ASTM B556-90(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B556 − 90(Reapproved 2012)
Standard Guide for
Measurement of Thin Chromium Coatings by Spot Test
This standard is issued under the fixed designation B556; 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 the hydrochloric acid to penetrate through the chromium
coating (penetration time) is measured. The coating thickness
1.1 This guide covers the use of the spot test for the
is proportional to this time.
measurement of thicknesses of electrodeposited chromium
coatings over nickel and stainless steel with an accuracy of
4. Significance and Use
about 620 % (Section 9). It is applicable to thicknesses up to
1.2 µm.
4.1 The thickness of a decorative chromium coating is often
critical to its performance.
NOTE 1—Although this test can be used for coating thicknesses up to
1.2 µm, there is evidence that the results obtained by this method are high
4.2 This procedure is useful for an approximate determina-
at thicknesses greater than 0.5 µm. In addition, for coating thicknesses
tion when the best possible accuracy is not required. For more
above 0.5 µm, it is advisable to use a double drop of acid to prevent
reliable determinations, the following methods are available:
depletion of the test solution before completion of the test.
Methods B504, B568, and B588.
1.2 The values stated in SI units are to be regarded as
4.3 This test assumes that the rate of dissolution of the
standard. No other units of measurement are included in this
chromium by the hydrochloric acid under the specified condi-
standard.
tions is always the same.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
5. Test Solutions
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5.1 For chromium on nickel the test solution is reagent
bility of regulatory limitations prior to use.
grade hydrochloric acid having a specific gravity at 16°C of
1.180 6 0.002. (This corresponds to 11.5 N 6 0.2 N, which
2. Referenced Documents
may be checked by titration.) For chromium on stainless steel
2.1 ASTM Standards:
the test solution is 20 g/L of antimony trioxide dissolved in
B504 Test Method for Measurement of Thickness of Metal-
reagent grade hydrochloric acid having a specific gravity at
lic Coatings by the Coulometric Method
16°C of 1.160.
B568 Test Method for Measurement of Coating Thickness
NOTE 2—As received, reagent grade hydrochloric acid is normally
by X-Ray Spectrometry
more concentrated than 11.5 N.
B588 Test Method for Measurement of Thickness of Trans-
parent or Opaque Coatings by Double-Beam Interference
6. Preparation of Test Area
Microscope Technique
6.1 The test area must be free of foreign material. Clean by
3. Summary of Guide
rubbing the test area with a paste of magnesium oxide, rinse it,
3.1 A drop of hydrochloric acid (test solution) is deposited and dry it with a clean cloth or filter paper. Draw a ring with a
on the surface of the test specimen, and the time required for
diameter of about 6 mm on the test area with melted paraffin or
with a wax pencil.
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
7. Procedure
Methods.
Current edition approved May 1, 2012. Published November 2013. Originally
7.1 Let the test specimen, the test solution, and the dropper
approved in 1971. Last previous edition approved in 2007 as B556 – 90 (2007).
stand long enough to reach room temperature, which should be
DOI: 10.1520/B0556-90R12.
between 16 and 25°C. Temperatures up to 30°C are
Blum, W., and Olson, W. A., Proceedings, Am. Electroplaters Soc., Vol 28,
permissible, but the measurements become less reliable at the
1940, p. 25.
DuRose,A. H., and Pierce,W. J., Metal Finishing ,Vol 57, March 1959, p. 54.
higher tempera
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