1、Designation: B799 95 (Reapproved 2014)Standard Test Method forPorosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor1This standard is issued under the fixed designation B799; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se 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 test method covers equipment and methods fordetermining the porosity of gold and pall
3、adium coatings,particularly electrodeposits and clad metals used on electricalcontacts.1.2 This 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 Avariety of other
4、 porosity testing methods are describedin the literature.2,3Other porosity test methods are B735,B741, B798, and B809. An ASTM Guide to the selection ofporosity tests for electrodeposits and related metallic coatingsis available as Guide B765.1.4 The values stated in SI units are to be regarded asst
5、andard. The values given in parentheses are for informationonly.1.5 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 become familiarwith all hazards including those identified in the appropri
6、ateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitations prior to use. For specific hazards, seeSection 6.2. Referenced Documents2.1 ASTM Standards:4B37
7、4 Terminology Relating to ElectroplatingB542 Terminology Relating to Electrical Contacts and TheirUseB735 Test Method for Porosity in Gold Coatings on MetalSubstrates by Nitric Acid VaporB741 Test Method for Porosity In Gold Coatings On MetalSubstrates By Paper Electrography (Withdrawn 2005)5B765 Gu
8、ide for Selection of Porosity and Gross Defect Testsfor Electrodeposits and Related Metallic CoatingsB798 Test Method for Porosity in Gold or Palladium Coat-ings on Metal Substrates by Gel-Bulk ElectrographyB809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor (“Flowers-of-Sulfur”)
9、3. Terminology3.1 DefinitionsMany terms used in this test method aredefined in Terminology B542 and terms relating to metalliccoatings are defined in Terminology B374.3.2 Definitions of Terms Specific to This Standard:3.2.1 corrosion products, nthose reaction products ema-nating from the pores that
10、protrude from, or are otherwiseattached to, the coating surface after a vapor test exposure.3.2.2 measurement area (or “significant surface”), nthesurface that is examined for the presence of porosity. Thesignificant surfaces or measurement areas of the part to betested shall be indicated on the dra
11、wing of the part or byprovision of suitably marked samples.3.2.2.1 DiscussionFor specification purposes, the signifi-cant surfaces or measurement areas are often defined as those1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct respons
12、ibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved Oct. 1, 2014. Published October 2014. Originallyapproved in 1988. Last previous edition approve in 2009 as B799 95 (2009). DOI:10.1520/B0799-95R14.2For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D.
13、 W., “PorosityTesting of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.3Krumbien, S. J., “Porosity Testing of Contact Platings,” Proceedings, Connec-tors and Interconnection Technology Symposium, Oct. 1987, p 47.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cu
14、stomer 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.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
15、, West Conshohocken, PA 19428-2959. United States1portions 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 coati
16、ngs, ninclude 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 un
17、derplate, 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 The test method employs concentrated sulfurous acid(H2SO3), which emits sulfur dioxide (SO2) gas according to th
18、eequilibrium reaction:H2SO35 SO21H2O (1)The procedure is similar to one first proposed by Lee andTernowski.64.2 Exposure periods may vary, depending upon the degreeof porosity to be revealed. Reaction of the gas with acorrodable base metal at pore sites produces reaction productsthat appear as discr
19、ete spots on the gold or palladium surface.Individual spots are counted with the aid of a loupe orlow-power stereo microscope.4.3 This test method is suitable for coatings containing95 % or more of gold or palladium on substrates of copper,nickel, and their alloys which are commonly used in electric
20、alcontacts.4.4 This porosity test involves corrosion reactions in whichthe products delineate defect sites in coatings. Since thechemistry and properties of these products may not resemblethose found in natural or service environments this test is notrecommended for prediction of the electrical perf
21、ormance ofcontacts unless correlation is first established with serviceexperience.5. Significance and Use5.1 Gold coatings are often specified for the contacts ofseparable electrical connectors and other devices. Electrode-posits are the form of gold that is most used on contacts,although it is also
22、 employed as inlay or clad metal and asweldments on the contact surface. The intrinsic nobility of goldenables it to resist the formation of insulating oxide films thatcould interfere with reliable contact operation.5.2 Palladium coatings are sometimes specified as alterna-tives to gold on electrica
23、l contacts and similar electricalcomponent surfaces, both as electrodeposits and as inlay orclad metal. This test method is particularly suitable for deter-mining porosity in palladium coatings, since the reactiveatmosphere that is used does not attack the palladium if thespecified test conditions a
24、re followed. In contrast, palladiumcoatings are attacked by nitric acid (HNO3) and other strongoxidizing agents, so that Test Method B735 cannot be used fordetermining the porosity in such coatings.5.3 In order for these coatings to function as intended,porosity, cracks, and other defects in the coa
25、ting that exposebase-metal substrates and underplates must be minimal orabsent, except in those cases where it is feasible to use thecontacts in structures that shield the surface from the environ-ment or where corrosion inhibiting surface treatments for thedeposit are employed. The level of porosit
26、y in the coating thatmay be tolerable depends on the severity of the environment tothe underplate or substrate, design factors for the contactdevice like the force with which it is mated, circuit parameters,and the reliability of contact operation that it is necessary tomaintain. Also, when present,
27、 the location of pores on thesurface is important. If the pores are few in number and areoutside of the zone of contact of the mating surfaces, theirpresence can often be tolerated.5.4 Methods for determining pores on a contact surface aremost suitable if they enable their precise location and numbe
28、rsto be determined. Contact surfaces are often 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 highly porous conditions.5.5 The
29、 present test method is capable of detecting virtuallyall porosity or other defects that could participate in corrosionreactions with the substrate or underplate. The test is rapid,simple, and inexpensive. In addition, it can be used on contactshaving complex geometry such as pin-socket contacts (al
30、-though with deep recesses it is preferred that the contactstructures be opened to permit reaction of the sulfur dioxidewith the interior significant surfaces).5.6 The relationship of porosity levels revealed by particulartests to contact behavior must be made by the user of these teststhrough pract
31、ical experience or by judgment. Thus, absence ofporosity in the coating may be a requirement for someapplications, while a few pores in the contact zone may beacceptable for others.5.7 This test is considered destructive in that it reveals thepresence of porosity by contaminating the surface with co
32、rro-sion products and by undercutting the coating at pore sites orat the boundaries of the unplated areas. Any parts exposed tothis test shall not be placed in service.5.8 This test is intended to be used for quantitative descrip-tions of porosity (such as number of pores per unit area or percontact
33、) only on coatings that have a pore density sufficientlylow that the corrosion sites are well separated and can bereadily resolved. As a general guideline this can be achievedfor pore densities up to about 100/cm2. Above this value thetests are useful for the qualitative detection and comparisons of
34、porosity.5.9 For these purposes, the measurement area,orsignificantsurface, shall be defined as those portions of the surface that6Lee, F. and Ternowski, M., Proceedings Ninth International Conference onElectrical Contact Phenomena, Chicago, 1978, p. 215.B799 95 (2014)2are essential to the serviceab
35、ility 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. The significant surfaces shall be indicatedon the drawings of the parts, or by the provision of suitablymarked samples.6. Safety
36、 Hazards6.1 Carry out these test procedures in a clean, working fumehood. The SO2gas that is emitted is toxic, corrosive, andirritating.6.2 Use caution, however, in actually performing the teststhat the drafts often found in hoods do not cause significantcooling of the chamber walls which may lead t
37、o condensationof water and acceleration of the test. It is often convenient toenclose the reaction vessel in a box with a loose-fitting cover,and to keep the box in a hood during the test.6.3 Observe normal precautions in handling corrosive acids.In particular, wear eye protection completely enclosi
38、ng theeyes, and make eye wash facilities readily available.7. Apparatus7.1 Test ChamberMay be any convenient size, glass oracrylic resin vessel having a gastight lid, such as a glassdesiccator of 9 to 10-L capacity. The ratio of chamber volumein cubic centimeters to the generating solution (sulfurou
39、s acid)surface area in square centimeters shall not exceed 25 6 1.7.2 Specimen Holders or SupportsMay be made of glass,polytetrafluoroethylene, or other inert materials. It is essentialthat the specimens be arranged so as not to impede circulationof the gas. Specimens shall not be closer than 25 mm
40、(1 in.)from the wall and 75 mm (3 in.) from the solution surface.Also, the measurement areas of the specimens shall be at least12 mm (0.5 in.) from each other.7.2.1 Do not use a porcelain plate or any other structure thatwould cover more than 30 % of the liquid surface cross-sectional area. This is
41、to insure that movement of air and vaporwithin the vessel will not be restricted during the test.7.3 Stereomicroscope having a 10 magnification shall beused for pore counting. In addition a movable source ofillumination capable of giving oblique lighting on the specimensurface is required. It is pre
42、ferred that a graduated reticle befitted into one of the eyepieces of the microscope.8. Reagents8.1 Sulfurous Acid (H2SO3), “analyzed reagent grade,” orbetter, preferably in individual sealed 500-mL bottles.9. Procedure9.1 Handle specimens as little as possible, and only withtweezers, microscope-len
43、s tissue, or clean, soft cotton gloves.Prior to the test, inspect the samples under 10 magnificationfor evidence of particulate matter. If present, such particlesshall be removed by blowing them with clean, oil-free air. Ifthis is not successful discard the sample. Then, clean thesamples with solven
44、ts or solutions that do not contain chlori-nated hydrocarbons, CFCs or other known ozone-destroyingcompounds. The procedure outlined in Note 1 has been foundto give satisfactory results for platings with mild to moderatesurface contamination.NOTE 1Suggested cleaning procedure:(1) Keep individual con
45、tacts separated if there is a possibility ofdamage to the measurement areas during the various cleaning steps.(2) Clean samples for 5 min in an ultrasonic cleaner which contains ahot (6585C) 2 % aqueous solution of a mildly alkaline (pH 7.510)detergent (such as Micro or Sparkleen).(3) After ultrason
46、ic cleaning, rinse samples under warm running tapwater for at least 5 s.(4) Rinse samples ultrasonically for 2 min in fresh deionized water toremove the last detergent residues.(5) Immerse in fresh methanol or isopropanol, and ultrasonically“agitate” for at least 30 s in order to remove the water fr
47、om the samples.(6) Remove and dry samples until the alcohol has completely evapo-rated. If an air blast is used as an aid to drying, the air shall be oil free,clean, and dry.(7) Do not touch measurement area of the samples with bare fingersafter cleaning.(8) Re-inspect samples (under 10 magnificatio
48、n) for particulate matteron the surface. If particulates are found, repeat the cleaning steps. Surfacecleanliness is extremely important; contaminants, such as plating salts,organic films, and metal flakes may give erroneous indications of defects,and are unacceptable.NOTE 2Omit the cleaning steps f
49、or samples having corrosion-inhibiting, or lubricant coatings, or both, if it is desired to determine theefficacy of these coatings in the SO2atmosphere.9.2 The test temperature shall be 23 6 3C, unless other-wise specified, and the relative humidity in the immediatevicinity of the test chamber shall be no greater than 60 %. If therelative humidity is greater than 60 %, do not run the test.9.3 Carefully add the sulfurous acid (H2SO3) to the bottomof the clean and dry test chamber in a fume hood, load thesamples, using suitable fixtures, and replace the lid. Theam
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