1、Designation: G5 132G5 14Standard Reference Test Method forMaking Potentiodynamic Anodic PolarizationMeasurements1This standard is issued under the fixed designation G5; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of la
2、st revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1 NOTECorrected Research Report information in Section 7 editorially in December 2013.1. Scope1.1 This test method covers an experimenta
3、l procedure for checking experimental technique and instrumentation. If followed,this test method will provide repeatable potentiodynamic anodic polarization measurements that will reproduce data determinedby others at other times and in other laboratories provided all laboratories are testing refer
4、ence samples from the same lot of Type430 stainless steel.1.2 UnitsThe values stated in SI units are to be regarded as standard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is
5、 the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a
6、Test MethodE1338 Guide for Identification of Metals and Alloys in Computerized Material Property DatabasesG3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion TestingG107 Guide for Formats for Collection and Compilation of Corrosion Data for Metals for Computerized Dat
7、abase Input3. Significance and Use3.1 The availability of a standard procedure, standard material, and a standard plot should make it easy for an investigator tocheck his techniques. This should lead to polarization curves in the literature which can be compared with confidence.3.2 Samples of a stan
8、dard ferritic Type 430 stainless steel (UNS S43000) used in obtaining standard reference plot are availablefor those who wish to check their own test procedure and equipment.33.3 Standard potentiodynamic polarization plots are shown for a lot of material originally purchased in 1992. This test metho
9、dis not applicable for standard material purchased before 1992. These reference data are based on the results from differentlaboratories that followed the standard procedure, using that material in 1.0 N H2SO4. The four sigma probability bands for currentdensity values are shown at each potential to
10、 indicate the acceptable range of values.3.4 This test method may not be appropriate for polarization testing of all materials or in all environments.3.5 This test method is intended for use in evaluating the accuracy of a given electrochemical test apparatus, not for use inevaluating materials perf
11、ormance. Therefore, the use of the plots in Fig. 1 is not recommended to evaluate alloys other than Type430, or lots of Type 430 other than those available through Metal Samples. The use of the data in this test method in this manner1 This test method is under the jurisdiction of ASTM Committee G01
12、on Corrosion of Metals and is the direct responsibility of G01.11 on Electrochemical Measurementsin Corrosion Testing.Current edition approved Feb. 1, 2013Nov. 1, 2014. Published February 2013December 2014. Originally approved in 1969. Last previous edition approved in 20122013as G512.132. DOI: 10.1
13、520/G0005-13E02.10.1520/G0005-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 These standard samples are
14、 available from Metal Samples, 152 Metal Samples Rd., Mumford, AL 36268. Generally, one sample can be repolished and reused for manyruns. This procedure is suggested to conserve the available material.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard
15、an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is
16、to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1is beyond the scope and intended use of this test method. Users of this test method are advised to evaluate test results relative tothe scatter ban
17、ds corresponding to the particular lot of Type 430 stainless steel that was tested.4. Apparatus4.1 The test cell should be constructed to allow the following items to be inserted into the solution chamber: the test electrode,two auxiliary electrodes, a Luggin capillary with salt-bridge connection to
18、 the reference electrode, inlet and outlet for an inert gas,and a thermometer. The test cell shall be constructed of materials that will not corrode, deteriorate, or otherwise contaminate thetest solution.NOTE 1Borosilicate glass and TFE-fluorocarbon have been found suitable.4.1.1 A suitable cell is
19、 shown in Fig. 2 (1).4 A 1-L, round-bottom flask has been modified by the addition of various necks topermit the introduction of electrodes, gas inlet and outlet tubes, and a thermometer. The Luggin probe-salt bridge separates the bulksolution from the saturated calomel reference electrode, and the
20、probe tip can be easily adjusted to bring it in close proximity withthe working electrode.4.2 Potentiostat (Note 2):4.2.1 Apotentiostat that will maintain an electrode potential within 1 mV of a preset value over a wide range of applied currentsshould be used. For the type and size of standard speci
21、men supplied, the potentiostat should have a potential range from 0.6 to1.6 V and an anodic current output range from 1.0 to 105 A.4.3 Potential-Measuring Instruments (Note 2):4.3.1 The potential-measuring circuit should have high input impedance on the order of 1011 to 1014 to minimize currentdrawn
22、 from the system during measurements. Such circuits are provided with most potentiostats. Instruments should havesufficient sensitivity and accuracy to detect a change of 1.0 mV over a potential range between 0.6 and 1.6 V. Potentiostats thatscan potential by making frequent potential steps of less
23、than 1.0 mV and those that make continuous analog potential sweeps areboth suitable for this test method, providing that they can achieve the required potential scan rate.4.4 Current-Measuring Instruments (Note 2):4.4.1 An instrument that is capable of measuring a current accurately to within 1 % of
24、 the absolute value over a current rangebetween 1.0 and 105 A for a Type 430 stainless steel (UNS S43000) specimen with a surface area of approximately 5 cm2.4.5 Anodic Polarization Circuit:4 The boldface numbers in parentheses refer to the list of references at the end of this test method.CURRENT D
25、ENSITY (A/cm2)FIG. 1 Typical Standard Potentiodynamic Anodic Polarization PlotG5 1424.5.1 A schematic wiring diagram (2) is illustrated in Fig. 3.4.5.2 A scanning potentiostat is used for potentiodynamic measurements. For such measurements the potentiostat shall becapable of automatically varying th
26、e potential at a constant rate between two preset potentials.Arecord of the potential and currentis plotted continuously using such instruments as an X-Y recorder and a logarithmic converter incorporated into the circuit shownin Fig. 3. Some potentiostats have an output of the logarithm of the curre
27、nt as a voltage, which allows direct plotting of the potentiallog current curve using an X-Y recorder.NOTE 2The instrumental requirements are based upon values typical of the instruments in the laboratories that participated in the round robin.4.6 Electrode Holder (1):4.6.1 The auxiliary and working
28、 electrodes are mounted in the type of holder shown in Fig. 4. A longer holder is required forthe working electrode than for the auxiliary electrode.Aleakproof assembly is obtained by the proper compression fit between theelectrode and a TFE-fluorocarbon gasket. (Too much pressure may cause shieldin
29、g of the electrode or breakage of the glass holder,and too little pressure may cause leakage and subsequently crevice corrosion which may affect the test results.)4.7 Electrodes:4.7.1 Working Electrode, prepared from a 12.7-mm length of 9.5-mm diameter rod stock. Each electrode is drilled, tapped, a
30、ndmounted in the manner discussed in 4.6.1.NOTE 3If specimen forms are used other than those called for by this test method, for example, flat sheet specimen, care should be taken since itwas shown that crevices may be introduced which can lead to erroneous results (see Fig. X1.1).FIG. 2 Schematic D
31、iagram of Polarization Cell (1)FIG. 3 Schematic Wiring Diagram (2)G5 1434.7.1.1 The standardAISIType 430 stainless steel (UNS S43000) should be used if one wishes to reproduce a standard referenceplot. This material is prepared from a single heat of metal that is mill-annealed for 12 h at 815C and a
32、ir cooled. The chemicalcomposition of the standard stainless steel is supplied with the purchase of reference material.4.7.2 Auxiliary Electrodes:4.7.2.1 Two platinum auxiliary electrodes are prepared from high-purity rod stock. Each electrode is drilled, tapped, andmounted with a TFE-fluorocarbon g
33、asket in the same manner as the working electrode. A large platinum sheet sealed into a glassholder is also acceptable.4.7.2.2 A platinized surface may be utilized because of the increased surface area. This may be accomplished by cleaning thesurface in hot aqua regia (3 parts concentrated HCl and 1
34、 part concentrated HNO3), washing, and then drying. Both electrodes areplatinized by immersing them in a solution of 3 % platinic chloride and 0.02 % lead acetate and electrolyzing at a current densityof 40 to 50 mA/cm2 for 4 or 5 min (1, 3). The polarity is reversed every minute. Occluded chloride
35、is removed by electrolyzingin a dilute (10 %) sulfuric acid solution for several minutes with a reversal in polarity every minute. Electrodes are rinsedthoroughly and stored in distilled water until ready for use. Since certain ions can poison these electrodes, periodic checks ofplatinized platinum
36、potentials against a known reference electrode should be made.4.7.2.3 Alternatively, graphite auxiliary electrodes can be used, but material retained by the graphite may contaminatesubsequent experiments. This contamination can be minimized by using high-density graphite or avoided by routinely repl
37、acingthe graphite electrode.4.7.3 Reference Electrode (4):4.7.3.1 A saturated calomel electrode with a controlled rate of leakage (about 3 L/h) is recommended. This type of electrodeis durable, reliable, and commercially available. Precautions shall be taken to ensure that it is maintained in the pr
38、oper condition.The potential of the calomel electrode should be checked at periodic intervals to ensure the accuracy of the electrode. For otheralloy-electrolyte combinations a different reference electrode may be preferred in order to avoid contamination of the referenceelectrode or the electrolyte
39、.4.7.3.2 Alternatively, a saturated calomel electrode utilizing a semipermeable membrane or porous plug tip may be used. Thesemay require special care.5. Experimental Procedure5.1 Prepare 1 L of 1.0 N H2SO4 from A.C.S. reagent grade acid and distilled water, for example, by using 27.8 mL of 98 %H2SO
40、4 /L of solution. Transfer 900 mL of solution to the clean polarization cell.5.2 Place the platinized auxiliary electrodes, salt-bridge probe, and other components in the test cell and temporarily close thecenter opening with a glass stopper. Fill the salt bridge with test solution.FIG. 4 Specimen M
41、ounted on Electrode HolderG5 144NOTE 4When using a controlled leakage salt bridge, the levels of the solution in the reference and polarization cells should be the same to avoidsiphoning. If this is impossible, a closed solution-wet (not greased) stopcock can be used in the salt bridge to eliminate
42、siphoning, or a semipermeablemembrane or porous plug tip may be used on the salt bridge.5.3 Bring the temperature of the solution to 30 6 1C by immersing the test cell in a controlled-temperature water bath or byother convenient means.5.4 Reduce oxygen levels in solution prior to immersion of the te
43、st specimen. This may be accomplished by bubbling anoxygen-free gas such as hydrogen, argon, or nitrogen at a rate of 150 cm3/min for a minimum of 12 h.5.5 Prepare the working electrode surface within 1 h of the experiment. Wet grind with 240-grit SiC paper, wet polish with600-grit SiC paper until p
44、revious coarse scratches are removed, rinse, and dry. (Drilled and tapped specimens can be threaded ontoan electrode holder rod and secured in a lathe or electric drill for this operation.)5.6 Determine the surface area by measuring all dimensions to the nearest 0.01 mm, subtracting the area under t
45、he gasket(usually 0.20 to 0.25 cm2).5.7 Mount the specimen on the electrode holder as described in 4.6.1. Tighten the assembly by holding the upper end of themounting rod in a vise or clamp while tightening the mounting nut until the gasket is properly compressed.5.8 Degrease the specimen just prior
46、 to immersion and then rinse in distilled water.5.9 Transfer the specimen to the test cell and adjust the salt-bridge probe tip so it is about 2 mm or 2 times the tip diameter,whichever is larger from the specimen electrode.5.10 Record the open-circuit specimen potential, that is, the corrosion pote
47、ntial, after 55 min immersion. If platinum counterelectrodes and hydrogen gas are used, record the platinum potential 50 min after immersion of the specimen.5.11 Potential Scan:5.11.1 Start the potential scan 1 h after specimen immersion, beginning at the corrosion potential (Ecorr). Proceed through
48、 +1.60V versus saturated calomel electrode (SCE) (active to noble).5.11.2 Use a potentiodynamic potential sweep rate of 0.6 V/h (65 %) recording the current continuously with change inpotential from the corrosion potential to +1.6 V SCE.5.12 Plot anodic polarization data semilogarithmically in accor
49、dance with Practice G3, (potential-ordinate, current density-abscissa).6. Standard Reference Plots and Compliance Limits6.1 A standard polarization plot prepared from data obtained by following the standard procedure discussed in this test methodthe interlaboratory testing program is shown in Fig. 1 (. See5). The plotResearch Report RR:G01-1026shows.5 64 sigmaconfidence bands from round robin tests and indicate the acceptable current density values at each potential. The confidence bandswere calculated by determining logarithmic average of the current dens
