1、Designation: G215 17Standard Guide forElectrode Potential Measurement1This standard is issued under the fixed designation G215; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indi
2、cates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides guidance on the measurement ofelectrode potentials in laboratory and field studies both forcorrosion potentials and polarized potentials.1.2
3、The values stated in SI units are to be regarded asstandard. Any other units of measurements included in thisstandard are present because of their wide usage and accep-tance.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil
4、ity of the 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:2C876 Test Method for Corrosion Potentials of UncoatedReinforcing Steel in ConcreteF746 Test Method
5、 for Pitting or Crevice Corrosion ofMetallic Surgical Implant MaterialsF2129 Test Method for Conducting Cyclic PotentiodynamicPolarization Measurements to Determine the CorrosionSusceptibility of Small Implant DevicesF3044 Test Method for Test Method for Evaluating thePotential for Galvanic Corrosio
6、n for Medical ImplantsG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG59 Test Method for Conducting Potentiodynamic Polariza-tion Resistance MeasurementsG61 Test Method for C
7、onducting Cyclic PotentiodynamicPolarization Measurements for Localized Corrosion Sus-ceptibility of Iron-, Nickel-, or Cobalt-Based AlloysG69 Test Method for Measurement of Corrosion Potentialsof Aluminum AlloysG71 Guide for Conducting and Evaluating Galvanic Corro-sion Tests in ElectrolytesG82 Gui
8、de for Development and Use of a Galvanic Seriesfor Predicting Galvanic Corrosion PerformanceG96 Guide for Online Monitoring of Corrosion in PlantEquipment (Electrical and Electrochemical Methods)G97 Test Method for Laboratory Evaluation of MagnesiumSacrificial Anode Test Specimens for Underground Ap
9、pli-cationsG102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical MeasurementsG106 Practice for Verification of Algorithm and Equipmentfor Electrochemical Impedance MeasurementsG150 Test Method for Electrochemical Critical Pitting Tem-perature Testing of Stain
10、less SteelsG193 Terminology and Acronyms Relating to Corrosion2.2 NACE Standards:3TM04972012 Measurement Techniques Related to Criteriafor Cathodic Protection on Underground or SubmergedMetallic Piping SystemsTM01012012 Measurement Techniques Related to Criteriafor Cathodic Protection of Underground
11、 Storage TankSystemsTM01082012 Testing of Catalyzed Titanium Anodes forUse in Soils or Natural WatersTM01092009 Aboveground Survey Techniques for theEvaluation of Underground Pipeline Coating ConditionTM01902012 Impressed Current Laboratory Testing ofAluminum Alloy AnodesTM02112011 Durability Test f
12、or Copper/Copper SulfatePermanent Reference Electrodes for Direct Burial Appli-cationsTM01132013 Evaluating the Accuracy of Field Grade Ref-erence Electrode3. Terminology3.1 DefinitionsThe terminology used herein shall be inaccordance with Terminology G193.1This guide is under the jurisdiction of AS
13、TM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved Jan. 1, 2017. Published January 2017. Originallyapproved in 2016. Last previous edition approved in 2016 as G215 16. DOI:10.1520
14、/G0215-17.2For 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.3Available from NACE International (NACE), 15835 Pa
15、rk Ten Pl., Houston, TX77084, http:/www.nace.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the D
16、ecision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Summary of Practice4.1 Electrode potential measurements are made by electri-cally connecting a high impedance voltmet
17、er or electrometerbetween the specimen electrode and a suitable referencehalf-cell electrode. See Practice G3.5. Significance and Use5.1 Electrode potential is the reversible work that is requiredto transfer a unit of positive charge between the surface inquestion and a reference electrode through t
18、he electrolyte thatis in contact with both electrodes. The sign of the electrodepotential is determined by the Gibbs Stockholm Conventiondescribed in Practice G3.5.2 The electrode potential of a surface is related to theGibbs free energy of the oxidation/reduction reactions occur-ring at the surface
19、 in question compared to the Gibbs freeenergy of the reactions occurring on the reference electrodesurface.45.3 Electrode potentials are used together with potential-pH(Pourbaix) diagrams to determine the corrosion products thatwould be in equilibrium with the environment and the elec-trode surface.
20、55.4 Electrode potentials are used in the estimation of corro-sion rates by several methods. One example is by means ofTafel line extrapolation, see Practices G3 and G102. Polariza-tion resistance measurements are also determined using elec-trode potential measurements, see Test Method G59 and Guide
21、G96.5.5 Corrosion potential measurements are used to determinewhether metal surfaces are passive in the environment inquestion, see Test Method C876.5.6 Corrosion potential measurements are used in the evalu-ation of alloys to determine their resistance or susceptibility tovarious forms of localized
22、 corrosion, see Test Methods F746,F2129, G61, and G150.5.7 Corrosion potentials are used to determine the metallur-gical condition of some aluminum alloys, see Test MethodG69. Similar measurements have been used with hot dippedgalvanized steel to determine their ability to cathodicallypolarize steel
23、. See Appendix X2.5.8 Corrosion potentials are used to evaluate aluminum andmagnesium alloys as sacrificial anodes for underground andimmersion cathodic protection application, see Test MethodG97 and NACE TM01902012.5.9 Corrosion potentials are used to evaluate the galvanicperformance of alloy pairs
24、 for use in seawater and otherconductive electrolytes, see Test Method F3044, Guide G71,and Guide G82.5.10 Electrode potential measurements are used to establishcathodic protection levels to troubleshoot cathodic protectionsystems and to confirm the performance of these systems insoils, concrete, an
25、d natural waters, see NACE TM0497, NACETM0108, and NACE TM0109.5.11 Electrode potential measurements are necessary for thedetermination of hydrogen overvoltage values in testing forhydrogen embrittlement and related issues with hydrogencracking. See Appendix X3.6. Potential Measurement6.1 Electrode
26、potentials are measured by placing a referenceelectrode in the corrosive electrolyte and electrically connect-ing a high impedance potential measuring instrument, such asan electrometer, potentiometer, or high impedance voltmeter,between the reference electrode and the object with the surfacein ques
27、tion. The measuring instrument must be able to measurethe potential difference without affecting either electrode to anysignificant degree. In general, devices with input impedancesgreater than 107ohms have been found to be acceptable inmost corrosion related measurements. In cases where thespecimen
28、 is polarized by an external power source, it may bedesirable to connect the potential measuring instrument di-rectly to the specimen rather than using the conductor carryingthe polarizing current to the specimen.NOTE 1When using a potential measuring instrument such as a highimpedance voltmeter, th
29、e reference electrode should be connected to thenegative or ground (black) terminal in order to have the instrument recordthe proper sign of the reading in accordance with Practice G3. However,for instruments that read only positive potentials, it may be necessary toreverse these connections to obta
30、in the reading.6.2 Two types of reference electrodes have been used incorrosion testing: standard reference electrodes and nonstan-dard reference electrodes.6.2.1 Standard reference electrodes are widely used andthey provide a known half-cell potential value versus thestandard hydrogen electrode, SH
31、E, half-cell. These electrodesare stable, and in most cases commercially available. It ispossible also to construct them using known techniques.66.2.2 Nonstandard reference electrodes are used in caseswhere it is not necessary to know the actual value of thepotential with reference to a chemical rea
32、ction, but it isimportant to know how the potential has changed as a surfaceis polarized or when environmental changes occur. Thesenonstandard reference electrodes should be stable with time,and they should not be significantly affected by the measuringprocess. Guide G96 provides information on nons
33、tandardreference electrodes used in polarization resistance measure-ments. In some cases the nonstandard reference electrode isidentical with the test electrode. In these cases a drift in thepotential with time is acceptable as long as both the test andreference electrodes experience the same drift.
34、6.2.3 In some cases nonstandard reference electrodes areused because the environmental conditions are not suitable forstandard reference electrodes. Pure zinc and zinc alloy (UNSZ12001, and Z12002, or Z14002) reference electrodes havebeen used in seawater and similar aqueous solutions although4Moore
35、, Walter J. Physical Chemistry,2ndEdition, Prentice Hall, EnglewoodCliffs, NJ, 1955.5Pourbaix, Marcel, Atlas of Electrochemical Equilibria in Aqueous Solutions,NACE International, Houston, TX, 1974.6Ives, David J. G. and Janz, George, J., Reference Electrodes Theory andPractice, Academic Press, New
36、York, NY, 1961.G215 172they have been observed to have significant potential drift withexposure. The potentials of these electrodes are determined bythe corrosion potential of metal in the seawater. For pure zinc,the potential versus SHE is approximately -0.78 V, while forthe zinc alloys, the potent
37、ial is approximately -0.8 V. In somecases the corrosion potential of the zinc electrode has beenmeasured against a standard electrode in a known environmentbefore and after usage to obtain a measure of the drift thatoccurred.7. Standard Reference Electrodes7.1 Standard reference electrodes are based
38、 on having theprimary electrochemical reaction occurring on the electrodesurface at equilibrium. This implies that both the forward andreverse reactions are occurring at the same rate. In the generalcase, the electrochemical reaction can be expressed as shownin Eq 1:Me 5 Men11ne (1)Where Me represen
39、ts a metal with a valence of n, and e rep-resents an electron. The potential of this reaction is shown inEq 2:E 5 E010.0592T 1 273.2!n298.2!21log Men1# (2)where:E = the electrode potential of the half-cell V,E0= the electrode potential of the reaction at unitactivity, V,Men+ = activity of the Me ion
40、,n = the number of electrons transferred in the reaction,andT = electrode temperature, C.NOTE 2The activity of an ion is equal to the concentration of the ionmultiplied by its activity coefficient.7.1.1 Standard Hydrogen ElectrodeThe standard hydro-gen electrode, SHE, is a first kind standard refere
41、nce elec-trode.5This electrode is composed of a platinized platinumelectrode immersed in an acid solution with a hydrogen ionactivity of 1 (approximately 1 N) and in contact with hydrogengas at a pressure of 101.3 kPa (1 atm) and 25C. Althoughthese electrodes have been used extensively in electroche
42、micalstudies to determine the thermodynamic properties of ions,they are almost never used in corrosion studies. However, thiselectrode is the reference point for all other standard referenceelectrodes.7.1.2 Saturated Calomel ElectrodeThis electrode, desig-nated SCE, has been the most widely used sta
43、ndard referenceelectrode for corrosion studies. The reason for its popularity isthat it has been used in commercial electrometric pH meters,and consequently it has been easily available and is veryreproducible. The SCE is based on the following reactions:2Hg5 Hg21112e (3)Hg21112Cl25 Hg2Cl2(4)The com
44、pound, Hg2Cl2, mercurous chloride, is also knownas calomel, and that is the reason for the electrodes designa-tion. The mercury/mercurous chloride mixture is immersedin a saturated potassium chloride solution so that the mercu-rous ion concentration is determined by its solubility at thatchloride le
45、vel. This electrode has been designated a secondkind electrode.5See Table 1 for information on the potentialof this electrode. Although these standard reference elec-trodes have been widely used for many laboratory corrosiontests including Test Methods G5, G59, and others, their usemay be restricted
46、 because of bans on mercury and its com-pounds.NOTE 3The term “saturated” when used to describe standard refer-ence electrodes refers to the metal ion concentration, not the anion.7.1.3 Saturated Silver/Silver Chloride ElectrodeThere arefour silver/silver chloride electrodes, saturated with respect
47、tothe silver ion concentration, that have been used as standardreference electrodes. All of these electrodes are based onreactions (5) and (6) below:Ag 5 Ag11e (5)Ag11Cl25 AgCl (6)Because silver chloride is slightly soluble, the silver ion con-centration is based on the chloride concentration. The s
48、ilver/silver chloride combination is immersed in KCl solutions ofTABLE 1 Potentials of Standard Reference Electrodes and Related Information 25CNOTE 1sr= repeatability standard deviation,sR= reproducibility standard deviation, and = indicates no standard values available.Electrode DesignationPotenti
49、alCVsrmVsRmVThermal TemperatureCoefficientmV/C(Pt)H2(a = 1.0) SHE 0.000 +0.87Ag/AgCl/sat. KCl +0.196 Ag/AgCl/1.0 m KCl +0.235 +0.25Ag/AgCl/0.1 M KCl +0.288 +0.22Ag/AgCl/Seawater +0.25 Hg/Hg2Cl2/sat. KCl SCE +0.241 3A7A+0.22Hg/Hg2Cl2/1.0 M KCl +0.280 +0.59Hg/Hg2Cl2/0.1 M KCl +0.334 +0.79Hg/Hg2SO4/H2SO4+0.616 Cu/sat. CuSO4CSE +0.30 10B30B+0.90ASee Test Method G69.BSee Test Method C876.CSee Practice G3.G215 173various strengths. The solutions that have been used are 0.1M, 1.0 M, saturated KCl, and seawater. Each of these solu
