1、Designation: B 799 95 (Reapproved 2005)Standard Test Method forPorosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor1This standard is issued under the fixed designation B 799; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、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 methods fordetermining the porosity of gold and p
3、alladium 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 ot
4、her porosity testing methods are describedin the literature.2,3Other porosity test methods are B 735,B 741, B 798, and B 809. An ASTM Guide to the selection ofporosity tests for electrodeposits and related metallic coatingsis available as Guide B 765.1.4 The values stated in SI units are to be regar
5、ded asstandard. 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
6、appropriateMaterial 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 Standa
7、rds:4B 374 Terminology Relating to ElectroplatingB 542 Terminology Relating 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 Electrography5B 765 Guide
8、for Selection of Porosity and Gross DefectsTests for Electrodeposits and Related Metallic CoatingsB 798 Test Method for Porosity in Gold or PalladiumCoatings on Metal Substrates by Gel-Bulk ElectrographyB 809 Test Method for Porosity in Metallic Coatings ByHumid Sulfur Vapor (“Flowers-of-Sulfur”)3.
9、Terminology3.1 DefinitionsMany terms used in this test method aredefined in 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 corrosion products, nthose reaction products ema-nating from the pores that p
10、rotrude 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 draw
11、ing 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 thoseportions of the surface that are essential to the serviceability orfunction of the part, such as its contact properties, or
12、 which canbe the source of corrosion products or tarnish films thatinterfere with the function of the part.3.2.3 metallic coatings, ninclude platings, claddings, orother metallic layers applied to the substrate. The coatings cancomprise a single metallic layer or a combination of metalliclayers.3.2.
13、4 porosity, nthe presence of any discontinuity, crack,or hole in the coating that exposes a different underlying metal.1This 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 Me
14、thods.Current edition approved Nov. 1, 2005. Published November 2005. Originallyapproved in 1988. Last previous edition approve in 2000 as B 799 95 (2000).2For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “ PorosityTesting of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.3S. J. Kr
15、umbien, Porosity Testing of Contact Platings, Proceedings, Connectorsand Interconnection Technology Symposium, Oct. 1987, p 47.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information
16、, refer to the standards Document Summary page onthe ASTM website.5Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.5 underplate, na metallic coating layer between thesubstrate and the topmost layer or layers. The thickn
17、ess 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 theequilibrium reaction:H2SO35 SO21 H2O (1)The procedure is similar to one first proposed by Lee andTe
18、rnowski.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 discrete spots on the gold or palladium surface.Individual spots are counted with the aid of a loupe orl
19、ow-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 electricalcontacts.4.4 This porosity test involves corrosion reactions in whichthe products delineate defec
20、t 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 performance ofcontacts unless correlation is first established with serviceexperience.5. Significance a
21、nd 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 employed as inlay or clad metal and asweldments on the contact surface. The intrinsic nobility of
22、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 electrical contacts and similar electricalcomponent surfaces, both as electrodeposits and as inlay orclad me
23、tal. 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 are followed. In contrast, palladiumcoatings are attacked by nitric acid (HNO3) and other strongoxid
24、izing agents, so that Test Method B 735 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 coating that exposebase-metal substrates and underplates must be minimal orabsent, except in those ca
25、ses 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 porosity in the coating thatmay be tolerable depends on the severity of the environment tothe underplate
26、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, the location of pores on thesurface is important. If the pores are few in number and areoutside o
27、f 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 numbersto be determined. Contact surfaces are often curved or irregularin shape, and testing methods sh
28、ould 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 present test method is capable of detecting virtuallyall porosity or other defects that could par
29、ticipate 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-though with deep recesses it is preferred that the contactstructures be opened to permit reaction
30、 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 practical experience or by judgment. Thus, absence ofporosity in the coating may be a requirement for s
31、omeapplications, 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 corro-sion products and by undercutting the coating at pore sites orat the boundaries of the unplate
32、d 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) only on coatings that have a pore density sufficientlylow that the corrosion sites are well sepa
33、rated 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 ofporosity.5.9 For these purposes, the measurement area,orsignificantsurface, shall be defined as th
34、ose portions of the surface thatare essential to the serviceability 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
35、parts, or by the provision of suitablymarked samples.6. Safety 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
36、cause significantcooling of the chamber walls which may lead to condensationof water and acceleration of the test. It is often convenient to6Lee, F., and Ternowski, M., Proceedings Ninth International Conference onElectrical Contact Phenomena, Chicago, 1978, p. 215.B 799 95 (2005)2enclose the reacti
37、on 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 enclosing theeyes, and make eye wash facilities readily available.7. Apparatus7.1 Test ChamberMay be an
38、y 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 (sulfurous acid)surface area in square centimeters shall not exceed 25 6 1.7.2 Specimen Holders or Suppor
39、tsMay 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 (1 in.)from the wall and 75 mm (3 in.) from the solution surface.Also, the measurement areas of
40、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 to insure that movement of air and vaporwithin the vessel will not be restricted during the test
41、.7.3 Stereomicroscope having a 103 magnification shall beused for pore counting. In addition a movable source ofillumination capable of giving oblique lighting on the specimensurface is required. It is preferred that a graduated reticle befitted into one of the eyepieces of the microscope.8. Reagent
42、s8.1 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-lens tissue, or clean, soft cotton gloves.Prior to the test, inspect the samples under 103 magnifi
43、cationfor 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 solvents or solutions that do not contain chlori-nated hydrocarbons, CFCs or other known ozone-destr
44、oyingcompounds. 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 contacts separated if there is a possibility ofdamage to the measurement areas during the various
45、 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 ultrasonic cleaning, rinse samples under warm running tapwater for at least 5 s.(4) Rinse samples ultr
46、asonically 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 from the samples.(6) Remove and dry samples until the alcohol has completely evapo-rated. If an
47、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 103 magnification) for particulate matteron the surface. If particulates are found, repeat the cleaning steps
48、. 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 for samples having corrosion-inhibiting, or lubricant coatings, or both, if it is desired to d
49、etermine 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. Theambient relative humidity shall be no greater than 60 % duringboth the addition of the H2SO3and the
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