Iridium

Iridium — Material Page

View Products ↓

Iridium (Ir, atomic number 77) is a Group 9 platinum-group metal (PGM) with the second highest density of any element (22.56 g/cm³, after osmium at 22.59 g/cm³), the highest corrosion resistance of any metal, and the highest Young's modulus of any FCC metal (528 GPa) — combining extreme hardness with chemical near-inertness across the widest temperature range of any structural metal. Iridium has an FCC crystal structure stable from room temperature to its melting point of 2,446 °C and is the most corrosion-resistant metal known, being unattacked by all acids including aqua regia, by most molten metals, and by oxygen up to ~1,000 °C (above which IrO₂ forms but is volatile). It is one of the rarest elements in Earth's crust (~0.001 ppb), concentrated in the mantle and in PGM-rich sulfide ores; the Ir-rich layer at the Cretaceous-Paleogene boundary (the "K-Pg" clay) at 66 Ma is the primary evidence for the Alvarez impact hypothesis. Iridium is produced exclusively as a byproduct of nickel and copper mining, primarily from the Bushveld Complex (South Africa) and the Norilsk-Talnakh deposit (Russia), with global annual production of only ~7–8 tonnes.

The largest single application of iridium is as the active electrode material in proton exchange membrane (PEM) water electrolyzers — IrO₂ is the only practically viable anode catalyst for oxygen evolution in acidic PEM conditions, making Ir supply a critical bottleneck for green hydrogen scale-up. PEM electrolyzer anodes require ~0.3–2 g Ir/kW of installed capacity; at projected multi-GW deployment rates, Ir demand for electrolysis could approach or exceed current total supply within this decade, driving intense research into Ir loading reduction and non-Ir alternatives. Iridium spark plug tips (Ir or Ir-Rh alloy, typically 0.4–0.6 mm diameter) dominate automotive long-life spark plugs — Ir's extreme hardness (~1,760 HV cold-worked, ~220 HV annealed) and melting point enable 100,000+ mile service life compared to ~30,000 miles for Pt tips. The international prototype kilogram was historically made of Pt-10%Ir alloy, chosen for its hardness, stability, and corrosion resistance.

¹⁹²Ir (t½ = 73.83 days) produced by neutron irradiation of ¹⁹¹Ir is the most widely used radioisotope source for industrial gamma radiography and is a major brachytherapy source for cancer treatment, with ~500,000 patients treated annually worldwide with ¹⁹²Ir high-dose-rate (HDR) brachytherapy. In industrial radiography, ¹⁹²Ir sealed sources (specific activity up to ~450 GBq/g) are used to inspect welds and castings in oil and gas pipelines, pressure vessels, and aerospace components — the 316–468 keV gammas penetrate steel up to ~80 mm. IrO₂ electrodes are the standard for neural stimulation implants (cochlear implants, deep brain stimulators, retinal prostheses) due to high charge injection capacity, electrochemical stability, and biocompatibility in physiological saline over years of chronic use.

General Properties

Property	Value	Notes
Atomic Number	77	Group 9, Period 6; 4f¹⁴5d⁷6s²; dominant oxidation states +3 (Ir³⁺, IrCl₃, cyclometalated Ir complexes) and +4 (Ir⁴⁺, IrO₂, IrCl₄²⁻); +1 through +6 are accessible. Ir³⁺ complexes — particularly Ir(ppy)₃ and its derivatives — are the dominant phosphorescent emitters in organic LEDs (OLEDs), harvesting both singlet and triplet excitons for near-100% internal quantum efficiency.
Atomic Mass	192.217 u	Two stable isotopes: ¹⁹¹Ir (37.3%) and ¹⁹³Ir (62.7%), both with I = 3/2. The near-equal abundances make Ir isotope ratio measurement straightforward by MC-ICP-MS; Ir isotope fractionation in the K-Pg boundary layer and in PGM ore deposits is used in geochemical provenance studies.
Density (20 °C)	22.56 g/cm³	Second densest element after osmium (22.59 g/cm³); the two values are close enough that the ranking depends on measurement precision and sample purity. Ir's extreme density combined with chemical inertness is exploited in Ir counterweights, Ir-alloy pen nibs, and historically in the Pt-10%Ir international prototype kilogram.
Melting Point	2,446 °C (2,719 K)	Sixth highest melting point of any element; the highest of the FCC platinum-group metals. Processing requires either arc melting under inert atmosphere or powder metallurgy sintering — Ir cannot be hot-worked easily below ~1,200 °C due to its low-temperature brittleness.
Boiling Point	4,428 °C	High boiling point enables use of Ir crucibles for crystal growth of refractory oxides (GGG, YAG, LiNbO₃, BGO scintillators) at temperatures of 1,800–2,200 °C where Pt or Rh crucibles are unsuitable. Ir crucibles are the standard for Czochralski growth of high-melting-point single crystals.
Thermal Conductivity	147 W/m·K	Moderate-to-high for a PGM — much higher than Pt (71.6 W/m·K) and Pd (71.8 W/m·K). Relevant to Ir crucible thermal uniformity during crystal growth and to Ir-coated heat shields in high-temperature aerospace and nuclear applications.
Electrical Resistivity	47.1 nΩ·m (20 °C)	Low resistivity for a PGM — lower than Pt (105 nΩ·m) and Pd (105 nΩ·m). IrO₂ (resistivity ~30–50 µΩ·cm) is a conductive oxide used as a bottom electrode in ferroelectric capacitors (FeRAM) and as a neural stimulation electrode due to its stability under charge injection cycling.
Crystal Structure	FCC, a = 3.839 Å (room temperature)	FCC structure is stable from RT to the melting point with no allotropic transformation. Despite FCC symmetry, Ir is much less ductile than Au or Pt due to anomalously low stacking fault energy and high Peierls stress — a consequence of strong d-electron bonding that also accounts for its exceptional hardness and modulus.

Mechanical Properties

Property	Value	Notes
Tensile Strength	250–500 MPa	Moderate tensile strength for a refractory metal; Ir is stronger than Pt (~125 MPa) and Au (~120 MPa) but weaker than W (~600 MPa) in comparable processed forms. Work-hardened Ir wire or foil can reach higher values; strength improves significantly above ~800 °C as thermal activation aids dislocation motion.
Yield Strength	Not well-defined at room temperature (limited ductility)	Ir exhibits limited but non-zero room-temperature ductility in high-purity form — elongation of 5–10% has been measured in annealed polycrystalline Ir. The "brittle" character arises from grain boundary embrittlement (exacerbated by impurities such as S, P, Si) rather than intrinsic lattice brittleness; ultra-high-purity Ir is measurably more ductile.
Young's Modulus	528 GPa	Highest Young's modulus of any FCC metal and among the highest of any pure metal — reflecting the extremely strong d-electron bonding in Ir. Relevant to Ir AFM probe tips (high stiffness for contact-mode imaging of hard surfaces) and Ir structural components where maximum stiffness per unit volume is required.
Hardness	~220 HV (annealed); up to ~1,760 HV (cold-worked)	Source value of ~1,760 HV reflects heavily cold-worked Ir; annealed polycrystalline Ir is ~200–250 HV. The extreme work-hardening rate of Ir (due to low stacking fault energy) makes it the hardest of the platinum-group metals in the worked condition — the basis of its use in Ir-tipped spark plug electrodes and wear-resistant contacts.
Elongation at Break	5–10%	Limited but measurable ductility in annealed, high-purity polycrystalline form. Ductility is strongly degraded by grain boundary impurities (particularly S and P at ppm levels) and by grain growth after high-temperature processing. Ir alloyed with Rh (Ir-10%Rh, Ir-50%Rh) improves ductility for thermocouple wire drawing.
Poisson's Ratio	0.26	Typical for FCC metals with strong d-electron character. Used in stress modeling of Ir thin-film electrodes under cyclic electrochemical loading and in FEA of Ir spark plug tip wear under repeated ignition events.

Chemical Properties

Property	Value / Behavior	Notes
Oxidation States	+3 (most common: IrCl₃, Ir(ppy)₃, IrO(OH)); +4 (IrO₂, IrCl₄²⁻); range +1 to +6	Ir³⁺ cyclometalated complexes (Ir(ppy)₃ and hundreds of derivatives) are the dominant phosphorescent OLED emitter class — tunable across the visible spectrum by ligand design, with phosphorescent lifetimes of ~1–10 µs and near-unity photoluminescence quantum yields in thin film. IrO₂ (Ir⁴⁺) is the only practical acid-stable OER catalyst for PEM electrolysis.
Corrosion Resistance	Exceptional; inert to all acids including aqua regia at room temperature; resistant to most molten metals; attacked by fused alkalis and by O₂ above ~1,000 °C	Ir is the most corrosion-resistant metal known — it resists aqua regia (which dissolves Au and Pt) at room temperature and withstands molten Zn, Ga, and many other liquid metals. Above ~1,000 °C in air, volatile IrO₃ forms; in vacuum or inert atmosphere, Ir is stable to its melting point.
Surface Oxide	IrO₂ (rutile structure) forms above ~400 °C in air; IrO₃ (volatile) above ~1,000 °C	IrO₂ is a conductive oxide (metallic conductivity, ~30–50 µΩ·cm) used as an OER catalyst in PEM electrolyzers, as a bottom electrode in FeRAM, and as a neural stimulation electrode. Electrochemically grown hydrous IrOₓ films (anodic IrOₓ, "AIROF") have much higher charge injection capacity than thermally grown IrO₂ and are preferred for neural interfaces.

Identifier	Value
Symbol	Ir
Atomic Number	77
CAS Number	7439-88-5
UN Number	N/A
EINECS Number	231-095-9

Isotope	Type	Notes
¹⁹¹Ir	Stable	37.3% natural abundance; I = 3/2. ¹⁹¹Ir(n,γ)¹⁹²Ir (σ = 954 barn) is the neutron activation reaction used to produce ¹⁹²Ir brachytherapy and radiography sources — the very high cross-section enables production of high-specific-activity ¹⁹²Ir from natural or enriched ¹⁹¹Ir targets in research reactors. ¹⁹¹Ir NMR is accessible but rarely used due to broad quadrupolar lines.
¹⁹³Ir	Stable	62.7% natural abundance; I = 3/2 — the more abundant stable isotope. ¹⁹³Ir is used as a reference isotope for Ir isotope ratio measurements (¹⁹¹Ir/¹⁹³Ir by MC-ICP-MS) in K-Pg boundary geochemistry and PGM ore deposit provenance studies. ¹⁹³Ir Mössbauer spectroscopy (57.6 keV transition) characterizes Ir coordination and oxidation state in IrO₂ catalysts and Ir organometallic compounds.
¹⁹²Ir	Radioactive	t½ = 73.83 days; β⁻ (95.1%) to ¹⁹²Pt + γ (316, 468 keV principal lines); produced by ¹⁹¹Ir(n,γ)¹⁹²Ir. The dominant industrial gamma radiography source (specific activity up to ~450 GBq/g, penetrates steel to ~80 mm) and the most widely used HDR brachytherapy source (~500,000 patients/year for cervical, prostate, breast, and lung cancers). ¹⁹²Ir HDR sources (microSelectron, Flexitron systems) deliver dose rates of ~12 Gy/min at 1 cm, enabling outpatient fractionated treatment in minutes per fraction.

Scientific & Research Applications

Use Case	Form Typically Used	Description
OLED Phosphorescent Emitters	Ir(ppy)₃ and derivative cyclometalated complexes (synthesized from IrCl₃)	Ir³⁺ cyclometalated complexes are the dominant emitter class in OLED displays and lighting — strong spin-orbit coupling from Ir enables phosphorescence with near-unity photoluminescence quantum yield, harvesting both singlet and triplet excitons. Ligand design tunes emission color from blue (~460 nm) to deep red (~700 nm); FIrpic (blue), Ir(ppy)₃ (green), and Ir(MDQ)₂(acac) (red) are standard device emitters.
PEM Electrolyzer OER Catalysis	IrO₂ nanoparticles (2–5 nm on carbon or TiO₂ support); Ir black; Ir sputtering targets	IrO₂ is the only commercially viable anode catalyst for oxygen evolution in acidic PEM electrolyzers — stable under the highly oxidizing potential (+1.4–2.0 V vs. RHE), low pH (~2), and elevated temperature (50–80 °C) of PEM operation. Research targets reducing Ir loading (<0.1 mg/cm²), improving IrOₓ amorphous vs. rutile phase activity, and identifying non-Ir alternatives for green hydrogen scale-up.
High-Temperature Crystal Growth Crucibles	Ir crucibles and dies (99.9–99.95%, fabricated by PM sintering or arc casting)	Ir crucibles are the standard for Czochralski growth of high-melting-point single crystals — YAG (1,940 °C), GGG (1,750 °C), BGO (1,060 °C, but requiring inert atmosphere), and LiNbO₃ (1,257 °C). Ir's chemical inertness prevents melt contamination and enables repeated use; crucible lifetime is limited by grain growth and IrO₃ volatilization in air above ~1,000 °C.
Neural Stimulation Electrodes	Electrochemically grown IrOₓ films on Ir wire/foil (99.9%+); IrO₂ sputtered coatings	IrOₓ electrodes have charge injection capacities of 1–4 mC/cm² (geometric) — 10–100× higher than Pt — enabling smaller electrode geometries for high-density neural recording arrays. Used in cochlear implants, deep brain stimulators (Parkinson's, essential tremor), retinal prostheses (Argus II), and research electrocorticography (ECoG) arrays.
X-Ray Optics & Mass Spectrometry	Ir-coated grazing-incidence mirrors; Ir wire for ion sources	Ir-coated grazing-incidence mirrors reflect hard X-rays (>10 keV) with high efficiency at angles below the critical angle — used in X-ray telescopes (Chandra Observatory primary mirrors are Ir-coated) and synchrotron beamline optics. Ir wire tips are used in field ionization and field desorption mass spectrometry ion sources for non-volatile compound analysis.

Industrial & Commercial Applications

Sector	Form / Grade Used	Description
Spark Plugs	Ir or Ir-Rh alloy fine-wire tips (0.4–0.6 mm diameter, 99.95%+)	Ir-tipped spark plugs dominate the premium automotive and motorcycle market — Ir's extreme hardness (~1,760 HV worked) and high melting point enable fine-wire tips (0.4 mm vs. 1.1 mm for Ni) that reduce required ignition voltage, improve combustion efficiency, and last 100,000+ miles. Ir-10%Rh and Ir-25%Rh alloys improve ductility for tip wire drawing while retaining adequate hardness.
Industrial Gamma Radiography	¹⁹²Ir sealed sources (double-encapsulated, IAEA Type B(U) transport containers)	¹⁹²Ir sealed sources (specific activity ~400–450 GBq/g, source diameter 0.5–3.5 mm) are the standard for weld inspection of steel pipe and vessels in oil and gas, petrochemical, power generation, and aerospace industries — penetrating steel up to 80 mm with 316/468 keV gammas. Sources are used in panoramic, directional, and pipe crawler exposure configurations.
Electrical Contacts & Pen Nibs	Ir-Ru, Ir-Os, Ir-Rh alloy contacts and tips (99.9%+)	Ir alloy contacts are used in precision relays, aircraft instrumentation, and medical devices requiring low contact resistance and resistance to arc erosion over millions of switching cycles. Ir-Os and Ir-Ru alloy tips on fountain pen nibs provide extreme wear resistance — a single Ir-tipped nib can write hundreds of kilometers.
HDR Brachytherapy	¹⁹²Ir HDR sources (microSelectron v3, Flexitron — ~3.5 mm length, ~0.6 mm diameter)	¹⁹²Ir HDR brachytherapy delivers high-dose-rate radiation from within or adjacent to tumors — used for gynecological, prostate, breast, esophageal, and lung cancers. The miniature source steps through applicator catheters under robotic control (remote afterloader), generating individualized dose distributions. Sources are replaced every ~3–4 months as ¹⁹²Ir activity decays.
Aerospace & Defense	Ir-coated Re rocket nozzles; Ir-clad Pt-Rh thermocouples	Ir coatings on rhenium rocket nozzle throats protect against oxidation at temperatures above 2,000 °C in bipropellant engines (used on spacecraft attitude control thrusters, including Mars landers). Ir-Rh thermocouples (Ir-40%Rh vs. Ir, Type FIR) measure temperatures to 2,100 °C in oxidizing atmospheres where W-Re thermocouples cannot be used.

Purity	Description
99.9% (3N)	Used in industrial components and crucibles. Impurities: ≤1000 ppm. Standard industrial-grade iridium.
99.95% (3N5)	Suitable for electrodes, spark plugs, and high-temperature applications. Impurities: ≤500 ppm. Improved purity for electronic applications.
99.99% (4N)	Used in scientific equipment and catalyst applications. Impurities: ≤100 ppm. High-purity iridium for demanding environments.
99.995% (4N5)	Ideal for analytical standards and semiconductor use. Impurities: ≤50 ppm. Ultra-high purity for precision applications.

Synonym / Alternative Name	Context
Iridium precious metal	Trade designation used in PGM commodity markets, precious metal refinery documentation, and supply chain records distinguishing Ir from base metals; used in London Platinum and Palladium Market (LPPM) and Johnson Matthey PGM market reports.
Iridium metal	Commercial designation for elemental Ir in powder, pellet, foil, wire, or target form; used in ASTM standards, nuclear source manufacturing specifications (IAEA), and procurement documentation for crystal growth crucibles and spark plug tip materials.
Elemental Iridium	Scientific designation distinguishing the pure element from IrO₂, IrCl₃, Ir(ppy)₃, and other compounds; used in electrochemistry and materials science literature specifying Ir metal substrates or thin films as distinct from iridium oxide electrodes.
Element 77	Periodic table designation; used in XRF/ICP-MS analytical software, nuclear data libraries (ENDF/B), and geochemical databases (PetDB, GEOROC) where atomic number is the primary element identifier for PGM geochemistry studies.
Iridio	Spanish and Italian language name for iridium; used in scientific literature and regulatory documentation in Spanish- and Italian-speaking markets; also the name in Portuguese (iridio), relevant to Brazilian PGM mining and refining industry documentation.

My Wish List

Last Added Items

You have no items in your wish list.

Services

Applications

No minimum order

Free shipping included

Customized Materials

99% stock availability