1、Designation: G 106 89 (Reapproved 2004)Standard Practice forVerification of Algorithm and Equipment for ElectrochemicalImpedance Measurements1This standard is issued under the fixed designation G 106; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers an experimental procedure whichcan be used to check ones instrumen
3、tation and technique forcollecting and presenting electrochemical impedance data. Iffollowed, this practice provides a standard material, electro-lyte, and procedure for collecting electrochemical impedancedata at the open circuit or corrosion potential that shouldreproduce data determined by others
4、 at different times and indifferent laboratories. This practice may not be appropriate forcollecting impedance information for all materials or in allenvironments.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the
5、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:2D 1193 Specification for Reagent WaterG 3 Practice for Conventions Applicable to ElectrochemicalMeasurements
6、in Corrosion TestingG 5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG 15 Terminology Relating to Corrosion and CorrosionTestingG 59 Practice for Conducting Potentiodynamic PolarizationResistance Measurements3. Terminology3.1 DefinitionsFor defin
7、itions of corrosion related terms,see Terminology G 15.3.2 Symbols:C = capacitance (farad-cm2)E8 = real component of voltage (volts)E9 = imaginary component of voltage (volts)E = complex voltage (volts)f = frequency (s1)I8 = real component of current (amp-cm2)I9 = imaginary component of current (amp
8、-cm2)I = complex current (amp-cm2)j =21L = inductance (henry cm2)Rs= solution resistance (ohm-cm2)Rp= polarization resistance (ohm-cm2)Rt= charge transfer resistance (ohm-cm2)Z8 = real component of impedance (ohm-cm2)Z9 = imaginary component of impedance (ohm-cm2)Z = complex impedance (ohm-cm2)a = p
9、henomenological coefficients caused by depressionof the Nyquist plot below the real axis, a is theexponent and t is the time constant(s).u = phase angle (deg)v = frequency (radians-s1)Subscripts:x = in-phase componenty = out-of-phase component4. Summary of Practice4.1 Reference impedance plots in bo
10、th Nyquist and Bodeformat are included. These reference plots are derived from theresults from nine different laboratories that used a standarddummy cell and followed the standard procedure using aspecific ferritic type alloy UNS-S430003in 0.005 M H2SO4and 0.495 M Na2SO4. The plots for the reference
11、 material arepresented as an envelope that surrounds all of the data with andwithout inclusion of the uncompensated resistance. Plots forone data set from one laboratory are presented as well. Sincethe results from the dummy cell are independent of laboratory,only one set of results is presented.1Th
12、is practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemi-cal Measurements in Corrosion Testing.Current edition approved Nov 1, 2004. Published November 2004. Originallyapproved in 1989. Last previous edi
13、tion approved in 1999 as G 106 89 (1999).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.3These standard samp
14、les are available from ASTM Headquarters. Generally, onesample can be repolished and reused for many runs. This procedure is suggested toconserve the available material.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 A discussion
15、 of the electrochemical impedance tech-nique, the physics that underlies it, and some methods ofinterpreting the data are given in the Appendix X1-AppendixX6. These sections are included to aid the individual inunderstanding the electrochemical impedance technique andsome of its capabilities. The in
16、formation is not intended to beall inclusive.5. Significance and Use5.1 The availability of a standard procedure, standard ma-terial, and standard plots should allow the investigator to checkhis laboratory technique. This practice should lead to electro-chemical impedance curves in the literature wh
17、ich can becompared easily and with confidence.5.2 Samples of a standard ferritic type 430 stainless steel(UNS 430000) used to obtain the reference plots are availablefor those who wish to check their equipment. Suitable resistorsand capacitors can be obtained from electronics supply houses.5.3 This
18、test method may not be appropriate for electro-chemical impedance measurements of all materials or in allenvironments.6. Apparatus6.1 Dummy CellThe dummy cell used to check theequipment and method for generating electrochemical imped-ance data is composed of a 10 V precision resistor placed inseries
19、 with a circuit element composed of a 100 V precisionresistor in parallel with a 100 F capacitor. The resistors shouldhave a stated precision of 60.1 %. The capacitor can have aprecision of 620 %. The cell can be constructed from readilyavailable circuit elements by following the circuit diagramshow
20、n in Fig. 1.6.2 Test CellThe test cell should be constructed to allowthe following items to be inserted into the solution chamber:the test electrode, two counter electrodes or a symmetricallyarranged counter electrode around the working electrode, aLuggin-Haber capillary with salt bridge connection
21、to thereference electrode, an inlet and an outlet for an inert gas, anda thermometer or thermocouple holder. The test cell must beconstructed of materials that will not corrode, deteriorate, orotherwise contaminate the solution.6.2.1 One type of suitable cell is described in Reference TestMethod G 5
22、. Cells are not limited to that design. For example,a 1-L round-bottom flask can be modified for the addition ofvarious necks to permit the introduction of electrodes, gas inletand outlet tubes, and the thermometer holder. A Luggin-Habercapillary probe could be used to separate the bulk solution fro
23、mthe saturated calomel electrode. The capillary tip can be easilyadjusted to bring it into close proximity to the workingelectrode. The minimum distance should be no less than twocapillary diameters from the working electrode.6.3 Electrode HolderThe auxillary and working elec-trodes can be mounted i
24、n the manner shown in Reference TestMethod G 5. Precautions described in Reference Test MethodG 5 about assembly should be followed.6.4 PotentiostatThe potentiostat must be of the kind thatallows for the application of a potential sweep as described inReference Test Method G 5 and Reference Practice
25、 G 59. Thepotentiostat must have outputs in the form of voltage versusground for both potential and current. The potentiostat musthave sufficient bandwidth for minimal phase shift up to at least1000 Hz and preferably to 10 000 Hz. The potentiostat must becapable of accepting an external excitation s
26、ignal. Manycommercial potentiostats meet the specification requirementsfor these types of measurements.6.5 Collection and Analysis of Current-Voltage ResponseThe potential and current measuring circuits must have thecharacteristics described in Reference Test Method G 5 alongwith sufficient band-wid
27、th as described above. The impedancecan be calculated in several ways, for example, by means of atransfer function analyzer, Lissajous figures on an oscilloscope,or transient analysis of a white noise input using a Fast FourierTransform algorithm. Other methods of analysis exist.6.6 Electrodes:6.6.1
28、 Working electrode preparation should follow Refer-ence Test Method G 5, which involves drilling and tapping thespecimen and mounting it on the electrode holder.6.6.2 Auxillary electrode preparation should follow Refer-ence Test Method G 5. The auxillary electrode arrangementshould be symmetrical ar
29、ound the working electrode.6.6.3 Reference electrode type and usage should followReference Test Method G 5. The reference electrode is to be asaturated calomel electrode.7. Experimental Procedure7.1 Test of Algorithm and Electronic Equipment (DummyCell):7.1.1 Measure the impedance of a dummy cell co
30、nsisting ofa10V resistor in series with a parallel combination of a 100V resistor and a 100 F capacitor. The circuit diagram is shownin Fig. 1.FIG. 1 Circuit Diagram for Dummy Cell Showing Positions for Hook-Up to PotentiostatG 106 89 (2004)27.1.2 Typical connections from the potentiostat are shown
31、inFig. 1. Connect the auxillary electrode and reference electrodeleads to the series resistor side of the circuit. Connect theworking electrode lead to the opposite side of the circuitbeyond the resistor-capacitor parallel combination.7.1.3 Set the potential at 0.0V. Collect the electrochemicalimped
32、ance data between 10 000 Hz (10 kHz) and 0.1 Hz (100mHz) at 8 to 10 steps per frequency decade. The amplitudemust be the same as that used to check the electrochemical cell,10 mv. The resulting frequency response when plotted inNyquist format (the negative of the imaginary impedanceversus the real i
33、mpedance) must agree with that shown in Figs.2-4. Testing with the electrochemical cell should not beattempted until that agreement is established. Results using thedummy circuit were found to be independent of laboratory.7.2 Test of Electrochemical Cell:7.2.1 Test specimens of the reference materia
34、l should beprepared following the procedure described in Reference TestMethod G 5. This procedure involves polishing the specimenwith wet SiC paper with a final wet polish using 600 grit SiCpaper prior to the experiment. There should be a maximumdelay of 1 h between final polishing and immersion in
35、the testsolution.7.2.2 Prepare a 0.495 M Na2SO4solution containing 0.005MH2SO4from reagent grade sulfuric acid and sodium sulfateand Type IV reagent water described in Specification D 1193.The test is to be carried out at 30 6 1C.7.2.3 At least 1 h before specimen immersion, start purgingthe solutio
36、n with oxygen-free argon, hydrogen, or nitrogen gasat a flow rate of about 100 to 150 cm3/min. Continue the purgethroughout the test.7.2.4 Transfer the specimen to the test cell. Adjust theLuggin-Haber probe tip so that it is no less than two capillarydiameters from the sample. However, since this d
37、istance willaffect the uncompensated solution resistance, the greater thedistance, the larger the resistance. Therefore, close placementis important.7.2.5 Connect the potentiostat leads to the appropriateelectrodes, for example, working electrode lead to workingelectrode, counter electrode lead to c
38、ounter electrode, andreference electrode lead to reference electrode. Hook-up in-structions provided with the potentiostat must be followed.7.2.6 Record the open circuit potential, that is, the corrosionpotential, for 1 h. The potential should be about 645 mv 610mv relative to the saturated calomel
39、electrode. If the potentialFIG. 2 Nyquist Plot of Electrochemical Impedance Response forDummy CellFIG. 3 Bode Plot, Impedance Magnitude Versus Frequency, ofElectrochemical Impedance Response for Dummy CellFIG. 4 Bode Plot, Phase Angle Versus Frequency, ofElectrochemical Impedance Response for Dummy
40、CellG 106 89 (2004)3is more positive than 600 mv (SCE) then the specimen mayhave passivated. If so, remove the specimen and repolish with600 grit wet silicon carbide paper. Then reimmerse the sampleand monitor the corrosion potential for 1 h. If the potentialagain becomes more positive than 600 mv (
41、SCE) check foroxygen contamination of the solution.7.2.7 Record the frequency response between 10 000 Hz (10kHz) and 0.1 Hz (100 mHz) at the corrosion potential recordedafter1hofexposure using 8 to 10 steps per frequency decade.The amplitude must be the same as that used in 6.1.3, 10 mv.7.2.8 Plot t
42、he frequency response in both Nyquist format(real response versus the negative of the imaginary response)and Bode format (impedance modulus and phase angle versusfrequency). Frequency can be reported in units of radians/second or hertz (cycles/s).7.2.9 There was no attempt to estimate circuit analog
43、ues forthe electrochemical impedance curves since there is no univer-sally recognized, standard method for making such estimates.8. Standard Reference Results and Plots8.1 Dummy Cell:8.1.1 The results from nine different laboratories werevirtually identical and overlayed each other almost perfectly.
44、Typical plots of the raw data are shown in Figs. 2-4. No attempthas been made to estimate the variance and standard deviationof the results from the nine laboratories. The measured valuesof Rs,Rp, and the frequency at which the phase angle is amaximum must agree with these curves within the specific
45、a-tions of the instrumentation, resistors, and capacitors beforetesting of the electrochemical cell commences. See 9.1.1.8.2 Electrochemical Cell:8.2.1 Standard electrochemical impedance plots in bothNyquist format and Bode format are shown in Figs. 5-7. Theseare actual results from one laboratory.
46、Figs. 8-10 show plots inboth Nyquist and Bode formats which envelop all of the resultsfrom the nine laboratories. The solution resistance from eachlaboratory was not subtracted out prior to making this plot.8.2.2 The average solution resistance from the nine labora-tories in 3.3 V-cm26 1.8 V-cm2(one
47、 standard deviation). Thesolution resistance of the users test cell as measured by thehigh frequency intercept on the Nyquist plot must lie in thisrange to use agreement with Figs. 8-10 for verification of theelectrochemical test cell. If the uncompensated resistance liesoutside of this range, it sh
48、ould be subtracted from the results(see 7.2.4). Then, results from the electrochemical test cell canbe compared with the results in Figs. 11-13 to verify the testcell. Figs. 11-13 envelop all of the results from the ninelaboratories with the uncompensated resistance subtracted out.9. Precision and B
49、ias9.1 Dummy Cell:9.1.1 Reproducibility of the results for the dummy cell isdependent on the precision of the resistors and capacitor usedFIG. 5 Nyquist Plot of Typical Frequency Response for UNS-S43000 From One LaboratoryFIG. 6 Bode Plot, Impedance Magnitude Versus Frequency, forUNS-S43000 From One LaboratoryFIG. 7 Bode Plot, Phase Angle Versus Frequency, for UNS-S43000 From One LaboratoryG 106 89 (2004)4to construct the dummy cell. Precision resistors (60.1 %)should be used to construct the dummy cell. Most capacitorshave a precision of 620 %. A change in
