Rhenium (Re) is a scattered rare metal, atomic number - 75, atomic
mass - 186.31, density - 21.0 g / cm3, melting point - 3180 ± 20ОС,
coefficient of linear expansion - 12.45.10-5, electrical resistivity Ohm
Rhenium is a refractory heavy metal similar in appearance to steel. Unlike tungsten, rhenium is ductile in the cast and recrystallized state and can be deformed at room temperature. Rhenium has a very high modulus of elasticity. After a small degree of reduction, its hardness increases significantly (from work hardening), but after annealing in a protective medium - hydrogen or vacuum, it again acquires plasticity.
Rhenium is chemically stable in air at 20 ° C. The compact metal begins to oxidize with the formation of rhenium hetoxide when heated above 300 ° C and the process proceeds intensively at a temperature above 600 ° C. Fine powders of rhenium are humidified in air, which is explained by partial oxidation with the formation of rhenium hemioxide, which absorbs moisture. Rhenium does not react with hydrogen up to the melting point. Rhenium is significantly more chemically stable than tungsten, in an argon atmosphere or in a vacuum, in the presence of traces of moisture, at high temperatures. Rhenium does not react with nitrogen, although rhenium nitrides are known, which are formed not by the direct action of nitrogen on the metal, but by the reaction between rhenium chloride and ammonia. Rhenium does not form carbides, which distinguishes it from other refractory metals. Rhenium reacts with fluorine and chlorine when heated, with bromine and iodine, practically does not interact.
Despite the fact that rhenium began to be used in industry relatively recently (after 1950), at present its importance in modern technology is great and is constantly increasing.
The main fields of application of rhenium are bimetallic catalysts Pt / Re, and are used in the purification of gasoline to obtain light fractions — reforming of oil (90%); production of alloys for various purposes and thin-film coatings.
In addition, rhenium is used in electronics and electrical engineering. In electrovacuum devices, alloys with different contents of rhenium are used: tungsten-rhenium, nickel-rhenium, nickel-rhenium-iron, molybdenum-rhenium and others.
In the electrical industry, rhenium, its alloys and rhenium coatings are used for the manufacture of thermocouples with a measurement range from 0 to 2500 ° C, self-cleaning electrical contacts, and filaments. Rhenium is used in switch devices, where the high stability of the points-supports must be combined with high hardness and the least wear.
Rhenium is used in the rocket and aerospace industries, for the manufacture of combustion chambers, exhaust nozzles of jet engines, and turbine blades. Due to its unique qualities of hardness and high heat resistance of rhenium, it is difficult for these products to be replaced.
Rhenium is a catalyst for many chemical processes — powdered rhenium and some of its compounds serve as catalysts in the oxidation of ammonia and methane, and in the hydrogenation of ethylene.
High prices for rhenium somewhat limit its use.