1、Designation:G594(Reapproved 2004)Standard Reference Test Method forMaking Potentiostatic and Potentiodynamic AnodicPolarization Measurements1This standard is issued under the fixed designation G 5; the number immediately following the designation indicates the year of originaladoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers an experimental procedure forchecking experimental technique and i
3、nstrumentation. 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 laboratories are testing referencesamples from the same lot of T
4、ype 430 stainless steel.1.2 Values stated in SI units are to be regarded as thestandard. Inch-pound units given in parentheses are for infor-mation only.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 th
5、is 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:2E 1338 Guide for the Identification of Metals and Alloys inComputerized Material Property DatabasesG 3 Practice for Con
6、ventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG 107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized DatabaseInput3. Significance and Use3.1 The availability of a standard procedure, standard ma-terial, and a standard plot should
7、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 obtaining standard reference plot areavailable for those who wish
8、 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 laboratories that followed the standard procedure,using that mater
9、ial 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 test method is intended for use in evaluating theaccuracy o
10、f 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 those available through ASTM. The use of the data in thiste
11、st 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 was tested.4. Apparatus4.1 The test cell should be constru
12、cted 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 thermometer. The test cell shall beconstructed of materials that
13、 will not corrode, deteriorate, orotherwise contaminate the test solution.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 been modified by the addition of various1This test method is under the jurisdictio
14、n of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved Nov 1, 2004. Published November 1, 2004. Originallyapproved in 1969. Last previous edition approved in 1999 as G594(1999)e1.2For refer
15、enced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer 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, P.O. Box 8,Mu
16、mford, AL 36268. Generally, one sample can be repolished and reused for manyruns. This procedure is suggested to conserve the available material.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO
17、 Box C700, West Conshohocken, PA 19428-2959, United States.necks 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 t
18、o bringit in close proximity with the working electrode.4.2 Potentiostat (Note 2):4.2.1 A potentiostat 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 shou
19、ld 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 a highinput impedance on the order of 1011to 1014V to minimizecurrent drawn from the system during measurements
20、. Suchcircuits are provided with most potentiostats. InstrumentsCURRENT DENSITY (A/cm2)FIG. 1 Typical Standard Potentiostatic Anodic Polarization PlotCURRENT DENSITY (A/cm2)FIG. 2 Typical Standard Potentiodynamic Anodic Polarization PlotG594(2004)2should have sufficient sensitivity and accuracy to d
21、etect 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 a currentrange between 1.0 and 105A for a Type 430 stainless steel(UNS S43000)
22、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 potentiodynamicmeasurements. For such measurements the potentiostat shall becapa
23、ble 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 incorporated into thecircuit shown in Fig. 4. Some potentiostats have an outpu
24、t 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 laboratories.4.6 Electrode Holder (1):4.6.1 The auxiliary and working electrode
25、s 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 electrode and a TFE-fluorocarbon gasket. (Toomuch pressure may cause shielding of the e
26、lectrode 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 (12-in.)length of 9.5-mm (38-in.) diameter rod stock. Each electrode isdrilled, tap
27、ped, 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 s
28、tandard 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 (1500F) and aircooled. The chemical composition of the standard stainlesssteel is supplied
29、with the purchase of reference material.4.7.2 Auxiliary Electrodes:FIG. 3 Schematic Diagram of Polarization Cell (1)FIG. 4 Schematic Potentiostatic Anodic PolarizationWiring Diagram (2) FIG. 5 Specimen Mounted on Electrode HolderG594(2004)34.7.2.1 Two platinum auxiliary electrodes are prepared fromh
30、igh-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 be utilized because of theincreased surface area. This m
31、ay 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 acetate and electrolyzingat a current density of 40 to 5
32、0 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 and stored in distilledwater until ready for use. Since
33、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 may contaminatesubsequent experiments. This contaminatio
34、n 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 type ofelectrode is durable, reliable, and commercially a
35、vailable.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 may be preferred i
36、n 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 Procedure5.1 Prepare 1 L of 1.0 N H2SO4from A.C.S. reage
37、nt gradeacid and distilled water, for example, by using 27.8 mL of 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 test cell and temporarilyclose the center opening with a
38、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 used in the salt
39、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 convenient means.5.4 Reduce oxygen levels in solution prior to
40、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 with600-grit SiC pa
41、per 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, subtracting the area
42、 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 the specimen ju
43、st 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, thecorrosion
44、 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 specimenimmersion, beginning at the corrosion potential (Ecorr) forpo
45、tentiodynamic 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 potentiostaticpotential step rate of 50 mV every 5 min, recording t
46、he 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 continuously with change in potential from the corro-si
47、on potential to + 1.6 V SCE.5.12 Plot anodic polarization data on semilogarithmic paperin accordance with Practice G 3, (potential-ordinate, currentdensity-abscissa). If a potentiostat with a logarithmic converteris used, this plot can be produced directly during the measure-ment.6. Standard Referen
48、ce 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 showa range of acceptable current density values at each
49、 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 inAppendix X2 were developed from a round robin testing program on thelot of Type 430 stainless steel that is currently available from ASTM.G594(2004)46.2 Typical deviations from t
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