sample which has first been dried by allowing it to stand in an evacuated
desiccator in the presence of a suitable desiccant for approximately 2h.
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ISO 2002 – All rights reserved 3

c) Pour the molten pitch without turbulence, so as to avoid entrapping air bubbles, into an air-tight metal container,
allowing it to solidify and seal the container.
d) Note any froth formation during melting in the sample report and, in such cases; retain a separate portion of the
finely-divided sample, stored in a sealed air-tight container, for the determination of water content.
If a sample container is opened, it shall be securely closed again as soon as possible and any damaged sealing rings
shall be replaced.
4.3 Sampling for the determination of water content of pitch in solid form
For bulk shipments of solid pitch, a series of spot samples shall be taken for determination of water content, either
from the conveying system during charge or discharge, or from the hold or compartment, or lorry at the top, middle
or bottom during charge or discharge. The individual samples shall be sealed immediately in air-tight containers and
tested promptly to avoid loss of moisture.
4.4 Mass of laboratory and reference samples
The mass of the laboratory and reference samples shall be at least three times the amount required for testing and
shall never be less than 1kg unless otherwise agreed in accordance with an established quality procedure. The
sample mass shall be included in the sampling report (see clause 10).
The minimum recommended sample mass is 2kg.
4.5 Safety precautions
Comprehensive safety instructions are given in ISO 3165. Attention is drawn in particular to the following.
— When sampling hot liquid pitch from large containers such as ships, road or rail tanks, the sampler shall closely
follow the safety procedures laid down for that site or location. These procedures typically include protective
equipment and guidelines on safe working practice.
— Avoid inhalation of pitch vapour and dust.
— Sampling from ships, road or rail vehicles shall be strongly discouraged when in motion or when motion is likely
to begin.
4.6 Suspect consignment
A consignment shall be considered suspect if:
a) a container is damaged or defective;
b) there is any doubt as to the nature of the conten
...