ASTM B556-1990(2018) Standard Guide for Measurement of Thin Chromium Coatings by Spot Test.pdf

1、Designation: B556 90 (Reapproved 2018)Standard Guide forMeasurement of Thin Chromium Coatings by Spot Test1This standard is issued under the fixed designation B556; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r

2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 nicke

3、l 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, fo

4、r 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 this

5、standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.3 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decisi

6、on on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:4B504 Test Method for Measurement of Thickness of Metal-lic Coatings by the Coulomet

7、ric MethodB568 Test Method for Measurement of Coating Thicknessby X-Ray SpectrometryB588 Test Method for Measurement of Thickness of Trans-parent or Opaque Coatings by Double-Beam InterferenceMicroscope Technique (Withdrawn 2016)53. Summary of Guide3.1 A drop of hydrochloric acid (test solution) is

8、depositedon the surface of the test specimen, and the 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 oftencr

9、itical to its performance.4.2 This procedure is useful for an approximate determina-tion when the best possible accuracy is not required. For morereliable determinations, the following methods are available:Methods B504, B568, and B588.4.3 This test assumes that the rate of dissolution of thechromiu

10、m by the hydrochloric acid under the specified condi-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

11、chromium on stainless steelthe test solution is 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 mu

12、st be free of foreign material. Clean byrubbing 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 so

13、lution, and the dropperstand long enough to reach room temperature, which should be1This 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 approved Aug. 1, 2018. Published Aug

14、ust 2018. Originallyapproved in 1971. Last previous edition approved in 2013 as B556 90 (2013).DOI: 10.1520/B0556-90R18.2Blum, 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 referenced

15、 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.5The last approved version of this historical standard is referenced onwww.a

16、stm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment

17、of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1between 16 and 25C. Temperatures up to 30C arepermissible, but the measurements become less reliable at thehigher temperatures because of increasing sensitivity

18、to tem-perature. Thin test specimens should be set on a heavy metalplate to avoid a rapid change in temperature which could beproduced in 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 m

19、easure the time between the beginning of the gasformation and the first appearance of nickel. Make thismeasurement to the nearest12 s with a stop watch. If thereaction, that is, the formation of gas bubbles, does not startimmediately, it can be started by touching the test surfacewithin the ring wit

20、h 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 be an uncertainty of 2 or3sindetermining when the endpoint has been reached.7.3 If the basis metal is 18-8 stainless steel, gas

21、sing 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 trioxide-hydrochloric acidsolution, the absence of a black film will indicate that there isno chromium deposit; if a black film fo

22、rms, but if there is littleor no gassing, the chromium is estimated to be less than 0.1 mthick.FIG. 1 Temperature Factor for Hydrochloric Acid (sp gr 1.180) and Antimony Trioxide (20 g/L) in Hydrochloric Acid (sp gr 1.160)B556 90 (2018)27.5 Measure the room temperature near the test area to anaccura

23、cy of 0.2C.8. 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

24、is deposited fromthe 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.9

25、. 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 B504.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item ment

26、ionedin 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 rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee

27、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 standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting

28、 of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO B

29、ox 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 90 (2018)3