Dive into the intriguing world of Iridium, one of the rarest elements on Earth, known for its remarkable density and high resistance to corrosion. This guide explores iridium’s pivotal applications, from spark plugs to cancer treatment devices, highlighting its unparalleled strength and durability. Discover how iridium, despite its scarcity, plays a crucial role in advancing technology and improving our quality of life. Join us as we delve into the unique properties and groundbreaking uses of this precious metal, showcasing examples that illuminate iridium’s importance in modern science and industry.

What is Iridium?

Iridium is a dense, silvery-white metallic element known for its extraordinary properties and broad application spectrum, carrying the atomic number 77. It stands out for its remarkable resistance to corrosion and high density, making it exceptionally suitable for extreme environments. Iridium is one of the least abundant elements in Earth’s crust and is often found in alloys with other platinum group metals from which it is extracted. Its significant applications span various industries; in the chemical industry, iridium serves as a crucial catalyst for the Cativa and Monsanto processes, enhancing the production of acetic acid.  Its resistance to corrosion also makes it ideal for use in electrical contacts and electrodes for medical devices, underlining iridium’s critical role in advancing technology and supporting innovative solutions across multiple sectors.

Iridium Formula

  • Formula: Ir (Represents a single atom of iridium)
  • Composition: Pure element, consisting of one iridium atom.
  • Bond Type: Forms covalent and ionic bonds with other elements.
  • Molecular Structure: Metallic state with a face-centered cubic (fcc) crystalline structure.
  • Electron Sharing: Shares electrons covalently or ionically in compounds.
  • Significance: Known for its exceptional density and corrosion resistance, used in harsh environment applications like spark plugs and electrodes.
  • Role in Chemistry: Crucial for catalysis, particularly in automotive catalytic converters and the production of acetic acid, highlighting its importance in advanced technology and sustainable chemistry.

Atomic Structure of Iridium

Protons, Neutrons, and Electrons

  • Protons: 77, defining iridium’s chemical properties.
  • Neutrons: Varies, with iridium-191 and iridium-193 as stable isotopes.
  • Electrons: 77, arranged in shells around the nucleus.

Electron Configuration

  • Configuration: [Xe] 4f¹⁴ 5d⁷6s², showcasing its position as a transition metal.
  • Importance: Influences iridium’s chemical reactivity and bonding behavior.

Atomic and Ionic Radii

  • Atomic Radius: Approximately 135 picometers.
  • Ionic Radius: Changes with the ion’s charge, affecting compound formation.

Magnetic Properties

  • Paramagnetic: Iridium is paramagnetic due to unpaired d-electrons

Properties of Iridium

Pr_operties of Iridium

Physical Properties of Iridium

Property Value
Appearance Silvery-white metal, with a yellowish tint
Atomic Mass 192.217 u
Density Approximately 22.56 g/cm³ at 20°C
Melting Point 2446°C (4435°F)
Boiling Point 4428°C (8002°F)
Crystal Structure Face-centered cubic (fcc)
Electrical Conductivity 1.73×10⁶ S/m
Thermal Conductivity 147 W/(m·K)
Hardness Vickers hardness of 1760 HV
Magnetic Properties Paramagnetic

Chemical Properties of Iridium

Iridium is a platinum group metal with unique chemical properties that contribute to its wide range of applications.

  1. High Corrosion Resistance:
    • Iridium is remarkably resistant to corrosion, even at high temperatures, making it suitable for extreme environments.
    • It does not oxidize in air, even when heated, maintaining its integrity.
  2. Oxidation States:
    • Iridium commonly exhibits oxidation states ranging from -1 to +6, with +3 and +4 being the most stable.
    • Example Equation (Iridium(III) Chloride Formation): 2Ir+3Cl₂​→2IrCl₃
  3. Reaction with Halogens:
    • Iridium reacts with halogens at elevated temperatures to form hexahalides.
    • Example Equation (Reaction with Chlorine): Ir+3Cl₂​→IrCl₆
  4. Complex Formation:
    • Iridium forms complex compounds, particularly with carbon monoxide and phosphines, utilized in catalytic processes.
    • Example Equation (Formation of Vaska’s Complex): IrCl(CO)[P(C6​H₅ ​)₃​]₂​+CO+2P(C₆​H₅ ​)₃​→[Ir(CO)₂​(P(C6​H₅ )₃​)₂​]Cl
  5. Resistance to Acids:
    • Among its notable chemical properties, iridium’s resistance to acids, including aqua regia, is particularly significant, unlike most metals.
    • It only dissolves in molten salts, such as sodium cyanide or potassium cyanide, under the facilitation of oxygen.
  6. Catalytic Properties:
    • Iridium’s catalytic abilities are showcased in its use in the chemical industry for hydrogenation reactions and in automotive catalytic converters.
    • Example Application: Iridium is used as a catalyst in the Cativa process for the production of acetic acid from methanol and carbon monoxide.

Preparation of Iridium

The preparation of iridium, one of the rarest and most corrosion-resistant metals on Earth, involves complex processes due to its high melting point and resistance to most chemicals. Here’s an overview of the primary steps involved in producing pure iridium:

Mining and Initial Processing

  • Source: Iridium is primarily obtained as a by-product of nickel and copper mining.
  • Extraction: The metal is extracted from ore concentrates that contain various platinum group metals (PGMs), including iridium.

Separation and Purification

  • Dissolution: The ores are dissolved in a mixture of hydrochloric and nitric acids, known as aqua regia, which can dissolve iridium and other PGMs.
  • Precipitation: Through chemical reactions, iridium is separated from other metals by precipitating it as its ammonium salt.
  • Reduction: The iridium salt is then reduced to metallic iridium powder, often using hydrogen gas.


  • Melting: The powdered iridium is melted in a furnace. Given iridium’s high melting point, this process requires sophisticated equipment, like induction furnaces, capable of reaching temperatures above 2446°C (4435°F).
  • Forming: The molten iridium is then cooled and solidified into ingots or other desired forms.

Final Processing

  • Sintering: For certain applications, iridium powder may be sintered under high pressure and temperature, without melting, to achieve the desired density and shape

Chemical Compounds of Iridium

Chemical Compounds of Iridium

  1. Iridium Chloride (IrCl₃)
    Description: A red-brown solid used as a starting material for many iridium compounds.
    Equation: Ir + 1.5Cl₂ → IrCl₃
  2. Iridium Hexachloride (IrCl₆²⁻)
    Description: A dark green compound, known for its role in coordination chemistry.
    Equation: IrCl₃ + 3Cl⁻ → IrCl₆²⁻
  3. Iridium Oxide (IrO₂)
    Description: A black solid, used as an electrode material in electrochemical applications.
    Equation: Ir + O₂ → IrO₂
  4. Iridium Sulfide (IrS₂)
    Description: A dark solid, illustrating iridium’s ability to form compounds with sulfur.
    Equation: Ir + 2S → IrS₂
  5. Potassium Hexachloroiridate(IV) (K₂IrCl₆)
    Description: A yellow compound, used in the synthesis of other iridium complexes.
    Equation: K₂CrCl₆ + Ir → K₂IrCl₆ + Cr
  6. Iridium Trichloride Hydrate (IrCl₃·xH₂O)
    Description: Hydrated form of iridium chloride, crucial for catalysis and organic synthesis.
    Equation: IrCl₃ + xH₂O → IrCl₃·xH₂O

Isotopes of Iridium

Isotope Natural Abundance (%) Half-Life Mode of Decay
Ir-191 37.3 Stable N/A
Ir-193 62.7 Stable N/A
Ir-192 Synthetic 73.83 days Beta decay to Pt-192 or Os-192
Ir-194 Synthetic 19.3 hours Beta decay to Pt-194
Ir-190 Synthetic 11.8 days Beta decay to Pt-190
Ir-188 Synthetic 1.73 days Beta decay to Pt-188

Uses of Iridium

Uses of Iridium

  1. Electronics: Used in the production of crucibles and electrical contacts due to its high melting point and resistance to corrosion.
  2. Medicine: Iridium-192 isotopes are used in brachytherapy for targeted radiation treatments, offering precise cancer treatment options.
  3. Automotive Industry: Utilized in spark plugs and catalytic converters, enhancing efficiency and emission control.
  4. Chemical Industry: Acts as a catalyst in the production of acetic acid and hydrogenation reactions, improving reaction efficiencies.
  5. Aerospace: Employed in spacecraft components for its resistance to thermal stress and corrosion in space environments.
  6. Jewelry and Watchmaking: Alloyed with osmium to produce hard and durable alloys for high-quality pens, watches, and compass bearings.

Production of Iridium

Iridium, a rare and precious metal, is primarily extracted from the Earth’s crust as a by-product of nickel and copper mining. The process begins with the mining of ore, which contains minute quantities of iridium alongside other platinum group metals. The initial step in the extraction involves crushing the mined ore and subjecting it to a series of flotation processes to concentrate the metal content.

The concentrated ore is then smelted at high temperatures, which allows the separation of base metals from the platinum group metals. Following smelting, the resulting material undergoes further refining through chemical leaching, which extracts the individual metals. Iridium, due to its rarity and dispersed occurrence, is painstakingly isolated through these processes.

Refinement to pure iridium is achieved through a complex chemical process involving the conversion of iridium into its chloride or other compounds, which are then reduced back to the pure metal. This multi-stage refinement ensures the production of high-purity iridium, suitable for its various demanding applications.

Applications of Iridium

Iridium, with its remarkable properties, finds application in a wide array of fields, highlighting its importance and versatility. Its high melting point, corrosion resistance, and significant density make it an invaluable material in several high-tech and industrial sectors.

Aerospace and Aviation: Iridium’s high temperature resistance and durability make it ideal for use in aircraft spark plugs and in the aerospace industry for components that must withstand extreme thermal conditions.

Electronics: Due to its excellent electrical conductivity, iridium is used in the manufacturing of electrical contacts and electrodes. Its resistance to arc erosion makes it particularly valuable for critical components in telecommunications and electronic devices.

Medicine: Iridium’s biocompatibility sees its application in medical devices, notably in radiology for targeted radiation therapy. Iridium-192 isotopes are used in brachytherapy, a form of radiotherapy where a radiation source is placed inside or next to the area requiring treatment.

Chemical Industry: Iridium serves as a catalyst in the chemical industry, facilitating the production of crucial compounds and materials. Its use in the catalytic conversion of ammonia to nitric acid is a notable example, highlighting its role in fertilizer production and various organic syntheses.

Jewelry and Watchmaking: The metal’s resistance to tarnishing and wear, combined with its prestigious status, makes it a sought-after material in high-end jewelry and watchmaking, often alloyed with other platinum-group metals to enhance durability and finish.

Iridium stands as a metal of immense value and versatility, finding its place in high-tech industries, electronics, medicine, and luxury goods due to its exceptional properties. Despite its rarity, the strategic application of iridium drives innovations and efficiencies across diverse fields, making it a pivotal element in modern technology and industry.

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