Rhenium, a silver-white metal, has the third-highest melting point of any element after tungsten and carbon, and the highest boiling point. Its density ranks fourth in the element, the first three are osmium, iridium and platinum. Rhenium has hexagonal crystal structure with lattice constants a=276.1 PM and c=445.6 PM.
Commercial rhenium is generally in powder form and can be made into a high-density solid by pressing or sintering in vacuum or hydrogen, with a density of more than 90 per cent of the metal state. Rhenium metals are malleable in annealing and can be bent and rolled up. Rhenium - molybdenum alloys are superconductors at 10K, and tungsten-rhenium alloys have superconducting temperatures between 4 and 8 K. Rhenium metal becomes a superconductor at 1.697 ± 0.006k.
Rhenium metal block can resist alkali, sulfuric acid, hydrochloric acid, dilute nitric acid (non-concentrated nitric acid) and aqua regia at standard temperature and pressure.
Rhenium has only one stable isotope, rhenium 185, and its stock is very low. Naturally occurring rhenium contains 37.4 percent 185Re and 62.6 percent radioactive 187Re. The latter has a half-life of 1,010 years. The charge state of rhenium atom can affect this lifetime. Re disintegration can be used in rhenium osmium dating method to measure ore age. This kind of disintegration energy is 2.6keV, is one of the lowest radioactive nuclides. Rhenium -186m is one of the most long-lived isomers, with a half-life of about 200,000 years. There are 25 other known radioactive rhenium isotopes.
Rhenium can have an oxidation state between −3 and +7 in compounds, except −2. The most common oxidation states are +7, +6, +4, and +2. Commercial rhenium is generally sold as a perrhenate, such as white water-soluble sodium perrhenate and ammonium perrhenate.
