Platinum group metals are unique among the transition metals because (except for osmium) they combine excellent catalytic activity with low chemical reactivity. As a result, the platinum group metals at Ultramet are used primarily for two purposes: protective and catalytic coatings.
Iridium and platinum are most frequently used as protective coatings. Platinum generally offers better oxidation resistance than iridium, but iridium has a higher melting point and is thus better suited for higher temperature applications such as rocket engines. Protective coatings must be continuous and free of pores and other defects that would allow the reactive species to reach the underlying material that is being protected.
The morphology of a catalytic coating is different from that of a protective coating. In a catalytic coating, the metal is dispersed onto the substrate as small (10 nm) clusters, and uncoated areas of substrate exist between the clusters. This type of morphology maximizes the surface area of the metal and allows the sides of the clusters, not just the tops, to act as catalytic surfaces.