1、Designation: G5 94 (Reapproved 2011)1Standard Reference Test Method forMaking Potentiostatic and Potentiodynamic AnodicPolarization Measurements1This standard is issued under the fixed designation G5; the number immediately following the designation indicates the year of originaladoption or, in the
2、case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1NOTEUpdated units statement and text editorially in November 2011.1. Scope1.1 This test method covers a
3、n experimental procedure forchecking experimental technique and instrumentation. If fol-lowed, this test method will provide repeatable potentiostaticand potentiodynamic anodic polarization measurements thatwill reproduce data determined by others at other times and inother laboratories provided all
4、 laboratories are testing referencesamples from 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, a
5、ssociated 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 Standards:2E1338 Guide for Identification of Metals and Alloys in
6、Computerized 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 DatabaseInput3. Significance and Use3.1 The availability of a standard
7、procedure, standard ma-terial, and a standard plot should make it easy for an investi-gator to check his techniques. This should lead to polarizationcurves in the literature which can be compared with confi-dence.3.2 Samples of a standard ferritic Type 430 stainless steel(UNS S43000) used in obtaini
8、ng standard reference plot areavailable for those who wish to check their own test procedureand equipment.33.3 Standard potentiostatic and potentiodynamic polariza-tion plots are supplied with the purchase of the referencematerial. These reference data are based on the results fromdifferent laborato
9、ries that followed the standard procedure,using that material in 1.0 N H2SO4. Maximum and minimumcurrent values are shown at each potential to indicate theacceptable range of values.3.4 This test method may not be appropriate for polarizationtesting of all materials or in all environments.3.5 This t
10、est 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 Figs. 1 and 2 or Appendix X2 is not recommended toevaluate alloys other than Type 430, or lots of Type 430 otherthan t
11、hose available throughASTM. The use of the data in thistest method in this manner is beyond the scope and intendeduse of this test method. Users of this test method are advised toevaluate test results relative to the scatter bands correspondingto the particular lot of Type 430 stainless steel that w
12、as 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 andoutlet for an inert gas, and a thermom
13、eter. 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 ElectrochemicalMeasurements in Corr
14、osion Testing.Current edition approved Nov. 15, 2011. Published May 2012. Originallyapproved in 1969. Last previous edition approved in 2004 as G594(2004). DOI:10.1520/G0005-94R11E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
15、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, P.O. Box 8,Mumford, AL 36268. Generally, one sample can be repolished and reused for manyruns. This procedure is suggest
16、ed to conserve the available material.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 1Borosilicate glass and TFE-fluorocarbon have been foundsuitable.4.1.1 A suitable cell is shown in Fig. 3 (1).4A 1-L,roundbottom flask has bee
17、n modified by the addition of variousnecks to permit the introduction of electrodes, gas inlet andoutlet tubes, and a thermometer. The Luggin probe-salt bridgeseparates the bulk solution from the saturated calomel refer-ence electrode, and the probe tip can be easily adjusted to bringit in close pro
18、ximity 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 potentiostat should have a potentialrang
19、e from 0.6 to 1.6 V and an anodic current output rangefrom 1.0 to 105A.4.3 Potential-Measuring Instruments (Note 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 Potentiostatic Anodic Polarization Plo
20、tCURRENT DENSITY (A/cm2)FIG. 2 Typical Standard Potentiodynamic Anodic Polarization PlotG5 94 (2011)124.3.1 The potential-measuring circuit should have a highinput impedance on the order of 1011to 1014V to minimizecurrent drawn from the system during measurements. Suchcircuits are provided with most
21、 potentiostats. Instrumentsshould have sufficient sensitivity and accuracy to detect achange of 1.0 mV over a potential range between 0.6 and 1.6V.4.4 Current-Measuring Instruments (Note 2):4.4.1 An instrument that is capable of measuring a currentaccurately to within 1 % of the absolute value over
22、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 A schematic potentiostatic anodic polarization wiringdiagram (2) is illustrated in Fig. 4.4.5.2 A scanning potentiostat is used for p
23、otentiodynamicmeasurements. 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 logarithmic converter
24、 incorporated into thecircuit shown in Fig. 4. 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 instruments in 15
25、laboratories.4.6 Electrode Holder (1):4.6.1 The auxiliary and working electrodes are mounted inthe type of holder shown in Fig. 5. A longer holder is requiredfor the working electrode than for the auxiliary electrode. Aleak-proof assembly is obtained by the proper compression fitbetween the electrod
26、e 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:4.7.1 Working Electrode, prepared from a 12.7-mm leng
27、thof 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 sinceit was shown that crevices may be introduced whi
28、ch 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-annealed for12 h at 815C and air cooled.FIG. 3 Schemati
29、c Diagram of Polarization Cell (1)FIG. 4 Schematic Potentiostatic Anodic PolarizationWiring Diagram (2) FIG. 5 Specimen Mounted on Electrode HolderG5 94 (2011)13The chemical composition of the standard stainless steel issupplied with the purchase of reference material.4.7.2 Auxiliary Electrodes:4.7.
30、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 holder is also acceptable.4.7.2.2 A platinized surface may
31、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 them in a solution of3 % platinic chloride and 0.02 % lead
32、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 in polarity everyminute. Electrodes are rinsed thoroughly
33、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 electrodes can beused, but material retained by the graphite
34、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 controlled rateof leakage (about 3 L/h) is recommended. This t
35、ype 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 accuracy of theelectrode. For other alloy-electrolyte combin
36、ations 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 semi-permeable membrane or porous plug tip may be used.These may require special care.5. Experimental
37、Procedure5.1 Prepare 1 L of 1.0 N H2SO4from A.C.S. reagent gradeacid and distilled water, for example, by using 27.8 mLof 98 %H2SO4/L of solution. Transfer 900 mL of solution to the cleanpolarization cell.5.2 Place the platinized auxiliary electrodes, salt-bridgeprobe, and other components in the te
38、st cell and temporarilyclose the center 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 solu
39、tion-wet (not greased)stopcock can be used in the salt bridge to eliminate siphoning, or asemi-permeable 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 convenie
40、nt 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, argon, or nitrogen at a rateof 150 cm3/min for a minimum of12 h.5.5 Prepare the working electrode surface within1hoftheexperiment. Wet grind
41、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 threadedonto an electrode holder rod and secured in a lathe or electricdrill for this operation.)5.6 Determine the surface area by measuring all
42、 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 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 gas
43、ket 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 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
44、 open-circuit specimen potential, that is, 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 or step 1 h after specimenimmers
45、ion, beginning at the corrosion potential (Ecorr) forpotentiodynamic measurements and the nearest 50-mV incre-ment above Ecorrfor the potentiostatic measurements. Proceedthrough + 1.60 V versus saturated calomel electrode (SCE)(active to noble).5.11.2 In the potentiostatic method, use a potentiostat
46、icpotential step rate of 50 mV every 5 min, recording the currentat the end of each 5-min period at potential. These steps arerepeated until a potential of + 1.6 V SCE is reached.5.11.3 In the potentiodynamic method, use a potentiody-namic potential sweep rate of 0.6 V/h (65 %) recording thecurrent
47、continuously with change in potential from the corro-sion potential to + 1.6 V SCE.5.12 Plot anodic polarization data on semilogarithmic paperin accordance with Practice G3, (potential-ordinate, currentdensity-abscissa). If a potentiostat with a logarithmic converteris used, this plot can be produce
48、d directly during the measure-ment.6. Standard Reference Plots6.1 Standard polarization plots prepared from data obtainedby following the standard procedure discussed in this testmethod are supplied with the purchase of reference material.Typical data are shown in Fig. 1 and Fig. 2 (5). The plots sh
49、owa range of acceptable current density values at each potential.The average corrosion potential is 0.52 V, and the averageplatinized platinum potential is 0.26 V.NOTE 5The plots in Fig. 1 and Fig. 2 correspond to a lot of Type 430stainless steel that is no longer available from ASTM (after July 1992).Figs. 1 and 2 are presented primarily for the discussion of precision andbias in Sections 6, 7, and Appendix X1. The scatter bands presented inG5 94 (2011)14Appendix X2 were developed from a round robin testing program on thelot of Type 430 stainless steel t
