ASTM B764-04
(Test Method)Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)
Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)
SIGNIFICANCE AND USE
The ability of a multilayer nickel deposit to enhance corrosion resistance is a function of the difference in the electrode potentials of the nickel layers (as measured individually at a fixed current density in a given electrolyte versus a reference electrode) and the thicknesses of the layers. The potential differences must be sufficient to cause the bright nickel or top layer to corrode preferentially and sacrificially with respect to the semi-bright nickel layer beneath it.
This test procedure allows the measurement of these potential differences directly on an electroplated part rather than on separate foil specimens in such a way that time determines the thickness of each layer, while the potential difference between nickel layers is an indication of the corrosion resistance of the total nickel deposit.
The interpretation and evaluation of the results of this test should be by agreement between the purchaser and the manufacturer.
Note 1—This test may be used as a quality assurance test of the multilayer nickel coatings applied in production. It should be understood that due to many factors that influence the progress of corrosion during actual use of the part, the performance of different multilayer nickel deposits in the test cannot be taken as an absolute indicator of the relative corrosion resistance of these deposits in service.
SCOPE
1.1 This test method closely estimates the thickness of individual layers of a multilayer nickel electrodeposit and the potential differences between the individual layers while being anodically stripped at constant current density.
1.2 This test method does not cover deposit systems other than multilayer electroplated nickel deposits.
1.3 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.
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Standards Content (Sample)
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Designation:B764–04
Standard Test Method for
Simultaneous Thickness and Electrode Potential
Determination of Individual Layers in Multilayer Nickel
1
Deposit (STEP Test)
This standard is issued under the fixed designation B764; 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 3.2 Coulometric thickness testing instruments are based on
the anodic dissolution (stripping) of the deposit at constant
1.1 This test method closely estimates the thickness of
current, while the time is measured to determine thickness.As
individual layers of a multilayer nickel electrodeposit and the
commonly practiced, the method employs a small cell that is
potential differences between the individual layers while being
2,3
filled with an appropriate electrolyte, and the test specimen
anodically stripped at constant current density.
serves as the bottom of the cell. To the bottom of the cell is
1.2 This test method does not cover deposit systems other
attached a rubber or plastic gasket whose opening defines the
than multilayer electroplated nickel deposits.
measuring(stripping,anodic)area.Ifametalliccellisused,the
1.3 This standard does not purport to address all of the
rubber gasket also electrically insulates the test specimen from
safety concerns, if any, associated with its use. It is the
the cell.With the specimen as the anode and the cell or agitator
responsibility of the user of this standard to establish appro-
tube as the cathode, a constant direct current is passed through
priate safety and health practices and determine the applica-
the cell until the nickel layer is dissolved. A sudden change in
bility of regulatory limitations prior to use.
voltagebetweentheelectrodesoccurswhenadifferentmetallic
2. Referenced Documents layer starts to dissolve.
4
3.3 Each different metal or species of the same metal
2.1 ASTM Standards:
requires a given voltage to keep the current constant while
B456 Specification for Electrodeposited Coatings of Cop-
being stripped. As one nickel layer is dissolved away and the
per Plus Nickel Plus Chromium and Nickel Plus Chro-
next layer becomes exposed, there will be a voltage change
mium
(assuming a constant current and difference in the electro-
B504 Test Method for Measurement of Thickness of Me-
chemical characteristics of the two nickel layers). The elapsed
tallic Coatings by the Coulometric Method
timeatwhichthisvoltagechangeoccurs(relativetothestartof
D1193 Specification for Reagent Water
the test or previous voltage change) is a measure of the deposit
3. Summary of Test Method
thickness.
3.4 At the same time, the amplitude of the voltage change
3.1 This procedure is a modification of the well-known
canbeobserved.Thatis,theease(ordifficulty)withwhichone
coulometric method of thickness testing (Test Method B504).
layer can be dissolved or stripped with reference to another
It is also known as the anodic dissolution or electrochemical
layer can be compared. The lower the voltage needed the more
stripping method.
active the metal or the greater the tendency to corrode
preferentially to a more noble metal adjacent to it.
1
ThismethodisunderthejurisdictionofASTMCommitteeB08onMetallicand 3.5 Where the metallic layers are of such a similar nature
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
that change of the stripping voltage is small, there can be
Methods.
problems in detecting this change if the voltage between the
Current edition approved April 1, 2004. Published April 2004. Originally
deplating cell (cathode) and the sample (anode) is measured.
approved in 1986. Last previous edition approved in 2003 as B764 – 94 (2003).
DOI: 10.1520/B0764-04.
As the sample is dissolved anodically, cathodic processes are
2
For discussion of this test, see Harbulak, E. P., “Simultaneous Thickness and
occurring on the deplating cell (cathode) surface that can also
Electrochemical Potential Determination of Individual Layers in Multilayer Nickel
give rise to voltage changes, due to alterations of the cathode
Deposits,” Plating and Surface Finishing, Vol 67, No. 2, February 1980, pp. 49–54.
3
surface, thus obscuring the anode voltage change. This diffi-
U.S. Patent 4,310,389. Assignee: The Chrysler Corp., Highland Park, MI
48203.
culty can be avoided by measuring the potential of the
4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
dissolving anodic sample with respect to an unpolarized third
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
electrode (reference) placed in the cell. By recording this
Standards volum
...
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