1、Designation: B 556 90 (Reapproved 2007)Standard Guide forMeasurement of Thin Chromium Coatings by Spot Test1This standard is issued under the fixed designation B 556; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the use of the spot test for themeasurement of thicknesses of electrodeposited chromiumcoatings over ni
3、ckel and stainless steel with an accuracy ofabout 620 % (Section 9). It is applicable to thicknesses up to1.2 m.2NOTE 1Although this test can be used for coating thicknesses up to1.2 m, there is evidence that the results obtained by this method are highat thicknesses greater than 0.5 m.3In addition,
4、 for coating thicknessesabove 0.5 m, it is advisable to use a double drop of acid to preventdepletion of the test solution before completion of the test.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of th
5、is standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:4B 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB 568 Test Method for Mea
6、surement of Coating Thicknessby X-Ray SpectrometryB 588 Test Method for Measurement of Thickness of Trans-parent or Opaque Coatings by Double-Beam InterferenceMicroscope Technique3. Summary of Guide3.1 A drop of hydrochloric acid (test solution) is depositedon the surface of the test specimen, and t
7、he time required forthe hydrochloric acid to penetrate through the chromiumcoating (penetration time) is measured. The coating thicknessis proportional to this time.4. Significance and Use4.1 The thickness of a decorative chromium coating is oftencritical to its performance.4.2 This procedure is use
8、ful for an approximate determina-tion when the best possible accuracy is not required. For morereliable determinations, the following methods are available:Methods B 504, B 568, and B 588.4.3 This test assumes that the rate of dissolution of thechromium by the hydrochloric acid under the specified c
9、ondi-tions is always the same.5. Test Solutions5.1 For chromium on nickel the test solution is reagentgrade hydrochloric acid having a specific gravity at 16C of1.180 6 0.002. (This corresponds to 11.5 N 6 0.2 N, whichmay be checked by titration.) For chromium on stainless steelthe test solution is
10、20 g/L of antimony trioxide dissolved inreagent grade hydrochloric acid having a specific gravity at16C of 1.160.NOTE 2As received, reagent grade hydrochloric acid is normallymore concentrated than 11.5 N.6. Preparation of Test Area6.1 The test area must be free of foreign material. Clean byrubbing
11、the test area with a paste of magnesium oxide, rinse it,and dry it with a clean cloth or filter paper. Draw a ring with adiameter of about 6 mm on the test area with melted paraffin orwith a wax pencil.7. Procedure7.1 Let the test specimen, the test solution, and the dropperstand long enough to reac
12、h room temperature, which should bebetween 16 and 25C. Temperatures up to 30C are permis-sible, but the measurements become less reliable at the highertemperatures because of increasing sensitivity to temperature.Thin test specimens should be set on a heavy metal plate toavoid a rapid change in temp
13、erature which could be producedin such specimens by the heat of reaction.7.2 To determine the penetration time, t, deposit a drop(0.03 to 0.05 mL) of the test solution inside the ring of wax,and measure the time between the beginning of the gasformation and the first appearance of nickel. Make thism
14、easurement to the nearest12 s with a stop watch. If thereaction, that is, the formation of gas bubbles, does not start1This guide is under the jurisdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition a
15、pproved March 1, 2007. Published March 2007. Originallyapproved in 1971. Last previous edition approved in 2002 as B 556 90 (2002).2Blum, W., and Olson, W. A., Proceedings, Am. Electroplaters Soc., Vol 28,1940, p. 25.3DuRose, A. H., and Pierce, W. J., Metal Finishing , Vol 57, March 1959, p. 54.4For
16、 referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
17、, West Conshohocken, PA 19428-2959, United States.immediately, it can be started by touching the test surfacewithin the ring with a fine nickel wire. The end point of thepenetration is characterized by the cessation of the gassing andthe appearance of the yellow color of the nickel surface. Theremay
18、 be an uncertainty of 2 or3sindetermining when the endpoint has been reached.7.3 If the basis metal is 18-8 stainless steel, gassing will stopat the end point; if it is 17 % chromium stainless steel, the rateof gas liberation will decrease when the end point is reached.7.4 When using the antimony tr
19、ioxide-hydrochloric acidsolution, the absence of a black film will indicate that there isno chromium deposit; if a black film forms, but if there is littleor no gassing, the chromium is estimated to be less than 0.1 mthick.7.5 Measure the room temperature near the test area to anaccuracy of 0.2C.8.
20、Calculation of Thickness8.1 Calculate the thickness of the chromium coating by theequation:Thickness 5 ut (1)where:t = penetration time, andu = speed of dissolution of the chromium coating as afunction of the test temperature (see Fig. 1).NOTE 3Fig. 1 is applicable when chromium plate is deposited f
21、romthe conventional sulfate chromic acid solution under conventional oper-ating conditions. If these procedures are varied, it may be necessary torestandardize the test.8.2 In case of duplex chromium coatings, the thickness willcorrespond to the combined thickness of the two coatings.FIG. 1 Temperat
22、ure Factor for Hydrochloric Acid (sp gr 1.180) and Antimony Trioxide (20 g/L) in Hydrochloric Acid (sp gr 1.160)B 556 90 (2007)29. Precision and Bias9.1 This thickness determination has an uncertainty of about620 %, and is, therefore, much less accurate than the coulo-metric method covered by Method
23、 B 504.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such righ
24、ts, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional
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26、Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B 556 90 (2007)3
