Niobium is a gray white metal with a melting point of 2468 ℃, a boiling point of 4742 ℃, and a density of 8.57g/cm3. Niobium is a gray metal with luster, which has paramagnetism and belongs to 5 groups of periodic table. The ductility of high purity niobium metal is higher, but it will harden with the increase of impurity content. Its outermost electron layer arrangement is very different from other five family elements. The same phenomenon occurs in the elements of ruthenium (44), rhodium (45) and palladium (46) before and after.
Niobium shows superconductivity at low temperature. At standard atmospheric pressure, its critical temperature is 9.2k, which is the highest of all single superconductors. Its magnetic penetration depth is also the highest of all elements.  Niobium is one of the three type II superconductors, the other two are vanadium and technetium. The purity of niobium metal will greatly affect its superconductivity.
Niobium has a very low capture cross section for thermal neutrons, so it is quite useful in the nuclear industry.
chemical property
Niobium is stable in air at room temperature and not completely oxidized when it is red hot in oxygen. At high temperature, niobium is directly combined with sulfur, nitrogen and carbon to form alloy with titanium, zirconium, hafnium and tungsten. It does not react with inorganic acid or alkali, nor dissolve in aqua regia, but soluble in hydrofluoric acid. The oxidation states of niobium are - 1, + 2, + 3, + 4 and + 5, of which + 5 is the most stable.
Niobium metal is extremely stable in air at room temperature and does not interact with air. Although it has a high melting point (2468 ° C) in the simple state, its density is lower than that of other refractory metals. Niobium can resist all kinds of erosion and form dielectric oxide layer.
The electronegativity of niobium is lower than that of zirconium on the left. Its atomic size is almost the same as that of tantalum, which is caused by the lanthanide contraction effect. This makes the chemical properties of niobium very similar to that of tantalum. Although its corrosion resistance is not as high as tantalum, but it is cheaper and more common, so it is often used to replace tantalum in the case of low requirements, such as for chemical tank coating materials in chemical plants.