- Rhenium (Re) is a rare transition metal with atomic number 75, belonging to Group 7 of the periodic table, situated below manganese and technetium.
- Its electron configuration is [Xe] 4f¹⁴ 5d⁵ 6s², reflecting its placement among the heavy d-block metals. A rhenium atom contains seventy-five protons, seventy-five electrons, and typically one hundred and eleven to one hundred and fourteen neutrons in its stable isotopes.
- Naturally occurring rhenium consists primarily of rhenium-185 (¹⁸⁵Re, about 37%) and rhenium-187 (¹⁸⁷Re, about 63%), the latter being slightly radioactive with an extraordinarily long half-life of about 4.3 × 10¹⁰ years.
- Rhenium was one of the last naturally occurring stable elements to be discovered. In 1925, German chemists Ida Noddack, Walter Noddack, and Otto Berg identified it while analyzing platinum ores and columbite. They named it after the Latin word Rhenus, meaning the Rhine River in Germany. Its discovery confirmed the existence of an element predicted by Mendeleev’s periodic table and filled a gap between tungsten and osmium.
- Physically, rhenium is a silvery-white, heavy, and lustrous metal with remarkable properties. It has a high density of 21.02 g/cm³, making it one of the densest elements, surpassed only by osmium, iridium, and platinum. It has one of the highest melting points of all metals at 3,186 °C (5,767 °F) and an extremely high boiling point of 5,597 °C (10,107 °F). Rhenium is also highly ductile, resistant to corrosion, and stable under extreme heat.
- Chemically, rhenium exhibits a wide range of oxidation states, from –1 to +7, with +4, +6, and +7 being the most common. It forms compounds such as rhenium heptoxide (Re₂O₇), used as a catalyst, and perrhenic acid (HReO₄). Its high oxidation state chemistry is similar to that of manganese and technetium. Importantly, rhenium has exceptional resistance to wear, oxidation, and creep (deformation under stress at high temperature), making it indispensable in specialized industrial processes.
- Rhenium is most famously used in superalloys for jet engines and gas turbines, where it significantly improves strength, performance, and temperature resistance. Alloys containing rhenium can withstand the extreme conditions of aerospace propulsion systems. It is also employed in catalytic processes, such as platinum–rhenium catalysts for petroleum refining, which are vital for producing high-octane fuels. Other applications include electrical contacts, filaments, thermocouples, and medical isotopes—particularly rhenium-186 and rhenium-188, which are used in cancer therapy.
- Biologically, rhenium has no known role in living systems. It is considered relatively non-toxic in metallic form, but soluble rhenium compounds should be handled with care due to potential irritation effects.
- Environmentally, rhenium is one of the rarest elements in Earth’s crust, with an abundance of only about 1 part per billion. It does not form its own major ores but is typically obtained as a by-product of molybdenum refining from copper-molybdenum deposits. Because of its scarcity and importance in aerospace and energy industries, rhenium is considered a strategic and critical metal. Recycling from used catalysts and alloys is becoming increasingly important to ensure supply.
