Metallic coatings - Porosity tests - Porosity in gold or palladium coatings on metal substrates by gel-bulk electrography (ISO 15720:2001)
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 14647 and ISO 15721). 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/cm2 .
Other porosity testing methods are outlined in ISO 10308. Detailed critical reviews of porosity testing are also available. Other porosity test methods are described in ISO 12687, ISO 14647 and ISO 15721.