Iridium was first discovered in 1803 by Smithson Tennant, when he was dissolving a sample of platinum in strong acid and noticed some black solid left in the beaker. It was later found to be a mixture of osmium and iridium, the two densest elements.
One of iridium’s useful properties, is that it is extremely corrosion resistant, as shown in this experiment it did not react with a mixture of hydrochloric and nitric acid, which is so strong it dissolves platinum. Iridium also has a very high melting point of 2700 degrees Celsius, and even at these high temperatures it still does not oxidise.
Iridium is used in an alloy for the tips of spark plugs in petrol engines. The high temperatures required to ignite fuel, means that iridium is a great candidate to use here, and also the corrosion resistance at high temperatures means that iridium alloy spark plugs have a very long lifetime. With the aim of cutting down carbon emissions, electric cars will become more popular which do not require spark plugs, and so iridium’s demand will likely decrease for this use.
Iridium is also used to make crucibles for growing crystals of, for example yttrium aluminium garnet crystals used to make lasers for medical procedures and laser cutting. LEDs are also grown on sapphire wafers in these iridium crucibles.
Relative Atomic Mass
Iridium is the most corrosion-resistant element in the periodic table, and is among the rarest of thePGMs, with global production just 7.8mt per year! It is also the second densest of all metals (22.56g/cm3) after Osmium, weighing twice as much as Lead. This means that the entire global production of Iridium is only 0.34m3 in volume, which could fit into your average parcel box.
South Africa produces 80% of global Iridium supply, followed by Russia which produces 10%. It is the last metal to be processed in the PGM refining process, and so is the most severely affected when there are processing problems.
A third of Iridium demand comes from the electrical sector, where iridium is used in crucibles and hard disk drives (HDD). Iridium crucibles have a growing application in 5G smartphones, since 5G subscriptions are forecast to reach 2.8 billion (30% of all mobile subscriptions) by the end of 2025. Iridium crucibles are used to produce lithium tantalate, which is required in surface acoustic wave (SAW) filters to enhance performance for electronic devices. Higher SAW filter content is necessary for 5G smartphones compared to previous technologies.
A quarter of global Iridium production goes to the electrochemical sector, primarily the chlor-alkali industry, where Iridium and Ruthenium are used in the coating of Titanium anodes, to provide feedstock for vinyl. Read more about the chlor-alkali industry here.
Iridium demand from the automotive sector is expected to increase substantially from the current 6%, because Iridium is critical to the efficiency and longevity of PEM (Polymer electrolyte membrane) electrolysers. Iridium and Platinum catalysts coat the electrodes which convert water into hydrogen gas and oxygen. Many large PEM electrolyser facilities will begin hydrogen production in the next decade, and the UN has launched the Green Hydrogen Catapult initiative, which aims to halve the production cost of green hydrogen to $2/kg by 2026. This will make this renewable energy source a cost competitive alternative to fossil fuels, which will boost Iridium demand.
The remainder of Iridium demand comes from the chemical sector for catalysts, the medical industry (e.g. Iridium addition in dental alloys as grain refiners), and the jewellery sector.