Molybdenum is a chemical element with the symbol Mo and atomic number 42.Molybdenum does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. The free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element.
Phase at STP：solid
Melting point：2896 K (2623 °C, 4753 °F)
Boiling point：4912 K (4639 °C, 8382 °F)
Density (near r.t.)：10.28 g/cm3
when liquid (at m.p.)：9.33 g/cm3
Heat of fusion：37.48 kJ/mol
Heat of vaporization：598 kJ/mol
Molar heat capacity：24.06 J/(mol·K)
Molybdenum is mainly used in the steel industry.The 0.3% molybdenum additive can improve the strength and corrosion resistance of cast iron of several steel types.Rust-resistant and acid-resistant molybdenum steel alloys contain between 0.4 and 3.5% molybdenum.Surface treatment can improve the mechanical strength of molybdenum-containing steel.Some fast steels also have as much as 14.5% molybdenum.Molybdenum replaces nickel in some steels.In this case, cr-mo steel is obtained instead of cr-ni steel.At present, molybdenum is also used in the production of heat-resistant super alloys.