Terbium

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Terbium is a chemical element with the symbol Tb and atomic number 65. Terbium is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. It is reasonably stable in air, and two crystal allotropes exist, with a transformation temperature of 1289 °C. Terbium(III) cation is brilliantly fluorescent, in a beautiful bright lemon-yellow color that is the result of a strong green emission line in combination with other lines in the orange and red. The yttrofluorite variety of the mineral fluorite owes its creamy-yellow fluorescence in part to terbium.

 

Physical properties
Phase solid
Density (near r.t.) 8.23 g·cm−3
Liquid density at m.p. 7.65 g·cm−3
Melting point 1629K
(1356°C, 2473°F)
Boiling point 3503K
(3230°C, 5846°F)
Heat of fusion 10.15 kJ·mol-1
Heat of vaporization 293 kJ·mol-1
Heat capacity (25°C) 28.91 J·mol-1·K-1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1789 1979 (2201) (2505) (2913) (3491)
Atomic properties
Crystal structure hexagonal
Oxidation states 3, 4
(weakly basic oxide)
Electronegativity  ? 1.2 (Pauling scale)
Ionization energies
(more)
1st: 565.8 kJ·mol-1
2nd: 1110 kJ·mol-1
3rd: 2114 kJ·mol-1
Atomic radius 175 pm
Atomic radius (calc.) 225 pm
Miscellaneous
Magnetic ordering ferromagnetic
in dry ice
Electrical resistivity (r.t.) (α, poly)
1.150 µΩ·m
Thermal conductivity (300K) 11.1 W·m-1·K-1
Thermal expansion (r.t.) (α, poly)
10.3 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2620 m/s
Young's modulus (α form) 55.7 GPa
Shear modulus (α form) 22.1 GPa
Bulk modulus (α form) 38.7 GPa
Poisson ratio (α form) 0.261
Vickers hardness 863 MPa
Brinell hardness 677 MPa
CAS registry number 7440-27-9

 

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