1、BSI Standards Publication PD ISO/TR 16208:2014 Corrosion of metals and alloys Test method for corrosion of materials by electrochemical impedance measurementsPD ISO/TR 16208:2014 PUBLISHED DOCUMENT National foreword This Published Document is the UK implementation of ISO/TR 16208:2014. The UK partic
2、ipation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users
3、 are responsible for its correct application. The British Standards Institution 2014. Published by BSI Standards Limited 2014 ISBN 978 0 580 73110 5 ICS 77.060 Compliance with a British Standard cannot confer immunity from legal obligations. This Published Document was published under the authority
4、of the Standards Policy and Strategy Committee on 31 January 2014. Amendments issued since publication Date Text affectedPD ISO/TR 16208:2014 ISO 2014 Corrosion of metals and alloys Test method for corrosion of materials by electrochemical impedance measurements Corrosion des mtaux et alliages Mthod
5、e dessai pour la corrosion des matriaux par des mesures lectrochimiques dimpdance TECHNICAL REPORT ISO/TR 16208 First edition 2014-01-15 Reference number ISO/TR 16208:2014(E)PD ISO/TR 16208:2014ISO/TR 16208:2014(E)ii ISO 2014 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2014 All rights reser
6、ved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
7、 at the address below or ISOs member body in the country of the requester. 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 SwitzerlandPD ISO/TR 16208:2014ISO/TR 16208:2014(E) ISO 2014 All rights
8、reserved iii Contents Page Foreword iv 1 Scope . 1 2 Normative references 1 3 T erms and definitions . 1 4 Principles . 3 4.1 Simple corroding system 3 4.2 Presentation of impedance by a complex number . 5 4.3 Impedance spectra of circuit elements 6 4.4 Presentation of a simple corroding system 7 5
9、Apparatus . 9 5.1 General . 9 5.2 Test cell .10 5.3 Electrode holder .10 5.4 Electrode material .10 5.5 Reference electrode .11 5.6 Electrolyte 11 6 Specimen preparation .11 7 Solution preparation .11 8 Dummy cell 11 9 Procedure11 10 Data analysis 12 11 Test report 14 Annex A (informative) Dummy cel
10、l .15 Annex B (informative) Data analysis .17 Bibliography .23PD ISO/TR 16208:2014ISO/TR 16208:2014(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normal
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16、inciples in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/TC 156, Corrosion of metals and alloys.iv ISO 2014 All rights reservedPD ISO/TR 16208:2014TECHNICAL REPORT ISO/TR 16208:2014(E) Corrosion o
17、f metals and alloys Test method for corrosion of materials by electrochemical impedance measurements 1 Scope This Technical Report describes basic principles of electrochemical impedance spectroscopy (EIS), specially focusing on the corrosion of metallic materials. It also deals with how to use elec
18、trochemical apparatus, set up and connect electrical instruments, present measured data, and analyse results. However, a more detailed description of this methodology can be found in ISO 16773-1 and ISO 16773-2. 2 Normative references The following documents, in whole or in part, are normatively ref
19、erenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 16773-1, Paints and varnishes Electrochemical impedance spectroscopy
20、 (EIS) on high-impedance coated specimens Part 1: Terms and definitions ISO 16773-2, Paints and varnishes Electrochemical impedance spectroscopy (EIS) on high-impedance coated specimens Part 2: Collection of data ISO 16773-3, Paints and varnishes Electrochemical impedance spectroscopy (EIS) on high-
21、impedance coated specimens Part 3: Processing and analysis of data from dummy cells 3 T erms a nd definiti ons For the purposes of this document, the terms and definitions given in ISO 16773-1 and the following apply. 3.1 bode plot phase angle and the logarithm of the impedance magnitude |Z| plotted
22、 versus the logarithm of the applied frequency 3.2 constant phase element CPE equivalent circuit component that models the behaviour of an imperfect capacitor representing a constant phase shift through the whole frequency range Note 1 to entry: A capacitor has a phase shift of 90; for a CPE, the ab
23、solute value is smaller. 3.3 counter electrode inert electrode in the electrochemical cell through which the current passes from or to the working electrode Note 1 to entry: The counter electrode is also called auxiliary electrode. ISO 2014 All rights reserved 1PD ISO/TR 16208:2014ISO/TR 16208:2014(
24、E) 3.4 dummy cell printed circuit board with mounted electrical components according to the equivalent circuit with connection points to the measuring instrument 3.5 double-layer capacitance C dl capacitance values in the equivalent circuit representing the metal-electrolyte interface characteristic
25、s 3.6 impedance frequency-dependent, complex-valued proportionality factor, E/I, between the applied potential (or current) and the response current (or potential) in an electrochemical cell Note 1 to entry: This factor becomes the impedance when the perturbation and response are related linearly (t
26、he factor value is independent of the perturbation magnitude) and the response is caused only by the perturbation. The value can be related to the corrosion rate when the measurement is made at the corrosion potential. 3.7 magnitude of the impedance |Z| magnitude modulus square root of the sum of sq
27、uares of the real and imaginary component of impedance Note 1 to entry: This is given by the formula below. ZZ Z where Z is the complex impedance; Z is the real part of impedance; Z is the imaginary part of impedance. 3.8 Nyquist plot real component of impedance Z plotted versus the negative of the
28、imaginary component of impedance Z in rectangular coordinate values 3.9 phase angle phase difference between the periodically recurring voltage and the current of the same frequency, expressed in angular measure 3.10 polarization resistance R p slope (d e /d i ) at the corrosion potential of a poten
29、tial (e) versus current density (i) curve Note 1 to entry: For a simple corroding system, charge transfer resistance, R ct , is used. 3.11 potentiostat electronic instrument for automatically maintaining the working electrode in an electrolyte at a controlled potential with respect to a reference el
30、ectrode, and for measuring the resulting current between the working and counter electrodes2 ISO 2014 All rights reservedPD ISO/TR 16208:2014ISO/TR 16208:2014(E) 3.12 reference electrode electrode which allows the measurement of an electrode potential Note 1 to entry: This electrode has to present a
31、 thermodynamically stable potential versus the standard hydrogen electrode. 3.13 solution resistance R s resistance of the solution between the working electrode and the tip of Luggin capillary connected to the reference electrode Note 1 to entry: This term is not defined in ISO 16773-1. 3.14 workin
32、g electrode test or specimen electrode in an electrochemical cell Note 1 to entry: This definition is different from the definition in ISO 16773-1. 3.15 Kramers-Kronig relation mathematical relation connecting the real and imaginary parts of any complex function which is analytic in the upper half-p
33、lane Note 1 to entry: These relations are often used to relate the real and imaginary parts of response functions in physical systems because causality implies that the analyticity condition is satisfied, and conversely, analyticity implies causality of the corresponding physical system. 4 Principle
34、s 4.1 Simple corroding system Simple corrosion systems, which are under charge transfer control resulting in uniform corrosion on homogeneous surface, can be described by a simple equivalent circuit shown in Figure 1. The use of electrochemical impedance spectroscopy (EIS) on corroding metals requir
35、es that the measured system do not react in such a way that the measured system change during the measurement time, steady-state should be maintained. A metal immersed in the solution may corrode by anodic and cathodic reactions at the metal/solution interface, as shown in Figure 1. A simple corrodi
36、ng system in an electrolyte is represented by an anodic and cathodic reaction: A no de: Me 1 Me 1 n+ ne - Cathode: Me 2 n+ ne - Me 2 where n is the number of electrons e - ; Me is the metal. Metal 1 has less nobility than metal 2. The equivalent circuit represents the metal/solution interface of the
37、 metal surface which consists of a polarization resistance, R p , also commonly noted charge transfer resistance, R ct , in parallel with an electric double-layer capacitance, C dl , which is in series with a solution resistance, R s . ISO 2014 All rights reserved 3PD ISO/TR 16208:2014ISO/TR 16208:2
38、014(E) A metal sample in immersion develops an electric double layer at the interface. The double layer is represented by a capacitance in EIS. It is not a true capacitive value measured by EIS and the double layer is, therefore, represented by a constant phase element (CPE) to compensate the deviat
39、ion from the true capacitive value. The elements CPE and R pare not always dependent on corrosion resistance but can reflect the overall electrical resistance and dielectric properties of passive film oxides. For example, a passive film growth depends on the transport of cations and anions or their
40、vacancies across the oxide film. If defects such as pores, channels, or cracks are present in the passive film, the electrolyte will penetrate the film and impair its resistance. In addition, a surface oxide film might exhibit capacitive behaviour due to a dielectric nature of the oxide. The CPE is
41、a component of the equivalent circuit for modelling the behaviour of an electrical double layer, an imperfect capacitor. The impedance of a CPE is given by 1/ Z CPE= Q( j) n . The Q is the constant corresponding to the electric double-layer capacitance qualitatively. The factor n ranges from 0 to 1
42、as follows: n = 1 represents an ideal capacitor; n = 0 represents a pure resistor. 1 2 3 Rs Rp Cdl Figure 1 Schematic representation of a metal in solution and the equivalent circuit representing the metal/solution interface Key R s solutions resistance 1 solution C dl double layer capacitance 2 met
43、al R p polarization resistance 3 corroding metal For a simple corroding metal, the value of C dlis generally proportional to the actual surface area of the working electrode. When the anodic and cathodic reactions are controlled by the charge transfer step 4 ISO 2014 All rights reservedPD ISO/TR 162
44、08:2014ISO/TR 16208:2014(E) around the corrosion potential, the current flowing through the working electrode, I w , is represented by Formula (1). (1) where I is the corrosion current; aand c are Tafel constants (V/decade) in anodic and cathodic regions, respectively. The R pand I corhave the follo
45、wing relation: (2) where K (3) The value of K is dependent upon the type of specimen material and the environment, and the I corcan be obtained from R ptheoretically. When a semicircle of the impedance is depressed indicating an untrue capacitance in the Nyquist plot, the constant phase element (CPE
46、) may be incorporated in the equivalent circuit instead of C dl . The outline of CPE is revealed in Annex B. The theoretical relationship in Formula (3) might not hold for the corrosion system with a CPE because other electrochemical reactions than simple metallic corrosion might be involved in the
47、system. It is recommended that the correlation between R pvalues and I corvalues from weight-loss measurements be used to determine K values. 4.2 Presentation of impedance by a complex number The impedance Z is represented by the complex number with real part Z and imaginary part Z. Z = Z j Z (4) Th
48、e relation of Z and Z on the complex plane is depicted in Figure 2. The magnitude impedance, |Z|, and phase shift (in degrees) or (in radians) of Z are related by ZZ Z 22(5) Z Z(6) (7) The phase angle of vector Z is presented in (degrees) on the complex plane, as in Figure 2. ISO 2014 All rights reserved 5PD ISO/TR 16208:2014ISO/TR 16208:2014(E) 0 Figure 2 Impedance Z presented on the complex plane 4.3 Impedance spectra of circuit elements 4.3.1 The impedance spectra of circuit elements, R and C, and their combina
