Metallic and other inorganic coatings — Simultaneous thickness and electrode potential determination of individual layers in multilayer nickel deposits (STEP test)

This document specifies a method for measuring the thickness of the individual nickel layers in electroplated multilayer nickel coatings and measuring the potential differences between the individual nickel layers in electroplated multilayer nickel coatings. The measurement of coatings or layer systems other than electroplated multilayer nickel coatings is outside the scope of this document.

Revêtements métalliques et autres revêtements inorganiques — Détermination simultanée de l'épaisseur et du potentiel d'électrode de couches individuelles dans des dépôts de nickel multicouches (essai STEP)

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Status
Published
Publication Date
05-Oct-2020
Current Stage
6060 - International Standard published
Start Date
06-Oct-2020
Completion Date
06-Oct-2020
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ISO 16866:2020 - Metallic and other inorganic coatings -- Simultaneous thickness and electrode potential determination of individual layers in multilayer nickel deposits (STEP test)
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INTERNATIONAL ISO
STANDARD 16866
First edition
2020-10
Metallic and other inorganic
coatings — Simultaneous thickness
and electrode potential determination
of individual layers in multilayer
nickel deposits (STEP test)
Revêtements métalliques et autres revêtements inorganiques —
Détermination simultanée de l'épaisseur et du potentiel d'électrode
de couches individuelles dans des dépôts de nickel multicouches
(essai STEP)
Reference number
ISO 16866:2020(E)
ISO 2020
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ISO 16866:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2020 – All rights reserved
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ISO 16866:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Test equipment....................................................................................................................................................................................................... 1

4.1 Construction of the measuring cell........................................................................................................................................ 1

4.2 Composition of the test solution .............................................................................................................................................. 2

5 Requirements .......................................................................................................................................................................................................... 3

6 Sampling ........................................................................................................................................................................................................................ 3

7 Factors influencing measurement accuracy ............................................................................................................................ 3

7.1 Electrolyte ................................................................................................................................................................................................... 3

7.2 Conditioning .............................................................................................................................................................................................. 3

7.3 Ni deposits .................................................................................................................................................................................................. 3

7.4 Surface cleanliness .............................................................................................................................................................................. 3

7.5 Measurement area and contact pressure ......................................................................................................................... 3

7.6 Electrical contact ................................................................................................................................................................................... 4

7.7 Complete dissolution ......................................................................................................................................................................... 4

8 Procedure..................................................................................................................................................................................................................... 4

8.1 General ........................................................................................................................................................................................................... 4

8.2 Measurement ............................................................................................................................................................................................ 4

8.3 Evaluation .................................................................................................................................................................................................... 5

9 Measurement uncertainty .......................................................................................................................................................................... 8

10 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Precision data obtained by a round robin test ..........................................................................10

Bibliography .............................................................................................................................................................................................................................11

© ISO 2020 – All rights reserved iii
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ISO 16866:2020(E)
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.

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 documents 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).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions 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 the European Committee for Standardization (CEN) (as EN 16866:2017)

and was adopted, without modification, by Technical Committee ISO/TC 107, Metallic and other inorganic

coatings.

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.
iv © ISO 2020 – All rights reserved
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ISO 16866:2020(E)
Introduction

The abbreviated term “STEP” represents “Simultaneous Thickness and Electrode Potential

determination”.

The STEP test can be used to measure, in one single operating step, the parameters (thickness of the

individual nickel layers and the potential differences among them) relevant for the course of corrosion

in a multilayer nickel system. Provided suitable instruments are applied, it can also be used to

document them.

The test is a modification of the well-known coulometric method for the measurement of the coating

thickness. This method takes advantage of the fact that, following the anodic dissolution of a nickel

coating, a potential jump takes place of which the magnitude can be measured against a reference

electrode.

Although, nowadays, the STEP test has been incorporated into a number of company standards,

particularly in the automobile industry, there are currently no uniform and generally acknowledged

potential difference values available. At present, values between 80 mV and 150 mV are assumed for

double nickel layers, with the semi-bright nickel layer always being nobler than the bright one.

Likewise, no obligatory numerical values are available, currently, regarding the potential difference

between bright nickel layers and existing special nickel layers (e.g. in the case of micro-porous

chromium plating). According to the current practical experience, the potential difference is larger

than approximately 20 mV, with the bright nickel layer always having to be less noble than the special

nickel layer.
© ISO 2020 – All rights reserved v
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INTERNATIONAL STANDARD ISO 16866:2020(E)
Metallic and other inorganic coatings — Simultaneous
thickness and electrode potential determination of
individual layers in multilayer nickel deposits (STEP test)
1 Scope

This document specifies a method for measuring the thickness of the individual nickel layers in

electroplated multilayer nickel coatings and measuring the potential differences between the individual

nickel layers in electroplated multilayer nickel coatings.

The measurement of coatings or layer systems other than electroplated multilayer nickel coatings is

outside the scope of this document.
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 2177, Metallic coatings — Measurement of coating thickness — Coulometric method by anodic

dissolution
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Test equipment
4.1 Construction of the measuring cell

Figure 1 shows two examples of the typical schematic construction of a measuring cell used for the

simultaneous determination of layer thicknesses and potential differences in multilayer nickel systems.

The cells differ with regard to the implementation of the reference electrode. In Figure 1 a), the

reference electrode is a silver wire coated with silver chloride and positioned at the edge of the cell; in

Figure 1 b), it is a silver ring coated with silver chloride and positioned at the bottom of the cell. With

regard to measurement uncertainty, both variants provide the same result for the measurement of the

potential difference and (following calibration) the measurement of the layer thickness, independent of

the concrete implementation of the reference electrode.

NOTE 1 The silver ring used as the reference electrode in Figure 1 b) is of advantage insofar as the adjustment

of the silver wire, which would otherwise be required, becomes unnecessary, leading to results that are more

exact and more reproducible.

NOTE 2 The circulated volume of electrolyte solution is typically around 0,1 ml per s.

© ISO 2020 – All rights reserved 1
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ISO 16866:2020(E)

a) Measuring cell with silver wire, coated b) Measuring cell with silver ring, coated

with AgCl, used as the reference electrode with AgCl in the electrolyte-wetted area,

used as the reference electrode
Key
1 pump
2 measuring instrument (with constant-current source and voltmeter)
3 reference electrode
4 electrode surface wetted with electrolyte
5 dissolving electrolyte
6 counter electrode (cathode)
7 gasket
8 working electrode (anode, measurement object with nickel layer system)
Figure 1 — Typical schematic constructions of the measuring cell
4.2 Composition of the test solution
Nickel(II)-chloride hexahydrate (NiCl ⋅ 6 H O) 300 g/l
2 2
Sodium chloride (NaCl) 50 g/l
Boric acid (H BO ) 25 g/l
3 3
pH value 3,0
Water of grade 3 in accordance with ISO 3696.
2 © ISO 2020 – All rights reserved
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ISO 16866:2020(E)

The pH value should be complied with as closely as possible. If required, it is adjusted by means of

diluted hydrochloric acid or sodium hydroxide solution.
5 Requirements

The geometry of the parts to be tested shall be such that the measuring cell can be attached to the

surface in a liquid-tight way, at the respective points to be measured.

Prior to this, the surface to be measured shall be appropriately de-chromed and activated (e.g. in a

1:1 dilution of chemically pure, concentrated hydrochloric acid). When selecting the de-chroming

and activating procedures, it shall be ensured that the nickel coating is not visibly damaged by these

procedures.
6 Sampling

Sampling from the ongoing production of parts should be performed in accordance with ISO 2859-1 and

ISO 2859-2. The tolerable margin of error is specified by the client.
7 Factors influencing measurement accuracy
7.1 Electrolyte

Each measurement shall be carried out using a fresh electrolyte. Used electrolytes can result in falsified

measurement results.
7.2 Conditioning

New reference electrodes or ones which have not been in use for an extended period of time shall be

conditioned (creation of a silver chloride layer at the electrode surface) prior to use. The lack of or

inadequate conditioning results in falsified or atypical courses of measurement that cannot be correctly

interpreted. Any conditioning and potentially required cleaning are carried out in accordance with the

instrument manufacturer’s information.

NOTE The conditioning quality is checked on the basis of comparative measurements using reference

standards of known potential differences and layer thicknesses.
7.3 Ni deposits

As a result of repeated measurements, Ni is gradually deposited on the surface of the cathode. From

a certain thickness onwards, these Ni deposits can become dissolved from the cathode and move

around in the electrolyte in the form of “flocs”, leading to very noisy measurement curves and a faulty

evaluation. It is, therefore, necessary to remove any Ni deposits early enough from the surface of the

cathode (this is done mechanically or, in the case of persistent deposits, chemically).

...

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