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Niobium and its alloys are remarkably resistant to corrosion by certain
liquid metals, notably lithium metal and sodium-potassium alloys,
and to high temperatures (900 oC
to 1010
oC).
This resistance is coupled with a low-capture cross section for
thermal neutrons renders niobium materials most attractive for
reactor applications.
Typical Analysis in PPM:
Fe
<20
Ni
<20
Cr
<20
Cu
<10
Si
<20
Ti
<10
Mo
<20
W
<200
Ta
<200
Al
<20
Zr
<10
Hf
<20
Typical
Physical Properties:
Atomic Number: 41
Atomic Weight : 92.91
Atomic Volume : 10.83 cm3/g-atom
Lattice Type: Body centered cubic
Lattice Constant (Angstroms) : 3.30
Covalent Radius (Angstroms) : 1.34
Thermal Neutron Absorption Cross
Section (Barns/Atom) :
1.1
Density (20 oC, g/cm3): 8.57
Melting Point: 2468 oC
Boiling Point : 4927 oC
Thermal Conductivity:
0 oC J (sec cm oC): 0.523
1600 oC J (sec cm oC): 0.691
Coefficient of Thermal Expansion at 20
oC (x 10-6/oC): 7.1
Temperature Coefficient (x 10-3/oC) : 3.95
Specific Heat:
15 oC (J/g): 0.268
1227 oC (J/g): 0.320
Heat Capacity (J/mol oC):
0 oC:
24.9
1200 oC: 29.7
2700 oC: 33.5
Electronegativity (Pauling’s): 1.6
Electrical Resistivity
(Microhm) : 15
Volume Electrical Conductivity
(%IACS*) : 13.3
*International Annealed Copper
Standard
Typical Mechanical Properties:
Modulus of Elasticity (x 10-6
kg/cm2): 1.05
Poisson’s Ratio : 0.38
Hardness
(VHN) : 60-100
Resistance to Thermal Shock: Good
Workability (Ductile to Brittle
Transition) : -150 oC
Recrystallization Temperature: 900-1300 oC
Stress Relieving Temperature : 800 oC
Chemical Properties:
Niobium is moderately to highly
resistant to corrosion in most aqueous mediums that are usually
considered highly corrosive, such as dilute mineral acids, organic
acids, and organic liquids. Notable exceptions are dilute strong
alkalies, hot concentrated mineral acids, and hydrofluoric acid, all
of which attack the metal rapidly. Gaseous atmospheres at high
temperatures attack niobium rapidly, primarily by oxidation,
although oxygen contents may be very low.
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