Tantalum is a metal element with a symbol of Ta, an atomic number of 73, a density of 16.68 g/cm3, and a melting point of 2980°C. It is the third most refractory metal after tungsten and niobium. The pure tantalum has a blue color and excellent ductility. It can be rolled into a very thin (less than 0.01 mm) plate without cold annealing in the cold state. The anti-corrosion ability of tantalum is the same as that of glass. At medium temperature (about 150 ° C), only fluorine, hydrofluoric acid, sulfur trioxide (including fuming sulfuric acid), strong alkali and some molten salts have an effect on tantalum. The metal tantalum is stable in air at normal temperature, and heating to above 500°C accelerates oxidation to form Ta205. Tantalum has a series of excellent properties such as high melting point, low vapor pressure, good cold workability, high chemical stability, strong resistance to liquid metal corrosion, and large dielectric constant of surface oxide film. It is used not only in electronics, metallurgy, steel, chemicals, and hard alloys, but also in high-tech fields such as atomic energy, superconducting technology, automotive electronics, aerospace, medical and scientific researchs. 

Niobium, element symbol: Nb, atomic number 41, is a VB group metal. Niobium has a density of 8.57 g/cm3, a melting point of 2477°C, and a boiling point of 4744°C. Niobium is a silver-gray, soft, and ductile, high-melting point metal. At normal temperature, niobium does not react with air and is not completely oxidized when it is red in oxygen. Niobium can directly combine with sulfur, nitrogen and carbon at high temperatures. It does not react with inorganic acids or bases, and is insoluble in aqua regia, but soluble in hydrofluoric acid. The content of niobium in the earth's crust is 20 ppm, and the distribution of niobium resources is relatively concentrated. Because of its good superconductivity, high melting point, corrosion resistance and wear resistance, it is widely used in steel, superconducting materials, aerospace, atomic energy and other fields.