Rhenium (7440-15-5)

1. Rhenium (CAS NO.7440-15-5)  is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. The free element has the third-highest melting point of any element, exceeded only by tungsten and carbon. Rhenium resembles manganese chemically and is obtained as a by-product of molybdenum and copper refinement. Rhenium shows in its compounds a wide variety of oxidation states ranging from −1 to +7.
2.Nickel-based superalloys for the use in jet engines contain up to 6% of rhenium, making jet engine construction the largest use for the element, with chemical industry catalytic uses being next-most important. Because of the low availability relative to demand, rhenium is among the most expensive industrial metals.