BS EN ISO 15720:2001 pdf – Metallic coatings — Porosity tests — Porosity in gold or palladium coatings on metal substrates by gel-bulk electrography.
1 Scope This test method covers equipment and techniques for determining porosity in noble metal coatings, particularly electrodeposits of gold, palladium and palladium-nickel alloy (70 % to 90 % palladium) and clad metals used on electrical contacts. The gel-bulk procedure is not as sensitive to small pores and is more complex than porosity tests involving gaseous corrodants (see ISO 1 4647 and ISO 1 5721 ). It also involves more chemicals, preparation and auxiliary equipment. This test is intended to be used for quantitative descriptions of porosity (such as number of pores per unit area or per contact) only on measurement areas where coatings have a sufficiently low pore density such that the corrosion sites are well separated and can be readily resolved. As a general guideline this can be achieved for pore densities up to about 25/cm 2 . Other porosity testing methods are outlined in ISO 1 0308. Detailed critical reviews of porosity testing are also available. Other porosity test methods are described in ISO 1 2687, ISO 1 4647 and ISO 1 5721 . 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 2064, Metallic and other inorganic coatings — Definitions and conventions concerning the measurement of thickness. ISO 2079, Surface treatmentandmetallic coatings — Generalclassification ofterms. ISO 2080, Electroplating andrelatedprocesses — Vocabulary. ISO 1 0308, Metallic coatings — Reviewofporositytests.
3 Terms and definitions For the purposes of this International Standard, the terms and definitions given in ISO 2064, ISO 2079, ISO 2080 and ISO 1 0308 as well as the following apply. 3.1 decorations coloured reaction products emanating from the pores that provide visual contrast with the gel medium NOTE While non-standard terms are deprecated, the term decorations has had long-standing use in differentiating between coloured pore indicators and true corrosion products. The term can be found in the technical literature. 3.2 metallic coatings Includes platings, claddings, or other metallic layers applied to the substrate NOTE The coatings can comprise a single metallic layer or a combination of metallic layers. 3.3 porosity The presence of any discontinuity, crack, or hole in the coating that exposes a different underlying metal 4 Apparatus 4.1 Test vessel, of glass, acrylic resin or other inert colourless transparent material. It shall have thin-walled flat sides and be of a size appropriate to the sample to be tested. 4.2 Power supply, rated at 0 A to 1 A and 0 V to 1 0 V dc; an electronically regulated, constant-current (? 5 %) apparatus is preferred. 4.3 dc milliammeter. 4.4 Separate dc voltmeter. 4.5 Cathode material, in the form of plain expanded foil or wire and made of titanium and coated with platinum, gold or other inert coating. Alternatively, platinum, gold or other inert metals may be used.
The cathode and specimen (anode) areas shall be approximately the same. Additional, gold or platinum wires for cathode and anode are needed for that portion of the electrical connection that is in the reagent solution. If small alligator clips are used to secure the lead wires to the cathode and anode they shall be heavily gold-plated so as to be entirely free of porosity. A variation of this procedure, suitable for samples with relatively few pores, is to use a second identical test sample as the cathode. The test can be run with current first in the forward, then in the reverse direction so that the porosity in both samples may be determined. Figure 1 is a diagram of the test cell setup. NOTE A commonly used alternative cell design incorporates the cathode as part of the cell structure (as shown in Figure 2). In addition, the samples may be attached to a common carrier strip or holder, so that only the sample surfaces need be in the gel. 4.6 Timer, capable of indicating seconds. 4.7 Stereomicroscope, with 1 0 magnification and an illuminator for sample inspection after test. An eyepiece reticule is recommended for convenience in locating the contact area or other significant measurement areas.