Iridium (Ir, atomic number 77) is alloyed chiefly with platinum, tungsten and, in nature, osmium, because pure iridium is too brittle and too hard-melting to shape on its own. Iridium forms far fewer commercial alloys than platinum or palladium, and each one trades on the same trait: extreme hardness and heat resistance, added in small amounts to a workable host metal or paired with a trace hardener of its own. This page covers the alloys iridium actually forms, how they differ from the pure metal, and where each is used today.
What Is an Iridium Alloy?#
Iridium (Ir, atomic number 77) is alloyed with platinum as the hardening minority, in an alloy such as Pt-10Ir, or is itself the base metal with a small ductility-improving addition, since pure iridium is too brittle and too refractory to cast, machine or forge on its own. Iridium is one of the six platinum group metals, and its full identity sits on the iridium (Ir), element 77 page; commercial iridium hardware is shaped by powder metallurgy instead.
Why Iridium Is Alloyed#
Iridium is face-centred cubic, the same crystal structure as platinum and palladium, yet it stays brittle where those two metals are ductile. Iridium's fcc lattice provides the five independent slip systems the von Mises criterion requires for general plastic deformation, so the brittleness is not a slip-system shortage; it is grain-boundary failure under stress despite ample slip systems being available. That combination of hardness, brittleness and a 2,446 °C melting point is why solid iridium parts are normally made by powder metallurgy rather than cast or machined, and why iridium's heat-affected zone cracks during welding.
Common Iridium Alloys#
Iridium's single most-used alloy is Pt-10Ir, 90% platinum and 10% iridium by mass, alongside one aerospace alloy and a set of natural alloys with osmium that predate industrial metallurgy entirely.
| Alloy | Composition (wt%) | Typical field | Note |
|---|---|---|---|
| Pt-10Ir | 90% platinum, 10% iridium | Metrology, implantable electrodes | The historic International Prototype Kilogram and Metre alloy; now also used for implant electrodes and marker bands |
| DOP-26 | Iridium with 0.3 wt% tungsten and about 60 ppm (0.006%) thorium | Radioisotope thermoelectric generator (RTG) cladding | The thorium content is often misquoted as roughly 0.2%; DOP-26's actual doping level is thirty times smaller |
| Osmiridium / iridosmine | Natural osmium-iridium alloy; osmiridium below 32% osmium (cubic), iridosmine 32 to 80% osmium (hexagonal) | Historic pen nibs, phonograph needles, compass pivots | Displaced almost entirely by synthetic hard alloys during the 20th century |
Pt-10Ir is iridium's one significant engineered alloy by history, chosen because iridium hardens platinum without compromising platinum's oxidation resistance. DOP-26 is a specialist aerospace alloy in which iridium is the base metal, developed for radioisotope power-source cladding. Osmiridium and iridosmine are natural alloys, recovered directly from ore rather than melted in a foundry.
Properties of Iridium Alloys vs Pure Iridium#
Alloying changes iridium's mechanical behavior in two directions depending on which metal hosts which: adding iridium to platinum raises hardness sharply, while adding a small amount of titanium and zirconium to iridium itself raises ductility instead.
| Property | Pure iridium | Alloy value | Alloy | Source |
|---|---|---|---|---|
| Hardness (Vickers, annealed) | About 220 HV (2,157 MPa, Johnson Matthey legacy table) | Exceeds 500 HV | Pt-50Ir | Wikipedia, Platinum-iridium alloy |
| Ductility / workability | Brittle; hot-workable only, and its heat-affected zone cracks during welding | Measurably improved ductility | Iridium with 0.2% titanium and 0.2% zirconium | Wikipedia, Iridium |
Iridium is the most potent hardener of platinum per unit added, which is why a 50% addition more than doubles pure platinum's roughly 40 to 41 HV annealed hardness past 500 HV. Run the other direction, and adding titanium and zirconium to iridium metal instead improves its own ductility, with no published Vickers figure for that alloy, so this page states the effect rather than an unsupported number.
Why Iridium Needs Alloying to Be Workable#
Iridium's brittleness is grain-boundary controlled, not a slip-system shortage, an unusual combination for a face-centred-cubic metal and the reason iridium behaves nothing like platinum or palladium despite sharing their structure. Trace additions of 0.2% each of titanium and zirconium measurably improve iridium's ductility, documented directly against the pure metal. This limitation is also why iridium hardware is normally shaped by powder metallurgy, pressing and sintering rather than casting or machining, and why DOP-26 cladding fabrication stays specialized.
Osmium vs Iridium Density#
Osmium and iridium are effectively tied for the densest element, at 22.587 g/cm3 and iridium's own 22.562 g/cm3, a gap of just 0.025 g/cm3 resolved only by 1990s X-ray crystallography. Older handbook tables giving osmium a roughly 0.15 g/cm3 lead use a legacy, less precise pair of figures; modern crystallography narrows that gap sixfold. See the full osmium versus iridium density comparison for the calculation.
Uses of Iridium Alloys#
Iridium alloys' largest current use is Pt-10Ir in metrology and implantable medical hardware, since osmiridium's once-larger volume in pen nibs and instrument pivots has been displaced by synthetic hard alloys.
| Use | Typical alloy | Sector |
|---|---|---|
| Mass and length reference standards (retired 2019) | Pt-10Ir | Metrology |
| Implantable electrodes, marker bands | Pt-10Ir | Medical |
| Radioisotope thermoelectric generator cladding | DOP-26 | Aerospace and nuclear power |
| Pen nibs, phonograph needles, compass pivots (historic) | Osmiridium / iridosmine | Historic instruments |
Pt-10Ir's use as the Kilogram and Metre alloy ended in 2019, when the kilogram was redefined by the Planck constant, closing a role the alloy held since the 1870s and 1880s. Its remaining use is medical: implantable electrodes and marker bands draw on the same hardness and platinum-derived inertness. DOP-26 clads plutonium-238 fuel pellets in radioisotope thermoelectric generators for deep-space missions, where iridium's retained strength above 1,600 °C is the deciding property. Osmiridium's pen-nib and instrument-pivot uses are historic, displaced by synthetic hard alloys.
Iridium Alloys and the Iridium Price#
Iridium alloys are priced off the same USD iridium spot price as the pure metal, adjusted for iridium content by weight, with no number stated on this page. See iridium price today, part of the site's broader platinum group metal prices coverage, for today's figure.
Other PGM Alloys#
Iridium is not the only platinum group metal with a dedicated alloys page.
- Platinum alloys: the widest alloy family of any PGM, spanning jewelry, gauze and Pt-Ir metrology.
- Palladium alloys: palladium white gold and hydrogen-purification membranes.
- Osmium alloys: osmiridium's other natural-alloy partner, plus the Pt-Os implant alloy.
Buyers sourcing iridium alloy stock, including iridium powder feedstock, can request a quote below.
Frequently Asked Questions#
Is iridium rarer than gold? Yes; iridium is one of the rarest elements in Earth's crust, and how rare iridium is sets out the specific comparison against gold.
How much is 1 lb of iridium worth? Iridium tracks a dealer-quoted market, not an exchange price; see iridium price today for current values.
Why is iridium so rare on Earth? It is recovered only as a minor co-product of platinum-group-metal mining, never as a primary target; the rarity page above covers the abundance figures.
What is the price of 1 g of iridium? See the iridium price page above for the current per-gram figure; no live number is stated here.
What is the price of iridium per ounce today? As with the per-gram figure, this tracks live dealer quotes on that same price page.
Can iridium rust? No; solid iridium resists even aqua regia and does not rust in ordinary use.