Metallic coatings - Porosity tests - Porosity in gold or palladium coatings by sulfurous acid/sulfur dioxide vapour (ISO 15721:2001)
This test method covers equipment and methods for determining the porosity of gold or palladium coatings, particularly electrodeposits and clad metals used on electrical contacts.
It is designed to show whether the porosity level is less than or greater than a given value which by experience is considered by the user to be acceptable for the intended application.
This porosity test involves corrosion reactions in which the products delineate defect sites in coatings. Since the chemistry and properties of these products may not resemble those found in natural or service environments this test cannot be recommended for the prediction of the electrical performance of contacts unless correlation is first established with service experience.
This test is intended to be used for quantitative descriptions of porosity (such as number of pores per unit area or per contact) on coatings that have a sufficiently low pore density so 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 100/cm2. Above this value the tests are useful for the qualitative detection and comparisons of porosity.
A variety of other porosity testing methods are described in the literature , . Other ISO porosity test methods are described ISO 10308, ISO 12687, ISO 14647 and ISO 15720.