ISO 16429-2004 Implants for surgery - Measurements of open-circuit potential to assess corrosion behaviour of metallic implantable materials and medical devices.pdf

1、INTERNATIONAL STANDARD ISO 16429 First edition 2004-07-01 Reference number ISO 16429:2004(E) ISO 2004 Implants for surgery Measurements of open-circuit potential to assess corrosion behaviour of metallic implantable materials and medical devices over extended time periods Implants chirurgicaux Mesur

2、ages sur de longues priodes du potentiel en circuit ouvert pour lvaluation du comportement la corrosion des matriaux mtalliques et dispositifs mdicaux implantablesISO 16429:2004(E) ii ISO 2004 All rights reserved PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes

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5、s 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

6、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. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41

7、 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in SwitzerlandISO 16429:2004(E) ISO 2004 All rights reserved iii Contents Page 1 Scope 1 2 Normative references 1 3 Terms and definitions 1 4 Significance and application 2 4.1 Principle . 2 4.2 Significance of the

8、 measurements 4 4.3 Application . 4 5 Apparatus . 5 6 Specimen preparation . 5 6.1 Type of specimen 5 6.2 Surface preparation 6 6.3 Specimen mounting 6 7 Environmental conditions . 6 7.1 General . 6 7.2 Testing solution . 6 7.3 Testing temperature 6 7.4 pH value . 7 7.5 Aeration 7 7.6 Volume of test

9、ing solution 7 8 Test procedure . 7 8.1 Set-up of test . 7 8.2 Duration of test 7 8.3 Observations . 7 9 Test report 8 Annex A (informative) Additional test solutions 9 Bibliography . 10ISO 16429:2004(E) iv ISO 2004 All rights reserved Foreword ISO (the International Organization for Standardization

10、) 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 repr

11、esented 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 ar

12、e 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 Internation

13、al 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 16429 was pre

14、pared by Technical Committee ISO/TC 150, Implants for surgery, Subcommittee SC 1, Materials.ISO 16429:2004(E) ISO 2004 All rights reserved v Introduction This International Standard was developed because, in contrast to polarization measurements which are well described in ASTMG5 6and literature, th

15、ere is no standard available on typical open-circuit potential measurements over extended time periods. Relating to corrosion behaviour of implant materials and surgical implant devices, the long-term electrochemical behaviour in the body environment is of interest. Metal surfaces undergo spontaneou

16、s changes at their interface with an electrolytic environment to reach a state of equilibrium. Depending on the conditions, the corresponding physico-chemical and electrochemical reactions can be highly active and corrosive, or very sluggish and passive. For passivating metals such as those usually

17、used for surgical implants, the formation and stability of the passive film is an important prerequisite for corrosion resistance of these materials, under given conditions. With the measurement of the open-circuit potential over a longer time period, the spontaneous reaction to the environment (ele

18、ctrolyte) in the form of passivation or activation, the formation of a steady state potential and its stability can be assessed. Regarding surgical implant materials and devices, the measurements of these properties is of interest because they help to characterize implant material systems and to opt

19、imize processing, surface treatments and properties. Furthermore, measurements of the long-term open-circuit potential in combination with mechanical loading give information on the effect of mechanical, dynamic conditions on the electrochemical potential, passivity and corrosion behaviour. This Int

20、ernational Standard specifies conditions for the measurement of the open-circuit potential over extended periods of time. Isotonic NaCl (see 3.5) is used as the electrolyte (testing solution). This solution is related to body fluid in that it contains approximately the same concentration of Cl ions,

21、 and Cl ions are the most likely species in this solution to cause metal corrosion due to their aggressivity. For more stringent testing conditions, solutions with higher concentrations of Cl ions are given in Annex A. 0,9 %. vi INTERNATIONAL STANDARD ISO 16429:2004(E) ISO 2004 All rights reserved 1

22、 Implants for surgery Measurements of open-circuit potential to assess corrosion behaviour of metallic implantable materials and medical devices over extended time periods 1S c o p e This International Standard specifies a test method for measurements over extended time periods of the open- circuit

23、potential of implant materials and surgically implantable devices immersed in a test environment related to body fluid, using a standard corrosion test cell to study the electrochemical corrosion properties of the devices. This method of monitoring the open-circuit potential can also be combined wit

24、h mechanical static or dynamic loading tests. This International Standard is applicable in particular to metallic materials which form passive layers with protective properties against corrosion, as typical for surgical implant materials. This test method is intended for the investigation of single

25、metallic materials or alloys. It is not applicable to dissimilar material combinations, which require particular considerations in measuring and interpreting the results. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated refer

26、ences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696, Water for analytical laboratory use Specification and test methods ISO 16428, Implants for surgery Test solution and environmental conditions for

27、 static and dynamic corrosion and wear tests on implantable materials and medical devices 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 corrosion potential electrode potential of a metal in a given corrosion system 3.2 corrosion system syst

28、em consisting of one or more metals and those parts of the environment (including specimen, electrolyte, electrodes) that influence corrosion 3.3 environmental test conditions conditions under which a sample (specimen) is tested, including temperature, aerating elements, pH, and identification, volu

29、me and exchange rate of the contacting fluidISO 16429:2004(E) 2 ISO 2004 All rights reserved 3.4 free corrosion potential corrosion potential in the absence of net (external) electrical current flowing to or from the metal surface ISO 8044 3.5 isotonic NaCl solution aqueous solution of NaCl ( mass f

30、raction) which has the same surface tension as living tissues NOTE In surgical applications it prevents the collapsing of tissues. 3.6 open-circuit potential potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it ASTM G 15 cf

31、 free corrosion potential (3.4). 3.7 passive layer surface layer on a metal that forms as result of the reaction with the environment, or spontaneously under given conditions, and has the capacity to protect the metal against corrosion NOTE Passive layers are usually adherent and of submicroscopica

32、l thickness (see ISO 8044). 3.8 reference electrode electrode having a stable and reproducible potential that is used as a reference in the measurement of electrode potentials 3.9 working electrode test or working electrode in an electrochemical cell; the test specimen in the context of this standar

33、d 4 Significance and application 4.1 Principle In this electrochemical test method, the test specimens (samples) are immersed in an isotonic test solution of NaCl 9 , which relates to the physiological environment of the body as described in ISO 16428. Other test solutions and the other environmenta

34、l conditions are also described in ISO 16428. For more stringent test conditions, more acidic test solutions (lower pH) are suggested in Annex A. The tests are carried out in an electrochemical test cell similar to that described in the ASTM G 5 6 . The test cell provides access for the electrodes a

35、nd other necessary equipment (Figure 1). While the specimen is exposed to the environment for a specified period of time, the open-circuit potential is recorded continuously as a function of time. The specimen functions as the working electrode and its behaviour is measured against a reference elect

36、rode (Figure 2). 0,9 %ISO 16429:2004(E) ISO 2004 All rights reserved 3 Key 1 working electrode (test specimen) 2 gas inlet 3 gas outlet 4 water outlet 5 test solution (electrolyte) 6 water inlet 7 Luggin probe 8 reference electrode 9 thermometer Figure 1 Example of electrochemical test cell3ISO 1642

37、9:2004(E) 4 ISO 2004 All rights reserved 4.2 Significance of the measurements The open-circuit potential reflects (electrochemical) reactions which take place at the surface of the specimen (working electrode) in contact with the testing solution. Depending on the conditions, usually or after immers

38、ion of the specimen, an equilibrium of the specimen surface with the testing solution (electrolyte) will be reached, and the potential becomes steadier. During the initial phase, with passivating materials the potential increases, usually in the direction of (more) positive values, indicating passiv

39、ation or increasing passivation in the testing solution with increasing corrosion resistance. A decrease in the potential indicates an activation of the surface with decrease or loss in passivity, and thus susceptibility to corrosion. The value of the steady-state potential, shifts in the potential,

40、 and stability or instability of the potential are indicators of processes taking place within the passive film and of the corrosion behaviour of the material under investigation. NOTE The Cl ions are the aggressive species in the isotonic NaCl testing environment. An increase in passivation in this

41、 solution indicates a high initial level of corrosion resistance of the corresponding materials. This test method is very sensitive, and all steps shall be carried out with caution and understanding of the processes. In particular, the condition of the specimen surface is critical, and preparation p

42、rocedures require careful attention and reproducibility. 4.3 Application This electrochemical test method is suitable to study, on an extended time scale, the passivation and corrosion behaviour of materials and surgical implant devices as a function of their metallurgical properties, processing his

43、tory, and surface condition. Such open-circuit potential measurements, when combined with mechanical tests, can also give information on the mechanical stability of passive films. This test method can be used for screening of materials, for comparison of materials and surface treatments, for optimiz

44、ation of corrosion resistance, or for the study and characterization of material systems. For extended evaluation, this test method can be used in conjunction with other electrochemical corrosion tests. Key 1 working electrode (test specimen) 2 potential-measuring instrument (electrometer) 3 referen

45、ce electrode Figure 2 Example of electrical circuit measuring open-circuit potential 1h 2hISO 16429:2004(E) ISO 2004 All rights reserved 5 NOTE T erms such as corrosion system (3.2) or corrosion potential (3.1) do not mean that visible corrosion has to occur, but rather they are scientific definitio

46、ns related to corrosion mechanisms and their assessment. 5 Apparatus 5.1 Electrochemical test cell The electrochemical test cell consists of a suitable glass vessel, in principle similar to that shown in ASTM G 5 6 . An example of a test cell (flat bottom version) is shown in Figure 1. If the system

47、 is not intended to be also used for potentiostatic/potentiodynamic measurements, the counter-electrode (auxiliary electrode) may be removed. NOTE Borosilicate glass has been proven useful for the glass vessels (ISO3585 2 ). If open-circuit potential measurements are combined with mechanical tests,

48、or for other reasons, the vessel of the test cell can be of a different design and need not consist of glass (ISO 16428). 5.1.1 Working electrode, i.e. the test specimen. 5.1.2 Reference electrode. A saturated calomel electrode (SCE) or other electrode may be used. In the latter case, the measuremen

49、t results shall, however, also be reported in values relating to SCE using accepted conversion values 5for easy comparison with published data. 5.1.3 Luggin probe with salt bridge connecting to the reference electrode. The distance between the tip of the probe and the specimen surface (working electrode) should be or equal to the diameter of the probe tip, whichever is greater. 5.1.4 Gas inlet and gas outlet. 5.1.5 Thermometer, to check the temperature of the testing solution. 5.2 Potential