ASTM B809-95(2003)
(Test Method)Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")
Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")
SCOPE
1.1 This standard covers equipment and test methods for determining the porosity of metallic coatings, where the pores penetrate down to a silver, copper, or copper-alloy substrate.
1.2 This test method is suitable 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, and palladium, or their alloys.
1.3 This test method is designed to determine whether the porosity level is less than or greater than some value which by experience is considered by the user to be acceptable for the intended application.
1.4 Recent reviews of porosity testing and testing methods can be found in the literature. Guide B 765 is suitable to assist in the selection of porosity tests for electrodeposits and related metallic coatings. Other porosity test standards are Test Methods B 735, B 741, B 798, and B 799.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazards statements, see Section 8.
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Designation:B809–95 (Reapproved 2003)
Standard Test Method for
Porosity in Metallic Coatings by Humid Sulfur Vapor
(“Flowers-of-Sulfur”)
This standard is issued under the fixed designation B 809; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope B 735 Test Method for Porosity in Gold Coatings on Metal
Substrates by Nitric Acid Vapor
1.1 This standard covers equipment and test methods for
B 741 Test Method for Porosity in Gold Coatings on Metal
determining the porosity of metallic coatings, where the pores
Substrates by Paper Electrography
penetrate down to a silver, copper, or copper-alloy substrate.
B 765 Guide for Selection of Porosity Tests for Electrode-
1.2 This test method is suitable for coatings consisting of
posits and Related Metallic Coatings
single or combined layers of any coating that does not
B 798 Test Method for Porosity in Gold or Palladium
significantly tarnish in a reduced sulfur atmosphere, such as
Coatings on Metal Substrates by Gel-Bulk Electrography
gold, nickel, tin, tin-lead, and palladium, or their alloys.
B 799 Test Method for Porosity in Gold and Palladium
1.3 This test method is designed to determine whether the
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
porosity level is less than or greater than some value which by
experience is considered by the user to be acceptable for the
3. Terminology
intended application.
3.1 Definitions—Many terms used in this test method are
1.4 Recent reviews of porosity testing and testing methods
,
2 3 defined in Terminologies B 374 and B 542.
can be found in the literature. Guide B 765 is suitable to
3.2 Definitions of Terms Specific to This Standard:
assist in the selection of porosity tests for electrodeposits and
3.2.1 corrosion products—reaction products of the basis
related metallic coatings. Other porosity test standards are Test
metal or underplate, that protrude from, or are otherwise
Methods B 735, B 741, B 798, and B 799.
attached to, the coating surface after the test exposure.
1.5 The values stated in SI units are to be regarded as the
3.2.2 measurement area—in this test method,thatportionor
standard. The values given in parentheses are for information
portions of the surface that is examined for the presence of
only.
porosity. The measurement area shall be indicated on the
1.6 This standard does not purport to address all of the
drawings of the parts, or by the provision of suitably marked
safety concerns, if any, associated with its use. It is the
samples.
responsibility of the user of this standard to establish appro-
3.2.3 metallic coatings—in this test method, include plat-
priate safety and health practices and determine the applica-
ings, claddings, or other metallic coatings applied to the
bilityofregulatorylimitationspriortouse.Forspecifichazards
substrate. The coating can comprise a single metallic layer or
statements, see Section 8.
a combination of metallic layers.
2. Referenced Documents 3.2.4 porosity—the presence of any discontinuity, crack, or
hole in the coating that exposes a different underlying metal
2.1 ASTM Standards:
4 (see Guide B 765).
B 374 Terminology Relating to Electroplating
3.2.5 significant surface— of a coated part, is that portion
B 542 Terminology Relating to Electrical Contacts and
5 (or portions) of the coating surface that is essential to the
Their Use
serviceability or function of the part, or which can be the
source of corrosion products or tarnish films that interfere with
This test method is under the jurisdiction ofASTM Committee B08 on Metallic
the function of the part. For many plated products, the critical
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
surface is identical to the measurement area.
Test Methods.
3.2.6 tarnish—reaction products of copper or silver with
Current edition approved Feb. 10, 2003. Published May 2003. Originally
approved in 1990. Last previous edition approved in 1995 as B 809 – 95.
oxygen or reduced sulfur (that is, hydrogen sulfide (H S) and
Clarke, M., “Porosity and Porosity Tests,” Properties of Electrodeposits, Sard,
elemental sulfur vapor, but not sulfur dioxide (SO ) or other
Leidheiser, and Ogburn, eds., The Electrochemical Society, 1975, p. 122.
3 sulfur oxides). They consist of thin films or spots that do not
Krumbein, S. J., “Porosity Testing of Contact Platings,” Transactions of the
Connectors and Interconnection Technology Symposium, Philadelphia, PA, October protrude significantly from the surface of the metallic coating
1987, p. 47.
(in contrast to corrosion products).
Annual Book of ASTM Standards, Vol 02.05.
Annual Book of ASTM Standards, Vol 02.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B809–95 (2003)
3.2.7 tarnish creepage—movement of tarnish films across cracks in the top coating if such pores or cracks do not
the surface of the coating, the tarnish having originated either penetrate through the nickel underplate overlaying the copper.
from pores or cracks in the coating or from areas of bare silver, 5.6 Thelevelofporosityinthecoatingthatmaybetolerable
copper, or copper alloy near the measurement area (as in a cut depends on the severity of the environment that the product is
edge). likely to encounter during service or storage.Also, the location
3.2.8 underplate(s)—ametalliccoatinglayer(s)betweenthe of the pores on the surface is important. If the pores are few in
substrate and the topmost layer or layers. The thickness of an number or away from the significant surfaces, their presence
underplate is usually greater than 1 µm (40 µin.). can often be tolerated.
5.7 The present test method can be used on samples of
4. Summary of Test Method variousgeometries,suchascurvedsurfaces.Itcanalsobeused
for selective area coatings, if allowance is made for tarnish
4.1 The test specimens are suspended over “flowers-of-
creepage from bare copper alloy areas.
sulfur” (powdered sulfur) in a vented container at controlled
5.8 This test method is destructive in that it reveals the
elevated relative humidity and temperature. Elemental sulfur
presence of porosity by contaminating the surface with tarnish
vapor, which always exists in equilibrium with sulfur power in
films. Any parts exposed to this test method should not be
a closed system, attacks any exposed silver, copper, or copper
placed in service.
alloy, such as at the bottom of pores. Brown or black tarnish
5.9 The relationship of porosity levels revealed by this test
spots indicate porosity.
method to product performance and service life must be made
4.2 Exposure periods may vary, depending on the extent of
by the user of the test through practical experience or by
porosity to be revealed.
judgment. Thus, absence of porosity in the coating may be a
4.3 This test involves tarnish or oxidation (corrosion) reac-
requirement for some applications, while a few pores on the
tions in which the products delineate defect sites in coatings.
significant surfaces may be acceptable for others.
Since the chemistry and properties of these products may not
resemble those found in natural or service environments, this
6. Apparatus
test is not recommended for prediction of product performance
6.1 Test Vessel—May be any convenient-size vessel of
unless correlation is first established with service experience
glass, acrylic-resin (or of any other material that is not affected
(but see 5.3).
by high humidity or sulfur), such as a glass desiccator of 9 to
10 L capacity. It should have a lid or cover capable of being
5. Significance and Use
plugged with a stopper. The stopper shall havea1to4mm
5.1 A major use of this test procedure is for determining
diameter hole through it to serve as a vent.
coating quality. Porosity tests are indications of the complete-
6.2 Sample Fixture or Holders—Supports or hangers shall
nessofprotectionorcoverageofferedbythecoatings,sincethe
be made from material such as glass or acrylic plastic that will
coatings described in 1.2 are intended to be protective when
not be affected by sulfur or high humidity, and shall be
properly applied. The porosity test results are therefore a
arranged so that the samples will be at least 75 mm away from
measure of the deposition process control.
the humidity controlling solution or sulfur powder (see 6.3).
5.2 Aparticular purpose of the humid sulfur vapor test is for
The samples shall also be at least 25 mm from the vessel walls
determining the quality of underplates of nickel or nickel alloy
and at least 10 mm from other samples or other surfaces. Do
in those finish systems that have thin, 1.2 µm or less (50 µin. or
notuseadesiccatorplate.Thefixtureshallnotcovermorethan
less) top layers above the nickel, since porosity in the under-
20 % of the vessel’s cross-sectional area so that air movement
plate usually continues into such top layers.
within the vessel will not be restricted during the test.
5.3 The humid sulfur vapor test is often used as an envi-
6.3 Glass Dish—Petri or other shallow dish approximately
ronmental test to simulate many indoor humid atmosphere
15 cm in diameter to hold powdered sulfur. Dish may be
tarnishingandtarnishcreepageeffects.However,thechemistry
supported above the constant humidity solution with plastic
and properties of these tarnish films may not resemble those
blocks, or floated on the liquid.
found in other service environments. For such product perfor-
6.4 Oven, Air-circulating, capable of maintaining test vessel
mance evaluations, the test should only be used in combination
at a temperature of 50 6 2°C (122 6 4°F).
with other performance evaluation tests, as specified in the
6.5 Temperature and Relative Humidity (RH) Sensor, with a
referencing document for that product.
remote sensor probe having a range of approximately 76 to
5.4 Porositytestsdifferfromcorrosionandagingtests,since
95 % RH at 50°C, which can be kept in the desiccator during
the latter are intended to measure the chemical inertness of the
test.
coating. In contrast, in a good porosity test procedure the
6.6 Microscope, Optical, Stereo, 10 3—It is preferred that
corrosive agent should not attack the coating. It must instead,
one eyepiece contain a graduated reticle for measuring the
clean,depolarize,oractivatethesubstratemetalexposedbythe
diameter of tarnish spots. The reticle shall be calibrated for the
pore, or both, and attack it sufficiently to cause reaction
magnification at which the microscope is to be used.
products to fill the pore to the surface of the coating.
6.7 Light Source, incandescent or circular fluorescent.
5.5 The humid sulfur test is highly sensitive, and is capable
of detecting virtually all porosity that penetrates down to
copper or copper alloys. Since nickel is not attacked by moist
The Hygrodynamics Hygrometer, manufactured by Newport Scientific, Inc.,
sulfur vapor at 100°C or less, this test will not detect pores or has been found satisfactory for this purpose.
B809–95 (2003)
FIG. 1 Typical Test Equipment Setup
7. Reagents 9.1.3 Duringequilibration,opendesiccatoroccasionallyand
stir contents.As the temperature in the vessel approaches 50°C
7.1 Potassium Nitrate (KNO )—American Chemical Soci-
(122°F), as indicated by the temperature probe, adjust oven
ety analyzed reagent grade, or better.
temperature as needed to stabilize the vessel at 50°C.
7.2 Sulfur, Sublimed (“Flowers-of-Sulfur”), N.F. or labora-
9.1.4 Fill the glass dish half-full with sulfur (break up any
tory grade.
large lumps), and place the dish on supports above the
8. Safety and Health Precautions potassium nitrate solution or float the dish directly on the
solution (see Fig. 1).
8.1 All of the normal precautions shall be observed in
9.1.5 Replace the lid and insert the vented stopper in the lid
handling the materials required for this test. This shall also
opening. Monitor the vessel temperature over several hours,
include,butnotbelimitedto,procuringandreviewingmaterial
and adjust oven temperature as needed to keep the vessel at 50
Safety Data Sheets (MSDS) that meet the minimum require-
6 2°C (122 6 4°F). When stability has been attained, and the
ments of the U.S. Occupational Safety and HealthAdministra-
relative humidity is in the 86 to 90 % range, the apparatus is
tion (OSHA) Hazard Communication Standard for all chemi-
ready for insertion of test samples.
cals used in cleaning and testing, and observing the
recommendations given.
NOTE 3—The system described in this section may be reused for many
subsequent tests without replacing the chemicals, and will remain stable
9. Procedure
for up to 6 months as long as the chemicals do not become contaminated
with corrosion products or dirt. If allowed to cool, the potassium nitrate
9.1 Equilibration of Test Vessel—For the initial series of
mixture will solidify, but it will liquify again when the vessel is reheated
tests, the test vessel shall be prepared for equilibration at least
and the solution stirred. Crusts and lumps of hardened potassium nitrate
a day before the first exposure.
should be broken up and stirred into the slurry. Add a few millilitres of
deionizedwaterifnecessarytoreturnthesolutiontoitsoriginalcondition.
NOTE 1—For all subsequent tests, the initial 24-h equilibration proce-
dures do not have to be repeated (see Note 2 and 9.8).
9.2 Preparation of Test Samples:
9.1.1 Place the test vessel in the oven, with sample supports
9.2.1 Handle samples as little as possible, even prior to
in place. Make a saturated solution of potassium nitrate,
cleaning, and only with tweezers, microscope lens tissue, or
prepared by adding approximately 200 g of the salt to
clean soft cotton gloves.
approximately 200 mL of deionized water, with stirring, and
9.2.2 Prior to being cleaned, the samples shall be prepared
place it in the bottom of the vessel.
so that the measurement areas may be viewed easily through
themicroscope.Ifsamplesarepartofassembledproducts,they
NOTE 2—The saturated solution will contain undissolved potassium
may need to be disassembled to ensure proper access to these
nitrate salt. This condition is necessary to achieve a constant humidity
atmosphere above the solution. areas by the test environment. Since the test is specific to the
planted metallic portions of the product, the latter should be
9.1.2 Place lid on the vessel (do not seal it with grease),
separated from plastic housings, etc., whenever possible, prior
insert the temperature-humidity probe through t
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