It is a hard, silvery-grey metal which resists corrosion but tarnishes in moist air. It has a very high melting point of 3185°C, with only the elements Tungsten and Carbon exceeding it. This makes this material well suited for applications that demand resistance to high temperatures.
The fourth densest element in the periodic table, Rhenium is a largely stable metal; it does not easily react with Oxygen or other substances, with the exception of strong acids such as sulphuric and nitric acids. It does not occur in a free state in nature or as a compound in a distinct mineral; it is instead widely distributed in trace amounts in other minerals. As one of the rarest elements on the earth’s crust, the material is also expensive.
The most significant use of this material is as an additive to a variety of superalloys, lending them useful properties. Tungsten and Molybdenum alloys with Rhenium are used for x-ray machines and oven filaments. Nickel-based alloys that contain Rhenium are used to make single crystal turbine blades for high-pressure aero (such as fighter jet) and industrial gas turbine engines. Nearly 80 percent of the world’s approximately 50-55 million ton annual consumption of Rhenium is directed to such complex Nickel alloys. These alloys operate at extremely high temperatures, paving the way for more efficient fuel combustion and reduced emission of nitrous oxides. Since Rhenium and its alloys are an ideal metal for use at very high temperatures, they are suitable for rockets motors.
A second, significant application is in bi-metallic reforming catalysts: Platinum-Rhenium catalysts are used in the production of lead-free, high-octane gasoline. Such catalysts resist poisoning (deactivation) and can be used for the hydrogenation of fine chemicals. Nearly 15 million tonnes of Rhenium is used for such catalysts each year, of which 80 percent of the material remains in a closed recycle loop. This means that the consumption of virgin metal is relatively small.
Since it has good wear resistance and can withstand arc corrosion, it is used as an electrical contact material and in instrument-bearing points. Thermocouples made of Rhenium compounds are used for measuring temperatures up to 2200˚C, and Rhenium-Tungsten alloy wire is used in photographic flash lamps as a bulb filament.
Forms of the metal include foil, lump, rod, wire and powder, all of which are crucial for alloying and evaporation source material purposes. Thin Rhenium sheets and plates are used as electrode materials in high-temperature and harsh conditions, in the production of electronic components and ultra-high temperature heater tubes with metal evaporation in the electronics and semiconductor industries. Compared with other materials, Rhenium-based heating offers better electrical performance and longer life expectancy, making the material resistant to a harsh working atmosphere and favored by users. True to metal foils, Rhenium foil is used for chemical vapour phase deposition (CVD) coating and film and physical vapour deposition (PVD) processes.
This material has a natural concentration in the earth’s crust of roughly 1 part per billion. It is therefore extracted from a host ore – molybdenite – and porphyry Copper deposits. Molybdenite ores are the primary source of Rhenium as, typically, molybdenite created as a byproduct of mining porphyry Copper deposits contains about 100 to 3,000 parts per million of Rhenium. The material’s main recovery occurs where Copper is mined along the Pacific.
This metal can be further processed into various shapes, including lumps, foils, powders, rods, single crystals, sputtering targets and wire.