Symbol: Nb
Atomic Number: 41
Atomic Weight: 92.90638
Element Classification: Transition Metal
Discovered By: Charles Hatchet
Discovery Date: 1801 (England)
Name Origin: Niobe; daughter of the mythical Greek king Tantalus.

Density (g/cc): 8.57
Melting Point (K): 2741
Boiling Point (K): 5015
Appearance: Shiny white, soft, ductile metal
Atomic Radius (pm): 146
Atomic Volume (cc/mol): 10.8
Covalent Radius (pm): 134
Ionic Radius: 69 (+5e)
Specific Heat (@20C J/g mol): 0.268
Fusion Heat (kJ/mol): 26.8
Evaporation Heat (kJ/mol): 680
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): 275.00
Pauling Negativity Number: 1.6
First Ionizing Energy (kJ/mol): 663.6
Oxidation States: 5, 3
Electronic Configuration: [Kr] 4d4 5s1
Lattice Structure: Body-Centered Cubic (BCC)
Lattice Constant (): 3.300
Lattice C/A Ratio: n/a

Mineral hardness [no units]: 6.0
Brinell hardness [/MN m-2]: 736
Vickers hardness [/MN m-2]: 1320

Note: Pure niobium (columbium) is soft and ductile and difficult to prepare while its alloys are harder and simpler to prepare. Grinding and polishing rates have been reported to vary with crystallographic orientation. Some alloys can be cold worked easily, although they do not work harden appreciably, so it may be difficult to get completely deformation-free microstructures. Attack-polishing additions can be made to the final polishing abrasive slurry, or vibratory polishing may be employed.

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