SANS 2177-2008 Metallic coatings - Measurement of coating thickness - Coulometric method by anodic dissolution《金属镀层 涂层厚度测量 阳极溶解库仑法》.pdf

1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-21914-7 SANS 2177:2008Edition 2ISO 2177:2003Edition 3SOUTH AFRICAN NATIONAL STANDARD Metallic coatings Measurement of coating thickness Co

4、ulometric method by anodic dissolution This national standard is the identical implementation of ISO 2177:2003 and is adopted with the permission of the International Organization for Standardization. Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001Tel

5、: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS SANS 2177:2008 Edition 2 ISO 2177:2003 Edition 3 Table of changes Change No. Date Scope National foreword This South African standard was approved by National Committee SABS TC 107, Metallic and other inorganic coatings, in accordance with p

6、rocedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This SANS document was published in November 2008. This SANS document supersedes SABS ISO 2177:1985 (first edition). Reference numberISO 2177:2003(E)ISO 2003INTERNATIONAL STANDARD ISO2177Third edition2003-

7、03-15Metallic coatings Measurement of coating thickness Coulometric method by anodic dissolution Revtements mtalliques Mesurage de lpaisseur Mthode coulomtrique par dissolution anodique SANS 2177:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the

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11、ess given below. ISO 2003 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 ISOs

12、 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 Switzerland ii ISO 2003 All rights reservedSANS 2177:2008This s tandard may only be used and printed

13、by approved subscription and freemailing clients of the SABS .ISO 2177:2003(E) ISO 2003 All rights reserved iiiContents Page Foreword iv 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Principle . 2 5 Instrumentation . 2 6 Electrolyte 2 7 Factors affecting the measuring accuracy. 3

14、 7.1 Coating thickness . 3 7.2 Current variation . 3 7.3 Area variation 3 7.4 Agitation (if required) 4 7.5 Alloy layer between coating and substrate 4 7.6 Purity of coatings 4 7.7 Condition of test surface 4 7.8 Density of coating material 4 7.9 Cleanliness of the cell 4 7.10 Cleanliness of electri

15、cal connections. 4 7.11 Calibration standards (if used) 4 7.12 Non-uniform dissolution 5 8 Procedure. 5 8.1 General. 5 8.2 Preparation of test surface. 5 8.3 Cell application 5 8.4 Electrolysis 5 8.5 Undercoats. 5 8.6 Examination after test. 6 8.7 Coatings on cylindrical specimens. 6 9 Expression of

16、 results 6 10 Measurement uncertainty. 7 11 Test report 7 Annex A (informative) Typical electrolytes 8 Annex B (informative) Types of instrument. 13 SANS 2177:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO 2177:2003(E) iv ISO 2003 Al

17、l 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 carried out through ISO technical committees. Each member body interested in a subj

18、ect 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 (IE

19、C) 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 committ

20、ees 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

21、held responsible for identifying any or all such patent rights. ISO 2177 was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings, Subcommittee SC 2, Test methods. This third edition cancels and replaces the second edition (ISO 2177:1985), which has been technically revi

22、sed. SANS 2177:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .INTERNATIONAL STANDARD ISO 2177:2003(E) ISO 2003 All rights reserved 1Metallic coatings Measurement of coating thickness Coulometric method by anodic dissolution 1 Scope This

23、International Standard describes a coulometric method, by anodic dissolution, for measuring the thickness of metallic coatings. It is only applicable to conductive coatings. Typical combinations of coatings and substrates that can be tested by this method are given in Table 1. Other combinations may

24、 be tested with electrolytes in current use (see Annex A), or new electrolytes may be developed for them but, in both cases, it is necessary to verify the suitability of the complete system. This International Standard is also applicable to multi-layer systems, e.g Cu-Ni-Cr (see also 8.5). It may be

25、 used to measure the thickness of coatings applied by various means, if due account is taken of special features such as the presence of an alloy layer. In some cases, the presence and thickness of diffusion layers can also be measured. It can also be used to measure the thickness of coatings on cyl

26、indrical specimens and wires (see 8.7). 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 amendme

27、nts) applies. ISO 2064:1996, Metallic and other inorganic coatings Definitions and conventions concerning the measurement of thickness ISO 2080, Surface treatment, metallic and other inorganic coatings Vocabulary 3 Terms and definitions For the purposes of this document, the terms and definitions gi

28、ven in ISO 2064 and ISO 2080 as well as the following apply. 3.1 measuring area area of the significant surface over which a single measurement is made NOTE The measuring area for this method is the area enclosed by the sealing ring of the cell. SANS 2177:2008This s tandard may only be used and prin

29、ted by approved subscription and freemailing clients of the SABS .ISO 2177:2003(E) 2 ISO 2003 All rights reserved4 Principle A well-defined area of the coating is subjected to anodic dissolution using a suitable electrolyte. The virtually complete dissolution of the coating is detected by a change i

30、n cell voltage. The coating thickness is calculated from the quantity of electricity used, in coulombs, which in turn may be calculated from: a) the time interval between the start and the end of the test, if it is conducted at constant current density; b) the integrated quantity of electricity used

31、 in dissolving the coatings. 5 Instrumentation 5.1 Suitable instruments can be constructed from readily available components but proprietary instruments are usually used (see Annex B). 5.2 Proprietary direct-reading instruments are available for use with electrolytes recommended by the manufacturer.

32、 Other instruments record the quantity of electricity, in coulombs, used in dissolving the coating from the measuring area (see 3.1), usually in arbitrary units, from which the thickness is calculated using factors or tables. With direct reading instruments, the calculation of thickness from current

33、 density is made electronically. 5.3 The performance of the instrument shall be checked using specimens of known coating thickness. If the instrument readings agree to within 5 % of the known thicknesses of the specimens, the instrument may be used without further adjustment; otherwise, the cause of

34、 the discrepancy shall be removed. However, proprietary instruments shall always be calibrated in accordance with the manufacturers instructions. Suitable specimens of known coating thickness shall consist of the same type of coating and substrate as the specimen to be measured, and they shall have

35、an accuracy of 5 % or better. In measuring alloy coatings, the use of correct specimens is of particular importance. 6 Electrolyte The electrolyte shall have a known, adequate shelf-life and shall be such that: a) there is no reaction with the coating metal in the absence of an impressed flow of cur

36、rent; b) the coating dissolves anodically at an efficiency as close to 100 % as possible; c) a detectable change in electrode potential occurs as the coating is penetrated and an increasing area of substrate is exposed; d) the test area exposed in the test cell is completely wetted. The electrolyte

37、shall be chosen with reference to the coating and substrate materials, the current density and electrolyte circulation within the test cell. NOTE Typical electrolytes that have been found satisfactory for use with one type of test apparatus for testing various electrodeposited coatings on specific s

38、ubstrates are described in Annex A. For proprietary instruments, the electrolytes shall normally be chosen on the recommendations of the manufacturer. SANS 2177:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO 2177:2003(E) ISO 2003 All

39、 rights reserved 3Table 1 Typical combinations of coatings and substrates that can be tested by the coulometric method Coating Substrate (underlying material) AlaCu and Cu alloys Ni Ni-Co-Fe alloys Ag Steel Zn Non-metals Cd Cr Cu Only on brass and copper-beryllium Au Pb Ni Ni, autocatalyticb Ag Sn S

40、n-Ni alloys Sn-Pb alloysc Zn aThe detection of the change in the cell voltage may be difficult with some aluminium alloys. bThe coulometric method can only be used if the phosphorus or boron contents of these coatings are within certain limits. cThe method is sensitive to alloy composition. NOTE See

41、 Clause 5 for instrumentation. 7 Factors affecting the measuring accuracy 7.1 Coating thickness Generally, the accuracy is lower than optimum for coating thicknesses greater than 50 m and less than 0,2 m, unless special equipment is used. With coatings thicker than 50 m, there may be an appreciable

42、amount of bevelling or undercutting as the anodic dissolution proceeds. The amount of bevelling is largely dependent on the method employed for stirring the electrolyte. Undercutting may be eliminated, or reduced, by increasing the rate of dissolution, i.e. by increasing the current density used in

43、the test. 7.2 Current variation For instrumentation using the constant-current and time-measuring technique, current variation causes errors. For instruments using a current-time integrator, too large a change in current may change the anode current efficiency and interfere with the end-point thus c

44、ausing an error. 7.3 Area variation The accuracy of the thickness measurement will be no better than the accuracy to which the measuring area is known. Area variations due to gasket wear, gasket pressure, etc., may lead to measurement errors. Much greater accuracy can be obtained if the electrolytic

45、 cells are so designed that sealing rings consistently give SANS 2177:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO 2177:2003(E) 4 ISO 2003 All rights reservedwell defined measuring areas. In some cases it may be advantageous to mea

46、sure the area after it has been de-plated and compensate accordingly. NOTE Error due to variations of the measuring area may, in some instances, be minimized by modifying the instrument calibration using coating thickness calibration standards. Such standards should create similar test conditions to

47、 those during actual tests, particularly if testing curved surfaces. 7.4 Agitation (if required) Inadequate agitation and over-agitation can cause a false end-point. 7.5 Alloy layer between coating and substrate The measurement of coating thickness by the coulometric method assumes implicitly that a

48、 sharply defined interface exists between the coating and the substrate. If an alloy layer exists between the coating and the substrate as, for example, in the case of coatings applied by hot dipping, the coulometric end-point can occur at some point within the alloy later, thus giving falsely high

49、values for the thickness of the unalloyed coatings. See B.1.2. NOTE It is possible to use a potential recording chart recorder to detect the potential step where the alloy commences and also when the pure substrate is reached by the dissolution process. 7.6 Purity of coatings Materials that co-deposit with a coating metal (including alloy