Executive Summary

This deep dive into iridium’s history spans over 220 years – from Smithson Tennant’s discovery in 1803, to iridium’s current applications in catalysis, electronics, and hydrogen production. Several themes emerge from the chronology:

First, iridium’s extreme physical properties—high melting point, exceptional hardness, and corrosion resistance—initially made it difficult to work with but ultimately made it valuable for specialized applications. The century-long effort to develop melting and refining techniques, from Children’s galvanic battery experiments in 1813 to industrial-scale processes by the late 1800s, demonstrates how materials science advances through persistent problem-solving.

Second, iridium’s scarcity has shaped its applications. With global production around 7,000 kilograms annually, iridium is used primarily where its unique properties justify the cost. The progression from fountain pen nibs (requiring milligrams) to spark plugs (requiring milligrams) to crucibles (requiring grams) to industrial catalysts shows increasingly efficient use of limited supply.

Introduction

Named after the Greek goddess Iris for the rainbow of colors its compounds display, the story of iridium, the second-densest naturally occurring metal on Earth, is one of scientific discovery, technological innovation, and industrial transformation. Today, this silvery-white transition metal, with its extraordinary corrosion and temperature resistance, has become indispensable in numerous fields – despite being one of Earth’s rarest elements.

At roughly 7,000 kilograms of annual global production, this is not a metal for casual applications. Currently, applications cluster in several areas: catalysis (Cativa process for acetic acid, water electrolysis for hydrogen production), electronics (OLED phosphorescent emitters, though alternatives are being developed), automotive (spark plug electrodes), and materials science (crucibles for crystal growth). Today, the automotive sector represents the largest consumer of iridium, with most vehicles now using iridium spark plugs as standard equipment.

History

Reader note: Find out more about the six platinum group metals (PGMs) – Iridium, Osmium, Palladium, Platinum, Rhodium, and Ruthenium – as a group here. The complete history of platinum can be found here, while the complete history of all platinum group metals here. Finally, find out about the other critical raw materials (CRMs) here.

Discovery and Early Development (1803-1889)

Iridium was discovered in 1803 by British chemist Smithson Tennant and French chemists working independently, identified in platinum ore residues. The element was named after the Greek word for rainbow due to its colorful compounds. Early work focused on overcoming iridium’s extreme physical properties—it proved nearly impossible to melt or work with conventional methods. John George Children first melted iridium in 1813 using a massive galvanic battery, while Henri Sainte-Claire Deville and Jules Henri Debray achieved the first appreciable melting in 1860 using oxygen-hydrogen flames. By 1834, John Isaac Hawkins had developed iridium-tipped fountain pen nibs, the element’s first commercial application. In 1889, a platinum-iridium alloy became the international standard for the meter and kilogram.

Scientific Applications (1933-1965)

Iridium found specialized uses in scientific instruments and high-temperature applications. Otto Feussner developed iridium-ruthenium thermocouple alloys in 1933 for measuring temperatures up to 2,000°C. Iridium isotopes were progressively identified between 1934 and 2008. Rudolf Mössbauer’s 1957 discovery of the Mössbauer effect using iridium-191 earned him the Nobel Prize. By 1965, patents emerged for iridium crucibles coated with zirconium for crystal growth applications.

Planetary Science Breakthrough (1980-1991)

The 1980 discovery by Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel of an iridium-rich layer at the Cretaceous-Paleogene boundary provided evidence for the asteroid impact theory of dinosaur extinction. This finding connected iridium to catastrophic planetary events, as the element is rare in Earth’s crust but abundant in meteorites. The Chicxulub crater was identified in 1991 as the impact site.

Industrial Catalysis and Automotive Applications (1995-2013)

BP Chemicals commercialized the Cativa process in 1995, using iridium catalysts for acetic acid production. DENSO’s development of iridium spark plugs in 1997-1998, featuring 0.4 mm diameter electrodes, revolutionized automotive ignition systems. By 2013, 88% of new vehicles came equipped with iridium spark plugs, displacing traditional nickel plugs due to superior durability and performance.

Electronics and Modern Applications (1999-2023)

Iridium complexes became central to OLED technology after 1999 demonstrations showed phosphorescent iridium dyes could harvest triplet excitons for improved efficiency. Research continued through 2004 on specific iridium compounds for display applications, though by 2011 alternative TADF technologies began emerging to reduce iridium dependence. Iridium crucibles became essential for semiconductor and LED manufacturing by 2000. In 2019, the redefinition of the kilogram ended the 130-year role of the platinum-iridium International Prototype Kilogram. Current global production stands at approximately 6,800 kilograms annually, with applications spanning catalysis, automotive, electronics, and semiconductor manufacturing.

Chronology

1803 – British chemist Smithson Tennant discovered iridium in the acid-insoluble residues of platinum ores, naming it after the Greek word iris (rainbow) due to the various colors of its compounds; French chemists H.-V. Collet-Descotils, A.-F. Fourcroy, and N.-L. Vauquelin identified iridium at approximately the same time

1804 – Tennant’s discovery of iridium was documented in a letter to the Royal Society published in Philosophical Transactions on June 21, 1804

1813 – British scientist John George Children became the first to melt a sample of iridium using “the greatest galvanic battery that has ever been constructed” at Ferox Hall

1834 – John Isaac Hawkins created the first iridium-pointed gold fountain pen nib, establishing iridium’s use in writing instruments

1842 – Robert Hare obtained high-purity iridium, finding it had a density of around 21.8 g/cm³ and noting the metal as nearly immalleable and very hard

1860 – Henri Sainte-Claire Deville and Jules Henri Debray achieved the first melting of iridium in appreciable quantity, requiring burning more than 300 litres of pure O₂ and H₂ gas for each kilogram of iridium

1880 – John Holland and William Lofland Dudley patented a process for melting iridium by adding phosphorus in the United States

1889 – An alloy of 90% platinum and 10% iridium was used to construct the International Prototype Meter and kilogram mass at the International Bureau of Weights and Measures near Paris; The International Prototype of the Kilogram (IPK) made of platinum-iridium was formally ratified as the kilogram by the 1st CGPM

1933 – Otto Feussner developed the first alloy of iridium with ruthenium for use in thermocouples, allowing measurement of high temperatures in air up to 2,000°C

1934 – The first isotope of iridium was discovered, beginning a period that would see all known isotopes of iridium discovered between 1934 and 2008

1944 – Parker began fitting the Parker 51 fountain pen with nibs tipped by a ruthenium and iridium alloy containing 3.8% iridium

1948 – The International Prototype Kilogram, made of 90% platinum and 10% iridium alloy, underwent its second verification showing mass changes relative to other iridium-platinum copies

1952 – The last fountain pen nib found to contain actual iridium (2.6%) was sampled from a Parker 51

1957 – Rudolf Mössbauer discovered the Mössbauer effect using iridium-191 in Munich, Germany, leading to his Nobel Prize in Physics in 1961

1960 – The International Prototype Meter bar made of 90% platinum and 10% iridium was replaced as the definition of the meter

1965 – Jerry J. Rubin and Le Grand G. Van Uitert filed a patent for coating iridium crucibles with zirconium to extend their lifetime in crystal growth applications

1980 – Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel discovered an iridium-rich clay layer at the Cretaceous-Paleogene boundary, leading to the asteroid impact theory for dinosaur extinction based on high iridium concentrations; their findings were published in Science

1989 – The International Prototype Kilogram made of platinum-iridium alloy underwent its third and final verification, showing the iridium-containing standard had mass variations compared to its copies

1991 – The Chicxulub crater in the Yucatán Peninsula was identified as the impact site linked to the iridium anomaly discovered by the Alvarez team

1995 – BP Chemicals commercialized the Cativa process, using iridium catalysts for methanol carbonylation to produce acetic acid

1997 – DENSO developed iridium spark plugs with ultra-thin iridium electrodes, improving wear resistance and ignition performance

1998 – DENSO created IRIDIUM POWER spark plugs with 0.4 mm diameter iridium center electrodes, the world’s smallest at the time

1999 – Baldo et al. demonstrated that phosphorescent dyes containing iridium in OLEDs could achieve improved efficiency through triplet harvesting

2000 – Iridium crucibles became widely used for growing single crystals by the Czochralski method for semiconductor applications

2004 – Iridium complexes such as Ir(mppy)₃ became a focus of research for phosphorescent OLEDs containing iridium

2008 – The most recent iridium isotopes (²⁰⁰⁻²⁰²Ir) were discovered, completing identification of iridium isotopes from mass 164 to 202

2011 – Bosch introduced new iridium spark plugs using proprietary iridium alloy and 360-degree laser welding processes; Demonstration of thermally activated delayed fluorescence (TADF) in OLEDs offered alternative to iridium-based phosphorescent emitters

2013 – 88% of vehicles from 2013-2018 came with iridium spark plugs as original equipment, reversing decades of nickel plug dominance

2019 – The kilogram was redefined based on Planck’s constant on May 20, ending the role of the International Prototype Kilogram made of platinum-iridium alloy after 130 years

2020 – Iridium crucibles market continued growth for semiconductor manufacturing, with iridium crucibles essential for LED substrate manufacturing

2023 – Global iridium production estimated at 6,800 kilograms annually

Final Thoughts

It’s remarkable how the properties that made iridium nearly impossible to work with in 1813 are exactly what make it valuable today. When Smithson Tennant first isolated it, its melting point of 2,446°C, extreme hardness, and resistance to chemical attack made iridium extraordinarily difficult to study and manipulate with the tools available at the time. Two centuries later, these same characteristics are why we use iridium in spark plugs that must survive repeated thermal stress, in crucibles that contain corrosive molten materials, and in electrical contacts that cannot degrade. The oxidation resistance that frustrated early chemists now protects jet engine components and enables electrodes to survive harsh electrochemical environments. What was once an obstacle has become the reason for iridium’s modern applications.

But, iridium now faces competing pressures that make its future uncertain: The growing hydrogen economy is driving demand for iridium-based catalysts. As countries invest in hydrogen infrastructure, the need for efficient electrolysis could require far more iridium than current applications consume. This is problematic because iridium is among the rarest elements in Earth’s crust at just 0.001 parts per million. At the same time, researchers are actively working to develop alternatives—manganese oxides, nickel-iron compounds, and perovskite structures—that could reduce, or even eliminate, the need for iridium in these applications. Whether iridium becomes more essential, or gets replaced, depends on how these competing trends play out.

Yet, the most interesting possibility may not be replacement, but transformation through nanotechnology. When iridium is structured as nanoparticles, nanowires, or even single atoms dispersed on support materials, it can be effective at much smaller quantities—micrograms instead of milligrams. At these scales, the surface area relative to volume increases dramatically, and the metal exhibits catalytic behaviors that bulk iridium cannot.

Rather than finding substitutes, perhaps the path forward involves using iridium so efficiently through nanostructuring that its scarcity becomes a non-issue, turning a supply constraint into a driver for more sophisticated material science.

Thanks for reading!

References

[1] Iridium – Wikipedia – https://en.wikipedia.org/wiki/Iridium

[2] Iridium – New World Encyclopedia – https://www.newworldencyclopedia.org/entry/Iridium

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[4] International Prototype of the Kilogram – Wikipedia – https://en.wikipedia.org/wiki/International_Prototype_of_the_Kilogram

[5] Otto Feussner – Wikipedia – https://de.wikipedia.org/wiki/Otto_Feussner

[6] How can we talk about iridium? | Nibs – https://www.nibs.com/blog/nibster-writes/how-can-we-talk-about-iridium

[7] US3470017A – Iridium crucibles and technique for extending the lifetime thereof by coating with zirconium or zirconium oxide – Google Patents – https://patents.google.com/patent/US3470017A/en

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[9] Reactivity of Ir( iii ) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation – Dalton Transactions (RSC Publishing) – https://pubs.rsc.org/en/content/articlehtml/2013/dt/c3dt52092g

[10] The Cativa™ Process for the Manufacture of Acetic Acid | Johnson Matthey Technology Review – https://technology.matthey.com/content/journals/10.1595/003214000X44394105

[11] HISTORY OF DENSO SPARK PLUG | SPARK PLUG | Automotive Service Parts and Accessories | DENSO Global Website – https://www.denso.com/global/en/products-and-services/automotive-service-parts-and-accessories/plug/history/

[12] Phosphorescent Organic Light-Emitting Devices: Working Principle and Iridium Based Emitter Materials – PMC – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635741/

[13] Iridium Crucibles Supplier – SAM – https://www.samaterials.com/iridium/887-iridium-crucibles.html

[14] OLED – Wikipedia – https://en.wikipedia.org/wiki/OLED

[15] Bosch Introduces New Iridium Spark Plug – aftermarketNews – https://www.aftermarketnews.com/bosch-introduces-new-iridium-spark-plug/

[16] History of OLED materials and technology – https://noctiluca.eu/history-of-oled-materials-and-technology/

[17] The Evolution Of Spark Plugs – – https://www.tomorrowstechnician.com/spark-plug-evolution/

[18] Novel Design of Iridium Phosphors with Pyridinylphosphinate Ligands for High-Efficiency Blue Organic Light-emitting Diodes | Scientific Reports – https://www.nature.com/articles/srep38478

[19] Kilogram – Wikipedia – https://en.wikipedia.org/wiki/Kilogram

[20] Unveiling the Iridium Crucible in Artificial Crystal Growth – https://www.samaterials.com/content/the-container-of-artificial-crystal-growth-iridium-crucible.html

[21] Frontiers | Highly Efficient Phosphorescent Blue-Emitting [3+2+1] Coordinated Iridium (III) Complex for OLED Application – https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.758357/full

[22] A comprehensive quarterly iridium and ruthenium market report and iridium price outlook on SFA (Oxford)’s iridium market fundamentals and integration of future green hydrogen technologies for new and existing end-uses. – https://www.sfa-oxford.com/platinum-group-metals/pgm-market-reports/iridium-and-ruthenium-market-report/

[23] Global Iridium Crucibles Market Analysis: Size, Share & Industry Outlook 2033 – https://www.marketresearchintellect.com/product/global-iridium-crucibles-market-size-and-forecast/

[24] A comprehensive quarterly iridium and ruthenium market report and iridium price outlook on SFA (Oxford)’s iridium market fundamentals and integration of future green hydrogen technologies for new and existing end-uses. – https://www.sfa-oxford.com/platinum-group-metals/pgm-market-reports/iridium-and-ruthenium-market-report/