1、Designation: B 555 86 (Reapproved 2007)Standard Guide forMeasurement of Electrodeposited Metallic CoatingThicknesses by Dropping Test1This standard is issued under the fixed designation B 555; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last 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 dropping test tomeasure the thickness of electrodeposited zinc
3、, cadmium,copper, and tin coatings.NOTE 1Under most circumstances this method of measuring coatingthicknesses is not as reliable or as convenient to use as an appropriatecoating thickness gauge (see Test Methods B 499, B 504, and B 568).1.2 This standard does not purport to address all of thesafety
4、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:2B 487 Test Method for Measurement o
5、f Metal and OxideCoating Thickness by Microscopical Examination of CrossSectionB 499 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB
6、 568 Test Method for Measurement of Coating Thicknessby X-Ray SpectrometryD 1193 Specification for Reagent Water3. Summary of Guide3.1 A dropping test3consists of applying dropwise a corro-sive solution, at a constant rate, to the electroplated surface,and measuring the time required to penetrate th
7、e coating andexpose the substrate; this time is proportional to the coatingthickness.4. Significance and Use4.1 The thickness of a metal coating is often critical to itsperformance.4.2 This procedure is useful for an approximate determina-tion when the best possible accuracy is not required. For mor
8、ereliable determinations, the following methods are available:Test Methods B 487, B 499, B 504, and B 568.4.3 This test assumes that the rate of dissolution of thecoating by the corrosive reagent under the specified conditionsis always the same.5. Factors Affecting the Accuracy5.1 The following fact
9、ors will affect the accuracy of acoating thickness measurement made by this method:5.1.1 Cleanliness of SurfaceAny foreign material on thesurface to be tested, including lacquer, grease, corrosionproducts, and conversion coatings, will interfere with the testand must be removed. Tarnish and conversi
10、on coatings canoften be removed by mild burnishing with a soft, clean pencileraser.5.1.2 Concentration of Test SolutionVariation from thestated concentrations will introduce an error unless the thick-ness factor is adjusted accordingly. Test solutions cannot bereused.1This guide is under the jurisdi
11、ction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition approved March 1, 2007. Published March 2007. Originallyapproved in 1971. Last previous edition approved in 2002 as B 555 86 (2002).2For referenced AST
12、M 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.3Such tests were described by Hull, R. O., and Strausser, P., Monthly Review,Ame
13、rican Electroplaters Society, MRAEA, Vol 22, 1935, p. 9, and by Brenner, A.,Proceedings, American Electroplaters Society, AEPPB, Vol 27, 1939, p. 204.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.3 TemperatureThe thickness fact
14、or for a given solu-tion, being a function of the temperature, must be known forthe temperature at which the test is made. Specimens to betested should be allowed to reach room temperature beforetesting.5.1.4 Dropping RateThe thickness factor is also a func-tion of the dropping rate. The thickness f
15、actors given in Section10 are for a dropping rate of 100 drops/min and will remainvalid for the range of 95 to 105 drops/min.5.1.5 Solution DrainageThe thickness factors given inSection 10 are valid only if the test solution is rapidly drainedoff, as from a flat surface inclined 45 from the horizont
16、al. Thetest cannot be made on a horizontal surface or at a location thatdoes not permit rapid drainage.5.1.6 Drop SizeVariation in drop size may alter thepenetration rate. The tip of the dropping apparatus shouldconform to the dimensions given in Fig. 1 and should be keptclean.5.1.7 Alloy LayerThe p
17、resence of an alloy layer at thecoating-substrate interface may obscure the end point andintroduce an uncertainty as to the amount of alloy included inthe thickness measurement.5.1.8 Detection of End PointThe end point (the time atwhich the coating has been penetrated and the substrateexposed) is ch
18、aracterized by a change in the appearance of thesurface on which drops are falling. This is a matter of personaljudgment and may not always be clearly defined, dependingupon the coating-substrate combination and the extent ofalloying, if any. Such errors may be minimized by standardiz-ing the test m
19、ethod with identical specimens with a knowncoating thickness determined by other means.5.1.9 Composition of CoatingThe dropping tests de-scribed in this document are intended for use on nominally“pure” coatings. The thickness factors listed in Section 10 areexpected to vary with gross variations in
20、the composition of thecoating, as might result from codeposition of an alloyingcomponent. The specific effects, on the thickness factors, ofimpurities or of inclusions from brighteners or other additionagents can be appreciable. Uncertainty from these sources maybe minimized by standardizing the tes
21、t method against stan-dards, prepared from the same type of plating solution, thethicknesses of which have been determined by other methods.6. Apparatus6.1 Fig. 1 illustrates one form of apparatus used for drop-ping tests. Equivalent apparatus are commercially available, asis a solenoid operated uni
22、t with a digital readout.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in the preparation of all test solutions.7.2 Purity of WaterWater used in the preparation of testsolutions shall be reagent water as defined in SpecificationD 1193.8. Test Solutions8.1 Soluti
23、on for Cadmium and Zinc:Chromic acid (CrO3) 200 g/LSulfuric acid (96 % H2SO4, sp gr 1.84) 50 g/L or 27 mL/LNOTE 2Sulfuric acid is added slowly with stirring to at least 20 timesits volume of water.8.2 Solution for Cadmium only:Ammonium nitrate (NH4NO3) 110 g/LHydrochloric acid (37 % HCl, sp gr 1.19)
24、 10 mL/L8.3 Solution for Zinc only:Ammonium nitrate (NH4NO3) 100 g/LNitric acid (70 % HNO3, sp gr 1.42) 55 mL/LAGlass tube with one end open to atmosphere and one end submerged in the testsolution in funnel, C.BRubber stopper forms air tight seal between tube, A, and funnel, C.CSeparatory funnel.DWi
25、de-bore rubber tubing (75 to 125 mm in length) or sealed glass joints.ECapillary tubing (140 mm in length, 0.64-mm bore).FRubber tubing or sealed glass joints.GCapillary glass tip (with 12.7-mm taper to outside diameter of 3.5 mm).HSpecimen.ICollector of spent solution.NOTE 1Solution head is constan
26、t as long as air is being drawn through tube, A.FIG. 1 Dropping FunnelB 555 86 (2007)28.4 Solution for Tin:Trichloroacetic acid (CHCl3COOH) 100 g/L8.5 Solution for Copper:Hydrochloric acid (37 % HCl sp gr 1.19) 200 mL/LAntimony trioxide (Sb2O3)20g/LGlacial acetic acid (99.7 % CH3COOH) 250 mL/LFerric
27、 chloride (FeCl36H2O) 450 g/LNOTE 3For ease of preparation, dissolve the antimony trioxide in thehydrochloric acid, add 150 mL of water and the glacial acetic acid, andthen add the ferric chloride in small portions. Finally dilute to 1.00 L withwater.NOTE 4Variations of 62 % in the composition of a
28、test solution arepermissible.9. Procedure9.1 Clean the specimen and allow it and the test solution toreach room temperature, which should be recorded. Supportthe specimen so that the surface to be tested makes a 45 anglewith the horizontal, about 13 mm below the tip of the droppingapparatus. Drop th
29、e test solution onto the specimen at a rate of100 drops/min. Note and record the time required for thesolution to penetrate the coating at the point on which the dropsfall.10. Computation of Thickness10.1 Multiply the time required to penetrate the coating byan appropriate thickness factor to obtain
30、 the coating thickness.10.2 Below are the thickness factors, applicable to nomi-nally “pure” coatings (5.1.9), for the solutions given in Section8. They are valid for a dropping rate of 100 drops/min from acapillary tip, the dimensions of which are given in Fig. 1.Cadmium (chromic acid solution): 0.
31、35 m/sZinc (chromic acid solution): 0.26 m/sCadmium (nitrate solution): 0.25 m/sZinc (nitrate solution): 0.25 m/sTin 0.25 m/sCopper 0.13 m/s10.2.1 The first two thickness factors for cadmium and zincand the chromic acid solution are only valid for a temperatureof 24C; the factors for these metals an
32、d this test solution atother temperatures are given in Fig. 2 and Fig. 3.10.2.2 The last four thickness factors are valid for tempera-tures in a range from 20 to 30C.11. Reproducibility and Accuracy11.1 The reproducibility for a single operator is estimated tobe 62 drops (equivalent to 1.2 s) or 65
33、%, whichever isgreater.11.2 The over-all accuracy may be substantially poorer thanthe reproducibility, because of the uncertainties discussed inSection 5, and will depend upon the control exercised over thevariables. For maximum accuracy, the test method should bestandardized with specimens identica
34、l to those being tested,having known coating thicknesses determined by other meth-ods. Sometimes a chemical can be added to the droppingsolution to aid in determining the end point, for example,potassium ferricyanide (K3Fe(CN)6) has been added to the testsolution for zinc in 8.3.B 555 86 (2007)3FIG.
35、 2 Chart for Determining Thickness of Zinc Coating by the Chromic Acid Dropping TestB 555 86 (2007)4ASTM 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 dete
36、rmination 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 years andif not revised, either reapproved or
37、 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 committee, which you may attend. If you feel tha
38、t 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 19428-2959,United States. Individual reprints
39、(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).FIG. 3 Chart for Determining Thickness of Cadmium Coating by the Chromic Acid Dropping TestB 555 86 (2007)5
