Iridium (Ir, atomic number 77) is one of the rarest elements in the Earth’s crust and a member of the platinum group metals. It possesses a unique combination of extreme properties, making it indispensable for high-technology applications. Iridium has the highest melting point of any element, approximately 2,446 degrees Celsius. It also exhibits extraordinary resistance to chemical corrosion, remaining stable even when exposed to molten salts and highly aggressive acids at elevated temperatures. These unparalleled physical and chemical attributes dictate its specialized use across various industries.
Applications Requiring Extreme Heat and Corrosion Resistance
The exceptional thermal stability of Iridium makes it a preferred material for containing molten substances in high-temperature manufacturing. High-purity Iridium crucibles are used extensively in the production of synthetic single crystals for the electronics and optics industries. These vessels are essential for processes like Czochralski growth, synthesizing materials such as sapphire and gallium nitride. The Iridium container ensures the crystal melt remains uncontaminated and the crucible does not degrade under intense heat.
Iridium’s durability and resistance to wear are highly valued in the aerospace and automotive sectors. It is alloyed with other metals to create components that must withstand extreme thermal and mechanical stress, such as long-life parts in aircraft turbine engines. In high-performance engines, Iridium is used to form the electrical contacts in spark plugs. Iridium spark plugs resist arc erosion and ensure consistent, efficient ignition within the corrosive combustion chamber.
Essential Roles in Specialized Electronics
Iridium’s stability and conductivity are harnessed in precision electronic components operating in challenging environments. Iridium-coated electrodes are used in electrochemical processes, such as the chloralkali process. Here, the metal’s corrosion resistance prevents degradation from the aggressive chemical environment, ensuring the long-term reliability required for large-scale industrial operations.
The element is also fundamental to modern display technology, specifically in the manufacturing of high-efficiency Organic Light-Emitting Diodes (OLEDs). Iridium complexes are incorporated as phosphorescent emitter materials in devices known as PHOLEDs. Utilizing Iridium’s heavy-metal properties, these complexes enable the device to convert electrical energy into light with nearly 100% internal quantum efficiency. This efficiency is achieved by harvesting energy states that would typically be unused for light emission. Manufacturers can tune the chemical structure of the Iridium complex to precisely control the color of the emitted light, leading to vibrant, energy-efficient displays.
Catalyst and Chemical Processing Functions
Iridium compounds serve an important function as catalysts, accelerating chemical reactions without being permanently consumed. In large-scale chemical manufacturing, an iridium-iodide catalyst system is the foundation of the Cativa process, the dominant method for producing acetic acid. Acetic acid is a widely used industrial chemical in the production of plastics and adhesives.
This iridium-based system is superior to older catalyst technologies because it allows the reaction to proceed efficiently with very low water concentrations. Operating under these conditions reduces energy requirements and minimizes the formation of undesirable byproducts. Iridium is also investigated as an electrocatalyst in emerging clean energy technologies. Its compounds show promise in water electrolysis, specifically for the oxygen evolution reaction that is necessary to generate hydrogen fuel. This application leverages Iridium’s unique electronic structure to facilitate the complex chemical transformation required for efficient hydrogen production.
Scientific and Medical Instrumentation
Iridium alloys are used in highly specialized scientific research equipment that must withstand extreme compression. Due to its high density and mechanical strength, Iridium is used in components of high-pressure laboratory apparatus, such as diamond anvil cells, which study materials under extreme pressures.
In medicine, the radioisotope Iridium-192 (\(^{192}\)Ir) is a powerful tool in cancer treatment via brachytherapy. This technique involves placing a sealed radioactive source directly inside or next to the area requiring treatment, allowing for highly targeted radiation delivery. Iridium-192 emits gamma radiation to destroy cancerous cells while minimizing exposure to surrounding healthy tissue.
With a half-life of approximately 73.8 days, Iridium-192 is the most common isotope used in high-dose-rate brachytherapy. Beyond medicine, this same isotope is used in industrial radiography, a non-destructive testing method. The gamma rays from Iridium-192 are used to inspect the integrity of metal castings and critical welds in pipelines and pressure vessels.