ISO 17925:2004

INTERNATIONAL ISO
STANDARD 17925
First edition
2004-11-01
Zinc and/or aluminium based coatings on
steel — Determination of coating mass
per unit area and chemical
composition — Gravimetry, inductively
coupled plasma atomic emission
spectrometry and flame atomic
absorption spectrometry
Revêtements à base de zinc et/ou d'aluminium sur acier —
Détermination de la masse surfacique et de la composition chimique du
revêtement — Gravimétrie, spectrométrie d'émission atomique avec
plasma induit par haute fréquence et spectrométrie d'absorption
atomique dans la flamme
Reference number
©
ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
1 Scope. 1
2 Normative references . 1
3 Principle . 2
4 Reagents . 2
5 Apparatus. 5
5.1 General. 5
5.2 Inductively coupled plasma atomic emission spectrometer (ICP-AES). 5
5.3 Flame atomic absorption spectrometer (FAAS) . 6
5.4 Platinum crucible . 7
6 Sampling and samples . 7
7 Determination procedure . 7
7.1 Sample preparation. 7
7.2 Determination procedure for mass per unit area . 7
7.3 Procedure of determination of chemical composition by inductively coupled plasma
atomic emission spectrometric method. 8
7.4 Procedure of determination of chemical composition by flame atomic absorption method
— zinc, aluminium, nickel and iron contents. 14
8 Expression of results. 14
8.1 Expression of result in mass per unit area .14
8.2 Expression of result of chemical compositions . 15
9 Test report. 17
Annex A (informative) Analyte content . 18
Annex B (informative) Additional information on the international cooperative tests. 19
Annex C (informative) Graphical representation of precision data. 22

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 2.
The main task of technical committees is to prepare International Standards. 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 document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 17925 was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 1, Methods of
determination of chemical composition.

iv © ISO 2004 – All rights reserved

INTERNATIONAL STANDARD ISO 17925:2004(E)

Zinc and/or aluminium based coatings on steel —
Determination of coating mass per unit area and chemical
composition — Gravimetry, inductively coupled plasma atomic
emission spectrometry and flame atomic absorption
spectrometry
1 Scope
This International Standard specifies methods of determining the coating mass per unit area by gravimetry
and chemical composition on one side-surface of zinc- and/or aluminium-based coatings on steel by means of
inductively coupled plasma atomic emission spectrometric or flame atomic absorption spectrometry. For
example, this test method applies for zinc and/or aluminium based coatings on steel such as galvanize (hot
dip and electrolytic), galvaneal (hot-dip), zinc-nickel electrolytic, zinc-5 % aluminium coating (hot-dip) and zinc-
55 % aluminium coating (hot-dip). Galvanizing gives a pure zinc coating. Galvanealling gives a zinc-iron
alloyed coating. Zinc-nickel electrolytic methods give zinc-nickel alloyed coatings.
This method is applicable to zinc contents between 40 % (mass fraction) and 100 % (mass fraction);
aluminium contents between 0,02 % (mass fraction) and 60 % (mass fraction); nickel contents between 7 %
(mass fraction) and 20 % (mass fraction); iron contents between 0,2 % (mass fraction) and 20 % (mass
fraction); silicon contents between 0,2 % (mass fraction) and 10 % (mass fraction); lead contents between
0,005 % (mass fraction) and 2 % (mass fraction). For example, the applicable elements for these products are
as follows: galvanizing is specified for iron and aluminium; galvanealling is specified for zinc, iron and
aluminium; zinc-nickel electrolytic methods are specified for zinc, iron and nickel; zinc-5 % aluminium coating
is specified for zinc, iron, aluminium and silicon; zinc-55 % aluminium is specified for zinc, iron, aluminium and
silicon.
FAAS determination for the chemical composition of a coating layer is not applicable for zinc.
These test methods are intended as referee methods to test such materials for compliance with mass per unit
area and compositional specifications of International Standards.
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.
ISO 648:1977, Laboratory glassware — One-mark pipettes
ISO 1042:1998, Laboratory glassware — One-mark volumetric flasks
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 5725-2:1994, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic
method for the determination of repeatability and reproducibility of a standard measurement method
ISO 5725-3:1994, Accuracy (trueness and precision) of measurement methods and results — Part 3:
Intermediate measures of the precision of a standard measurement method
ISO 14284:1996, Steel and iron — Sampling and preparation of samples for the determination of chemical
composition
3 Principle
Stripping the coating on one side on the base steel in a mixture of hydrochloric acid solution containing an
inhibitor to prevent the attack on the base steel. Determination of the mass per unit area of coating from the
mass difference of the specimen before and after stripping. Calculating the coating mass as the mass
difference divided by the specimen's surface area.
Dilution of the stripped solution of the coating on one side. Filtration and nebulization of the solution into an
inductively coupled plasma atomic emission spectrometer (ICP-AES) or flame atomic absorption spectrometer
(FAAS). Calculating the chemical compositions of coating layer as the content of the analytical element
divided by the pre-measured coating mass.
Examples of the analytical lines are given in Table 1.
Table 1 — Examples of analytical lines together with interfering elements
ICP-AES FAAS
Analytical line Analytical line
Element
Interfering Interfering
elements elements
nm nm
481,0
Zinc
206,19
309,3
Aluminium 396,15
306,16
232,00
Nickel 231,60 231,10
233,75
271,44 248,33
Iron
259,94 252,29
251,61 251,61
Silicon Aluminium Aluminium
288,16 288,16
Zinc 217,00
Lead 220,35
Aluminium 283,31
4 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
grade 2 water as specified in ISO 3696.
4.1 Hydrochloric acid, HCl, ρ ≈ 1,18 g/ml.
4.2 Hydrochloric acid, HCl, diluted 1+10.
4.3 Nitric acid, HNO , ρ ≈ 1,40 g/lml.
2 © ISO 2004 – All rights reserved

4.4 Nitric acid, HNO , diluted 1+1.
4.5 Mixed acid, prepared by adding 50 ml of nitric acid (4.3) and 10 ml of hydrochloric acid (4.1) to a flask
containing 150 ml of water and mixing.
4.6 Sodium carbonate, Na CO .
2 3
4.7 Hexamethylenetetramine, C H N , capable of preventing acid attack of the base metal while
6 12 4
stripping the coating from the base steel.
4.8 Stripping solution, prepared by transferring from 170 ml to 500 ml of hydrochloric acid (4.1) to a 1 l
graduated cylinder containing from 450 ml to 820 ml of water and adding 3,5 g of hexamethylenetetramine
(4.7) then diluting to the mark with water followed by mixing.
NOTE For an electrolytic zinc coated steel such as one with a lower coating mass, it would be better to use diluted
hydrochloric acid for stripping in order to prevent the dissolution of base steel.
4.9 Stop-off materials, capable of protecting one side of a coated piece of steel sheet while the other side
is being stripped in hydrochloric acid solution, without contaminating the acid solution and either gaining or
losing mass thus avoiding interference with coating mass and chemical composition determination.
NOTE 1 Acid-resistant paints, lacquers or acid-resistant tapes are commonly used as stop-off materials.
NOTE 2 For this purpose mechanical devices may also be used, fastened to the test specimen instead of the above
materials.
4.10 Zinc stock standard solution, 1 000 mg/l, prepared as follows:
weigh, to the nearest 0,000 5 g, 0,5 g of high purity zinc (minimum 99,99 % by mass) and dissolve in 25 ml
hydrochloric acid (4.1). Cool and transfer the solution quantitatively to a calibrated 500 ml one-mark volumetric
flask. Keep the flask at the same temperature as that at which the flask was calibrated. Dilute to the mark with
water and mix.
4.11 Zinc standard solution A, 100 mg/l, prepared as follows:
using a calibrated pipette, transfer 100 ml of the zinc stock standard solution (4.10) into a calibrated 1 000 ml
one-mark volumetric flask. Add 10 ml of hydrochloric acid (4.1). Dilute to the mark with water and mix.
4.12 Zinc standard solution B, 10 mg/l, prepared as follows:
using a calibrated pipette, transfer 100 ml of the zinc standard solution A (4.11) into a calibrated 1 000 ml one-
mark volumetric flask. Add 10 ml of hydrochloric acid (4.1). Dilute to the mark with water and mix.
4.13 Zinc standard solution for matrix matching, 10 000 mg/l, prepared as follows:
weigh, to the nearest 0,01 g, 10 g of high purity zinc (minimum 99,99 % by mass) and dissolve in 200 ml
hydroc
...