1、Designation: B 798 95 (Reapproved 2005)Standard Test Method forPorosity in Gold or Palladium Coatings on Metal Substratesby Gel-Bulk Electrography1This standard is issued under the fixed designation B 798; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 the case of 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 test method covers equipment and techniques fordetermining porosity in noble
3、metal coatings, particularlyelectrodeposits and clad metals used on electrical contacts.1.2 The test method is designed to show whether theporosity level is less or greater than some value which byexperience is considered by the user to be acceptable for theintended application.1.3 Other porosity te
4、sting methods are outlined in GuideB 765. Detailed critical reviews of porosity testing are alsoavailable.2Other porosity test methods are B 735, B 741,B 799, and B 809.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility o
5、f the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory li
6、mitations prior to use. For specific hazard state-ments, see Sections 7 and 8.1.5 The values stated in SI units are to be regarded asstandard. The values in parentheses are for information only.2. Referenced Documents2.1 ASTM Standards:3B 374 Terminology Relating to ElectroplatingB 542 Terminology R
7、elating to Electrical Contacts andTheir UseB 735 Test Method for Porosity in Gold Coatings on MetalSubstrates by Nitric Acid VaporB 741 Test Method for Porosity In Gold Coatings On MetalSubstrates By Paper Electrography4B 765 Guide for Selection of Porosity and Gross DefectTests for Electrodeposits
8、and Related Metallic CoatingsB 799 Test Method for Porosity in Gold and PalladiumCoatings by Sulfurous Acid/Sulfur-Dioxide VaporB 809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor (“Flowers-of-Sulfur”)3. Terminology3.1 DefinitionsMany terms used in this test method aredefined in
9、 Terminology B 542 and terms relating to metalliccoatings are defined in Terminology B 374.3.2 Definitions of Terms Specific to This Standard:3.2.1 decorations, nthose reaction products emanatingfrom the pores that provide visual contrast with the gelmedium.3.2.2 measurement area (or “significant su
10、rface”), nthesurface that is examined for the presence of porosity. Thesignificant surfaces or measurement areas of the part to betested shall be indicated on the drawing of the part or byprovision of suitably marked samples.3.2.2.1 DiscussionFor specification purposes, the signifi-cant surfaces or
11、measurement areas are often defined as thoseportions of the surface that are essential to the serviceability orfunction of the part, such as its contact properties, or which canbe the source of corrosion products or tarnish films thatinterfere with the function of the part.3.2.3 metallic coatings, n
12、include platings, claddings, orother metallic layers applied to the substrate. The coatings cancomprise a single metallic layer or a combination of metalliclayers.3.2.4 porosity, nthe presence of any discontinuity, crack,or hole in the coating that exposes a different underlying metal.3.2.5 underpla
13、te, na metallic coating layer between thesubstrate and the topmost layer or layers. The thickness of anunderplate is usually greater that 0.8 m (30 in.).4. Summary of Test Method4.1 This test method is an electrographic technique, “gel-bulk electrography.” The specimen is made the anode in a cell1Th
14、is test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved Nov. 1, 2005. Published February 2006. Originallyapproved in 1988. Last previous edition ap
15、proved in 2000 as B 798 95 (2000).2Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “Porosity Testing of GoldDeposity,” Plating, Vol 52, 1965, p. 1001, and Krumbein S. J., “Porosity Testing ofContact Platings,” Proceedings, Connectors and Interconnection Technology Sym-posium, October 1987, p. 47.3
16、For 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.4Withdrawn.1Copyright ASTM International, 100 Barr Harbor Driv
17、e, PO Box C700, West Conshohocken, PA 19428-2959, United States.containing a solid or semisolid electrolyte of gelatin, conduct-ing salts, and an indicator. Application of current to this cellresults in the migration of base medal ions through continuouspores. Reaction of cations with an indicator g
18、ives rise tocolored reaction products at pore sites which may be countedthrough the clear gel. Individual spots are counted with the aidof a loupe or low power stereomicroscope.4.2 This test method is suitable for coatings containing75 % or more of gold on substrates of silver, nickel, copper,and it
19、s alloys, which are commonly used in electrical contacts.This test method is also suitable for coatings of 95 % or moreof palladium on nickel, copper and its alloys.4.3 These porosity tests involve corrosion reactions inwhich the products delineate defect sites in coatings. Since thechemistry and pr
20、operties of these products do not resemblethose found in natural or service environments, these tests arenot recommended for prediction of the electrical performanceof contacts unless correlation is first established with serviceexperience.5. Significance and Use5.1 Noble metal coatings, particularl
21、y gold or palladium, areoften specified for the contacts of separable electrical connec-tors and other devices. Electrodeposits are the form of gold orpalladium which is most used on contacts, although gold andpalladium are also employed as clad metal and as weldmentson the contact surface. The intr
22、insic nobility of gold and to acertain extent palladium enables them to resist the formation ofinsulating films that could interfere with reliable contactoperation.5.2 In order that the nobility of gold be assured, porosity,cracks, and other defects in the coating that expose base metalsubstrates an
23、d underplates must be minimal or absent, exceptin those cases where it is feasible to use the contacts instructures that shield the surface from the environment orwhere corrosion inhibiting surface treatments for the depositare employed. The level of porosity in the coating that may betolerable depe
24、nds on the severity of the environment to theunderplate or substrate, design factors for the contact devicelike the force with which it is mated, circuit parameters, and thereliability of contact operation that it is necessary to maintain.Also, when present, the location of pores on the surface isim
25、portant. If the pores are few in number or are outside of thezone of contact of the mating surfaces, their presence can oftenbe tolerated.5.3 Methods for determining pores on a contact surface aremost suitable if they enable their precise location and numbersto be determined. Contact surfaces are of
26、ten curved or irregularin shape, and testing methods should be suitable for them. Inaddition, the severity of porosity-determining tests may varyfrom procedures capable of detecting all porosity to proceduresthat detect only gross defects. The test method in this documentis generally regarded as sev
27、ere.5.4 The relationship of porosity levels revealed by particulartests to contact behavior must be made by the user of these teststhrough practical experience or judgment. Thus, absence ofporosity in the coating may be a requirement for someapplications, while a few pores in the contact zone may be
28、acceptable for others.5.5 This test method is capable of detecting porosity orother defects in gold or palladium coatings that could partici-pate in substrate corrosion reactions. In addition, it can be usedon contacts having complex geometry such as pin-socketcontacts (although difficulty may be ex
29、perienced in inspectingdeep recesses).6. Limitations6.1 This test is considered destructive in that it reveals thepresence of porosity by contaminating the surface with corro-sion products and by under-cutting the corrodible metal at poresites and at unplated areas. In addition, the surface is coate
30、dwith a corrosive gel mixture which is difficult to removecompletely. Any parts exposed to the gel test shall not beplaced in service.6.2 The gel-bulk procedure is not as sensitive to small poresand is more complex than porosity tests involving gaseouscorrodants5(see Test Methods B 735 and B 799). I
31、t alsoinvolves more chemicals, preparation, and auxiliary equip-ment.6.3 This test is intended to be used for quantitative descrip-tions of porosity (such as number of pores per unit area or percontact) only on measurement areas where coatings have poredensities that are sufficiently low so that the
32、 corrosion sites arewell separated and can be readily resolved. As a generalguideline this can be achieved for pore densities up to about25/cm2.6.4 For this purpose, the measurement area, or “significantsurface, shall be defined as those portions of the surface thatare essential to the serviceabilit
33、y or function of the part, suchas its contact properties, or which can be the source ofcorrosion products or tarnish films that interfere with thefunction of the part. When necessary, the significant surfacesshall be indicated on the drawings of the parts, or by theprovision of suitably marked sampl
34、es.6.5 The test applicability to platings of varying thickness isa function of the quality of the plating.6.6 The applicability of this test method to localized plat-ings or claddings with adjacent exposed substrate is limited bythe efficacy of coatings applied to mask the non-noble areas toprevent
35、gross decoration of the surfaces under test. Users ofthis method are required to develop their own techniques formasking such exposed substrate areas.7. Apparatus7.1 Test Vessel may be made of glass, acrylic resin, or otherinert uncolored transparent material. It shall have thin-walledflat sides, an
36、d be of a size appropriate to the sample to betested.7.2 Power Supply,0to1Aand0to10Vdc,anelectronically-regulated, constant-current (65 %) apparatus ispreferred.7.3 dc Milliammeter and Separate dc Voltmeter.5For example, Clarke, M., “Porosity and Porosity Tests,” in “Properties ofElectrodeposits,” e
37、dited by Sard, Leidheiser, and Ogburn, The ElectrochemicalSociety, 1975, p. 122.B 798 95 (2005)27.4 Cathode Material in the form of foil or wire made ofplatinum or gold is required. The cathode and specimen(anode) areas shall be approximately the same. Additionally,gold or platinum wire for cathode
38、and anode are needed for thatportion of the hook-up that is in the reagent solution. It may beconvenient to use small alligator clips to secure the lead wiresto the cathode and anode. These clips must be heavily goldplated so as to be entirely free of porosity. A variation of thisprocedure, suitable
39、 for samples having relatively few pores, isto use a second identical test sample as the cathode. The testcan be run with current first in the forward, then in the reversedirection so that the porosity in both samples may be deter-mined. Fig. 1 is a schematic of the test cell setup.NOTE 1A commonly-
40、used alternate cell design incorporates thecathode as part of the cell structure (as shown in Fig. 2). In addition, thesamples may be attached to a common carrier strip or holder, so that onlythe sample surfaces need be in the gel.7.5 Timer capable of indicating seconds. It is convenient touse a tim
41、er switch to control the test current.7.6 Stereomicroscope having 103 magnification and anilluminator are required for sample inspection after test. Aneyepiece reticle is recommended for convenience in locatingthe contact area or other significant measurement areas.8. Reagent8.1 Note that some of th
42、e indicating reagents are sensitive toheat and light, particularly the rubeanic acid (dithio-oxamide).The indicator solutions should be stored in the dark instoppered bottles. For rubeanic acid, do not store for more thana month, and filter prior to use.8.2 Food-Grade GelatinThis type is preferred t
43、o USPgrade gelatin, because the latter may not give transparentsolutions. A 10 % solution is prepared by mixing9gofthegelatin in 91 mL of distilled or deionized water, and slowlyheating to 60 to 65C with stirring, until all the gelatindissolves.NOTE 2If the storage bottle is tightly capped, the plai
44、n gelatinsolution may be stored for up to 2 days in a refrigerator and kept at 5 to10C, discard it if mold appears on its surface.9. Safety Hazards9.1 Reagents identified in Table 1 have the potential to causeinjury or skin discoloring if improperly handled. Good labora-tory practice including the u
45、se of a fume hood and skin and eyeprotection should be observed, especially during solutionpreparative and the cleaning of the test samples. Properprecautions in the use of electrical power supplies and electri-cal connections should also be scrupulously observed.10. Procedure10.1 This test is suita
46、ble for gold coated on silver, nickel, orcopper and its alloys, and palladium coated on nickel, copperand its alloys either as underlayers or substrates, in accordancewith the reagents chosen in Table 1.10.2 Sequence of Operations:10.2.1 Solution Preparation:10.2.1.1 Electrolyte.10.2.1.2 Indicator.1
47、0.2.2 Calculate the current to be used.10.2.3 Prepare the samples prior to cleaning.10.2.4 Clean the samples.10.2.5 Prepare the gel while the samples are cleaning.Remove from heat when dissolved.10.2.6 Dry the samples.10.2.7 Suspend the samples in the test cells.10.2.8 Prepare the composite gel solu
48、tion and add to thecells.10.2.9 Solidify the gel thoroughly.FIG. 1 Schematic of Typical Test-Cell Setup with Anode (Sample)and Cathode Facing Each Other (Preferred Orientation)FIG. 2 Exploded View of Alternate Cell Design IncorporatingCathode as Part of Cell StructureB 798 95 (2005)310.2.10 Set up t
49、he equipment and make electrical attach-ments.10.2.11 Apply the calculated current.10.2.11.1 Examine immediately for gross defects.10.2.11.2 Take readings after the prescribed time period.10.2.12 Record the results.10.3 CleaningHandle specimens as little as possible, andonly with tweezers, microscope-lens tissue, or clean, softcotton gloves. Prior to the test, inspect the samples under 103magnification for evidence of particulate matter. If present,such particles shall be removed by blowing them off withclean, oil-free air. If this is not successful discard the sam
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