|Name, symbol||Niobium, Nb|
Silvery gray metallic|
|Niobium in the periodic table|
|Standard atomic weight (Ar)||92.90637(2)|
|Group, block||5; d-block|
|Electron configuration||[Kr] 4d4 5s1|
|2, 8, 18, 12, 1|
|Melting point||2750 K (2477 °C, 4491 °F)|
|Boiling point||5017 K (4744 °C, 8571 °F)|
|Density near r.t.||8.57 g/cm3|
|Heat of fusion||30 kJ/mol|
|Heat of||689.9 kJ/mol|
|Molar heat capacity||24.60 J/(mol·K)|
|Oxidation states||5, 4, 3, 2, 1, −1, −3 (a mildly acidic oxide)|
|Electronegativity||Pauling scale: 1.6|
1st: 652.1 kJ/mol |
2nd: 1380 kJ/mol
3rd: 2416 kJ/mol
|Atomic radius||empirical: 146 pm|
|Covalent radius||164±6 pm|
|Crystal structure||body-centered cubic (bcc)|
|Speed of sound thin rod||3480 m/s (at 20 °C)|
|Thermal expansion||7.3 µm/(m·K)|
|Thermal conductivity||53.7 W/(m·K)|
|Electrical resistivity||152 Ω·m|
|Young's modulus||105 GPa|
|Shear modulus||38 GPa|
|Bulk modulus||170 GPa|
|Vickers hardness||870–1320 MPa|
|Brinell hardness||735–2450 MPa|
|CAS Registry Number||7440-03-1|
|Naming||after Niobe in Greek mythology, daughter of Tantalus|
|Discovery||Charles Hatchett (1801)|
|First isolation||Christian Wilhelm Blomstrand (1864)|
Niobium is a chemical element with symbol Nb and atomic number 41. It was formerly known as columbium (Cb), before its name was changed in 1949.
Niobium is highly resistant to corrosion. At room temperature is only attacked by hydrofluoric acid, but hot minerals acids will corrode it. It also reacts with fluorine at room temperature. At higher temperatures it reacts with chlorine and hydrogen, at 200 °C, while at 400 °C niobium reacts with nitrogen. Niobium is resistant to fused alkalis.
Niobium is a lustrous, grey, ductile, transition metal when pure, but becomes brittle if impurities are present. In the presence of air, the surface of the metal develops a protective oxide coating, giving the metal a blueish color.
Niobium becomes a superconductor at cryogenic temperatures, and has the highest critical temperature of the elemental superconductors, 9.2 K. The superconductive properties are strongly dependent on the purity of the niobium metal. It is also one of the three elemental Type II superconductors, along with vanadium and technetium. Niobium has the largest magnetic penetration depth of any element.
Niobium is sold by various chemical suppliers and other metal companies.
Niobium can be obtained by reducing niobium pentoxide with a reducing agent, such as carbon, hydrogen. Another way involves the aluminothermic reaction a mixture of niobium pentoxide, iron(III) oxide and aluminium:
- 3 Nb2O5 + Fe2O3 + 12 Al → 6 Nb + 2 Fe + 6 Al2O3
Oxidizers like sodium nitrate can be added to speed up the reaction. The resulting ferroniobium can be further purified.
- Make lithium niobate
- Make superalloys
Niobium has no known biological role, however elemental niobium on a larger scale is physiologically inert (and thus hypoallergenic) and harmless, being used in jewelry and in some medical implants. Niobium dust is an eye and skin irritant and a potential fire hazard.
Niobium halides hydrolyze in the presence of moisture and thus will cause burns to the skin.
Niobium can be stored in any container.
Niobium doesn't require special disposal. Its compounds can be converted to niobium oxide, which is harmless.