1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 17474:2012Corrosion of metals and alloys Conventions applicable toelectrochemical measurementsin corrosion testingBS ISO 17474:2012 BRITISH STANDARDNational forewordThis B
2、ritish Standard is the UK implementation of ISO 17474:2012.The UK participation in its preparation was entrusted to TechnicalCommittee ISE/NFE/8, Corrosion of metals and alloys.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not
3、purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 70246 4ICS 77.060Compliance with a British Standard cannot confer immunity fromlegal obligation
4、s.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 29 February 2012.Amendments issued since publicationDate Text affectedBS ISO 17474:2012Reference numberISO 17474:2012(E)ISO 2012INTERNATIONAL STANDARD ISO17474First edition2012-02-01Corrosion o
5、f metals and alloys Conventions applicable to electrochemical measurements in corrosion testing Corrosion des mtaux et alliages Conventions applicables aux mesures lectrochimiques lors des essais de corrosion BS ISO 17474:2012ISO 17474:2012(E) COPYRIGHT PROTECTED DOCUMENT ISO 2012 All rights reserve
6、d. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester
7、. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2012 All rights reservedBS ISO 17474:2012ISO 17474:2012(E) ISO 2012 All rights reserved iiiContents Page Foreword iv Introduct
8、ion . v 1 Scope 1 2 Normative references 1 3 Terms and definitions . 1 4 Significance and use . 1 5 Sign convention for electrode potential 1 6 Sign convention for current and current density . 3 7 Conventions for displaying polarization data 3 7.1 Sign conventions . 3 7.2 Current density-potential
9、plots 3 7.3 Potential reference point 4 7.4 Units 5 7.5 Sample polarization curves 5 8 Conventions for displaying electrochemical impedance data . 8 8.1 General . 8 8.2 The Nyquist format (complex plane) . 9 8.3 The Bode format 10 Annex A (informative) References electrodes and their temperature dep
10、endence . 12 Bibliography 13 BS ISO 17474:2012ISO 17474:2012(E) iv ISO 2012 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carri
11、ed out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. I
12、SO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare Internati
13、onal Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the el
14、ements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 17474 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys. BS ISO 17474:2012ISO 17474:2012(E) ISO 2012 All rights reserved vInt
15、roduction Electrochemical test methods are useful for studying corrosion, because it is one particular phenomena of electrochemistry. They can provide quantitative data such as electrode potential, electrochemical current, electrochemical impedance, etc. This International Standard describes how the
16、se data are presented, being derived from basic methodology in ASTM G3-8911. BS ISO 17474:2012BS ISO 17474:2012INTERNATIONAL STANDARD ISO 17474:2012(E) ISO 2012 All rights reserved 1Corrosion of metals and alloys Conventions applicable to electrochemical measurements in corrosion testing WARNING Thi
17、s International Standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope
18、 This International Standard is intended to provide conventions for reporting and displaying electrochemical corrosion data. Conventions for potential, current density and electrochemical impedance, as well as conventions for graphical presentation of such data, are included. 2 Normative references
19、The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 8044, Corrosion of metals and alloys Basic te
20、rms and definitions 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 8044 apply. 4 Significance and use This practice provides guidance for reporting, displaying and plotting electrochemical corrosion data and includes recommendations on signs and con
21、ventions. Use of this practice will result in the reporting of electrochemical corrosion data in a standard format, facilitating comparison between data developed at different laboratories or at different times. The recommendations outlined in this International Standard may be utilized when recordi
22、ng and reporting corrosion data obtained from electrochemical tests, such as potentiostatic and potentiodynamic polarization, polarization resistance, electrochemical impedance, galvanic corrosion, and open-circuit potential measurements. 5 Sign convention for electrode potential 5.1 In this convent
23、ion, the positive direction of electrode potential implies an increase in oxidizing condition at the electrode in question. The positive direction also denotes a noble direction because the corrosion potentials of most noble metals, such as platinum, are more positive than the other non-passive base
24、 metals. On the other hand, the negative direction is associated with an increase in the reducing condition, and also denotes an active direction since corrosion potentials of active metals, such as potassium, are more negative than the other metals used. This convention was adopted unanimously by t
25、he 1953 International Union of Pure and Applied Chemistry1 as the standard for electrode potential. BS ISO 17474:2012ISO 17474:2012(E) 2 ISO 2012 All rights reserved5.2 To measure a potential of a specimen electrode in an aqueous electrolyte, an experimental set-up may be composed of an electrometer
26、, a reference electrode, an electrochemical cell, the electrolyte, etc. as shown in Figure 1. If the electrometer reads on scale in the negative range, the specimen electrode potential is negative to the reference electrode. Conversely, if the electrometer reads on scale in the positive range, the s
27、pecimen potential is positive to the reference electrode. In cases where the polarity of a measuring instrument is in doubt, a simple verification test can be performed as follows: connect the measuring instrument to a dry cell with the lead previously on the reference electrode to the negative batt
28、ery terminal, and the lead previously on the specimen electrode to the positive battery terminal. The meter deflection shall be in the direction of positive potential. The corrosion potential of magnesium or zinc shall be negative in a 1 N NaCl solution if measured against, for example, a KCl-satura
29、ted silver/silver chloride electrode (KCl (sat.)/AgCl/Ag: sat. SSCE). For accuracy, an input impedance of the electrometer should be more than 1011. Key 1 electrometer 2 reference electrode 3 electrolyte 4 salt bridge 5 electrochemical cell 6 specimen electrode Figure 1 Schematic diagram of an appar
30、atus to measure electrode potential of a specimen BS ISO 17474:2012ISO 17474:2012(E) ISO 2012 All rights reserved 36 Sign convention for current and current density A convention for the sign of current and current density, in which anodic and cathodic values are designated as positive and negative,
31、respectively, is recommended. When the potentials are plotted against the logarithm of the current densities, only the absolute values of the latter can be plotted. In such plots, the values which are cathodic should be clearly differentiated from the anodic values, if both are present. 7 Convention
32、s for displaying polarization data 7.1 Sign conventions The standard mathematical practice for plotting graphs is recommended for displaying electrochemical corrosion data. In this practice, positive values are plotted above the origin on the ordinate (y axis) and to the right of the origin on the a
33、bscissa (x axis). In logarithmic plots, the abscissa value increases from left to right and the ordinate value increases from bottom to top. 7.2 Current density-potential plots A convention for plotting current density vs. potential data, in which current density is plotted along the ordinate and po
34、tential along the abscissa, is recommended. In current density/potential plots, the current density may be plotted on either linear or logarithmic axes. In general, logarithmic plots are used to incorporate wide ranges of current density data and to demonstrate Tafel relationships. Linear plots are
35、used for studies in case the current density or potential range is small, or in case the region of the current density change from anodic to cathodic is assessed. Linear plots are also used for the determination of the polarization resistance Rp, which is defined as the inverse of the slope of a pot
36、ential-current density plot at the corrosion potential Ecor. The relationship between the polarization resistance Rpand the corrosion current density icoris as follows (References 23): EbbERibacpac0 cord( )d2,30(bi)(1)where ab is the anodic Tafel slope; cb is the cathodic Tafel slope. BS ISO 17474:2
37、012ISO 17474:2012(E) 4 ISO 2012 All rights reservedKey E potential i current density Ecorcorrosion potential Rp polarization resistance Figure 2 Linear polarization plot The solid line in Figure 2 is a plot of current density i versus potential E around the corrosion potential Ecor, from which the p
38、olarization resistance Rpmay be determined as an inverse of the slope of the same curve at the potential Ecor. 7.3 Potential reference point In plots where electrode potentials are displayed, some indication for conversion from the displayed values to the standard hydrogen electrode scale (SHE) shal
39、l be shown. Expressing the used reference electrode in such a way as E(V) vs. 1M KCl (1M KCl/AgCl/Ag) is recommended. The electrode potential may be plotted on the abscissa, at the bottom of which is the scale against the reference electrode used, together with that at the top with the converted sca
40、le against the standard hydrogen electrode (SHE). If the latter is not shown, a relationship such as the following may be used for the conversion according to Annex A. E vs. SHE = vs. 1M KCl/AgCl/Ag + 0,235 V (2) Ewhere E vs. SHE represents the electrode potential, in volts, against the standard hyd
41、rogen electrode; E(V) vs. 1M KCl/AgCl/Ag represents the electrode potential, in volts, measured against the silver/silver chloride electrode in 1M KCl. NOTE A table of potentials for various common reference electrodes is given in Annex A. BS ISO 17474:2012ISO 17474:2012(E) ISO 2012 All rights reser
42、ved 57.4 Units The recommended unit of potential is volt (V). If only small potential ranges are covered, millivolts (mV) or microvolts (V) may be used. The SI units for current density are amperes per square metre (Am2) or amperes per square centimetre (Acm2). Units expressed in milli-amperes per s
43、quare centimetre (mAcm2), and microamperes per square centimetre (Acm2) are still in use. 7.5 Sample polarization curves Sample polarization plots employing these recommended practices are shown in Figures 2 to 6. Figures 3 and 4 are hypothetical curves showing active and active-passive anode behavi
44、ours, respectively. Figures 5 and 6 are actual anodic polarization data for Type 430 stainless steel (UNS 43000)4and cathodic polarization data of Type 2024-T3 aluminium alloy5. The purpose of Figures 3 and 4 is to illustrate the location of various points used in discussion of electrochemical metho
45、ds for corrosion testing. The purpose of Figures 5 and 6 is to show how various types of electrode behaviours are plotted in accordance with this convention. Key 1 cathodic branch 2 anodic branch 3 observed polarization plot baanodic Tafel slope bccathodic Tafel slope E electrode potential Ecorcorro
46、sion potential i current density icor corrosion current density Figure 3 Hypothetical cathodic and anodic polarization diagram BS ISO 17474:2012ISO 17474:2012(E) 6 ISO 2012 All rights reservedKey 1 oxygen evolution 2 secondary passivity 3 transpassive region 4 passive region 5 anodic current 6 catho
47、dic current 7 active region E electrode potential Eppprimary passivation potential Ecorcorrosion potential i current density icor corrosion current density icc critical current density ip passive current density Figure 4 Hypothetical cathodic and anodic polarization curves for a passivating metal BS
48、 ISO 17474:2012ISO 17474:2012(E) ISO 2012 All rights reserved 7Key E electrode potential i current density Figure 5 Typical anodic polarization plot for type 430 stainless steel in 0,5M H2SO4 BS ISO 17474:2012ISO 17474:2012(E) 8 ISO 2012 All rights reservedKey E electrode potential i current density
49、 Figure 6 Typical cathodic polarization plots for aluminium alloys of type 2024-T3 in 0,2M NaCl solution 8 Conventions for displaying electrochemical impedance data 8.1 General Two graphical formats in common use for reporting electrochemical impedance data are the Nyquist and the Bode formats. A simple electrode system modelled by the equivalent electrical circuit as shown in Figure 7 is discussed. By convention, the impedance Z is defined as: BS ISO 17474:2012ISO 17474:2012(
