ASTM B825-19
(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
SIGNIFICANCE AND USE
4.1 The present trend in environmental testing of materials with electrically conductive surfaces is to produce, under accelerated laboratory conditions, corrosion and film-forming reactions that are similar to those that cause failures in service environments. In many of these procedures the parts under test are exposed for days or weeks to controlled quantities of both water vapor and pollutant gases, which may be present in extremely dilute concentrations.
Note 2: Descriptions of such tests can be found in Practice B827.
4.2 Many of these environmental test methods require monitoring of the conditions within the chamber during the test in order to confirm that the intended environmentally related reactions are actually taking place. The most common type of monitor consists of copper, silver, or other thin metallic coupons of a few square centimeters that are placed within the test chamber and that react with the corrosive environment in much the same way as the significant surfaces of the parts under test.
4.3 In practice, a minimum number of control coupons are placed in each specified location (see Test Method B810) within the chamber for a specified exposure time, depending upon the severity of the test environment. At the end of this time interval, the metal samples are removed and analyzed by the coulometric reduction procedure.
4.4 Other corrosion film evaluation techniques for metallic coupons are also available. The most common of these is mass gain, which is nondestructive to the surface films, but is limited to the determination of the total amount of additional mass acquired by the metal as a result of the environmental attack. The most common is weighing using high performance microbalances or for purposes of real-time monitoring, quartz crystal microbalances (see Specification B808).
Note 3: Detailed instructions for conducting such weighings, as well as coupon cleaning and surface preparation procedures, are included as part of Test Met...
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 used in customer product environments.
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 4.6 for limitations.)
1.4 This test method has been demonstrated to be applicable particularly to copper and silver test samples (see (1)).2 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 (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety, health, and environmental practices, and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B825 − 19
Standard Test Method for
Coulometric Reduction of Surface Films on Metallic Test
1
Samples
This standard is issued under the fixed designation B825; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 This test method covers procedures and equipment for
Barriers to Trade (TBT) Committee.
determining the relative buildup of corrosion and tarnish films
(including oxides) on metal surfaces by the constant-current
2. Referenced Documents
coulometric technique, also known as the cathodic reduction
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2.1 ASTM Standards:
method.
B808 Test Method for Monitoring of Atmospheric Corrosion
1.2 This test method is designed primarily to determine the
Chambers by Quartz Crystal Microbalances
relative quantities of tarnish films on control coupons that
B809 Test Method for Porosity in Metallic Coatings by
result from gaseous environmental tests, particularly when the
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
latter are used for testing components or systems containing
B810 Test Method for Calibration of Atmospheric Corrosion
electrical contacts used in customer product environments.
Test Chambers by Change in Mass of Copper Coupons
1.3 This test method may also be used to evaluate test
B827 Practice for Conducting Mixed Flowing Gas (MFG)
samples that have been exposed to indoor industrial locations
Environmental Tests
or other specific application environments. (See 4.6 for limi-
D1193 Specification for Reagent Water
tations.)
3. Summary of Test Method
1.4 This test method has been demonstrated to be applicable
2
particularly to copper and silver test samples (see (1)). Other 3.1 In constant-current coulometry, a fixed reduction-
metals require further study to prove their applicability within current density is applied to the sample in an electrolytically
the scope of this test method. conductive solution, and the resulting variations in potential—
measured against a standard reference electrode in the same
1.5 The values stated in SI units are the preferred units. The
solution—are followed as a function of time. Typically, with
values provided in parentheses are for information only.
well-behaved surface films, the voltage-time plot should show
1.6 This standard does not purport to address all of the
a number of horizontal portions, or steps, each corresponding
safety concerns, if any, associated with its use. It is the
to a specific reduction potential or voltage (Fig. 1). The final
responsibility of the user of this standard to become familiar
potential step, which is always present with all substances,
with all hazards including those identified in the appropriate
corresponds to the reduction of hydrogen ions in the solution
Material Safety Data Sheet (MSDS) for this product/material
(to form hydrogen gas), and represents a limit beyond which no
as provided by the manufacturer, to establish appropriate
higher potential reduction process can occur.
safety, health, and environmental practices, and determine the
NOTE 1—As shown in Figs. 1 and 2, a differential circuit is recom-
applicability of regulatory limitations prior to use.
mended to help in resolving the individual voltage steps by pinpointing the
1.7 This international standard was developed in accor-
corresponding inflection points on the main reduction curve (see 6.2.3).
dance with internationally recognized principles on standard-
3.2 From the elapsed times at the various steps, conclusions
ization established in the Decision on Principles for the
can often be drawn regarding the corrosion processes that have
taken place to produce the surface films. Also, calculations can
1
This test method is under the jurisdiction of ASTM Committee B02 on
be made from the time at each voltage step in order to calculate
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
the number of coulombs of electrical charge required to
B02.05 on Precious Metals and Electrical Contact Materials and Test Methods.
Current edition approved Nov. 1, 2019. Published November 2019. Originally
approved in 1997. Last previous edition approved in 2013 as B825 – 13 which was
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withdrawn November 2018 and reinstated in November 2019. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
B0825-19. contact ASTM Customer Service at service@astm
...
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