ISO 4443:2022

INTERNATIONAL ISO
STANDARD 4443
First edition
2022-01
Cryolite primarily used for the
production of aluminium —
Determination of elements —
Wavelength-dispersive X-ray
fluorescence spectrometric method
using pressed powder tablets
Cryolithe principalement utilisée pour la production de
l'aluminium — Dosage des éléments — Méthode par spectrométrie
de fluorescence des rayons X à dispersion de longueur d'onde utilisant
des pastilles de poudre pressée
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Test procedure .2
7.1 Test specimen preparation . 2
7.2 Test tablet preparation . 2
7.3 X-ray fluorescence spectrometer application . 2
7.3.1 Instrumental conditions . 2
7.3.2 Calibration and calibration reference materials . 3
7.3.3 Verification of the calibration . 3
7.4 Monitoring of the sample for correction of instrumental drift . 3
7.5 Analyses, calculation and expression of results . 4
8 Precision . 4
8.1 General . 4
8.2 Repeatability . 4
8.3 Reproducibility . 4
9 Test report . 5
Annex A (informative) Conversion table . 6
Annex B (informative) Example of how to use Table 2 using sulfur (SO ) .7
Bibliography . 8
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 226, Materials for the production of
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iv
Introduction
In the production of aluminium, cryolite is used as a flux in order to lower the melting points of
aluminium smelting baths and increase the conductivity of the electrolyte. This use is critical during
the start-up and normal operation stages of electrolysis cells.
v
INTERNATIONAL STANDARD ISO 4443:2022(E)
Cryolite primarily used for the production of aluminium —
Determination of elements — Wavelength-dispersive X-ray
fluorescence spectrometric method using pressed powder
tablets
1 Scope
This document specifies a wavelength-dispersive X-ray fluorescence spectrometric (XRF) method for
the determination of cryolite (Na AlF ) from the content of fluorine to the content of trace elements.
3 6
The calibration reference materials are not specified in this method.
The method is applicable to cryolite, which is primarily used for the production of aluminium. Annex A
provides conversion factors for converting elements to compounds. The validity and precision of test
results for concentrations outside these ranges has not been determined.
The concentration range of fluorine (given as F) is from 510 g/kg to 560 g/kg. The concentration range
of aluminium (given as Al) is from 120 g/kg to 150 g/kg. The concentration range of sodium (given as
Na) is from 270 g/kg to 330 g/kg. The concentration range of silicon (given as SiO ) is from the lowest
limit of detection (LLD) to 4,0 g/kg. The concentration range of iron (given as Fe O ) is from LLD to
2 3
0,37 g/kg. The concentration range of sulfur (given as SO ) is from LLD to 5,0 g/kg. The concentration
range of phosphorus (given as P O ) is from LLD to 0,40 g/kg. The concentration range of calcium
2 5
(given as CaO) is from LLD to 0,80 g/kg.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
A representative sample of cryolite is milled. A test portion is packed and pressed on a powder tablet
press to make the test tablets.
The test tablets are analysed on an X-ray fluorescence spectrometer instrument that has been calibrated
using a series of cryolite reference materials covering the required concentration range of the elements
to be determined.
5 Reagents and materials
5.1 Acetone or ethyl alcohol, analytical pure, used as dispersing agent.
5.2 Boric acid, analytical pure.
6 Apparatus
6.1 Wavelength-dispersive X-ray fluorescence spectrometer (XRF), with vacuum path and
equipped with crystals required as shown in Table 1.
6.2 Vibratory disc mill, with tray, ring and puck made of non-contaminating material. Tungsten-
carbide and chrome steel have been found to be satisfactory.
6.3 Tablet press, capable of providing 340 kN for 20 s.
6.4 Balance, with precision ±0,01 g.
6.5 Flat spatula.
7 Test procedure
7.1 Test specimen preparation
See ISO 1619 for guidance.
7.2 Test tablet preparation
7.2.1 Dry the sample to constant mass at (110 ± 2) °C. A typical drying time is 2 h.
7.2.2 Weigh 10,0 g of sample and put it into the mill. Then add 10 drops of acetone or ethyl alcohol and
vibrate for 60 s to make the particle size below 45 μm fineness.
7.2.3 Transfer 2,0 g of milled sample to the tablet press, use boric acid backing to prepare the pressed
tablet with a pressure of 340 kN and hold for 20 s. Tablet thickness should be a minimum of 4 mm, with
a diameter of 40 mm.
7.2.4 Remove the tablets from the tablet press. Touch the edge of the tablets only during measurement.
Trim the edges. Avoid polluting the surface during X-ray measurement.
Always use the same mass and proportion of sample and reagents as for the calibration reference
materials.
Results are particle-size dependent. Short milling times give larger spread in intralaboratory precision.
The particle size should be determined by using a suitable sieving technique. Erroneous data will be
collected if analytical samples contain particles varying significantly in size that cause different beam
penetration depth and a different surface roughness from those in the calibration reference samples.
The surface of the pressed powder tablet should be smooth and firm and should not drop out power
after trimming. The measuring surface should not be mixed with boric acid.
7.3 X-ray fluorescence spectrometer application
7.3.1 Instrumental conditions
Follow the control setting and operation instructions of the spectrometer manufacturer, including
monitoring and calibrating angles and monitoring and correcting for X-ray tube intensity.
Suggested conditions of measurement are given in Table 1. All measurements shall be made under
vacuum. The Kα analytical lines are preferred. Use spectral lines overlap correction if required. Correct
for background, using the lines recommended in Table 1.
Table 1 — Measurement lines and suggested conditions of measurement
Angle Time for Time for Collimator Voltage Current
peak background
Element Crystal Counter
°2θ ° kV mA
s s
30 % of time for
Fluorine XS-55 38,694 Flow 60 0,46 27 111
peak
30 % of time for
Aluminium PET 144,584 Flow 30 0,46 27 60
peak
30 % of time for
Sodium XS-55 24,962 Flow 60 0,46 27 80
peak
30 % of time for
Silicon PET 108,985 Flow 10 0,46 27 111
peak
Scintilla- 30 % of time for
Iron LiF200 57,556 2 0,46 60 50
tion peak
30 % of time for
Sulfur PET 75,73 Flow 10 0,46 27 111
peak
30 % of time for
Phosphorus Ge 141,009 Flow 10 0,46 27 111
peak
30 % of time for
Calcium LiF200 113,135 Flow 2 0,46 50 60
peak
7.3.2 Calibration and calibration reference materials
The calibration reference materials are not specified in this method. The user of this document shall
obtain suitable calibration reference material
...