ASTM B825-02
(Test Method)Standard Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples
Standard Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples
SCOPE
1.1 This test method covers procedures and equipment for determining the relative buildup of corrosion and tarnish films (including oxides) on metal surfaces by the constant-current coulometric technique, also known as the cathodic reduction method.
1.2 This test method is designed primarily to determine the relative quantities of tarnish films on control coupons that result from gaseous environmental tests, particularly when the latter are used for testing components or systems containing electrical contacts.
1.3 This test method may also be used to evaluate test samples that have been exposed to indoor industrial locations or other specific application environments. (See for limitations.)
1.4 This test method has been demonstrated to be applicable particularly to copper and silver test samples (see (1)). Other metals require further study to prove their applicability within the scope of this test method.
1.5 The values stated in SI units are the preferred units. The values provided 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 become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet for this product/material as provided by the manufacturer, to establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use.
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Designation: B 825 – 02
Standard Test Method for
Coulometric Reduction of Surface Films on Metallic Test
1
Samples
This standard is issued under the fixed designation B 825; 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 sion Test Chambers by Change in Mass of Copper Cou-
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pons
1.1 This test method covers procedures and equipment for
B 827 Practice for Conducting Mixed Flowing Gas (MFG)
determining the relative buildup of corrosion and tarnish films
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Environmental Tests
(including oxides) on metal surfaces by the constant-current
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D 1193 Specification for Reagent Water
coulometric technique, also known as the cathodic reduction
method.
3. Summary of Test Method
1.2 This test method is designed primarily to determine the
3.1 In constant-current coulometry, a fixed reduction-
relative quantities of tarnish films on control coupons that
current density is applied to the sample in an electrolytically
result from gaseous environmental tests, particularly when the
conductive solution, and the resulting variations in potential—
latter are used for testing components or systems containing
measured against a standard reference electrode in the same
electrical contacts.
solution—are followed as a function of time. Typically, with
1.3 This test method may also be used to evaluate test
well-behaved surface films, the voltage-time plot should show
samples that have been exposed to indoor industrial locations
a number of horizontal portions, or steps, each corresponding
or other specific application environments. (See 4.6 for limi-
to a specific reduction potential or voltage (Fig. 1). The final
tations.)
potential step, which is always present with all substances,
1.4 Thistestmethodhasbeendemonstratedtobeapplicable
2 corresponds to the reduction of hydrogen ions in the solution
particularly to copper and silver test samples (see (1)). Other
(toformhydrogengas),andrepresentsalimitbeyondwhichno
metals require further study to prove their applicability within
higher potential reduction process can occur.
the scope of this test method.
1.5 The values stated in SI units are the preferred units. The
NOTE 1—As shown in Figs. 1 and 2, a differential circuit is recom-
values provided in parentheses are for information only. mendedtohelpinresolvingtheindividualvoltagestepsbypinpointingthe
corresponding inflection points on the main reduction curve (see 6.2.3).
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.2 From the elapsed times at the various steps, conclusions
responsibility of the user of this standard to become familiar
can often be drawn regarding the corrosion processes that have
with all hazards including those identified in the appropriate
taken place to produce the surface films.Also, calculations can
Material Safety Data Sheet for this product/material as pro-
bemadefromthetimeateachvoltagestepinordertocalculate
vided by the manufacturer, to establish appropriate safety and
the number of coulombs of electrical charge required to
health practices, and determine the applicability of regulatory
complete the reduction process at that particular voltage.
limitations prior to use.
Furthermore, since the reduction of any particular chemical
compound takes place at a characteristic reduction potential or
2. Referenced Documents
voltage range, this voltage can be used to indicate the presence
2.1 ASTM Standards:
of a compound or compounds whose characteristic reduction
B 809 Test Method for Porosity in Metallic Coatings by
potential has already been established under the conditions of
3
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
the test. Under ideal conditions it may also be possible to
B 810 Test Method for Calibration of Atmospheric Corro-
determine the number of reducible compounds present in the
tarnish film.
3.3 Forthepurposeofthistestmethod,tarnishfilmsshallbe
1
This test method is under the jurisdiction of ASTM Committee B02 on
defined as the corrosion products of the reactions of oxygen or
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
B02.11 on Electrical Contact Test Methods.
Current edition approved Oct. 10, 2002. Published December 2002. Originally
published as B 825 - 97. Last previous edition B 825 - 97.
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The boldface numbers in parentheses refer to the list of references at the end of Annual Book of ASTM Standards, Vol 02.04.
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this standard. Annual Book of ASTM Standards, Vol 03.04.
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Annual Book of ASTM Standards, Vol 02.05. Annual Book of ASTM Standards, Vol 11.01.
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