niobium, element symbol: Nb, atomic number 41, is a VB group metal. Niobium has a density of 8.57g/cm³, a melting point of 2477°C, and a boiling point of 4744°C. Niobium is a silver-gray, soft and ductile rare high melting point metal. At room temperature, niobium does not react with air and will not be completely oxidized when red hot in oxygen. Niobium can combine directly with sulfur, nitrogen and carbon at high temperature. Niobium 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 crust is 20 ppm, and the distribution of niobium resources is relatively concentrated. Because niobium has good superconductivity, high melting point, corrosion resistance, wear resistance and other characteristics, it is widely used in steel, superconducting materials, aerospace, atomic energy and other fields.