EN ISO 12687:1998
(Main)Metallic coatings - Porosity tests - Humid sulfur (flowers of sulfur) test (ISO 12687:1996)
Metallic coatings - Porosity tests - Humid sulfur (flowers of sulfur) test (ISO 12687:1996)
Specifies a method of revealing discontinuities and porosity in metallic coatings, where they penetrate the coating layer down to a substrate. Especially useful for coatings consisting of single or combined layers.
Metallische Überzüge - Prüfung der Porosität - Naß-Schwefelverfahren (mit Schwefelblüte) (ISO 12687: 1996)
Diese internationale Norm legt ein Verfahren zum Sichtbarmachen von Fehlstellen und Porosität in metallischen Überzügen fest, bei denen sie die Überzugsschicht oder Zwischenschichten bis auf den aus Silber, Kupfer oder einer Kupferlegierung bestehenden Grundwerkstoff durchdringen. Dieses Verfahren ist besonders nützlich für Überzüge, die aus einer einzigen oder kombinierten Schicht eines Überzugs bestehen, der nur unwesentlich in einer aus redurziertem Schwefel bestehenden Atmosphäre anläuft, wie z.B. Gold, Nickel, Zinn-Blei-Palladium und deren Legierungen.
Revêtements métalliques - Essais de porosité - Essai à la fleur de soufre par voie humide (ISO 12687:1996)
Kovinske prevleke - Ugotavljanje poroznosti - Preskus z žveplovimi parami v vlažni atmosferi (žvepleni cvet) (ISO 12687:1996)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-1999
Kovinske prevleke - Ugotavljanje poroznosti - Preskus z žveplovimi parami v vlažni
atmosferi (žvepleni cvet) (ISO 12687:1996)
Metallic coatings - Porosity tests - Humid sulfur (flowers of sulfur) test (ISO 12687:1996)
Metallische Überzüge - Prüfung der Porosität - Naß-Schwefelverfahren (mit
Schwefelblüte) (ISO 12687: 1996)
Revetements métalliques - Essais de porosité - Essai a la fleur de soufre par voie
humide (ISO 12687:1996)
Ta slovenski standard je istoveten z: EN ISO 12687:1998
ICS:
25.220.40 Kovinske prevleke Metallic coatings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
IS0
INTERNATIONAL
STANDARD
First edition
1996-12-15
Metallic coatings - Porosity tests -
Humid sulfur (flowers of sulfur) test
Revetements m&alliques - Essais de porositk - Essai ;i la fleur de
soufre par voie humide
Reference number
IS0 12687:1996(E)
IS0 12687:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 12687 was prepared by Technical Committee
lSO/TC 107, Metallic and other inorganic coatings, Subcommittee SC 7,
Corrosion tests.
Annexes A and B of this International Standard are for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization
for Standardization
Case Postale 56 l CH-121 1 Geneve 20 l Swit :zerland
Printed in Switzerland
IS0 12687:1996(E)
INTERNATIONAL STANDARD @ IS0
Humid sulfur (flowers
Metallic coatings - Porosity tests -
of sulfur) test
1 Scope
This International Standard specifies a method of revealing discontinuities and porosity in metallic coatings, where
they penetrate the coating layer or layers down to a silver, copper or copper-alloy substrate.
This method is especially useful for coatings consisting of single or combined layers of any coating that does not
significantly tarnish in a reduced-sulfur atmosphere, such as gold, nickel, tin, tin-lead palladium and their alloys.
This test method is designed to show whether or not the coating meets the requirement concerning an acceptable
porosity level specified by the user. The value specified is usually determined by user’s experience to be
acceptable for the intended application.
Recent reviews of porosity testing and test methods can be found in the literature [IL 121. An IS0 general guide to
porosity tests for metallic and other inorganic coatings is available as IS0 10308:1995, Metallic coatings - Review
of porosity tests.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
IS0 2079:1981, Surface treatment and metallic coatings - General classification of terms.
IS0 2080:1981, Electroplating and related processes - Vocabulary.
- Specification and test methods.
IS0 3696: 1987, Water for analytical laboratory use
3 Definitions
For the purposes of this International Standard, the following definitions apply (other relevant definitions can be
found in IS0 2079 and IS0 2080).
3.1 corrosion products: Chemical products, derived from the substrate that usually protrude from the surface at
discontinuities. The chemical reaction products form during the test and can be readily examined after the test
exposure. They cannot be readily removed by mild air dusting [see clause 10, item b) 21.
0 IS0
IS0 12687:1996(E)
3.2 discontinuity: Any opening through an otherwise continuous coating. Typically the openings are pores or
cracks in the coating. They may also be voids or breaks in the coating caused by mechanical damage such as
scratches or non-conductive inclusions in the basis materials.
3.3 measurement area: In this method, that portion or portions of the surface that is examined for the presence
of porosity. The measurement area may be indicated on the drawings of the parts or by the provision of suitably
marked samples.
3.4 metallic coatings: Autocatalytic coatings, chemical (non-electrolytic) platings, claddings, electroplatings and
hot-dip coatings applied to the substrate. The coating may comprise a single metallic layer or a combination of
metallic layers.
3.5 pore: A hole, typica microscopic in size and ra ndomly located, often with a circular shape, that penetrates
IlY
he bas is-metal.
through the coating to an un derlying coat ing or t
3.6 porosity: The presence of any crack, d iscontinuity, hole or scratch in the coating that exposes a different
underlying metal.
3.7 significant surface: That portion or portions of the coating surface that is essential to the serviceability or
function of the part, or which can be the source of corrosion products or tarnish films that interfere with the
function of the part. For many coated products, the significant surface is identical to the measurement area.
3.8 tarnish: The reaction products of copper or silver with oxygen or reduced sulfur (i.e. HzS and elemental sulfur
vapour, but not SO2 or other sulfur oxides). They consist of thin films or marks and spots that do not protrude
significantly from the surface of the metallic finish (in contrast with corrosion products).
3.9 tarnish creepage: Movement of tarnish films across the surface of the coating. The tarnish originates either
from pores or cracks in the coating or from areas of bare basis metal near the measurement area (as in a cut edge).
It is also called creep corrosion.
3.10 underplate: A metallic coating layer between the substrate and the topmost layer or layers. The thickness
of an underplate is usually greater than 1 pm. There may be more than one.
4 Principle
This test relies on the formation of basis metal or underplate sulfides and oxides, formed by reaction with sulfur
vapour in a humid atmosphere and exposed through discontinuities in the metallic coating. The sulfide corrosion
products of both silver and copper and copper oxide form black or brown-coloured markings or spots that are
readily observed by visual inspection.
5 Summary of method
Test specimens are suspended over flowers of sulfur (powdered sulfur) in a container equipped with a vent and at
controlled, elevated relative humidity and temperature. Elemental-sulfur vapour, which always exists in equilibrium
with sulfur powder in a closed system, attacks any exposed copper, copper alloy, silver or silver alloy such as that
found at the bottom of pores. Brown or black tarnish marks or spots indicate porosity.
Exposure periods may vary, depending on the extent of porosity to be revealed.
This test involves in which
tarnish or oxi dation (corrosion) reactions the corrosion produ cts deli neate defect sites in
coatings. The the mistry and p roperties of the corrosion products formed as a result test usually do not
of the
@ IS0 IS0 12687:1996(E)
resemble those found in natural or service environments. Therefore, this test is not recommended for prediction of
product performance unless correlation is first established with service experience.
6 Reagents
6.1 Purity
The potassium nitrate used shall be of recognized analytical-reagent grade. The water used shall be distilled or
deionized and have a conductivity not greater than 20 pS/cm (measured as specified in IS0 3696). The sulfur shall
be of commercial laboratory grade.
6.2 Potassium nitrate solution
Prepare a saturated solution of potassium nitrate (KN03) by adding approximately 200 g of the reagent to
approximately 200 ml of water (see 6.1).
potassium nitrate salt. This condition is necessary to achieve a
NOTE - The saturated solution will contain undissolved
constant-humidity atmosphere above the solution.
6.3 Dry reagent
Sulfur, precipitated (flowers of sulfur).
7 Apparatus
7.1 Test vessel, consisting of any convenient-sized transparent vessel of glass or acrylic resin (or any other
material that it not affected by high humidity or sulfur), such as a glass desiccator of approximately 10 litre capacity.
It shall have a lid or cover with an access hole capable of being plugged with a stopper. The hole shall be large
enough to allow the insertion of the humidity sensor with a remote read-out device into the vessel. The stopper
shall contain a 1 mm to 4 mm diameter hole to serve as a vent.
7.2 Sample supports, designed as holders or hangers and made from material such as glass, acrylic resin or
polypropylene which will not be affected by sulfur or high humidity, and arranged so that the test specimen will be
at least 75 mm distance from the humidity-controlling solution and the sulfur powder (see 7.3). The test specimen
shall also be at least 25 mm from the vessel walls and at least 10 mm from other test specimen and other
surfaces. Do not use a desiccator plate as a primary support; it may be used as an under-support. The fixture and
any supports shall not cover more than 20 % of the vessel’s cross-sectional area so that air movement (convection)
within the vessel shall not be restricted during the test.
7.3 Glass dish, consisting of a petri or other shallow dish approximately 150 mm in diameter to hold powdered
sulfur. The dish may be supported above the constant-humidity solution with plastic blocks or floated on the liquid.
The free space of the liquid surface shall be large enough to guarantee equilibrium conditions in the test vessel for
the entire test period.
7.4 Air-circulating oven, capable of maintaining the test vessel at a temperature of 50 “C + 2 “C.
7.5 Thermometer or other temperature sensor, having a range of at least 40 “C + 1 “C to 60 “C + 1 OC, which
can be kept in the test vessel during the test.
7.6 Dielectric-detector hygrometer, with a remote sensor probe that can be placed in the test vessel, for the
range of 75 % to 95 % RH.
@ IS0
IS0 12687:1996(E)
7.7 Optical stereomicroscope, magnification x 10. One eyepiece should preferably contain a graduated reticule
for measuring the diameter of tarnish spots. If fitted, the reticule shall be calibrated for the magnification at which
the microscope is to be used.
78 . Light source, incandescent or circular fluorescent.
8 Test specimen preparation
specimens, and then handle only with tweezers, microscope lens tissue or
Avoid unnece ssary handling of the
any
clean, soft cotton
or nylon gloves.
Prior to the test, inspect the sample at x 10 magnification under the stereomicroscope (7.7) for any evidence of
particulate matter. If present, the particles shall be removed by dusting with clean, oil-free air. Then, thoroughly
clean the particle-free samples by gently rinsing with solvents or solutions that do not contain CFCs, chlorinated
hydrocarbons or other known ozone-destroying compounds, and air-dry with clean air. A hot, analytical-reagent-
grade methanol, ethanol, denatured ethanol or isopropanol dip is often useful in speeding up the drying.
The following procedure has been found to be useful in avoiding the use of chlorinated hydrocarbons:
Keep individual specimens separated if there is a possibility of damage to the measurement area during the
a)
various cleaning steps.
b) Clean the specimens for 5 min in an ultrasonic cleaner which contains a hot (65 “C to 85 “C) 2 % aqueous
solution of a mildly alkaline (pH 7,5 to 10) detergent.
c) After ultrasonic cleaning, rinse thoroughly under warm running tap water for at least 5 s.
d) Rinse ultrasonically for 2 min in fresh distilled or deionized water (see 6.1) to remove the last detergent
residues.
e) Immerse in fresh analytical-reagent-grade methanol, ethanol, denatured ethanol or isopropanol, and
ultrasonically “agitate” for at least 30 s in order to remove the water from the specimens.
f) Remove and air-dry specimens until the alcohol has completely evaporated. If an air-dusting is used as an aid
to drying, the air shall be oil-free, clean and dry.
g) Do not touch the measurement area of the specimens with bare fingers after cleaning.
Re-inspect samples under x 10 magnification for particulate matter on the surface. If particles are found, repeat the
cleaning step. Surface cleanliness is extremely important. Contaminants, such as plating salts and flakes of metal,
may give erroneous indications of porosity.
Omit the cleaning steps for samples having tarnish-inhibiting or lubricant coatings, or both, if it is desired to
determine the efficiency of the coating in the reduced-sulfur atmosphere.
s so that the measurement areas (i.e. the significant
For nominal porosity-testing purpose s, prepare the specimen
surfaces) have optimum exposure to the test environment.
...
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