Rhenium, element symbol: Re, atomic number 75, is a metal of the VIIB group. Rhenium has a density of 21.04g/cm³ and a melting and boiling point of 3186°C (5767°F, 3459K) and 5596°C(10105°F, 5869K), respectively. Rhenium is a silver-white rare high-melting metal, its melting point ranks third among all elements (the first two are tungsten, carbon), the boiling point ranks first, and the density ranks fourth (the first three are platinum, iridium and osmium). Metal rhenium is hard, wear-resistant and corrosion-resistant. Rhenium is stable in air and is synthesized by steam with sulfur at high temperatures to form halides with fluorine, chlorine and bromine. Rhenium is insoluble in hydrochloric acid, but soluble in nitric acid and hot concentrated sulfuric acid. Rhenium does not interact with hydrogen and nitrogen, but can absorb hydrogen. Rhenium is a rare element found in 10^(-7)% of the Earth’s crust, mainly in molybdenite. Today, rhenium and its alloys are widely used in aerospace, electronics, petrochemical and other fields.