Iridium

Iridium was discovered in 1803 by the British chemist Smithson Tennant. While analyzing a sample of platinum ore from the Río de la Plata in South America, Tennant encountered a series of dark, insoluble residues which he believed contained a new element. Through his careful experimentation, he was able to isolate iridium by dissolving the platinum in aqua regia (a mixture of nitric and hydrochloric acids) and then precipitating the iridium compound with potassium chloride. The name 'iridium' is derived from the Greek word 'iris,' meaning rainbow, reflecting the colorful compounds that iridium forms. Since its discovery, iridium has piqued the interest of scientists and industry alike due to its unique properties and rarity. Over the decades, iridium's availability was primarily sourced from platinum mining, often found in ores containing platinum and other metals.

Iridium is one of the rarest elements in the Earth's crust, occurring at an average concentration of about 0.001 parts per million (ppm). It is predominantly found in platinum ores, often occurring alongside metals such as platinum, palladium, and osmium. Due to its high density and significant resistance to erosion, iridium tends to aggregate in heavy mineral deposits. A notable natural source of iridium is the meteorite impact layers, where its presence can be observed, serving as a marker for significant geological events, such as the extinction of the dinosaurs around 66 million years ago. Additionally, this element can also be found in tiny amounts in seawater and in widely dispersed minerals across the Earth’s crust.

Iridium does not play any known role in biological systems; it is considered to be non-essential for any living organisms. While it shows low toxicity in human systems, the effects of exposure to iridium compounds can lead to harmful health consequences if ingested or inhaled. Moreover, research into the potential applications of iridium in biotechnology and as a catalyst in chemical reactions is ongoing, but no biological necessity has been established.

Iridium is characterized by its exceptional properties, including a melting point of 2,446 degrees Celsius and a boiling point of 4,428 degrees Celsius, making it one of the highest melting and boiling metals. It has a density of about 22.56 grams per cubic centimeter, ranking it amongst the densest elements. One of iridium's most remarkable features is its resistance to corrosion and tarnishing, which allows it to maintain its luster even in harsh environments. Chemically, iridium can form compounds with a variety of oxidation states, typically ranging from -1 to +6, although +4 and +3 are the most stable. Iridium can react with halogens and certain acids to form complex halides and oxides, which are studied in various chemical and industrial applications.

Iridium has a variety of important applications due to its unique properties. It is predominantly used in the manufacturing of spark plugs, especially in high-performance engines, because it can withstand extreme conditions and wear. Additionally, iridium is utilized in the production of electrical contacts and connectors, where reliability against corrosion is crucial. It is also employed in the medical field, particularly in cancer treatment, where iridium-192, a radioisotope, is used in brachytherapy. Furthermore, iridium is being explored for use as a catalyst in various chemical reactions, particularly in the production of fuels and hydrogenation processes. Its rarity and valuable properties make iridium highly sought after in scientific research and industry.

• Iridium is one of the heaviest non-radioactive elements and is about twice as dense as lead.
• Less than 5 tons of iridium are mined each year, making it extremely scarce.
• Iridium’s involvement in meteor impacts is significant; it is often found in the clay layer that marks the boundary associated with the mass extinction of the dinosaurs.
• The metal is so resistant to corrosion that a sample can be submerged in aqua regia without dissolving.