1、Designation: G 59 97 (Reapproved 2009)Standard Test Method forConducting Potentiodynamic Polarization ResistanceMeasurements1This standard is issued under the fixed designation G 59; the number immediately following the designation indicates the year of originaladoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers an experimental procedure forpolarization resistance measurements which can be use
3、d for thecalibration of equipment and verification of experimentaltechnique. The test method can provide reproducible corrosionpotentials and potentiodynamic polarization resistance mea-surements.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are inclu
4、ded 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 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to
5、 use.2. Referenced Documents2.1 ASTM Standards:2G3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG 102 Practice for Calculation of Corrosion Rates andRelated
6、Information from Electrochemical Measurements3. Significance and Use3.1 This test method can be utilized to verify the perfor-mance of polarization resistance measurement equipment in-cluding reference electrodes, electrochemical cells, poten-tiostats, scan generators, measuring and recording device
7、s. Thetest method is also useful for training operators in samplepreparation and experimental techniques for polarization resis-tance measurements.3.2 Polarization resistance can be related to the rate ofgeneral corrosion for metals at or near their corrosion potential,Ecorr. Polarization resistance
8、 measurements are an accurate andrapid way to measure the general corrosion rate. Real timecorrosion monitoring is a common application. The techniquecan also be used as a way to rank alloys, inhibitors, and so forthin order of resistance to general corrosion.3.3 In this test method, a small potenti
9、al scan, DE(t), definedwith respect to the corrosion potential (DE=EEcorr), isapplied to a metal sample. The resultant currents are recorded.The polarization resistance, RP, of a corroding electrode isdefined from Eq 1 as the slope of a potential versus currentdensity plot at i =0(1-4):3Rp5SDE iDi50
10、, dE/dt0(1)The current density is given by i. The corrosion currentdensity, icorr, is related to the polarization resistance by theStern-Geary coefficient, B. (3),icorr5 106BRp(2)The dimension of Rpis ohm-cm2, icorris muA/cm2, and B isin V. The Stern-Geary coefficient is related to the anodic, ba,an
11、d cathodic, bc, Tafel slopes as per Eq 3.B 5babc2.303ba1 bc!(3)The units of the Tafel slopes are V. The corrosion rate, CR,in mm per year can be determined from Eq 4 in which EW isthe equivalent weight of the corroding species in grams and ris the density of the corroding material in g/cm3.CR 5 3.27
12、 3 103icorrEWr(4)1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2009. Published May 2009. Originallyapproved in 1978. L
13、ast previous edition approved in 2003 as G 5997(2003).2For referenced 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.3The bo
14、ldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Refer to Practice G 102 for derivations of the above equa-tions and methods for estimating Tafel
15、 slopes.3.4 The test method may not be appropriate to measurepolarization resistance on all materials or in all environments.See 8.2 for a discussion of method biases arising from solutionresistance and electrode capacitance.4. Apparatus4.1 The apparatus is described in Test Method G5.Itincludesa1Lr
16、ound bottom flask modified to permit theaddition of inert gas, thermometer, and electrodes. This stan-dard cell or an equivalent cell can be used. An equivalent cellmust be constructed of inert materials and be able to reproducethe standard curve in Test Method G5.4.2 A potentiostat capable of varyi
17、ng potential at a constantscan rate and measuring the current is needed.4.3 A method of recording the varying potential and result-ing current is needed.5. Test of Electrical Equipment5.1 Before the polarization resistance measurement is made,the instrument system (potentiostat, X-Y recorder or data
18、acquisition system) must be tested to ensure proper function-ing. For this purpose, connect the potentiostat to a testelectrical circuit (5). While more complex dummy cells aresometimes needed in electrochemical studies, the simple resis-tor shown in Fig. 1 is adequate for the present application.5.
19、2 Use R = 10.0 V. Set the applied potential on thepotentiostat to E = 30.0 mV and apply the potential. Thecurrent should be 3.0 mA by Ohms Law, I = E/R.NOTE 1When polarization resistance values are measured for systemswith different corrosion currents, the value of R should be chosen to coverthe cur
20、rent range of the actual polarization resistance measurement.Expected corrosion currents in the microampere range requireR=1to10kV.5.3 Record the potentiodynamic polarization curve at a scanrate of 0.6 V/h from DE = 30 mV to DE = +30 mV and backto DE = 30 mV. The plot should be linear, go through th
21、eorigin, and have a slope 10 V. The curves recorded for theforward and reverse scans should be identical.5.4 If the observed results are different than expected, theelectrochemical equipment may require calibration or servicingin accordance with the manufacturers guidelines.6. Experimental Procedure
22、6.1 The 1.0 N H2SO4test solution should be prepared fromAmerican Chemical Society reagent grade acid and distilledwater as described in Test Method G5. The standard test cellrequires 900 mL of test solution. The temperature must bemaintained at 30C within 1.6.2 The test cell is purged at 150 cm3/min
23、 with an oxygen-free gas such as hydrogen, nitrogen, or argon. The purge isstarted at least 30 min before specimen immersion. The purgecontinues throughout the test.6.3 The working electrode should be prepared as detailed inTest Method G5. The experiment must commence within 1 hof preparing the elec
24、trode. Preparation includes sequential wetpolishing with 240 grit and 600 grit SiC paper. Determine thesurface area of the specimen to the nearest 0.01 cm2andsubtract for the area under the gasket (typically 0.20 to 0.25cm2).6.4 Immediately prior to immersion the specimen is de-greased with a solven
25、t such as acetone and rinsed with distilledwater. The time delay between rinsing and immersion shouldbe minimal.NOTE 2Samples of the standard AISI Type 430 stainless steel (UNSS45000) used in this test method are available to those wishing to evaluatetheir equipment and test procedure from Metal Sam
26、ples, P.O. Box 8,Mumford, AL 36268.6.5 Transfer the test specimen to the test cell and positionthe Luggin probe tip 2 to 3 mm from the test electrode surface.The tip diameter must be no greater than 1 mm.6.6 Record the corrosion potential Ecorrafter 5 and 55-minimmersion.6.7 Apply a potential 30 mV
27、more negative that the re-corded 55 min corrosion potential (See Note 3).NOTE 3Practice G3 provides a definition of sign convention forpotential and current.6.8 One minute after application of the 30 mV potential,begin the anodic potential scan at a sweep rate of 0.6 V/h(within 5 %). Record the pote
28、ntial and current continuously.Terminate the sweep at a potential 30 mV more positive thanthe 55 min corrosion potential.6.9 Plot the polarization curve as a linear potential-currentdensity plot as shown in Practice G3. Determine the polariza-tion resistance, Rp, as the tangent of the curve at i=0.7
29、. Report7.1 Report the following information:7.1.1 The 5 and 55 min corrosion potentials and the polar-ization resistance value,7.1.2 Duplicate runs may be averaged, and7.1.3 Note any deviation from the procedure or test condi-tions established in this test method.FIG. 1 Arrangement for Testing of E
30、lectrical Equipment (Potentiostat, X-Y Recorder)G 59 97 (2009)28. Precision and Bias8.1 PrecisionPrecision in this test method refers to thecloseness of agreement between randomly selected measuredvalues. There are two aspects of precision, repeatability andreproducibility. Repeatability refers to t
31、he closeness of agree-ment between measurements by the same laboratory on iden-tical Type 430 stainless steel specimens repeated with as closeas possible adherence to the same procedure. Reproducibilityrefers to the closeness of agreement between different labora-tories using identical Type 430 stai
32、nless steel specimens andthe procedure specified. An interlaboratory test program with13 laboratories participating and two, three or four replicatemeasurements was carried out to establish the precision. Themeasured values included (Table 1) the corrosion potentialmeasured after 5 and 55 min and th
33、e polarization resistance. Aresearch report has been filed with the results of this program.8.1.1 Repeatability The lack of repeatability is measuredby the repeatability standard deviation sr. The 95 % confidenceinterval was calculated as 6 2.8 sr. The values obtained areshown in Table 2. The 95 % c
34、onfidence interval refers to theinterval around the average that 95 % of the values should befound.8.1.2 Reproducibility The lack of reproducibility is mea-sured by the reproducibility standard deviation, sR. The 95 %confidence interval was calculated as 6 2.8 sR. The valuesobtained are shown in Tab
35、le 3.8.2 BiasThe polarization resistance as measured by theTest Method G 59 has two sources of bias. The potentiody-namic method includes a double layer capacitance chargingeffect that may cause the polarization resistance to be under-estimated. There is also a solution resistance effect that maycau
36、se the polarization resistance to be overestimated. This biaswill depend on the placement of the reference electrode andelectrolyte conductivity. Refer to Practice G 102 for furtherdiscussion on the effects of double layer capacitance andsolution resistance on polarization resistance measurements.9.
37、 Keywords9.1 anodic polarization; auxiliary electrode; cathodic polar-ization; corrosion; corrosion potential; corrosion rate; currentdensity; electrochemical cell; electrochemical potential; Lug-gin probe; mixed potential; open-circuit potential; overvoltage;polarization resistance; potentiodynamic
38、; reference electrode;solution resistance; Stern-Geary coefficient; Tafel slope; work-ing electrodeTABLE 1 Interlaboratory Test Program Polarization Data forStainless Steel Type 430 in 1.0 N H2SO4at 30CLaboratory Ecorr5min Ecorr55min Rp(mV) (mV) (ohm-cm2)1 0.519 0.506 6.470.519 0.505 5.882 0.542 0.5
39、21 5.950.540 0.519 5.043 0.524 0.513 6.930.520 0.508 6.404 0.555 0.545 7.700.565 0.545 7.705 0.539 0.524 7.580.530 0.510 6.186 0.519 0.510 7.600.522 0.512 7.160.521 0.509 6.657 0.522 0.510 9.060.520 0.511 7.070.523 0.510 5.858 0.520 0.508 7.110.520 0.508 7.520.521 0.510 6.949 0.529 0.513 7.110.530 0
40、.513 7.220.529 0.514 7.190.529 0.515 7.1910 0.514 0.505 5.170.516 0.506 6.9011 0.543 0.529 5.070.538 0.524 4.6412 0.520 0.505 5.630.519 0.507 6.1613 0.531 0.519 5.080.529 0.517 5.380.529 0.517 5.90G 59 97 (2009)3REFERENCES(1) Stern, M., and Roth, R. M., Journal of the Electrochemical Society,Vol 104
41、, 1957, p. 390.(2) Stern, M., Corrosion, Vol 14, 1958, p. 440.(3) Mansfeld, F., “The Polarization Resistance Technique for MeasuringCorrosion Currents,” Corrosion Science and Technology, PlenumPress, New York, NY, Vol VI, 1976, p.163.(4) Mansfeld, F., “Evaluation of Polarization Resistance Round Rob
42、inTesting Conducted by ASTM G01.11,” Paper No. 106, CORROSION/76, NACE, Houston, TX, March 22-26, 1976.(5) Gileadi, E., Kirowa-Eisner, E., and Penciner, J. Interfacial Electro-chemistry, an Experimental Approach, Chapter III.1, Addison-WesleyPublishing Co., Reading, MA 1975.ASTM International takes
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44、nsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed
45、 to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the a
46、ddress shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone
47、), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE 2 Repeatability StatisticsAverage Sr95 % ConfidenceIntervalEcorr5 min, mV versus SCE 0.5287 0.00260 6 0.0073 VEcorr55 min, mV versus SCE 0.5151 0.00273 6 0.0076 VRp, ohm-cm26.46 0.713 62.00 ohm-cm2TABLE 3 Reproducibility StatisticsAverage SR95 % ConfidenceIntervalEcorr5 min, mV versus SCE 0.5287 0.0127 6 0.0356 mVEcorr55 min, mV versus SCE 0.5151 0.0111 6 0.0311 mVRpohm-cm26.46 1.01 62.83 ohm-cm2G 59 97 (2009)4
