Iridium is a rare and intriguing element in the periodic table, identified by the symbol Ir and atomic number 77. This precious metal is one of the densest elements known, surpassed only by osmium. Characterized by its silvery-white appearance, iridium is remarkably resistant to corrosion, even at high temperatures, making it exceptionally durable. This metal is found in the Earth's crust in minute quantities and is often discovered in alloys with other platinum-group metals in alluvial deposits. Its scarcity and the complex process required to isolate it contribute to its high market value and limited industrial availability.
The discovery of iridium can be traced back to 1803 when it was identified by English chemist Smithson Tennant in the residue left when crude platinum was dissolved in aqua regia (a mixture of nitric and hydrochloric acid). The name iridium comes from the Latin word “iris,” meaning rainbow, which refers to the colorful salts it forms. Tennant recognized the unique properties of iridium and its potential, thus marking a significant milestone in the field of chemistry. Over the years, iridium has become crucial in scientific research and technological applications due to its robust physical and chemical properties.
One of the most notable uses of iridium is in the manufacturing of high-performance spark plugs for the automotive industry. The application leverages iridium's high melting point and density, making these spark plugs more efficient and durable than their conventional counterparts. Additionally, iridium is used in the making of crucibles and devices for high-temperature scientific experiments due to its ability to retain its strength and shape under extreme conditions. Another critical application is in the field of medicine, where iridium is used in radiotherapy to treat certain types of cancer, exploiting its radioactive isotopes.
On a larger cosmic scale, iridium has played a fascinating role in geological and extraterrestrial research. A notable increase in the Earth's iridium concentration is often associated with the Cretaceous-Paleogene boundary, around 66 million years ago. This anomaly is linked to the theory that a massive asteroid impact was responsible for the extinction of the dinosaurs, with iridium-rich dust spread across the globe as a result of the impact. This layer of iridium-enriched clay serves as compelling evidence supporting this mass extinction event, highlighting the broader implications of elemental distribution and its effects on Earth's history.