ASTM B764-2004(2009) Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)《多层镍镀层中单层的同步.pdf
《ASTM B764-2004(2009) Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)《多层镍镀层中单层的同步.pdf》由会员分享,可在线阅读,更多相关《ASTM B764-2004(2009) Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)《多层镍镀层中单层的同步.pdf(6页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: B764 04 (Reapproved 2009)Standard Test Method forSimultaneous Thickness and Electrode PotentialDetermination of Individual Layers in Multilayer NickelDeposit (STEP Test)1This standard is issued under the fixed designation B764; the number immediately following the designation indicates
2、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 test method closely estimates the thickness
3、 ofindividual layers of a multilayer nickel electrodeposit and thepotential differences between the individual layers while beinganodically stripped at constant current density.2,31.2 This test method does not cover deposit systems otherthan multilayer electroplated nickel deposits.1.3 This standard
4、 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
5、Standards:4B456 Specification for Electrodeposited Coatings of Cop-per Plus Nickel Plus Chromium and Nickel Plus Chro-miumB504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodD1193 Specification for Reagent Water3. Summary of Test Method3.1 This procedure is a
6、 modification of the well-knowncoulometric method of thickness testing (Test Method B504).It is also known as the anodic dissolution or electrochemicalstripping method.3.2 Coulometric thickness testing instruments are based onthe anodic dissolution (stripping) of the deposit at constantcurrent, whil
7、e the time is measured to determine thickness. Ascommonly practiced, the method employs a small cell that isfilled with an appropriate electrolyte, and the test specimenserves as the bottom of the cell. To the bottom of the cell isattached a rubber or plastic gasket whose opening defines themeasurin
8、g (stripping, anodic) area. If a metallic cell is used, therubber gasket also electrically insulates the test specimen fromthe cell. With the specimen as the anode and the cell or agitatortube as the cathode, a constant direct current is passed throughthe cell until the nickel layer is dissolved. A
9、sudden change involtage between the electrodes occurs when a different metalliclayer starts to dissolve.3.3 Each different metal or species of the same metalrequires a given voltage to keep the current constant whilebeing stripped. As one nickel layer is dissolved away and thenext layer becomes expo
10、sed, there will be a voltage change(assuming a constant current and difference in the electro-chemical characteristics of the two nickel layers). The elapsedtime at which this voltage change occurs (relative to the start ofthe test or previous voltage change) is a measure of the depositthickness.3.4
11、 At the same time, the amplitude of the voltage changecan be observed. That is, the ease (or difficulty) with which onelayer can be dissolved or stripped with reference to anotherlayer can be compared. The lower the voltage needed the moreactive the metal or the greater the tendency to corrodeprefer
12、entially to a more noble metal adjacent to it.3.5 Where the metallic layers are of such a similar naturethat change of the stripping voltage is small, there can beproblems in detecting this change if the voltage between thedeplating cell (cathode) and the sample (anode) is measured.As the sample is
13、dissolved anodically, cathodic processes areoccurring on the deplating cell (cathode) surface that can alsogive rise to voltage changes, due to alterations of the cathodesurface, thus obscuring the anode voltage change. This diffi-culty can be avoided by measuring the potential of thedissolving anod
14、ic sample with respect to an unpolarized thirdelectrode (reference) placed in the cell. By recording thispotential any difference in electrochemical activity between1This method is under the jurisdiction ofASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subco
15、mmittee B08.10 on TestMethods.Current edition approved Sept. 1, 2009. Published December 2009. Originallyapproved in 1986. Last previous edition approved in 2004 as B764 94 (2004).DOI: 10.1520/B0764-04R09.2For discussion of this test, see Harbulak, E. P., “Simultaneous Thickness andElectrochemical P
16、otential Determination of Individual Layers in Multilayer NickelDeposits,” Plating and Surface Finishing, Vol 67, No. 2, February 1980, pp. 4954.3U.S. Patent 4,310,389. Assignee: The Chrysler Corp., Highland Park, MI48203.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontac
17、t ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.layers is more readily d
18、etected. The equipment may becalibrated against standards with known STEP values.3.6 The thickness of any specific nickel layer may becalculated from the quantity of electricity used (current multi-plied by time), area dissolved, electrochemical equivalent ofnickel, anode efficiency, and density of
19、the nickel layer.3.7 Commercial instruments using this principle are avail-able. They are usually a combination coulometric and STEPinstrument. Reference standards are available to calibrate theinstrument. The STEP Test, as is the Coulometric Test, is rapidand destructive to the coating.4. Significa
20、nce and Use4.1 The ability of a multilayer nickel deposit to enhancecorrosion resistance is a function of the difference in theelectrode potentials of the nickel layers (as measured individu-ally at a fixed current density in a given electrolyte versus areference electrode) and the thicknesses of th
21、e layers. Thepotential differences must be sufficient to cause the brightnickel or top layer to corrode preferentially and sacrificiallywith respect to the semi-bright nickel layer beneath it.4.2 This test procedure allows the measurement of thesepotential differences directly on an electroplated pa
22、rt ratherthan on separate foil specimens in such a way that timedetermines the thickness of each layer, while the potentialdifference between nickel layers is an indication of the corro-sion resistance of the total nickel deposit.4.3 The interpretation and evaluation of the results of thistest shoul
23、d be by agreement between the purchaser and themanufacturer.NOTE 1This test may be used as a quality assurance test of themultilayer nickel coatings applied in production. It should be understoodthat due to many factors that influence the progress of corrosion duringactual use of the part, the perfo
24、rmance of different multilayer nickeldeposits in the test cannot be taken as an absolute indicator of the relativecorrosion resistance of these deposits in service.5. Apparatus5.1 Composition of the Electrolyte5:Nickel Chloride (NiCl26H2O) 300g/LSodium Chloride (NaCl) 50g/LBoric Acid (H3BO3)2g/LpH 3
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