How to identify iridium

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Category: Metallurgy

Subject: How to identify iridium

Question

How can I test if a metal is iridium?

Answer

The easiest method I can suggest is to try X-ray fluorescence (XRF) or solid phase inductively coupled plasma (ICP) analysis. 

There is no simple chemical method that identifies its presence. There is a complex procedure for analysis that involves melting powdered Ir in Zn, dissolving in HCl and reacting the residues in HCl/H2O2 before boiling off the acid and testing by liquid phase ICP.  There is no distinctive colouration imparted by Ir (it varies with oxidation state) and it can be masked by other constituents.

Ir is extremely difficult to dissolve, which can be used as a negative test. If you immerse it in boiling aqua regia you should see no reaction, i.e. if it dissolves it’s not Ir.  Ir alloys are only very slowly dissolvable.

Answer posted 20th October 2014

Answered by: Robert McGrath and Roger Wilkinson

Affiliation: Johnson Matthey Noble Metals