ISO 12988-2:2004

INTERNATIONAL ISO
STANDARD 12988-2
First edition
2004-09-15
Carbonaceous materials used in the
production of aluminium — Baked
anodes — Determination of the reactivity
to carbon dioxide —
Part 2:
Thermogravimetric method
Produits carbonés utilisés pour la production de l'aluminium — Anodes
cuites — Détermination de la réactivité au dioxyde de carbone —
Partie 2: Méthode thermogravimétrique

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 2
5 Apparatus. 2
6 Reagents . 5
7 Sample. 5
8 Calibration. 5
9 Procedure. 7
10 Calculation of results. 7
11 Precision and bias . 9
12 Test report. 11
Bibliography . 12

Foreword
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(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
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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.
ISO 12988-2 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 12988 consists of the following parts, under the general title Carbonaceous materials used in the
production of aluminium — Baked anodes — Determination of the reactivity to carbon dioxide:
 Part 1: Loss in mass method
 Part 2: Thermogravimetric method
iv © ISO 2004 – All rights reserved

Introduction
The CO reactivities, or reaction rates, are used to quantify the tendency of a carbon artifact to react with
carbon dioxide. Carbon consumed by these unwanted side reactions is unavailable for the primary reactions
of reducing alumina to the primary metal. CO reactivities and dusting rates are used to quantify the tendency
of the coke aggregate or binder coke of a carbon artifact to selectively react with these gases. Preferential
attack of the binder coke or coke aggregate of a carbon artifact by these gases causes some carbon to fall off
or dust, making the carbon unavailable for the primary reaction of reducing alumina and, more importantly,
reducing the efficiency of the aluminium reduction cell.
Comparison of CO reactivities and dusting rates is useful in selecting raw materials for the manufacture of

commercial anodes for specific smelting technologies in the aluminium reduction industry.
CO reactivities are used for evaluating effectiveness and beneficiation processes, or for research purposes.
Sampling guidelines are under development.
This part of ISO 12988 is based on ASTM D 6558-00.

INTERNATIONAL STANDARD ISO 12988-2:2004(E)

Carbonaceous materials used in the production of aluminium —
Baked anodes — Determination of the reactivity to carbon
dioxide —
Part 2:
Thermogravimetric method
WARNING — This part of ISO 12988 does not purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the user of this part of ISO 12988 to establish
appropriate safety and health practices and determine the applicability of regulatory limitations prior
to use.
1 Scope
This test method covers the thermogravimetric (TGA) determination of CO reactivities and dusting of shaped
carbon anodes used in the aluminium reduction industry. Many types of apparatus are available with a wide
variety of thermal conditions, sample-size capability, materials of construction and procedures for determining
the mass loss and subsequent rate of reaction. This test method standardizes the variables of sample
dimensions, reaction temperature, gas velocity over the exposed surfaces, and reaction time such that results
obtained on different types of apparatus are correlatable.
2 Normative references
The following referenced documents are indispensable for the application 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.
ASTM E 691-99, Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a
Test Method
3 Terms and definitions
For the purposes of this part of ISO 12988, the following terms and definitions apply.
3.1
dusting
a
RCD
that quantity of carbon that falls off the carbon artifact during the test and is collected in the container at the
bottom of the reaction chamber
3.2
final CO reactivity
a
RCf
rate of mass loss of the carbon artifact during the final 30 min of exposure to CO in the reaction chamber
divided by the initial geometric (right cylindrical) exposed surface area of the sample
NOTE The final CO reactivity is expressed in milligrams per square centimetre per hour.
3.3
initial CO reactivity
a
RCi
rate of mass loss of the carbon artifact during the first 30 min of exposure to CO in the reaction chamber
divided by the initial geometric (right cylindrical) exposed surface area of the sample
NOTE The initial CO reactivity is expressed in milligrams per square centimetre per hour.
3.4
total CO reactivity
a
RCt
rate of mass loss of the carbon artifact (including dusting) during the total time that the sample is exposed to
CO (420 min) in the reaction chamber divided by the initial geometric (right cylindrical) exposed surface area
of the sample
NOTE The total CO reactivity is expressed in milligrams per square centimetre per hour.
4 Principle
The dusting rate and the initial, final and total CO reactivities are determined by passing carbon dioxide gas
at a flow rate that gives a standard velocity of reactant gas around cylindrically shaped carbon artifacts under
isothermal conditions for a specified length of time. The reactivity is determined by continuously monitoring the
sample mass loss. The CO dusting rate is determined by collecting and determining the mass of carbon

particles that fall off the sample during reaction.
5 Apparatus
The apparatus to be used should be as simple as possible and be commensurate with what is to be achieved.
The principal criterion is that the reaction rate be determined under isothermal conditions and be unaffected
by physical and chemical properties inherent to the apparatus (such as gas diffusion patterns, gas
temperature, exposed sample surface area, and so forth). A typical apparatus that has been found to be
suitable is illustrated in Figure 1.
5.1 Furnace and controller, capable of maintaining constant temperature, within ± 2 °C in the 100-mm
reaction zone in which the sample is centred.
A typical apparatus, as illustrated in Figure 1, employs a three-zone heating element and associated controls
to accomplish this, but other types of heaters such as tapered windings or long linear heaters are also suitable.
The control thermocouple is a grounded type and shall be located within the reaction chamber near the
surface of the test sample. This is to allow the furnace controller to compensate for the exothermic reactions
that occur when the furnace is used for air reactivity testing. The control thermocouple shall be positioned
4 mm ± 1 mm from the side surface of the sample and within 5 mm vertically of the centre of the reaction
chamber. The furnace shall be large enough to accommodate the reaction chamber.
5.2 Reaction chamber, consisting of a vertical tube constructed of a material capable of withstanding the
temperature of the reaction, e.g. 960 °C ± 2 °C with a sufficiently large inside diameter to accommodate the
sample and sample suspension device while not affecting the gas flow past the sample. An inside diameter of
100 mm ± 25 mm is recommended.
The reaction chamber shall be constructed with a removable dust-collection cup at the bottom capable of
capturing all the dust that falls off the sample during the test. The most common materials of construction are
1)
quartz and Inconel .
1) Inconel is an example of a suitable product available commercially. This information is given for the convenience of

users of this part of ISO 12988 and does not constitute an endorsement by ISO of this product.
2 © ISO 2004 – All rights reserved

5.3 Sample suspension device, capable of supporting the sample in the reaction chamber for the duration
of the test and which should be reusable.
The sample holder shall not change in mass during the test, shall not affect the flow pattern of the gas past
the sample, shall not limit the gas-accessible surface area of the test sample and shall not interfere with the
production of dust by the sample. A typical sample holder is illustrated in Figure 2.
Dimensions in millimetres
Key
1 balance 9 dust-collection cup
2 gas outlet (10 mm hole) 10 gas inlet
3 three-zone furnace 11 air or CO
4 connecting wire (see Figure 2) 12 N
5 reaction chamber 13 pressure-reducing valve
6 sample 14 needle valve
7 control thermocouple 15 flow meter
8 preheat tube
Figure 1 — Typical CO reactivity apparatus
Dimensions in millimetres
Key
2)
1 suspension wire (Nichrome) 3 cylindrical sample
2 sample support wire (platinum, 1 mm diameter) 4 stainless steel ball
Figure 2 — Typical sample suspension arrangement
5.4 Gas preheat tube, extending into the first heating zone of the reaction chamber, to preheat the gas
prior to entering the reaction chamber.
The length and diameter of the tube may vary, as long as the gas leaving the tube is at the same temperature
as the reaction chamber. The inlet gas shall leave the preheat tube downward to prevent chan
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