1、Designation: G5 12G5 13Standard 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 case of revisi
2、on, 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. Scope1.1 This test method covers an experimental procedure for checking experimental technique and instrumentation.
3、 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 provided all laboratories are testing reference samples from thesame lot of Type 430 stainle
4、ss 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, if any, associated with its use. It is the responsibilityof the user of this standard t
5、o 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 Alloys in Computerized Material Property DatabasesG3 Practice for Conventions Applicable t
6、o 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 standard procedure, standard material, and a standard plot should make it easy for an
7、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 obtaining standard reference plot are availablefor those who wish to check their own t
8、est procedure and equipment.33.3 Standard potentiostatic and potentiodynamic polarization plots are shown for a lot of material originally purchased in 1992.This test method is not applicable for standard material purchased before 1992. These reference data are based on the results fromdifferent lab
9、oratories that followed the standard procedure, using that material in 1.0 N H2SO4. The four sigma probability bandsfor current density values are shown at each potential to indicate the acceptable range of values.3.4 This test method may not be appropriate for polarization testing of all materials
10、or in all environments.3.5 This test method is intended for use in evaluating the accuracy of a given electrochemical test apparatus, not for use inevaluating materials performance. Therefore, the use of the plots in Figs. 1 and 2Fig. 1 is not recommended to evaluate alloys otherthanType 430, or lot
11、s ofType 430 other than those available throughASTM. Metal Samples.The use of the data in this test methodin 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 particul
12、ar lot of Type 430 stainless steel that was tested.1 This test method is under the 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, 2012Feb. 1, 2013. Published Fe
13、bruary 2013. Originally approved in 1969. Last previous edition approved in 20112012 asG594(2011)G51.12. DOI: 10.1520/G0005-12.10.1520/G0005-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvo
14、lume information, refer to the standards Document Summary page on the ASTM website.3 These standard samples are available from Metal Samples, P.O. Box 8, 152 Metal Samples Rd., Mumford,AL36268. Generally, one sample can be repolished and reusedfor many runs. This procedure is suggested to conserve t
15、he available material.This document is not an ASTM standard and is intended only 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 u
16、sers consult prior editions as appropriate. In all cases only the current versionof 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 States14. Apparatus4.1 The test c
17、ell 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 thermometer. The test cell shall be constru
18、cted 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 A suitable cell is shown in Fig. 32 (1).4 A 1-L, round-bottom flask has been modified by the addition of various necks topermit
19、 the introduction of electrodes, gas inlet and outlet tubes, and a thermometer. The Luggin probe-salt bridge separates the bulksolution from the saturated calomel reference electrode, and the probe tip can be easily adjusted to bring it in close proximity withthe working electrode.4.2 Potentiostat (
20、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 range from 0.6 from0.6 to 1.6 V and an anodic current
21、 output range from 1.0 to 105 A.4.3 Potential-Measuring Instruments (Note 2):4.3.1 The potential-measuring circuit should have high input impedance on the order of 1011 to 1014 to minimize currentdrawn from the system during measurements. Such circuits are provided with most potentiostats. Instrumen
22、ts should havesufficient sensitivity and accuracy to detect a change of 1.0 mV over a potential range between 0.6 between 0.6 and 1.6 V.Potentiostats that scan potential by making frequent potential steps of less than 1.0 mV and those that make continuous analogpotential sweeps are both suitable for
23、 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 % 1 % of the absolute value over a currentrange between 1.0 and 105 A for a Type 430 stainl
24、ess 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. 43.4 The boldface numbers in parentheses refer to the list of references at the end of this test m
25、ethod.CURRENT DENSITY (A/cm2)FIG. 21 Typical Standard Potentiodynamic Anodic Polarization PlotG5 1324.5.2 A scanning potentiostat is used for potentiodynamic measurements. For such measurements the potentiostat shall becapable of automatically varying the potential at a constant rate between two pre
26、set 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 shownin Fig. 43. Some potentiostats have an output of the logarithm of the current as a voltage, which allows direct plotting
27、 of thepotential log current curve using an X-Y recorder.NOTE 2The instrumental requirements are based upon values typical of the instruments in the laboratories that participated in the round robin.4.6 Electrode Holder (1):4.6.1 The auxiliary and working electrodes are mounted in the type of holder
28、 shown in Fig. 54. A longer holder is required forthe working electrode than for the auxiliary electrode. A leak-proofleakproof assembly is obtained by the proper compression fitbetween the electrode and a TFE-fluorocarbon gasket. (Too much pressure may cause shielding of the electrode or breakage o
29、f theglass holder, 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 discusse
30、d in 4.6.1.NOTE 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).4.7.1.1 The standardAISIType 430 stainless steel (
31、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 chemicalcomposition of the standard stainless steel is supplied with the purchase of reference material.FIG
32、. 32 Schematic Diagram of Polarization Cell (1)FIG. 43 Schematic Potentiostatic Anodic PolarizationWiring Diagram (2)(2)G5 1334.7.2 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-fluoroc
33、arbon gasket in the same 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 HC
34、l and 1 part concentrated HNO3), washing, and then drying. Both electrodes areplatinized by immersing them in a solution of 3 % 3 % platinic chloride and 0.02 % 0.02 % lead acetate and electrolyzing at acurrent density of 40 to 50 mA/cm2 for 4 or 5 min (1, 3). The polarity is reversed every minute.
35、Occluded chloride is removedby electrolyzing in a dilute (10 %) (10 %) sulfuric acid solution for several minutes with a reversal in polarity every minute.Electrodes are rinsed thoroughly and stored in distilled water until ready for use. Since certain ions can poison these electrodes,periodic check
36、s of platinized platinum potentials against 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
37、avoided by routinely replacingthe graphite 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 i
38、t is maintained in the proper condition.The 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 referenceele
39、ctrode or the electrolyte.4.7.3.2 Alternatively, a saturated calomel electrode utilizing a semi-permeablesemipermeable membrane or porous plug tip maybe used. These may 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, fo
40、r example, by using 27.8 mL of 98 % 98% H2SO4 /L of solution. 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
41、 bridge with test solution.NOTE 4When using a controlled leakage 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 sipho
42、ning, or asemi-permeablesemipermeable membrane or porous plug tip may be used on the salt bridge.FIG. 54 Specimen Mounted on Electrode HolderG5 1345.3 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 Re
43、duce oxygen levels in solution prior to immersion of the test specimen. This may be accomplished by bubbling anoxygen-free gas 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 24
44、0-grit SiC paper, wet polish with600-grit SiC paper until previous coarse scratches are removed, rinse, and dry. (Drilled and 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 dime
45、nsions 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 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
46、is properly compressed.5.8 Degrease the specimen just prior to immersion and then rinse in distilled water.5.9 Transfer the 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 o
47、pen-circuit specimen potential, that is, the corrosion potential, after 55 min immersion. If platinum counterelectrodes and 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 immer
48、sion, beginning at the corrosion potential (Ecorr) forpotentiodynamic measurements and the nearest 50-mV increment above ). Ecorr for the potentiostatic measurements. Proceedthrough + 1.60 Proceed through +1.60 V versus saturated calomel electrode (SCE) (active to noble).5.11.2 In the potentiostatic
49、 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.5.11.2 In the potentiodynamic method, use Use a potentiodynamic potential sweep rate of 0.6 V/h (65 %) (65 %) recordingthe current continuously with change in potential from the corrosion potential to + 1.6 to +1.6 V SCE.5.12 Plot anodic polarization data on semilogarithmic paper semilogarithmically in accordance with Practice G3, (potential-ordinate, c
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