Properties and Overview of Iridium

Overview:

Iridium (Ir) is a transition metal with the chemical symbol Ir and atomic number 77. It is part of the platinum group metals (PGMs) and is known for its remarkable physical and chemical properties. Discovered in 1803 by the English chemist Smithson Tennant in the residues of platinum ore, iridium was named after the Greek word "iris," meaning rainbow, due to the colorful nature of its salts. Physically, iridium is a dense, silvery-white metal with a very high melting point of 2,446°C and a boiling point of approximately 4,428°C. Its density is about 22.56g/cm³, making it the second densest element known, slightly less dense than osmium. Iridium is extremely hard and brittle, making it challenging to work with in its pure form. It is also one of the most corrosion-resistant metals, remaining unaffected by air, water, acids, and even molten metals, contributing to its durability and longevity in various applications.
Chemically, iridium is notable for its resistance to oxidation and corrosion, even at high temperatures. It typically exhibits oxidation states ranging from +1 to +6, with +3 and +4 being the most common in its compounds. Iridium forms various complex compounds, including halides, oxides, and organometallic complexes. It is less reactive than most other metals, which is why it is often found in nature in uncombined form or as an alloy with platinum or osmium. Iridium compounds, such as iridium(IV) oxide (IrO₂) and iridium chloride (IrCl₃), are used in specialized industrial processes and catalysis.
From a safety perspective, iridium metal is generally considered safe to handle, as it is not toxic and does not pose significant health risks in its solid form. However, fine iridium dust or powder can be hazardous if inhaled, as it may cause respiratory irritation. Iridium compounds, particularly in soluble forms, can be more toxic and should be handled carefully, as they can cause skin and eye irritation or be harmful if ingested. Due to its high melting point and chemical resistance, iridium is typically processed and handled using specialized equipment to withstand extreme conditions.

Production:

The production of iridium is relatively limited due to its rarity and the complexity of its extraction. Iridium is typically obtained as a byproduct of platinum and nickel mining, mainly from ores mined in South Africa and Russia, where most of the world's iridium supply is produced. The extraction process involves separating iridium from other platinum group metals using chemical treatments, including dissolution in aqua regia, precipitation, and refining. Due to its scarcity and the challenges associated with its extraction, iridium is one of the most expensive metals.

Applications:

Iridium has a variety of specialized applications, primarily due to its exceptional durability and resistance to corrosion. One of iridium's most notable uses is in producing high-temperature crucibles and devices that must withstand extreme conditions, such as spark plugs, electrical contacts, and electrodes in the chlor-alkali industry. Iridium's high melting point and stability make it an ideal material for these applications.
In catalysis, iridium compounds are used as catalysts in several chemical reactions, including the hydrogenation of alkenes and the production of acetic acid. Iridium catalysts are valued for their efficiency and ability to operate under harsh conditions, contributing to their use in industrial processes and research.
Iridium is also used in the medical industry, particularly in radiation therapy for cancer treatment. Radioactive isotopes of iridium, such as iridium-192, are used in brachytherapy, where the isotope is placed close to or inside the tumor, providing a targeted radiation dose while minimizing exposure to surrounding healthy tissues.
Additionally, iridium's corrosion resistance is key in producing durable and reliable fountain pen nibs, often alloyed with osmium or ruthenium to enhance their wear resistance. Iridium is also used in the aerospace industry for parts that require high durability and resistance to environmental extremes, such as aircraft engine components and space exploration equipment.

Summary:

Iridium is a rare and precious metal known for its exceptional physical properties, including high density, melting point, and corrosion resistance. Its chemical stability and resistance to oxidation make it suitable for various industrial, medical, and technological applications. While it is generally safe to handle in its metallic form, caution is required when dealing with iridium compounds, especially in powdered or soluble forms. The limited production and high demand for iridium contribute to its status as one of the world's most expensive and sought-after metals.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for iridium below: