SIST EN ISO 17081:2008
(Main)Method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique (ISO 17081:2004)
Method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique (ISO 17081:2004)
This International Standard specifies a laboratory method for the measurement of hydrogen permeation and for the determination of hydrogen atom uptake and transport in metals, using an electrochemical technique. The term "metal" as used in this International Standard includes alloys. This International Standard describes a method for evaluating hydrogen uptake in metals, based on measurement of steady-state hydrogen flux. It also describes a method for determining effective diffusivity of hydrogen atoms in a metal and for distinguishing reversible and irreversible trapping. This International Standard gives requirements for the preparation of specimens, control and monitoring of the environmental variables, test procedures and analysis of results. This International Standard may be applied, in principle, to all metals for which hydrogen permeation is measurable and the method can be used to rank the relative aggressivity of different environments in terms of the hydrogen uptake of the exposed metal.
Elektrochemisches Verfahren zur Messung der Wasserstoffpermeation und zur Bestimmung von Wasserstoffaufnahme und -transport in Metallen (ISO 17081:2004)
1.1 In dieser Internationalen Norm wird ein elektrochemisches Laboratoriumsverfahren zur Messung der Wasserstoffpermeation und zur Bestimmung der Aufnahme und des Transports von Wasserstoffatomen in Metallen festgelegt. In dieser Internationalen Norm werden mit der Benennung Metall auch Legierungen erfasst.
1.2 Diese Internationale Norm beschreibt ein Verfahren zur Bewertung der Wasserstoffaufnahme in Metallen, das auf der Messung der Wasserstoffströmung (des Wasserstoffflusses) im stationären Zustand beruht. Ferner werden Verfahren zur Bestimmung des effektiven Diffusionsvermögens von Wasserstoffatomen in einem Metall und zur Unterscheidung reversibler und irreversibler Fehlstellen beschrieben.
1.3 In dieser Internationalen Norm werden Anforderungen an die Vorbereitung der Proben, die Kontrolle und Überwachung der Umgebungsvariablen, die Prüfverfahren und die Auswertung der Ergebnisse festgelegt.
1.4 Diese Internationale Norm darf prinzipiell auf alle Metalle, bei denen Wasserstoffpermeation messbar ist, angewendet werden, und das Verfahren kann zur Klassifizierung der relativen Aggressivität unterschiedlicher Umgebungen in Bezug auf die Wasserstoffaufnahme des beanspruchten Metalls angewendet werden
Méthode de mesure de la perméation de l'hydrogene et détermination de l'absorption d'hydrogene et de son transport dans les métaux a l'aide d'une technique électrochimique (ISO 17081:2004)
L'ISO 17081:2004 spécifie une méthode de laboratoire pour le mesurage de la perméation de l'hydrogène et la détermination de l'absorption et du transport des atomes d'hydrogène dans les métaux à l'aide d'une technique électrochimique. Le terme «métal» utilisé dans la présente Norme internationale comprend les alliages.
L'ISO 17081:2004 décrit une méthode permettant d'évaluer l'absorption d'hydrogène dans les métaux sur la base du mesurage d'un flux stationnaire d'hydrogène. Elle décrit également une méthode permettant de déterminer le coefficient de diffusion effective des atomes d'hydrogène dans un métal et de faire une distinction entre le piégeage réversible et le piégeage irréversible.
L'ISO 17081:2004 fournit des exigences concernant la préparation des éprouvettes, le contrôle et le suivi des variables environnementales, les méthodes d'essai et l'analyse des résultats.
L'ISO 17081:2004 peut s'appliquer, en principe, à tous les métaux pour lesquels la perméation de l'hydrogène est mesurable et la méthode peut être utilisée pour classer l'agressivité relative de différents environnements en termes d'absorption d'hydrogène par le métal exposé.
Metoda merjenja prodiranja vodika ter določanje njegovega vpijanja in prenosa v kovinah z elektrokemijsko tehniko (ISO 17081:2004)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 17081:2008
01-julij-2008
0HWRGDPHUMHQMDSURGLUDQMDYRGLNDWHUGRORþDQMHQMHJRYHJDYSLMDQMDLQSUHQRVDY
NRYLQDK]HOHNWURNHPLMVNRWHKQLNR ,62
Method of measurement of hydrogen permeation and determination of hydrogen uptake
and transport in metals by an electrochemical technique (ISO 17081:2004)
Méthode de mesure de la perméation de l'hydrogene et détermination de l'absorption
d'hydrogene et de son transport dans les métaux a l'aide d'une technique
électrochimique (ISO 17081:2004)
Ta slovenski standard je istoveten z: EN ISO 17081:2008
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 17081:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
EN ISO 17081
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2008
ICS 77.060
English Version
Method of measurement of hydrogen permeation and
determination of hydrogen uptake and transport in metals by an
electrochemical technique (ISO 17081:2004)
Méthode de mesure de la perméation de l'hydrogène et Elektrochemisches Verfahren zur Messung der
détermination de l'absorption d'hydrogène et de son Wasserstoffpermeation und zur Bestimmung von
transport dans les métaux à l'aide d'une technique Wasserstoffaufnahme und -transport in Metallen (ISO
électrochimique (ISO 17081:2004) 17081:2004)
This European Standard was approved by CEN on 21 March 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17081:2008: E
worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
EN ISO 17081:2008 (E)
Contents Page
Foreword.3
2
---------------------- Page: 3 ----------------------
EN ISO 17081:2008 (E)
Foreword
The text of ISO 17081:2004 has been prepared by Technical Committee ISO/TC 156 “Corrosion of metals and
alloys” of the International Organization for Standardization (ISO) and has been taken over as EN ISO
17081:2008 by Technical Committee CEN/TC 262 “Metallic and other inorganic coatings” the secretariat of
which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by October 2008, and conflicting national standards shall be withdrawn at
the latest by October 2008.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 17081:2004 has been approved by CEN as a EN ISO 17081:2008 without any modification.
3
---------------------- Page: 4 ----------------------
INTERNATIONAL ISO
STANDARD 17081
First edition
2004-11-01
Method of measurement of hydrogen
permeation and determination of
hydrogen uptake and transport in metals
by an electrochemical technique
Méthode de mesure de la perméation de l'hydrogène et détermination
de l'absorption d'hydrogène et de son transport dans les métaux à l'aide
d'une technique électrochimique
Reference number
ISO 17081:2004(E)
©
ISO 2004
---------------------- Page: 5 ----------------------
ISO 17081:2004(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2004
All rights reserved. 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
ISO's 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 copyright@iso.org
Web www.iso.org
Published in Switzerland
©
ii ISO 2004 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 17081:2004(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Principle . 3
6 Samples . 4
6.1 Dimensions . 4
6.2 Preparation . 5
7 Apparatus . 5
8 Test environment considerations . 7
9 Test procedure . 8
10 Control and monitoring of test environment . 9
11 Analysis of results . 10
11.1 General . 10
11.2 Analysis of steady-state current . 10
11.3 Analysis of permeation transient . 10
12 Test report . 13
Annex A (informative) Recommended test environments for specific alloys . 14
Bibliography . 16
©
ISO 2004 – All rights reserved iii
---------------------- Page: 7 ----------------------
ISO 17081:2004(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 normally carried 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. ISO 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 International 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 elements 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 17081 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
©
iv ISO 2004 – All rights reserved
---------------------- Page: 8 ----------------------
INTERNATIONAL STANDARD ISO 17081:2004(E)
Method of measurement of hydrogen permeation and
determination of hydrogen uptake and transport in metals by an
electrochemical technique
1Scope
1.1 This International Standard specifies a laboratory method for the measurement of hydrogen permeation
and for the determination of hydrogen atom uptake and transport in metals, using an electrochemical technique.
The term “metal” as used in this International Standard includes alloys.
1.2 This International Standard describes a method for evaluating hydrogen uptake in metals, based on
measurement of steady-state hydrogen flux. It also describes a method for determining effective diffusivity of
hydrogen atoms in a metal and for distinguishing reversible and irreversible trapping.
1.3 This International Standard gives requirements for the preparation of specimens, control and monitoring of
the environmental variables, test procedures and analysis of results.
1.4 This International Standard may be applied, in principle, to all metals for which hydrogen permeation is
measurable and the method can be used to rank the relative aggressivity of different environments in terms of
the hydrogen uptake of the exposed metal.
2 Normative references
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.
1)
ISO 17475:— , Corrosion of metals and alloys — Electrochemical test methods — Guidelines for conducting
potentiostatic and potentiodynamic polarization measurements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
charging
method of introducing atomic hydrogen into the metal by exposure to an aqueous environment under
galvanostatic control (constant charging current), potentiostatic control (constant electrode potential), free
corrosion or by gaseous exposure
3.2
charging cell
compartment in which hydrogen atoms are generated on the sample surface, including both aqueous and
gaseous charging
1) To be published.
©
ISO 2004 – All rights reserved 1
---------------------- Page: 9 ----------------------
ISO 17081:2004(E)
3.3
decay current
decay of the hydrogen atom oxidation current, after attainment of steady state, following a decrease in charging
current
3.4
Fick's second law
second-order differential equation describing, in this case, the concentration of atomic hydrogen in the sample
as a function of position and time
2 2
NOTE The equation is of the form ∂C(x,t)/t=D∂ C(x,t)/∂x for lattice diffusion in one dimension where diffusivity is
independent of concentration. See Table 1 for an explanation of the symbols.
3.5
hydrogen flux
amount of hydrogen passing through the metal sample per unit area per unit time
3.6
hydrogen uptake
atomic hydrogen absorbed into the metal as a result of charging
3.7
irreversible trap
microstructural site at which the residence time for a hydrogen atom is infinite or extremely long compared to
the time-scale for permeation testing at the relevant temperature
3.8
mobile hydrogen atoms
hydrogen atoms in interstitial sites in the lattice (lattice sites) and reversible trap sites
3.9
oxidation cell
compartment in which hydrogen atoms exiting from the metal sample are oxidized
3.10
permeation current
current measured in oxidation cell associated with oxidation of hydrogen atoms
3.11
permeation flux
hydrogen flux exiting the test sample in the oxidation cell
3.12
permeation transient
variation of the permeation current with time, from commencement of charging to the attainment of steady state,
or modification of charging conditions
3.13
recombination poison
chemical within the test environment in the charging cell which enhances hydrogen absorption by retarding the
recombination of hydrogen atoms on the metal surface
3.14
reversible trap
microstructural site at which the residence time for a hydrogen atom is greater than that for the lattice site but is
small in relation to the time to attain steady-state permeation
©
2 ISO 2004 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 17081:2004(E)
4 Symbols
Table 1 gives a list of symbols and their designations.
Table 1 — Symbols and their designations and units
Symbol Designation Unit
2
A Exposed area of sample in the oxidation cell m
−3
C(x,t) Lattice concentration of hydrogen as a function of position and time mol·m
Sub-surface concentration of atomic hydrogen in interstitial lattice sites on the
−3
C mol·m
0
charging side of the sample
Summation of the sub-surface concentration of hydrogen in interstitial lattice sites
−3
C mol·m
0R
and reversible trap sites on the charging side of the sample
2 −1
D Lattice diffusion coefficient of atomic hydrogen m ·s ;
l
Effective diffusion coefficient of atomic hydrogen based on elapsed time
2 −1
D m ·s ;
eff
corresponding to J(t)/J = 0,63
ss
−1 −1
FFFaraday's constant ( = 96 485 C·mol ) C·mol
Time-dependent atomic hydrogen permeation flux as measured on the oxidation
−2 −1
J(t) mol·m s
side of the sample
Atomic hydrogen permeation flux at steady-state as measured on the oxidation side
−2 −1
J mol·m s
ss
of the sample
J(t)/J Normalized flux of atomic hydrogen 1
ss
−2
I(t) Time-dependent atomic hydrogen permeation current A·m
−2
I Steady-state atomic hydrogen permeation current A·m
ss
L Sample thickness m
t Time elapsed from commencement of hydrogen charging s
Elapsed time measured by extrapolating the linear portion of the rising permeation
t s
b
current transient
t Time to achieve a value of J(t)/J = 0,63 s
lag ss
x Distance in sample measured in the thickness direction m
2
τDNormalized time ( t/L ) 1
l
τ Normalized time to achieve a value of J(t)/J = 0,63 1
lag ss
5 Principle
5.1 The technique involves locating the metal sample of interest between the charging and oxidation cells,
where the charging cell contains the environment of interest. Hydrogen atoms are generated on the sample
surface exposed to this environment.
5.2 In gaseous environments, the hydrogen atoms are generated by adsorption and dissociation of the
gaseous species. In aqueous environments, hydrogen atoms are produced by electrochemical reactions. In
both cases, some of the hydrogen atoms diffuse through the metal sample and are then oxidized to hydrogen
cations on exiting from the other side of the metal in the oxidation cell.
A palladium coating is sometimes applied to one or both sides of the membrane following initial removal of oxide
films. A palladium coating on the charging face of the membrane affects the sub-surface hydrogen
concentration in the substrate and the measured permeation current. It is important to verify that the calculated
diffusivity is not influenced by the coating. Palladium coating is particularly useful for gaseous charging.
5.3 The environment and the electrode potential on the oxidation side of the membrane are selected so that
the metal is either passive or immune to corrosion. The background current established prior to hydrogen
transport is steady, and small compared to the hydrogen atom oxidation current.
©
ISO 2004 – All rights reserved 3
---------------------- Page: 11 ----------------------
ISO 17081:2004(E)
5.4 The electrode potential of the sample in the oxidation cell is controlled at a value sufficiently positive to
ensure that the kinetics of oxidation of hydrogen atoms are limited by the flux of hydrogen atoms, i.e. the
hydrogen atom oxidation current density is transport limited.
NOTE Palladium coating of the oxidation side of the sample can enhance the rate of oxidation and thereby enable
attainment of transport-limited oxidation of hydrogen atoms at less positive potentials than for the uncoated sample.
5.5 The oxidation current is monitored as a function of time. The total oxidation current comprises the
background current and the permeation current.
5.6 The thickness of the sample, L, is usually selected to ensure that the measured flux reflects volume (bulk)
controlled hydrogen atom transport.
NOTE Thin specimens may be used for evaluation of the effect of surface processes on hydrogen entry (absorption kinetics
or transport in oxide films).
5.7 In reasonably pure metals with a sufficiently low density of microstructural trap sites, atomic hydrogen
transport through the material is controlled by lattice diffusion.
5.8 The effect of alloying and of microstructural features such as dislocations, grain boundaries, inclusions,
and precipitate particles is to introduce traps for hydrogen atoms, which retard hydrogen transport.
The rate of hydrogen atom transport through the metal during a first permeation test can be affected by both
irreversible and reversible trapping. At steady state, all of the irreversible traps are occupied. If the mobile
hydrogen atoms are then removed and a subsequent permeation test conducted on the sample, the difference
between the first and second permeation transients may be used to evaluate the influence of irreversible
trapping on transport.
For some environments the conditions on the charging side of the sample may be suitably altered to induce a
decay of the oxidation current after attainment of steady state. The rate of decay is determined by diffusion and
reversible trapping only and hence can also be used to evaluate the effect of irreversible trapping on transport
during the first transient.
NOTE 1 Reversible and irreversible traps can both be present in a particular metal.
NOTE 2 Comparison of repeated permeation transients with those obtained for the pure metal can be used, in principle, to
evaluate the effect of reversible trapping on atomic hydrogen transport.
NOTE 3 The technique is suitable for systems in which hydrogen atoms are generated uniformly over the charging surface
of the sample. It is not usually applicable to corroding systems in which pitting attack occurs, unless the charging cell
environment is designed to simulate the localized pit environment and the entire metal surface is active.
5.9 The method may be used for stressed and unstressed samples but testing of stressed samples requires
loading procedures to be taken into consideration.
6Samples
6.1 Dimensions
Samples shall be in the form of plate or pipe. The dimensions shall be such as to enable analysis of the
permeation transient based on one-dimensional diffusion, e.g. for plates with a circular exposed area, the radius
exposed to the solution should be sufficiently large relative to thickness.
A ratio of radius to thickness of 10:1 or greater is recommended. This condition may be made less stringent if
the exposed area on the oxidation side is smaller than that on the charging side. A ratio of radius to thickness of
5:1 or greater is recommended if the radius of the exposed area on the oxidation side is reduced to 90 % of the
area of the charging side.
For pipes, the ratio of the outer radius to the inner radius shall be less than 1,1:1 if the experimental results are
to be analysed based on planar one-dimensional diffusion.
©
4 ISO 2004 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 17081:2004(E)
6.2 Preparation
6.2.1 As hydrogen atom permeation can be influenced by microstructural orientation, the form of the original
material shall be recorded (e.g. bar) as well as the location and orientation of the sample relative to that of the
original material (see Clause 12).
6.2.2 Samples shall be prepared using one of the following methods:
a) electrochemical discharge machining (EDM) plus final machining;
b) mechanical cutting.
EDM is particularly useful for preparing thin sheets of material but can introduce hydrogen into the metal.
Although hydrogen atoms dissolved in lattice sites or reversible trap sites are gradually lost subsequent to EDM,
hydrogen atoms can be retained in irreversible trap sites. The amount of hydrogen generated and the extent of
ingress into the metal depends on the details of the EDM process and the material characteristics but sufficient
material should be removed by subsequent machining to ensure that all residual hydrogen atoms are removed.
NOTE 1 Careful consideration should be given to the method of manufacture of sheet samples.
NOTE 2 The preferred method for the preparation of thin sheets of material is fine mechanical cutting.
6.2.3 Sheet samples shall be machined to the required thickness. Care shall be taken in machining to
minimize surface damage.
6.2.4 The thickness of the sample in the region of interest shall be as uniform as possible with a maximum
variation no greater than ±5%.
6.2.5 The oxidation side of the sample shall be mechanically ground or polished to a repeatable finish. The
charging side may be similarly treated or used as for an intended service application.
NOTE Electropolishing of samples may also be employed in appropriate cases.
6.2.6 After polishing, traces of polishing chemicals shall be removed by an appropriate cleaning procedure.
NOTE Rinsing with distilled water, followed by alcohol and a non-chlorinated solvent, is adequate for most cases.
6.2.7 The final thickness shall be measured in at least five locations in the exposed region of the membrane.
The sample shall then be degreased and the specimen stored in a dry environment.
Palladium coating of the sample may be undertaken at this stage. Electrochemical methods of forming the
coating can introduce hydrogen atoms into the material and can influence the subsequent permeation
measurements. Argon etching of the surface followed by sputter coating with palladium can avoid this problem.
6.2.8 A suitable electrical connection shall be made to the sample remote from the active areas.
6.2.9 The sample shall be uniquely identified. Stamping or scribing on the sample remote from the active
areas is recommended.
7 Apparatus
Two-compartmental environmental cell consisting of separate charging and oxidation cells (e.g., as shown in
Figure 1) constructed from inert materials, with reference electrodes and auxiliary electrodes (usually platinum).
Sealed oxidation cells, in which an additional membrane (usually palladium) is clamped against the test sample
and the flux exiting this additional membrane is measured, may be used provided that it is demonstrated that
the introduction of this additional interface has no effect on the calculated diffusivity.
A Luggin capillary should be used for more accurate measurement of potential where the current is large. In
order to avoid shielding effects, the tip of the Luggin should be no closer to the surface than twice the diameter
of the tip. Typically the distance is 2mm to 3mm.
©
ISO 2004 – All rights reserved 5
---------------------- Page: 13 ----------------------
ISO 17081:2004(E)
Key
A charging cell
B oxidation cell
1 reference electrode
2 counter electrode
3test sample
a
Gas in.
b
Gas out.
Figure 1 — Hydrogen permeation cell (constructed of polytetrafluoroethylene)
with double junction electrodes
Non-metallic materials are recommended for cell construction.
◦
50 C
At temperatures above leaching from the cell material (e.g. silica dissolution from glass) can modify the
solution chemistry and may influence hydrogen permeation. Polytetrafluoroethylene is an example of a suitable
◦
material for elevated temperatures up to about C.
90
Where metallic chambers are necessary, the materials chosen shall have a very low passive current to ensure
minimal effect on the solution composition, and shall be electrically isolated from the membrane.
When testing at elevated temperatures the O-ring material shall be selected to minimize possible degradation
products from the seals and contamination of the solution.
The choice of reference electrode depends on the particular exposure conditions. Saturated calomel electrodes
(SCE) or silver/silver chloride electrodes are often used, although use of the former is no longer permitted in
some countries because of environmental concerns. The chloride concentration in the latter shall be specified.
The solution contained in the reference electrode shall not contaminate the test solution.
©
6 ISO 2004 – All rights reserved
---------------------- Page: 14 ----------------------
ISO 17081:2004(E)
Contamination may be avoided by the use of double junction reference electrodes or by remote monitoring
using a solution conductivity bridge arrangement with inert materials.
A standard resistor and a digital voltmeter should be used for recording of oxidation current (and, as
appropriate, charging current), or a current monitoring device used for direct measurement, all traceable to
appropriate national standards and calibrated on a regular basis, typically once per year. The resistor should be
positioned in series in the auxiliary electrode line.
The potentiostats used for each cell shall be configured such that they do not have a common earth.
8 Test environment considerations
8.1 The test environment shall be chosen on the basis of one of the following criteria:
a) relevance to the intended service application;
b) ease and reliability of measurement.
NOTE Suggestions for suitable systems for item b) are given in Annex A.
8.2 The environments in the oxidation cell and in the charging cell shall be of sufficient purity for the intended
purpose.
8.3 The environment in the oxidation cell shall be prepared using analytical grade chemicals and distilled or
deionized water of purity sufficient to avoid unintentional contamination.
8.4 Where the environment in the charging cell is aqueous, the solution shall be either that directly used in
service or a laboratory environment prepared with the purity as indicated in 8.3. Gaseous environments shall
simulate those for the intended applications.
In some cases for which higher purity of the charging solution is desirable, the solution may be prepared by
using appropriate high purity analytical grade chemicals or by pre-electrolysis. Pre-electrolysis may be used to
remove certain cationic contaminants by cathodic deposition and usually involves applying a voltage difference
between two platinum electrodes in the solution of interest. The area of the cathode should be as large as is
reasonable in order to enhance the rate of removal of contaminants.
8.5 The ratio of volume of solution (in millilitres) to metal area (in square centimetres) in the oxidation chamber
shall be greater than 20:1.
NOTE A large volume of solution in the oxidation chamber is not necessary as the extent of the reaction is usually relatively
small.
8.6 The solution composition in the charging cell shall be maintained constant during the experiment.
The volume of solution in the charging cell depends on the particular choice of environment and the extent of
reaction on the specimen. Recombination poisons added to enhance hydro
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.