1、Designation: G5 132Standard 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 last re
2、vision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1NOTECorrected Research Report information in Section 7 editorially in December 2013.1. Scope1.1 This test method covers an experimental proc
3、edure forchecking experimental technique and instrumentation. Iffollowed, this test method will provide repeatable potentiody-namic anodic polarization measurements that will reproducedata determined by others at other times and in other labora-tories provided all laboratories are testing reference
4、samplesfrom the same lot of Type 430 stainless steel.1.2 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theres
5、ponsibility 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 Standards:2E1338 Guide for Identification of Metals and Alloys inComputerized Material Property Datab
6、asesG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized DatabaseInput3. Significance and Use3.1 The availability of a standard procedure, standardmaterial, and a s
7、tandard plot should make it easy for aninvestigator to check his techniques. This should lead topolarization curves in the literature which can be comparedwith confidence.3.2 Samples of a standard ferritic Type 430 stainless steel(UNS S43000) used in obtaining standard reference plot areavailable fo
8、r those who wish to check their own test procedureand equipment.33.3 Standard potentiodynamic polarization plots are shownfor a lot of material originally purchased in 1992. This testmethod is not applicable for standard material purchasedbefore 1992. These reference data are based on the results fr
9、omdifferent laboratories that followed the standard procedure,using that material in 1.0 N H2SO4. The four sigma probabilitybands for current density values are shown at each potential toindicate the acceptable range of values.3.4 This test method may not be appropriate for polarizationtesting of al
10、l materials or in all environments.3.5 This test method is intended for use in evaluating theaccuracy of a given electrochemical test apparatus, not for usein evaluating materials performance. Therefore, the use of theplots in Fig. 1 is not recommended to evaluate alloys other thanType 430, or lots
11、of Type 430 other than those availablethrough Metal Samples. The use of the data in this test methodin this manner is beyond the scope and intended use of this testmethod. Users of this test method are advised to evaluate testresults relative to the scatter bands corresponding to theparticular lot o
12、f Type 430 stainless steel that was tested.4. Apparatus4.1 The test cell should be constructed to allow the follow-ing items to be inserted into the solution chamber: the testelectrode, two auxiliary electrodes, a Luggin capillary withsalt-bridge connection to the reference electrode, inlet andoutle
13、t for an inert gas, and a thermometer. The test cell shall beconstructed of materials that will not corrode, deteriorate, orotherwise contaminate the test solution.1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of G01.11 on El
14、ectrochemicalMeasurements in Corrosion Testing.Current edition approved Feb. 1, 2013. Published February 2013. Originallyapproved in 1969. Last previous edition approved in 2012 as G512. DOI:10.1520/G0005-13E02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cust
15、omer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3These standard samples are available from Metal Samples, 152 Metal SamplesRd., Mumford, AL 36268. Generally, one sample can be repolished and reused
16、formany runs. This procedure is suggested to conserve the available material.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 1Borosilicate glass and TFE-fluorocarbon have been foundsuitable.4.1.1 A suitable cell is shown in Fig.
17、2 (1).4A 1-L,round-bottom flask has been modified by the addition ofvarious necks to permit the introduction of electrodes, gas inletand outlet tubes, and a thermometer. The Luggin probe-saltbridge separates the bulk solution from the saturated calomelreference electrode, and the probe tip can be ea
18、sily adjusted tobring it in close proximity with the working electrode.4.2 Potentiostat (Note 2):4.2.1 Apotentiostat that will maintain an electrode potentialwithin 1 mV of a preset value over a wide range of appliedcurrents should be used. For the type and size of standardspecimen supplied, the pot
19、entiostat should have a potentialrange from 0.6 to 1.6 V and an anodic current output rangefrom 1.0 to 105A.4.3 Potential-Measuring Instruments (Note 2):4.3.1 The potential-measuring circuit should have highinput impedance on the order of 1011to 1014 to minimizecurrent drawn from the system during m
20、easurements. Suchcircuits are provided with most potentiostats. Instrumentsshould have sufficient sensitivity and accuracy to detect achange of 1.0 mV over a potential range between 0.6 and 1.6V. Potentiostats that scan potential by making frequent poten-tial steps of less than 1.0 mV and those that
21、 make continuousanalog potential sweeps are both 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 currentaccurately to within1%oftheabsolute value over a curren
22、trange between 1.0 and 105A for a Type 430 stainless steel(UNS S43000) specimen with a surface area of approximately5cm2.4.5 Anodic Polarization Circuit:4.5.1 Aschematic wiring diagram (2) is illustrated in Fig. 3.4.5.2 A scanning potentiostat is used for potentiodynamicmeasurements. For such measur
23、ements the potentiostat shall becapable of automatically varying the potential at a constant ratebetween two preset potentials. A record of the potential andcurrent is plotted continuously using such instruments as an4The boldface numbers in parentheses refer to the list of references at the end oft
24、his test method.CURRENT DENSITY (A/cm2)FIG. 1 Typical Standard Potentiodynamic Anodic Polarization PlotFIG. 2 Schematic Diagram of Polarization Cell (1)G51322X-Y recorder and a logarithmic converter incorporated into thecircuit shown in Fig. 3. Some potentiostats have an output ofthe logarithm of th
25、e current as a voltage, which allows directplotting of the potential log current curve using an X-Yrecorder.NOTE 2The instrumental requirements are based upon values typicalof the instruments in the laboratories that participated in the round robin.4.6 Electrode Holder (1):4.6.1 The auxiliary and wo
26、rking electrodes are mounted inthe type of holder shown in Fig. 4. A longer holder is requiredfor the working electrode than for the auxiliary electrode. Aleakproof assembly is obtained by the proper compression fitbetween the electrode and a TFE-fluorocarbon gasket. (Toomuch pressure may cause shie
27、lding of the electrode or break-age of the glass holder, and too little pressure may causeleakage and subsequently crevice corrosion which may affectthe test results.)4.7 Electrodes:4.7.1 Working Electrode, prepared from a 12.7-mm lengthof 9.5-mm diameter rod stock. Each electrode is drilled,tapped,
28、 and mounted in the manner discussed in 4.6.1.NOTE 3If specimen forms are used other than those called for by thistest method, for example, flat sheet specimen, care should be taken sinceit was shown that crevices may be introduced which can lead to erroneousresults (see Fig. X1.1).4.7.1.1 The stand
29、ard AISI Type 430 stainless steel (UNSS43000) should be used if one wishes to reproduce a standardreference plot. This material is prepared from a single heat ofmetal that is mill-annealed for12 h at 815C and air cooled.The chemical composition of the standard stainless steel issupplied with the pur
30、chase of reference material.4.7.2 Auxiliary Electrodes:4.7.2.1 Two platinum auxiliary electrodes are prepared fromhigh-purity rod stock. Each electrode is drilled, tapped, andmounted with a TFE-fluorocarbon gasket in the same manneras the working electrode. A large platinum sheet sealed into aglass
31、holder is also acceptable.4.7.2.2 A platinized surface may be utilized because of theincreased surface area. This may be accomplished by cleaningthe surface in hot aqua regia (3 parts concentrated HCl and 1part concentrated HNO3), washing, and then drying. Bothelectrodes are platinized by immersing
32、them in a solution of 3% platinic chloride and 0.02 % lead acetate and electrolyzingat a current density of 40 to 50 mA/cm2for4or5min(1, 3).The polarity is reversed every minute. Occluded chloride isremoved by electrolyzing in a dilute (10 %) sulfuric acidsolution for several minutes with a reversal
33、 in polarity everyminute. Electrodes are rinsed thoroughly and stored in distilledwater until ready for use. Since certain ions can poison theseelectrodes, periodic checks of platinized platinum potentialsagainst a known reference electrode should be made.4.7.2.3 Alternatively, graphite auxiliary el
34、ectrodes can beused, but material retained by the graphite may contaminatesubsequent experiments. This contamination can be minimizedby using high-density graphite or avoided by routinely replac-ing the graphite electrode.4.7.3 Reference Electrode (4):4.7.3.1 A saturated calomel electrode with a con
35、trolled rateof leakage (about 3 L/h) is recommended. This type ofelectrode is durable, reliable, and commercially available.Precautions shall be taken to ensure that it is maintained in theproper condition. The potential of the calomel electrode shouldbe checked at periodic intervals to ensure the a
36、ccuracy of theelectrode. For other alloy-electrolyte combinations a differentreference electrode may be preferred in order to avoid con-tamination of the reference electrode or the electrolyte.4.7.3.2 Alternatively, a saturated calomel electrode utilizinga semipermeable membrane or porous plug tip m
37、ay be used.These may require special care.FIG. 3 Schematic Wiring Diagram (2)FIG. 4 Specimen Mounted on Electrode HolderG513235. Experimental Procedure5.1 Prepare 1 L of 1.0 N H2SO4from A.C.S. reagent gradeacid and distilled water, for example, by using 27.8 mL of 98%H2SO4/L of solution. Transfer 90
38、0 mL of solution to theclean polarization cell.5.2 Place the platinized auxiliary electrodes, salt-bridgeprobe, and other components in the test cell and temporarilyclose the center opening with a glass stopper. Fill the saltbridge with test solution.NOTE 4When using a controlled leakage salt bridge
39、, the levels of thesolution 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 siphoning, or asemipermeable membrane or porous plug tip may be used on the saltbri
40、dge.5.3 Bring the temperature of the solution to 30 6 1C byimmersing the test cell in a controlled-temperature water bathor by other convenient means.5.4 Reduce oxygen levels in solution prior to immersion ofthe test specimen. This may be accomplished by bubbling anoxygen-free gas such as hydrogen,
41、argon, or nitrogen at a rateof 150 cm3/min for a minimum of12 h.5.5 Prepare the working electrode surface within1hoftheexperiment. Wet grind with 240-grit SiC paper, wet polish with600-grit SiC paper until previous coarse scratches are removed,rinse, and dry. (Drilled and tapped specimens can be thr
42、eadedonto an electrode holder rod and secured in a lathe or electricdrill for this operation.)5.6 Determine the surface area by measuring all dimensionsto the nearest 0.01 mm, subtracting the area under the gasket(usually 0.20 to 0.25 cm2).5.7 Mount the specimen on the electrode holder as de-scribed
43、 in 4.6.1. Tighten the assembly by holding the upper endof the mounting rod in a vise or clamp while tightening themounting nut until the gasket is properly compressed.5.8 Degrease the specimen just prior to immersion and thenrinse in distilled water.5.9 Transfer the specimen to the test cell and ad
44、just thesalt-bridge probe tip so it is about 2 mm or 2 times the tipdiameter, whichever is larger from the specimen electrode.5.10 Record the open-circuit specimen potential, that is, thecorrosion potential, after 55 min immersion. If platinumcounter electrodes and hydrogen gas are used, record thep
45、latinum 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+1.60 V versus saturated calomel electrode (SCE) (active tonoble).5.11.2 Use a potentiodynamic potent
46、ial sweep rate of 0.6V/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 inaccordance with Practice G3, (potential-ordinate, currentdensity-abscissa).6. Standard Reference Plots6.1 Ast
47、andard polarization plot prepared from data obtainedby following the standard procedure discussed in this testmethod is shown in Fig. 1 (5). The plot shows 64 sigmaconfidence bands from round robin tests and indicate theacceptable current density values at each potential. The aver-age corrosion pote
48、ntial is 0.52 V, and the average platinizedplatinum potential is 0.26 V.6.2 Table 1 gives the 64 sigma confidence interval forcurrent densities at specific potentials and can be used forcompliance verification.6.3 Typical deviations from the standard plot are shown anddiscussed in Appendix X1. Refer
49、ence to this discussion may behelpful in determining the reasons for differences between anexperimental curve and the standard plots.7. Precision and Bias57.1 The repeatability and reproducibility of this test havebeen developed by an interlaboratory test with 5 participatinglaboratories. The detailed results of this testing are presented inASTM Research Report RR:G01-1026.The 99.994% probabil-ity bands (4 standard deviation) calculated from the data in thisstudy are included in Fig. 1.7.2 There is no bias in this test method because thepotentiodynamic curve is
