1、Designation: G215 16Standard 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 May 1, 2016. Published May 2016. DOI: 10.1520/G0215-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
14、ontact 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 Park Ten Pl., Houston, TX77084, http:/www.nace.org.Copyright ASTM International, 100
15、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Practice4.1 Electrode potential measurements are made by electri-cally connecting a high impedance voltmeter or electrometerbetween the specimen electrode and a suitable referencehalf-cell electrode. See Pr
16、actice 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 the electrolyte thatis in contact with both electrodes. The sign of the electrodepotential is determi
17、ned 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 in question compared to the Gibbs freeenergy of the reactions occurring on the reference electrodes
18、urface.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.55.4 Electrode potentials are used in the estimation of corro-sion rates by several methods. One exa
19、mple 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 GuideG96.5.5 Corrosion potential measurements are used to determinewhether metal surfaces are passive in
20、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 corrosion, see Test Methods F746,F2129, G61, and G150.5.7 Corrosion potentials are used to determin
21、e 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. See Appendix X2.5.8 Corrosion potentials are used to evaluate aluminum andmagnesium alloys as sacr
22、ificial 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 for use in seawater and otherconductive electrolytes, see Test Method F3044, Guide G71,and Guide G8
23、2.5.10 Electrode potential measurements are used to establishcathodic protection levels to troubleshoot cathodic protectionsystems and to confirm the performance of these systems insoils, concrete, and natural waters, see NACE TM0497, NACETM0108, and NACE TM0109.5.11 Electrode potential measurements
24、 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 potentials are measured by placing a referenceelectrode in the corrosive electrolyte and electricall
25、y 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 question. The measuring instrument must be able to measurethe potential difference without affecting eit
26、her 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 is polarized by an external power source, it may bedesirable to connect the potential measuring ins
27、trument 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, the reference electrode should be connected to thenegative or ground (black) terminal in order to have
28、 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 obtain the reading.6.2 Two types of reference electrodes have been used incorrosion testing: standard re
29、ference 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, SHE, half-cell. These electrodesare stable, and in most cases commercially available. It ispossible al
30、so 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 reaction, but it isimportant to know how the potential has changed as a surfaceis polarized or when env
31、ironmental 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 nonstandardreference electrodes used in polarization resistance measure-ments. In some cases the nonstan
32、dard 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.6.2.3 In some cases nonstandard reference electrodes areused because the environmental conditions ar
33、e 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, Walter J. Physical Chemistry,2ndEdition, Prentice Hall, EnglewoodCliffs, NJ, 1955.5Pourbaix, Marce
34、l, 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 York, NY, 1961.G215 162they have been observed to have significant potential drift withexposure. The
35、 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 potential is approximately -0.8 V. In somecases the corrosion potential of the zinc electrode has beenmeas
36、ured 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 on having theprimary electrochemical reaction occurring on the electrodesurface at equilibrium. Thi
37、s 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 represents a metal with a valence of n, and e rep-resents an electron. The potential of this reaction is sho
38、wn 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,n = the number of electrons transferred in the reaction,andT = electrode temperature, C.NOTE 2The a
39、ctivity 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 reference elec-trode.5This electrode is composed of a platinized platinumelectrode immersed in an acid sol
40、ution 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 electrochemicalstudies to determine the thermodynamic properties of ions,they are almost never used in corrosi
41、on 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 standard referenceelectrode for corrosion studies. The reason for its popularity isthat it has been use
42、d 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 compound, Hg2Cl2, mercurous chloride, is also knownas calomel, and that is the reason for the electrode
43、s 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 level. This electrode has been designated a secondkind electrode.5See Table 1 for information on the p
44、otentialof 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 because of bans on mercury and its com-pounds.NOTE 3The term “saturated” when used to describe stan
45、dard 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 tothe silver ion concentration, that have been used as standardreference electrodes. All of these el
46、ectrodes 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 silver/silver chloride combination is immersed in KCl solutions ofvarious strengths. The solutions th
47、at have been used are 0.1M, 1.0 M, saturated KCl, and seawater. Each of these solu-tions produces a different standard potential versus SHE. SeeTABLE 1 Potentials of Standard Reference Electrodes and Related Information 25CNOTE 1sr= repeatability standard deviation,sR= reproducibility standard devia
48、tion, and = indicates no standard values available.Electrode DesignationPotentialVsrmVsRmVThermal TemperatureCoefficientmV/C(Pt)H2(a = 1.0) SHE 0.000 +0.87Ag/AgCl/sat. KCl +0.194 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+0.2
49、2Hg/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.G215 163Table 1 for information on the potentials of these electrodes.These electrodes are also second kind reference electrodes.5Because of the ban on mercury compounds, the KCl satu-rated silver/silver chloride electrode may supplant the SCEelectrode for laboratory corrosion studies.NOTE 4Silver mesh electrodes for seawater usage are coated with asilver chlorid
