ASTM G5-2014e1 Standard Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements.pdf

1、Designation: G5 141Standard 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.1NOTEEditorially corrected Table 1 in August 2018.1. Scope1.1 This test method covers an experimental procedure forchecking experimental tech

3、nique 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 samplesfrom the same lot of Type 43

4、0 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 theresponsibility of the user of this sta

5、ndard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision

6、on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a T

7、est MethodE1338 Guide for Identification of Metals and Alloys inComputerized Material Property DatabasesG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized Databas

8、eInput3. Significance and Use3.1 The availability of a standard procedure, standardmaterial, and a standard 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 fer

9、ritic Type 430 stainless steel(UNS S43000) used in obtaining standard reference plot areavailable for 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 app

10、licable for standard material purchasedbefore 1992. These reference data are based on the results fromdifferent 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

11、acceptable range of values.3.4 This test method may not be appropriate for polarizationtesting of all 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. Therefo

12、re, the use of theplots in Fig. 1 is not recommended to evaluate alloys other thanType 430, or lots 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 ar

13、e advised to evaluate testresults relative to the scatter bands corresponding to theparticular lot of Type 430 stainless steel that was tested.1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of G01.11 on ElectrochemicalMeasurem

14、ents in Corrosion Testing.Current edition approved Nov. 1, 2014. Published December 2014. Originallyapproved in 1969. Last previous edition approved in 2013 as G5132. DOI:10.1520/G0005-14E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serv

15、iceastm.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 formany runs. This p

16、rocedure is suggested to conserve the available material.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established

17、in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Apparatus4.1 The test cell should be constructed to allow the follow-ing items to be inserted into the soluti

18、on chamber: the testelectrode, two auxiliary electrodes, a Luggin capillary withsalt-bridge connection to the reference electrode, inlet andoutlet for an inert gas, and a thermometer. The test cell shall beconstructed of materials that will not corrode, deteriorate, orotherwise contaminate the test

19、solution.NOTE 1Borosilicate glass and TFE-fluorocarbon have been foundsuitable.4.1.1 A suitable cell is shown in Fig. 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 p

20、robe-saltbridge separates the bulk solution from the saturated calomelreference electrode, and the probe tip can be easily 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

21、value over a wide range of appliedcurrents should be used. For the type and size of standardspecimen supplied, the potentiostat 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

22、 circuit should have highinput impedance on the order of 1011to 1014 to minimizecurrent drawn from the system during measurements. Suchcircuits are provided with most potentiostats. Instrumentsshould have sufficient sensitivity and accuracy to detect achange of 1.0 mV over a potential range between

23、0.6 and 1.6V. Potentiostats that scan potential by making frequent poten-tial steps of less than 1.0 mV and those that 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 (Not

24、e 2):4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.CURRENT DENSITY (A/cm2)FIG. 1 Typical Standard Potentiodynamic Anodic Polarization PlotFIG. 2 Schematic Diagram of Polarization Cell (1)G514124.4.1 An instrument that is capable of measuring a cur

25、rentaccurately to within1%oftheabsolute value over a currentrange 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 potentiost

26、at is used for potentiodynamicmeasurements. For such measurements 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 anX-Y recorder and a logar

27、ithmic converter incorporated into thecircuit shown in Fig. 3. Some potentiostats have an output ofthe logarithm of the 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 in

28、struments in the laboratories that participated in the round robin.4.6 Electrode Holder (1):4.6.1 The auxiliary and working 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 obtai

29、ned by the proper compression fitbetween the electrode and a TFE-fluorocarbon gasket. (Toomuch pressure may cause shielding 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:

30、4.7.1 Working Electrode, prepared from a 12.7-mm lengthof 9.5-mm diameter rod stock. Each electrode is drilled,tapped, 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

31、sinceit was shown that crevices may be introduced which can lead to erroneousresults (see Fig. X1.1).4.7.1.1 The standard 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-an

32、nealed for12 h at 815C and air cooled.The chemical composition of the standard stainless steel issupplied with the purchase 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

33、 with a TFE-fluorocarbon gasket in the same manneras the working electrode. A large platinum sheet sealed into aglass 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 part

34、s concentrated HCl and 1part concentrated HNO3), washing, and then drying. Bothelectrodes are platinized by immersing 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. Occ

35、luded chloride isremoved by electrolyzing in a dilute (10 %) sulfuric acidsolution for several minutes with a reversal in polarity everyminute. Electrodes are rinsed thoroughly and stored in distilledwater until ready for use. Since certain ions can poison theseelectrodes, periodic checks of platini

36、zed platinum potentialsagainst a known reference electrode should be made.4.7.2.3 Alternatively, graphite auxiliary electrodes can beused, but material retained by the graphite may contaminatesubsequent experiments. This contamination can be minimizedby using high-density graphite or avoided by rout

37、inely replac-ing the graphite electrode.FIG. 3 Schematic Wiring Diagram (2)FIG. 4 Specimen Mounted on Electrode HolderG514134.7.3 Reference Electrode (4):4.7.3.1 A saturated calomel electrode with a controlled rateof leakage (about 3 L/h) is recommended. This type ofelectrode is durable, reliable, a

38、nd 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 accuracy of theelectrode. For other alloy-electrolyte combinations a differentreference electrode m

39、ay 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 may be used.These may require special care.5. Experimental Procedure5.1 Prepare 1 L of 1.0 N H2SO4f

40、rom A.C.S. reagent gradeacid and distilled water, for example, by using 27.8 mL of 98%H2SO4/L of solution. Transfer 900 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

41、opening with a glass stopper. Fill the saltbridge with test solution.NOTE 4When using a controlled leakage salt bridge, 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 us

42、ed in the salt bridge to eliminate siphoning, or asemipermeable membrane or porous plug tip may be used on the saltbridge.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 solu

43、tion prior to immersion ofthe test specimen. This may be accomplished by bubbling anoxygen-free gas such as hydrogen, 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 with6

44、00-grit SiC paper until previous coarse scratches are removed,rinse, and dry. (Drilled and tapped specimens can be threadedonto 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, subtra

45、cting the area under the gasket(usually 0.20 to 0.25 cm2).5.7 Mount the specimen on the electrode holder as de-scribed 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 t

46、he specimen just prior to immersion and thenrinse in distilled water.5.9 Transfer the specimen to the test cell and adjust 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

47、, thecorrosion potential, after 55 min immersion. If platinumcounter electrodes and hydrogen gas are used, record theplatinum 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)

48、. Proceed through+1.60 V versus saturated calomel electrode (SCE) (active tonoble).5.11.2 Use a potentiodynamic potential 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 semilogarithm

49、ically inaccordance with Practice G3, (potential-ordinate, currentdensity-abscissa).6. Standard Reference Plots and Compliance Limits6.1 Astandard polarization plot prepared from the interlabo-ratory testing program is shown in Fig. 1. See Research ReportRR:G01-1026.5The confidence bands were calculated bydetermining logarithmic average of the current densities ateach potential and plotting the current density limits at fourlogarithmic standard deviations on either side of the logarith-mic average. The average corrosion potential was -0.52 V, andthe average plat