ASTM B556-90(2007)
(Guide)Standard Guide for Measurement of Thin Chromium Coatings by Spot Test
Standard Guide for Measurement of Thin Chromium Coatings by Spot Test
SIGNIFICANCE AND USE
The thickness of a decorative chromium coating is often critical to its performance.
This procedure is useful for an approximate determination when the best possible accuracy is not required. For more reliable determinations, the following methods are available: Methods B 504, B 568, and B 588.
This test assumes that the rate of dissolution of the chromium by the hydrochloric acid under the specified conditions is always the same.
SCOPE
1.1 This guide covers the use of the spot test for the measurement of thicknesses of electrodeposited chromium coatings over nickel and stainless steel with an accuracy of about ±20 % (Section 9). It is applicable to thicknesses up to 1.2 μm.
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 at thicknesses greater than 0.5 μm. In addition, for coating thicknesses above 0.5 μm, it is advisable to use a double drop of acid to prevent depletion of the test solution before completion of the test.
1.2 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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Designation: B556 − 90 (Reapproved2007)
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 coating (penetration time) is measured. The coating thickness
is proportional to this time.
1.1 This guide covers the use of the spot test for the
measurement of thicknesses of electrodeposited chromium
4. Significance and Use
coatings over nickel and stainless steel with an accuracy of
4.1 The thickness of a decorative chromium coating is often
about 620 % (Section 9). It is applicable to thicknesses up to
critical to its performance.
1.2 µm.
4.2 This procedure is useful for an approximate determina-
NOTE 1—Although this test can be used for coating thicknesses up to
tion when the best possible accuracy is not required. For more
1.2 µm, there is evidence that the results obtained by this method are high
reliable determinations, the following methods are available:
at thicknesses greater than 0.5 µm. In addition, for coating thicknesses
above 0.5 µm, it is advisable to use a double drop of acid to prevent
Methods B504, B568, and B588.
depletion of the test solution before completion of the test.
4.3 This test assumes that the rate of dissolution of the
1.2 This standard does not purport to address all of the
chromium by the hydrochloric acid under the specified condi-
safety concerns, if any, associated with its use. It is the
tions is always the same.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. Test Solutions
bility of regulatory limitations prior to use.
5.1 For chromium on nickel the test solution is reagent
grade hydrochloric acid having a specific gravity at 16°C of
2. Referenced Documents
1.180 6 0.002. (This corresponds to 11.5 N 6 0.2 N, which
2.1 ASTM Standards:
may be checked by titration.) For chromium on stainless steel
B504 Test Method for Measurement of Thickness of Metal-
the test solution is 20 g/L of antimony trioxide dissolved in
lic Coatings by the Coulometric Method
reagent grade hydrochloric acid having a specific gravity at
B568 Test Method for Measurement of Coating Thickness
16°C of 1.160.
by X-Ray Spectrometry
NOTE 2—As received, reagent grade hydrochloric acid is normally
B588 Test Method for Measurement of Thickness of Trans-
more concentrated than 11.5 N.
parent or Opaque Coatings by Double-Beam Interference
Microscope Technique
6. Preparation of Test Area
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
the hydrochloric acid to penetrate through the chromium
with a wax pencil.
7. Procedure
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
7.1 Let the test specimen, the test solution, and the dropper
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
stand long enough to reach room temperature, which should be
Methods.
between 16 and 25°C. Temperatures up to 30°C are
Current edition approved March 1, 2007. Published March 2007. Originally
permissible, but the measurements become less reliable at the
approved in 1971. Last previous edition approved in 2002 as B556 – 90 (2002).
DOI: 10.1520/B0556-90R07.
higher temperatures because of increasing sensitivity to tem-
Blum, W., and Olson, W. A., Proceedings, Am. Electroplaters Soc., Vol 28,
perature. Thin test specimens should be set on a heavy metal
1940, p. 25.
3 plate to avoid a rapid change in
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