1、Designation: B556 90 (Reapproved 2012)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 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not
5、 purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this 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
6、:4B504 Test Method for Measurement of Thickness of Metal-lic Coatings by the Coulometric 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 Technique3.
7、Summary of Guide3.1 A drop of hydrochloric acid (test solution) is 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 a
8、nd Use4.1 The thickness of a decorative chromium coating is oftencritical 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 B5
9、88.4.3 This test assumes that the rate of dissolution of thechromium 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 cor
10、responds to 11.5 N 6 0.2 N, whichmay be checked by titration.) For 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 conce
11、ntrated than 11.5 N.6. Preparation of Test Area6.1 The test area must 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 orw
12、ith a wax pencil.7. Procedure7.1 Let the test specimen, the test solution, and the dropperstand long enough to reach room temperature, which should bebetween 16 and 25C. Temperatures up to 30C arepermissible, but the measurements become less reliable at thehigher temperatures because of increasing s
13、ensitivity 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.1This guide is under the jurisdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct
14、responsibility of Subcommittee B08.10 on TestMethods.Current edition approved May 1, 2012. Published November 2013. Originallyapproved in 1971. Last previous edition approved in 2007 as B556 90 (2007).DOI: 10.1520/B0556-90R12.2Blum, W., and Olson, W. A., Proceedings, Am. Electroplaters Soc., Vol 28,
15、1940, p. 25.3DuRose, A. H., and Pierce, W. J., Metal Finishing , Vol 57, March 1959, p. 54.4For 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 Su
16、mmary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17.2 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 begin
17、ning 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 with a fine nickel wire. The end poi
18、nt 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, gassing will stopat the end point; i
19、f 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 forms, but if there is littleor no
20、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.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 (2012)28. Calculation of Thic
21、kness8.1 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 fromthe conventional
22、 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. Precision and Bias9.1 This thic
23、kness 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 mentionedin this standard. Users of t
24、his 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 and must be reviewed every five y
25、ears 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 of theresponsible technical comm
26、ittee, 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 Box C700, West Conshohocken, PA 19
27、428-2959,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 ASTM website (www.astm.org/COPYRIGHT/).B556 90 (2012)3
