Iridium is the most corrosion-resistant material known. It is used in special alloys and forms an alloy with osmium, which is used for pen tips and compass bearings: Osmium Alloy (1926).
It is also used for the contacts in spark plugs because of its high melting point and low reactivity:
Supported iridium alloys can be used in catalysis: Hydroforming With Promoted Iridium Catalyst (1971).
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All patent information has been obtained from Espacenet (European Patent Office).