Rhenium is a chemical element. It has the chemical symbol Re. It has the atomic number 75. It is a rare noble metal. It is silver white. In chemistry it is placed in a group of metal elements called the transition metals. The chemistry of rhenium is similar to manganese. Discovered in 1908, rhenium was the second-last stable element to be discovered ('stable' meaning not radioactive). It was named after the river Rhine in Europe.

Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization.

Rhenium found as a by-product of molybdenum refinement.

Rhenium is used in some manganese alloys. Rhenium-molybdenum alloys are superconductors.

Rhenium was discovered by Walter Noddack, Ida Noddack, and Otto Berg in Germany. In 1925, they reported that they detected the element in a platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite.^[1] In 1928, they were able to remove 1 g of the element from 660 kg of molybdenite.^[1]

Rhenium is a silvery-white metal. It has the third highest melting points of all elements. It is also the third densest element.^[2]

Rhenium has one stable isotope which is rhenium-185. Rhenium that is found in nature is made up of 37.4% rhenium-185 and 62.6% rhenium-187.^[3][4] Rhenium has 33 known radioisotopes. They range from rhenium-160 to rhenium-194. The longest-lived radioisotope of rhenium is rhenium-183 which have a half-life of 70 days.^[5]

Rhenium is one of the rarest elements in Earth's crust.^[6] It the 77th most abundant element in the Earth's crust.^[7] Rhenium may not be found free in nature.^[6] It is found in small amounts in the mineral molybdenite.^[8]

Commercial rhenium is gotten from molybdenum roaster-flue gas. Some molybdenum ores contain 0.001% to 0.2% rhenium.^[6][8] Rhenium metal is made by reducing ammonium perrhenate with hydrogen at high temperatures.^[9]

Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. Rhenium is used in superalloys, such as CMSX-4 (2nd generation) and CMSX-10 (3rd generation). These superalloys are used in industrial gas turbine engines like the GE 7FA.^[10] Rhenium filaments are used in mass spectrometers, ion gauges and photoflash lamps in photography.^[11][12] Rhenium-platinum alloys are used as a catalyst for catalytic reforming.^[13] Rhenium-188 and Rhenium-186 are used to treat of liver cancer.^[14]