ISO 3549:2024

International
Standard
ISO 3549
Third edition
Zinc dust pigments for paints —
2024-02
Specifications and test methods
Pigments à base de poussière de zinc pour peintures —
Spécifications et méthodes d'essai
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Required characteristics and tolerances . 1
5 Sampling . 3
6 Determination of residue on sieve . 3
6.1 Principle .3
6.2 Apparatus .3
6.3 Checking and cleaning the sieve .5
6.4 Procedure .5
6.5 Expression of results . .5
7 Determination of total zinc content . 6
7.1 Principle .6
7.2 Reagents .6
7.3 Procedure .7
7.3.1 Test portion .7
7.3.2 Determination .7
7.4 Expression of results . .7
8 Determination of metallic zinc content . 8
8.1 Principle .8
8.2 Reagents and materials .8
8.3 Procedure .9
8.3.1 General .9
8.3.2 Test portion .9
8.3.3 Determination .9
8.4 Expression of results .9
9 Determination of lead, cadmium and iron content .10
9.1 Principle .10
9.2 Reagents and materials .10
9.3 Apparatus .11
9.4 Procedure .11
9.4.1 Test portion .11
9.4.2 Preparation of test solutions .11
9.4.3 Determination . 12
9.5 Expression of results . 12
10 Determination of arsenic content .13
10.1 Principle . 13
10.2 Reagents and materials . 13
10.3 Apparatus .14
10.4 Procedure . 15
10.4.1 Preparation of the calibration graph . 15
10.4.2 Test portion . 15
10.4.3 Preparation of the test solution .16
10.4.4 Determination .16
10.5 Expression of results .18
11 Determination of chloride content .18
11.1 Principle .18
11.2 Reagents and materials .18
11.3 Apparatus .18
11.4 Procedure .19

iii
11.4.1 Preparation of the calibration graph .19
11.4.2 Determination .19
12 Determination of matter insoluble in acid . 19
12.1 Reagents and materials .19
12.2 Apparatus .19
12.3 Procedure .19
12.3.1 Test portion .19
12.3.2 Determination . 20
12.4 Expression of results . . 20
13 Test report .20
Bibliography .21

iv
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
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
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Any trade name used in this document is information given for the convenience of users and does not
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 256, Pigments, dyestuffs and extenders, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 298,
Pigments and extenders, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 3549:1995), which has been technically
revised.
The main changes are as follows:
— the maximum residue on the 45 µm sieve has been changed from 5 % mass fraction to 0,5 % mass
fraction;
— three types of zinc dust pigments (I, II and III) have been introduced with different requirements;
— inductively coupled plasma-optical emission spectroscopy (ICP-OES) has been added as an analytical
technique used for elemental analysis;
— the nominal size of sieve aperture has been changed from 125 µm – 90 µm – 45 µm to 125 µm –75 µm –
45 µm; ®
— CAS Registry Numbers have been added to the reagents;
— the normative references have been updated;
— a bibliography has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
International Standard ISO 3549:2024(en)
Zinc dust pigments for paints — Specifications and test
methods
1 Scope
This document specifies the requirements and corresponding test methods for zinc dust pigments suitable
for use in protective coatings.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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.
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 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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/
3.1
zinc dust pigment
fine grey powder of essentially spheroidal particles, mainly consisting of metallic zinc
Note 1 to entry: Zinc dust pigments for paints can vary in their metallic zinc content, chemical purity, particle shape,
particle size distribution, mean and maximum diameter, etc. These variations are all likely to have an influence on the
zinc dust behaviour in paints with regard to parameters such as dispersibility, fineness of grind, reactivity, electrical
conductivity and packing properties.
4 Required characteristics and tolerances
4.1 For zinc dust pigments conforming to this document, the essential requirements are specified in
Table 1 and Table 2.
Table 1 — Composition of zinc dust pigment
Characteristic Unit Requirement Test method
Type I Type II Type III
Total zinc content % (mass min. 98 min. 98 min. 99 See Clause 7
fraction)
Metallic zinc content % (mass min. 94 min. 94 min. 97 See Clause 8
fraction)
a
Lead (Pb) content % (mass max. 0,1 max. 0,01 max. 0,002 See Clause 9
fraction)
a
Cadmium (Cd) content % (mass max. 0,03 max. 0,01 max. 0,001 See Clause 9
fraction)
a
Iron (Fe) content % (mass max. 0,005 max. 0,005 max. 0,002 See Clause 9
fraction)
a
Arsenic (As) content % (mass max. 0,000 5 max. 0,000 5 max. 0,000 5 See Clause 10
fraction)
Chloride (Cl) content % (mass max. 0,005 max. 0,005 max. 0,005 See Clause 11
fraction)
Matter insoluble in acid % (mass max. 0,05 max. 0,05 max. 0,05 See Clause 12
fraction)
a
Other suitable methods such as the induction coupled plasma (ICP-OES or ICP-MS) method may be agreed upon between the
interested parties.
NOTE If the zinc oxide content is required, this can be calculated by multiplying the difference between the total zinc content
and the metallic zinc content by 1,244 7.
Table 2 — Residue on sieve
Nominal size of sieve aperture Residue on sieve
Test method
µm % (mass fraction)
125 max. 0,01
75 max. 0,1 See Clause 6
45 max. 0,5
4.2 Requirements for other physical properties (surface area, particle size distribution, etc.) and the
choice of reference pigment to which these properties refer shall be the subject of agreement between the
1) 2)
interested parties. Particle size and/or particle size distribution data as D10 , D50 , shall be given with
reference to the measurement method and test conditions.
4.3 The reference pigment shall also conform to the requirements given in Table 1 and Table 2.
4.4 Inductively coupled plasma–optical emission spectroscopy (ICP-OES) is an analytical technique used
for elemental analysis. The ICP-OES instrument is used in atomic spectroscopy. During analysis, the sample
is decomposed by intense heat into a cloud of hot gases containing free atoms and ions of the element(s)
of interest. The high temperatures cause significant amounts of collisional excitation and ionization of the
sample atoms. Once the atoms or ions are in their excited state, they can decay to lower states through
thermal or radiative (emission) energy transitions. During ICP-OES analysis, the intensity of the light
emitted at specific wavelengths is measured and used to determine the concentration of the element(s) of
interest. In ICP-OES analysis the thermal excitation sources can populate a large number of different energy
levels for several different elements at the same time. All of the excited atoms and ions can then emit their
1) Industry term meaning the value of the particle diameter below which 10 % of the particles fall in the cumulative
particle size distribution.
2) Industry term meaning the value of the particle diameter below which 50 % of the particles fall in the cumulative
particle size distribution. It is also known as the median diameter.

characteristic radiation at the same time. This results in the flexibility to choose from several different
emissions concurrently and allows detection of multiple elements concurrently.
Sample preparation for ICP-OES analysis is very similar to the sample preparation for atomic absorption (AA;
see Clause 9 and Clause 10) with a variant. (0,500 0 ± 0,000 2) g of sample is dissolved in 100 ml 5 % (volume
fraction) HNO 68 % (mass fraction). For very resistant samples, an additional 10 % (volume fraction)
HCl 37 % (mass fraction) may be used in combination with microwave digestion. The 5 g/l solutions are
further diluted (1/200) with 5 % (volume fraction) HNO while adding 50 µg/l of Sc, Y, Rh and Lu as internal
standards. ICP measurement and standard preparation can be derived from ISO 22036.
5 Sampling
Take a representative sample of the product to be tested, in accordance with ISO 15528.
WARNING — The sample shall not be dried before testing, and any portion of the sample not used
shall not be returned to the sample container after having been manipulated.
6 Determination of residue on sieve
6.1 Principle
A suitable test portion of the sample is passed through an air-jet sieve apparatus, having sieves with nominal
mesh apertures of 45 µm, 75 µm and 125 µm. The residue on each of these sieves is determined.
6.2 Apparatus
6.2.1 Sieves, circular, with a sieving area of diameter 200 mm and with nominal mesh apertures of 45 µm,
75 µm and 125 µm, conforming to ISO 565. A transparent lid shall be provided to cover the sieve during use.
6.2.2 Air-jet sieve apparatus (see Figure 1), consisting of a cylindrical casing which contains a sieve (see
6.2.1). The base of the casing has an outlet (to which an extractor fan is connected) and an air inlet to permit
the injection of air.
−1 −1
The air inlet is connected to a jet rotating at 20 min to 25 min and consists of a slot-shaped nozzle located
beneath and very close to the sieve (see Figure 1). When the jet rotates, it blows air continuously through
the sieve, preventing the powder particles from settling. The air is extracted through the outlet, drawing the
finer particles through the sieve. The flow of air is controlled by adjusting a slot at the outlet.
The vacuum obtained shall be 1 250 Pa or lower.

Key
1 transparent lid
2 sieve
3 casing
4 rotating jet
5 manometer
6 adjustable slot
a
Air inlet.
b
To extractor fan.
Figure 1 — Air-jet sieve apparatus
6.2.3 Timer (for example a stopwatch), recording to the nearest 1 s or better. It may be equipped with a
switch for stopping the motor of the sieve apparatus (6.2.2).
6.2.4 Analytical balance, capable of weighing at least 50 g to the nearest 1 mg.
6.2.5 Mallet, of light construction, with a plastic head, suitable for tapping the apparatus to dislodge
powder adhering to the lid and sieve.
6.2.6 Clean brush
6.2.7 Stainless-steel boat
6.3 Checking and cleaning the sieve
Check that the sieve is clean, undamaged and not blocked by material used in a previous determination. A
magnifying glass of sufficient magnification is recommended to aid this inspection.
If cleaning of the sieve is necessary, an ultrasonic system is recommended for this purpose. It is also possible
to clean the sieve by turning it upside down on a clean sheet of paper and tapping vigorously to eliminate
any residual particles.
6.4 Procedure
Carry out the determination in duplicate.
6.4.1 Weigh, to the nearest 1 mg, a test portion of approximately 50 g (m ).
6.4.2 Secure the 45 µm sieve (6.2.1) in position in the sieve apparatus (6.2.2) and transfer the test portion
to the sieve.
6.4.3 Cover the sieve with the transparent lid, switch on the extractor fan and sieve apparatus (6.2.2)
and tap the lid and the sieve lightly from time to time with the mallet (6.2.5) to distribute the material and
dislodge adhering particles.
6.4.4 After 120 s, switch off the apparatus and remove the transparent lid and sieve. Recover the sieve
residue by turning the sieve upside down on a clean sheet of paper and tapping vigorously to ensure that all
particles are recovered.
6.4.5 Weigh the stainless-steel boat (6.2.7) to the nearest 1 mg (m ). Transfer the sieve residue to it and
reweigh to the nearest 1 mg (m ).
6.4.6 Repeat the operations described in 6.4.1 to 6.4.5 with the 75 µm sieve and then with the 125 µm
sieve on fresh 50 g portions of the sample.
6.5 Expression of results
Calculate the residue on each sieve, R, expressed as mass fraction in percent, using Formula (1):
mm−
()
R= ×100 (1)
m
where
m is the mass, in grams, of the test portion;
m is the mass, in grams, of the steel boat;
m is the mass, in grams, of the boat and the sieve residue.
If the two results (duplicates) for each sieve differ by more than one tenth of the maximum limit for that
sieve in Table 2, repeat the procedure.
Calculate the mean of two valid results (replicates) and report the result to three decimal places for the
125 µm sieve, two decimal places for the 75 µm sieve and one decimal place for the 45 µm sieve.

7 Determination of total zinc content
7.1 Principle
The zinc is titrated against (ethylenedinitrilo)tetraacetic acid (EDTA) solution.
7.2 Reagents
During the analysis, use only reagents of recognized analytical grade and only water of at least grade 3 purity
as specified in ISO 3696.
®3)
7.2.1 Hydrochloric acid, CAS Registry Number 7647-01-0, concentrated, 37 % (mass fraction),
ρ ≈ 1,19 g/ml.
7.2.2 Hydrochloric acid, CAS RN 7647-01-0, diluted 1 + 4.
Dilute 200 ml of concentrated hydrochloric acid (7.2.1) to 1 l with water.
7.2.3 Sulfuric acid, CAS RN 7664-93-9, diluted 1 + 1.
Slowly add, while cooling, 1 part by volume of concentrated sulfuric acid [approximately 96 % (mass
fraction), ρ ≈ 1,84 g/ml] to 1 part by volume of water.
7.2.4 Nitric acid, CAS RN 7697-37-2, concentrated, approximately 68 % (mass fraction), ρ ≈ 1,42 g/ml.
7.2.5 Ammonia solution, CAS RN 1336-21-6, approximately 25 % (mass fraction), ρ ≈ 0,81 g/ml.
7.2.6 Buffer solution
Dissolve 200 g of hydroxylammonium chloride (NH OH∙HCl) (CAS RN 5470-11-1) in approximately 300 ml of
water. Dissolve 28 g of sodium hydroxide (CAS RN 1310-73-2) in approximately 300 ml of water. Combine the
two solutions, cool and dilute to 1 l with water.
7.2.7 (Ethylenedinitrilo)tetraacetic acid (EDTA), disodium salt dihydrate, CAS RN 6381-92-6, standard
volumetric solution.
7.2.7.1 Preparation
Weigh, to the nearest 1 mg, about 20 g of disodium EDTA dihydrate, dissolve in water and make up to 1 l.
Store in a polyethylene bottle.
7.2.7.2 Standardization
Weigh, to the nearest 1 mg, approximately 1,5 g of 99,99 % pure zinc metal (m ) into a 250 ml beaker. Dissolve
in 20 ml of hydrochloric acid (7.2.1) and add 1 ml or 2 ml of nitric acid (7.2.4). After complete dissolution,
transfer quantitatively into a 500 ml volumetric flask, make up to the mark with water and mix thoroughly.
Pipette 50 ml of the zinc solution into a 500 ml conical flask. Add 200 ml of water and 3 drops of bromothymol
blue indicator (7.2.9), followed by ammonia solution (7.2.5), drop by drop, until the colour changes to blue.
Then add dilute hydrochloric acid (7.2.2) until the yellow colour returns. Finally add 20 ml of buffer solution
(7.2.6) and 3 drops of xylenol orange indicator (7.2.8) and titrate with EDTA solution (7.2.7.1) until the red
colour changes to pale yellow. ®
3) Chemical Abstracts Service (CAS) Registry Number is a trademark of the American Chemical Society (ACS). This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the
product named. Equivalent products may be used if they can be shown to lead to the same results.

Calculate the zinc equivalent of the EDTA solution, ρ(Zn), expressed in grams per millilitre (i.e. the mass, in
grams, of zinc forming a complex with 1 ml of EDTA solution), using Formula (2):
m ×50 m
0 0
ρ()Zn = = (2)
500×V 10×V
0 0
where
m is the mass, in grams, of zinc metal used;
V is the volume, in millilitres, of EDTA solution used for the titration.
Carry out the titration three times and calculate the mean value of the zinc equivalent ρ(Zn), in grams per
millilitre.
7.2.8 Xylenol orange, CAS RN 1202864-39-8, 1 g/l indicator solution of the sodium salt in water.
7.2.9 Bromothymol blue, CAS RN 76-59-5, 1 g/l indicator solution in 96 % (volume fraction) ethanol.
7.3 Procedure
7.3.1 Test portion
Weigh, to the nearest 1 mg, 1,5 g
...