THE SIX PLATINUM-GROUP METALS (PGMs), listed in order of their atomic numbers, are ruthenium, rhodium, palladium, osmium, iridium, and platinum. The PGMs are among the scarcest of metallic elements, and thus their cost is high. Their most exceptional trait in the metallic form is their excellent corrosion resistance. The electroplating of PGMs from aqueous electrolytes for engineering applications is limited principally to palladium and, to a much lesser extent, to platinum, rhodium, and thin layers of ruthenium. There are practically no electrolytes on the market for the deposition of osmium or iridium. While solution formulations have been published for these last two metals, they have not proven themselves in practical use for any significant applications, and thus will be discussed only briefly in this article.

Detailed information about the general availability, properties, and applications of PGMs is provided in Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, Volume 2 of ASM Handbook. Good overview coverage of plating of these metals is available in Ref 1, 2, and 3.

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