1、Designation: G5 94 (Reapproved 2011)1G5 12Standard 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
2、 the 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.1 NOTEUpdated units statement and text editorially in November 2011.1. Scope1.1 This test method co
3、vers an experimental procedure for checking experimental technique and instrumentation. If followed,this test method will provide repeatable potentiostatic and potentiodynamic anodic polarization measurements that will reproducedata determined by others at other times and in other laboratories provi
4、ded all laboratories are testing reference samples from thesame lot of Type 430 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,
5、if any, associated with its use. It is 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:2E1338 Guide for Identification of Metals and All
6、oys 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 Database Input3. Significance and Use3.1 The availability of a
7、 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 standard ferritic Type 430 stainless steel (UNS S43000) used in
8、 obtaining standard reference plot are availablefor those who wish to check their own test procedure and equipment.33.3 Standard potentiostatic and potentiodynamic polarization plots are supplied with the purchase of the reference material.shown for a lot of material originally purchased in 1992. Th
9、is test method is not applicable for standard material purchased before1992. These reference data are based on the results from different laboratories that followed the standard procedure, using thatmaterial in 1.0 N H2SO4. Maximum and minimum current The four sigma probability bands for current den
10、sity values are shownat each potential to 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
11、, not for use inevaluating materials performance. Therefore, the use of the plots in Figs. 1 and 2 or Appendix X2is not recommended to evaluatealloys other than Type 430, or lots of Type 430 other than those available through ASTM. The use of the data in this test method1 This test method is under t
12、he jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of G01.11 on Electrochemical Measurementsin Corrosion Testing.Current edition approved Nov. 15, 2011Nov. 15, 2012. Published May 2012February 2013. Originally approved in 1969. Last previous edition approve
13、d in 20042011 asG594(2004).G594(2011)1. DOI: 10.1520/G0005-94R11E01.10.1520/G0005-12.2 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 p
14、age on the ASTM website.3 These standard samples are available from Metal Samples, P.O. Box 8, Mumford, AL 36268. Generally, one sample can be repolished and reused for many runs. Thisprocedure is suggested to conserve the available material.This document is not an ASTM standard and is intended only
15、 to provide the user of an ASTM standard 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 versio
16、nof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1CURRENT DENSITY (A/cm2)FIG. 1 Typical Standard Potentiostatic Anodic Polarization PlotCURRENT DENSITY (A/c
17、m2)FIG. 2 Typical Standard Potentiodynamic Anodic Polarization PlotG5 122in this manner is beyond the scope and intended use of this test method. Users of this test method are advised to evaluate test resultsrelative to the scatter bands corresponding to the particular lot of Type 430 stainless stee
18、l 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 the reference electrode, inlet and outlet for an inert gas,and a
19、 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 Asuitable cell is shown in Fig. 3 (1).4A1-L, roundbottomround-bottom flask has been
20、 modified by the addition of variousnecks to permit the introduction of electrodes, gas inlet and outlet tubes, and a thermometer.The Luggin probe-salt bridge separatesthe bulk solution from the saturated calomel reference electrode, and the probe tip can be easily adjusted to bring it in closeproxi
21、mity with the 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 specimen supplied, the potentiostat should have a potential ran
22、ge 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 a high input impedance on the order of 1011 to 1014 to minimize currentdrawn from the system during measurements. Such circuits are
23、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 than 1.0 mV and those make continuous analog potential s
24、weeps are bothsuitable 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 the absolute value over a current rangebetween 1.0 and 105 A
25、 for a Type 430 stainless steel (UNS S43000) specimen with a surface area of approximately 5 cm2.4.5 Anodic Polarization Circuit:4.5.1 A schematic potentiostatic anodic polarization wiring diagram (2) is illustrated in Fig. 4.4.5.2 A scanning potentiostat is used for potentiodynamic measurements. Fo
26、r such measurements the potentiostat shall becapable of automatically varying the 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
27、 shownin Fig. 4. Some potentiostats have an output of the logarithm of the current 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 15 laboratories.the laboratori
28、es that participated in theround robin.4 The boldface numbers in parentheses refer to the list of references at the end of this test method.FIG. 3 Schematic Diagram of Polarization Cell (1)G5 1234.6 Electrode Holder (1):4.6.1 The auxiliary and working electrodes are mounted in the type of holder sho
29、wn in Fig. 5. A longer holder is required forthe working electrode than for the auxiliary electrode. A leak-proof assembly is obtained by the proper compression fit betweenthe electrode and a TFE-fluorocarbon gasket. (Too much pressure may cause shielding of the electrode or breakage of the glasshol
30、der, 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, andmounted in the manner discussed in 4.6.1.NOT
31、E 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. 4 Schematic Potentiostatic Anodic PolarizationWiring Diagra
32、m (2)FIG. 5 Specimen Mounted on Electrode HolderG5 1244.7.1.1 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 air cooled. The che
33、micalcomposition 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 gasket in the same
34、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 part concentrated
35、 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 is removed by elec
36、trolyzingin 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 potentials against
37、 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 replacingthe graphite
38、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 proper condition.The
39、 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.4.7.3.2 Alternati
40、vely, a saturated calomel electrode utilizing a semi-permeable 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 %H2SO4 /L of solution.
41、 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.NOTE 4When using a controlled leak
42、age 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 siphoning, or a semi-permeablemembrane or porous plug tip may be u
43、sed 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 test specimen. This may be accomplished by bubbling anoxygen-free g
44、as 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 previous coarse scratches are removed, rinse, and dry. (Drilled an
45、d 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 the gasket(usually 0.20 to 0.25 cm2).5.7 Mount the specimen on the
46、 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 to immersion and then rinse in distilled water.5.9 Transfer the
47、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 potential, after 55 min immersion. If platinum counterelectrodes and
48、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 or step 1 h after specimen immersion, beginning at the corrosion potential (Ecorr) forpotentiodynamic measurements and the nearest 50-mV increment above Eco
49、rr for the potentiostatic measurements. Proceedthrough + 1.60 V versus saturated calomel electrode (SCE) (active to noble).G5 1255.11.2 In the potentiostatic method, use a potentiostatic potential step rate of 50 mV every 5 min, recording the current at theend of each 5-min period at potential. These steps are repeated until a potential of + 1.6 V SCE is reached.5.11.3 In the potentiodynamic method, use a potentiodynamic potential sweep rate of 0.6 V/h (65 %) recording the currentcontinuously with change in potential from the corrosion potential to + 1.
