ASTM_B_556_-_90_2013.pdf

Designation:B55690(Reapproved 2013)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 revision.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 nickel and stainless steel with an accuracy ofabout 620%(Section 9).It is applicable to thicknesses up to1.2 m.2NOTE1Although 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,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 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: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.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 and 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 B588.4.3 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 corresponds 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.NOTE2As 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 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 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 sensitivity 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,1This 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 Dec.1,2013.Published December 2013.Originallyapproved in 1971.Last previous edition approved in 2007 as B556 90(2007).DOI:10.1520/B0556-90R13.2Blum,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 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 and measure the time between the beginning of the gasformation and the first appearance of nickel.Make thismeasurement to the nearest12s 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 point of thepenetration is characterized by the cessation of the gassing andthe appearance of the yellow color of the nickel