ISO 20292:2009

INTERNATIONAL ISO
STANDARD 20292
First edition
2009-05-15
Materials for the production of primary
aluminium — Dense refractory bricks —
Determination of cryolite resistance
Matériaux pour la production de l'aluminium de première fusion —
Briques réfractaires denses — Détermination de la résistance de la
cryolite
Reference number
©
ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword .iv
1 Scope .1
2 Principle.1
3 Sampling.1
4 Reagents.1
5 Apparatus.1
6 Procedure.3
7 Precision statement .5
8 Test report.6
Bibliography.7

Foreword
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ISO 20292 was prepared by Technical Committee ISO/TC 226, Materials for the production of primary
aluminium.
iv © ISO 2009 – All rights reserved

INTERNATIONAL STANDARD ISO 20292:2009(E)

Materials for the production of primary aluminium — Dense
refractory bricks — Determination of cryolite resistance
1 Scope
This International Standard covers materials for the production of primary aluminium.
This International Standard specifies a method for the determination of the resistance of dense refractory
bricks to cryolite melt with excess sodium fluoride.
2 Principle
A mixture of fine powders (< 100 µm) of cryolite and sodium fluoride are allowed to react at 950 °C in a
furnace for 24 h in air, on a crucible-shaped test piece made of the dense refractory brick material to be
tested.
Reacted and/or infiltrated areas of brick material are calculated. Together with the calculation, a visual
description of the reaction extent is recommended and photographs should also be used to illustrate the
attack.
3 Sampling
Take a number of different bricks from within the batch to be tested. Take a minimum of two sample bricks to
prepare test pieces. The test pieces are taken from different bricks.
4 Reagents
4.1 Cryolite (Na AlF ) powder, with a minimum purity of 97 % mass fraction and a particle size < 100 µm.
3 6
4.2 Sodium fluoride (NaF) powder, with a minimum purity of 99 % mass fraction and a particle size
< 100 µm.
IMPORTANT — The electrolyte used in aluminium electrolysis will penetrate through the carbon block
materials and then into the refractory. It is essential that this electrolyte penetration be stopped by
reaction with the refractory. It is hence important to test the different refractory materials for
resistance towards penetration. This test correlates well with penetration in industrial cells.
5 Apparatus
5.1 Diamond saw, with water cooling.
5.2 Core drilling apparatus, standard drilling machine with water cooling.
5.3 Three drill pieces, to be mounted on the drilling machine:
a) a 50 mm diamond core drill that gives a (57 ± 1) mm hole;
b) a 30 mm core drill;
c) a 48 mm to 50 mm steel disk mounted on a stem, where pieces from a diamond core drill, that are 3 mm
high with the same radius of curvature as the disk, are glued on underneath (see Figure 1).
5.4 Furnace, capable of heating the test crucibles as required to (950 ± 5) °C.
5.5 Thermocouples, at least three, capable of measuring temperatures of 950 °C.
5.6 Drying cabinets, capable of drying the test crucibles as required at (110 ± 5) °C.
5.7 Photocopy machine.
5.8 Photocopy paper.
5.9 Balance, accurate to 0,01 g.
SAFETY PRECAUTIONS — During exposure, fluoride gas will be generated. The corrosive gasses will
react and accumulate in
...