Rhenium is a silvery white metal that has the third-highest melting point of all elements after Tungsten and Carbon, and the highest boiling point. It is the fourth most dense element, after Osmium, Iridium and Platinum, mainly used in the manufacture of high temperature alloys and catalysts. Like Tantalum and Tungsten, Rhenium, has high melting point and low vapor pressure, so it can be used to make heating element of MOCVD equipment, also can be used to make filaments under oxygen environment, mass spectrometer, ionization pressure gauge and photographic flash lamp, etc.