Handbook Properties and Selection Nonferrous Alloys and Spl Purpose Mtls (1992) WW Part 14 doc

Resistance to specific according agents. Lutetium does not react with cold or hot water, but it reacts vigorously
with dilute acids. Concentrated sulfuric acid slowly attacks lutetium. The presence of the fluoride ion retards acid attack
due to the formation of LuF
3
on the surface of the metal.
Mechanical Properties
Tensile properties. About the same as those of erbium
Hardness. 44 HV
Poisson's ratio. 0.261
Elastic modulus. At 27 °C: tension, 68.6 GPa; shear, 27.2 GPa; bulk, 47.6 GPa
Elastic constants along crystal axes. At 27 °C: c
11
= 86.23 GPa; c
12
= 32.0 GPa; c
13
= 28.0 GPa; c
33
= 80.86 GPa;
c
44
= 26.79 GPa
Liquid surface tension. 0.940 N/m at 1665 °C
Mischmetal (MM)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Mischmetal is used as an alloying additive in ferrous alloys to scavenge sulfur, oxygen, and other substances. Mischmetal
is also added to magnesium-base alloys to improve high-temperature strength and to ductile irons to nodularize graphite.
It is used as a reductant to produce the volatile rare earth metals (samarium, europium, and ytterbium) from their oxides.
Other uses of mischmetal include lighter flints, galvanizing alloys, and mischmetal cobalt (cerium-free mischmetal-nickel
alloys are used as hydrogen storage alloys), and permanent magnets.

Mischmetal oxidizes at room temperature in air. Turnings can be ignited easily and burn white hot. Finely divided
mischmetal should not be handled in air.
Because mischmetal is an indefinite mixture of rare earth metals, the properties of a particular mischmetal depend on its
composition, which in turn depends on the mineral source for the mixture. Listed below are the properties of two of the
most common high-purity mischmetal mixtures. Because most commercial mischmetals contain several atomic percent of
iron and magnesium (about 1 wt%), their properties may differ somewhat from those listed below. Many values are
estimated and are marked as such.
Bastnasite-Derived Mischmetal
Specifications
UNS number. E21000
Chemical Composition
Composition limits. Total mixed rare earths: 99.0 min; mixture consists of 39 La, 38 Ce, 16 Nd, 6 Pr, 1 other rare
earth
Structure
Crystal structure. α phase, double close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.3718 nm, c = 1.1978 nm at 24 °C. β
phase, body-centered cubic
Minimum interatomic distance. At 24 °C: r
a
= 0.1859 nm; r
c
= 0.1842 nm; radius CN
12
= 0.1851
Mass Characteristics

Atomic weight. 140.1
Density. 6.490 g/cm
3
at 24 °C;
Volume change on freezing. 0.1% expansion (estimated)
Thermal Properties
Melting point. Melts over a range of temperatures from 888 to 895 °C
Boiling point. Expected to evaporate incongruently with the initial loss of a major constituent (neodymium) by boiling
at ~3100 °C
Phase transformation temperature. α to β phase, 801 °C
Coefficient of thermal expansion. At 24 °C. Linear: 8.7 μm/m · K. Volumetric: 26 × 10
-6
per K (both estimated)
Specific heat. 0.193 kJ/kg · K at 25 °C
Entropy. 467 J/kg · K at 25 °C (estimated)
Latent heat of fusion. 47 kJ/kg
Latent heat of transformation. 22 kJ/mol (estimated)
Latent heat of combustion. For hexagonal R
2
O
3
at 25 °C:
c
H
∆
o
= -6.4 MJ/kg MM (estimated);
f
G
∆

o
= -6.0 MJ/kg MM
(estimated)
Recrystallization temperature. ~350 °C (estimated)
Thermal conductivity. 13 W/m · K at 25 °C (estimated)
Electrical Properties
Electrical resistivity. Solid: 800 nΩ · m at 25 °C (estimated). Liquid: 1300 nΩ · m at 900 °C (estimated)
Magnetic Properties
Magnetic susceptibility. Volume, 1.6 × 10
-3
mks at 25 °C (estimated)
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. Liquid, 30% (estimated)
Chemical Properties
General corrosion behavior. Commercial mischmetal is stable in air at room temperature due to presence of
magnesium. Vacuum-melted mischmetal oxidizes in air at room temperature. Oxidation rates increase with increasing
temperature and humidity.
Resistance to specific corroding agents. Mischmetal reacts vigorously with dilute acids. The presence of the
fluoride ion retards acid attack by the formation of rare earth fluoride (RF
3
) on the surface of the metal.
Mechanical Properties
Tensile properties. At 24 °C: tensile strength, 138 MPa; yield strength, 48 MPa; elongation, 25%; reduction in area,
50% (all estimated)
Hardness. 27 DPH
Poisson's ratio. 0.27 (estimated)
Elastic modulus. At 27 °C: tension, 35 GPa; shear, 14 GPa; bulk, 25 GPa (all estimated)
Kinematic liquid viscosity. 0.46 mm
2

/s at 900 °C (estimated)
Liquid surface tension. 0.70 N/m at 900 °C (estimated)
Monazite-Derived Mischmetal
Specifications
UNS number. E31000
Chemical Composition
Composition limits. Total mixed rare earths, 99.0 min; mixture consists of 50 Ce, 20 La, 20 Nd, 6 Pr, 2 Gd, 1.6 Y, <1
other rare earths
Structure
Crystal structure. α phase, double close-packed hexagonal, P6
3
/mmc
4
6h
D
; a = 0.3695 nm; c = 1.1900 nm at 24 °C. β
phase, probably body-centered cubic; a = 0.415 nm (estimated)
Minimum interatomic distance. At 24 °C: r
a
= 0.1848 nm; r
c
= 0.1830 nm; radius CN
12
= 0.1839 nm
Mass Characteristics
Atomic weight. 140.1
Density. 6.612 g/cm
3
at 24 °C
Volume change on freezing. 0.1% expansion (estimated)

Thermal Properties
Melting point. Melts over a range of temperatures from 899 to 913 °C
Boiling point. Expected to evaporate incongruently with the initial loss of a major constituent (neodymium) by boiling
at ~3100 °C
Phase transformation temperature. α to β phase, 782 °C
Coefficient of thermal expansion. At 24 °C. Linear: 8.6 μm/m · K. Volumetric: 26 × 10
-6
per K (both estimated)
Specific heat. 0.195 kJ/kg · K at 25 °C (estimated)
Entropy. At 298.15 K, 477 J/kg · K (estimated)
Latent heat of fusion. 46 kJ/kg (estimated)
Latent heat of transformation. 22 kJ/kg (estimated)
Latent heat of combustion. For hexagonal R
2
O
3
at 25 °C:
c
H
∆
o
= -6.4 MJ/kg MM (estimated);
f
G
∆
o
= -6.0 MJ/kg MM
(estimated)
Recrystallization temperature. ~350 °C (estimated)
Thermal conductivity. 13 W/m · K at 25 °C (estimated)

Electrical Properties
Electrical resistivity. Solid, 800 nΩ · m at 25 °C (estimated); liquid, 1300 nΩ · m at 925 °C (estimated)
Magnetic Properties
Magnetic susceptibility. Volume: 5.2 × 10
-3
mks at 25 °C (estimated)
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. Liquid, 30% (estimated)
Chemical Properties
General corrosion behavior. Commercial mischmetal is stable in air at room temperature due to the presence of
magnesium. Vacuum-melted mischmetal oxidizes in air at room temperature. Oxidation rates increase with increasing
temperature and humidity.
Resistance to specific corroding agents. Mischmetal reacts vigorously with dilute acids. The presence of the
fluoride ion retards acid attack by the formation of rare earth fluoride (RF
3
) on the surface of the metal.
Mechanical Properties
Tensile properties. At 24 °C: tensile strength, 138 MPa; yield strength, 48 MPa; elongation, 25%; reduction in area,
50% (all estimated)
Hardness. 28 HV
Poisson's ratio. 0.27 (estimated)
Elastic modulus. At 27 °C: tension, 37 GPa; shear, 15 GPa; bulk, 27 GPa (all estimated)
Kinematic liquid viscosity. 0.47 mm
2
/s at 920 °C (estimated)
Liquid surface tension. 0.71 N/m at 920 °C (estimated)

Neodymium (Nd)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

The major use of neodymium is in high-strength Nd-Fe-B permanent magnets, which are the strongest magnets known.
Neodymium, as a component (~20%) of mischmetal, is used as an alloying additive in ferrous alloys to scavenge sulfur,
oxygen, and other elements, and to strengthen magnesium alloys. It is also used as a laser material and glass-coloring
agent, and in petroleum cracking catalysts, carbon arc lights, lighter flints, and ceramic capacitors.
Neodymium oxidizes at room temperature in air. It should be stored in a vacuum or inert atmosphere; storage in oil is not
recommended. Turnings can be ignited easily and will burn white hot. Finely divided neodymium should not be handled
in air.
Structure
Crystal structure. α phase, double close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.36582 nm, c = 1.17966 nm at 24 °C.
β phase, body-centered cubic, Im3m
9
h
O
; a = 0.413 nm at 883 °C
Minimum interatomic distance. At 24 °C: r
a
= 0.18291 nm; r
c
= 0.18137 nm; radius CN
12
= 0.18214 nm

Mass Characteristics
Atomic weight. 144.24
Density. α phase, 7.008 g/cm
3
at 24 °C; β phase, 6.80 g/cm
3
at 883 °C; liquid, 6.72 g/cm
3
at 1025 °C;
Volume change on freezing. 0.9% contraction
Volume change on phase transformation. α to β phase, 0.1% volume expansion on heating
Thermal Properties
Melting point. 1021 °C
Boiling point. 3074 °C
Phase transformation temperature. α to β phase, 863 °C
Coefficient of thermal expansion. At 24 °C. Linear: 9.6 μm/m · K. Linear along crystal axes: 7.6 μm/m · K along a
axis, 13.5 μm/m · K along c axis. Volumetric: 28.7 × 10
-6
per K
Specific heat. 0.1900 kJ/kg · K at 25 °C
Entropy. At 25 °C: 492.9 J/kg · K
Latent heat of fusion. 49.5 kJ/kg
Latent heat of transformation. 21.0 kJ/kg
Latent heat of vaporization. 2.271 MJ/kg at 25 °C
Thermal conductivity. 16.5 W/m · K at 25 °C
Heat of combustion. Hexagonal Nd
2
O
3
at 25 °C:

c
H
∆
o
= -6.27 MJ/kg Nd;
f
G
∆
o
= -5.96 MJ/kg Nd
Recrystallization temperature. 400 °C
Vapor pressure. 0.001 Pa at 955 °C; 0.101 Pa at 1175 °C; 10.1 Pa at 1500 °C; 1013 Pa at 2029 °C
Electrical Properties
Electrical resistivity. 643 nΩ · m at 25 °C; 68 nΩ · m at 4K. Liquid: 1510 nΩ · m at 1022 °C
Ionization potential. Nd(I), 5.499 eV; Nd(II), 10.73, eV; Nd(III), 22.1 eV; Nd(IV), 40.41 eV
Hall coefficient. +0.0971 nV · m/A · T at 25 °C
Temperature of superconductivity. Bulk neodymium is not superconducting down to 0.25 K atmospheric pressure.
Magnetic Properties
Magnetic susceptibility. Volume: 3.62 × 10
-3
mks at 25 °C; obeys Curie-Weiss law above 35 K with an effective
moment of 3.45 μ
B
, θ
a
= 5 K and θ
c
= 0 K
Saturation magnetization. >35T at 2 K along <11
2

0>
Magnetic transformation temperature. Néel temperatures at 7.5 K (cubic sites) and 19.9 K (hexagonal sites)
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. 39.4% for λ= 645 nm from 1021 to 1567 °C
Nuclear Properties
Thermal neutron cross section. 48 b
Chemical Properties
General corrosion behavior. Neodymium oxidizes in air at room temperature, but at a slower rate than lanthanum or
cerium. Oxidation rates increase with increasing temperature and humidity; interstitial impurities increase the rate of
oxidation. Hydrogen will react with neodymium at room temperature.
Resistance to specific corroding agents. Neodymium reacts vigorously with dilute acids and slowly with
concentrated sulfuric acid. The presence of the fluoride ion retards acid attack due to the formation of NdF
3
on the surface
of the metal.
Mechanical Properties
Tensile properties. Tensile strength, 164 MPa; yield strength, 71 MPa; elongation, 25%; reduction in area, 72%
Hardness. 18 HV
Poisson's ratio. 0.281
Strain-hardening exponent. 0.28
Elastic modulus. At 27 °C: tension, 41.4 GPa; shear, 16.3 GPa; bulk, 31.8 GPa
Elastic constants along crystal axes. At 27 °C: c
11
= 54.77 GPa; c
12
= 24.60 GPa; c
13
= 16.56 GPa; c
33

= 60.80
GPa; c
44
= 15.01 GPa
Liquid surface tension. 0.687 N/m at 1021 °C
Praseodymium (Pr)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Praseodymium, as a component (~5%) of mischmetal, is used as an alloying additive to ferrous alloys to scavenge
impurities such as sulfur and oxygen, and to strengthen magnesium. It is also used as a glass-and ceramic-coloring agent,
and in petroleum cracking-coloring catalysts, carbon arc lights, and PrCo
5
permanent magnets. PrNi
5
is used in adiabatic
demagnetization refrigerators to attain ultralow temperatures (<1 mK).
Praseodymium oxidizes at room temperature in air. It should be stored in vacuum or inert atmosphere; storage in oil is not
recommended. Turnings can be ignited easily and will burn white hot. Finely divided praseodymium should not be
handled in air.
Structure
Crystal structure. α phase, double close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.36721 nm, c = 1.18326 nm at 24 °C.
β phase, body-centered cubic, Im3m
9
h

O
; a = 0.1413 nm at 821 °C
Minimum interatomic distance. At 24 °C: r
a
= 0.18360 nm; r
c
= 0.18197 nm; radius CN
12
= 0.18279 nm
Mass Characteristics
Atomic weight. 140.90765
Density. α phase, 6.773 g/cm
3
at 24 °C; β phase, 6.64 g/cm
3
at 821 °C; liquid, 6.59 g/cm
3
at 935 °C
Volume change on freezing. 0.02% contraction
Volume change on phase transformation. α to β phase, 0.5% volume expansion on heating
Thermal Properties
Melting point. 931 °C
Boiling point. 3520 °C
Phase transformation temperature. α to β phase, 795 °C
Coefficient of thermal expansion. α phase at 24 °C. Linear: 6.7 μm/m · K. Linear along crystal axes: 4.5 μm/m · K
along a axis, 11.2 μm/m · K along c axis. Volumetric: 20.2 × 10
-6
per K
Specific heat. 0.1946 kJ/kg · K at 25 °C
Entropy. At 25 °C, 524.5 J/kg · K

Latent heat of fusion. 48.9 kJ/kg
Latent heat of transformation. 22.5 kJ/kg
Latent heat of vaporization. 2.524 MJ/kg at 25 °C
Heat of combustion. For cubic Pr
6
O
11
at 25 °C:

c
H
∆
o
= -6.73 MJ/kg Pr;
f
G
∆
o
= -6.34 MJ/kg Pr
Recrystallization temperature. About 400 °C
Thermal conductivity. 12.5 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 1083 °C; 0.101 Pa at 1333 °C; 10.1 Pa at 1701 °C; 1013 Pa at 2305 °C
Electrical Properties
Electrical resistivity. 700 nΩ · m at 25 °C; 22 nΩ · m at 4 K. Liquid: 1390 nΩ · m at 932 °C
Ionization potential. Pr(I), 5.422 eV; Pr(II), 10.55 eV; Pr(III), 21.624 eV; Pr(IV), 38.98 eV; Pr(V), 57.45 eV
Hall coefficient. +0.0709 nV · m/A · T at 25 °C
Temperature of superconductivity. Bulk praseodymium is not superconducting down to 0.25 K at atmospheric
pressure.
Magnetic Properties
Magnetic susceptibility. Volume: 3.34 × 10-3 mks at 25 °C; obeys Curie-Weiss law above 100 K with an effective

moment of 3.56 μ
B
and θ 0 K
Saturation magnetization. >35 T at 4 K along <11
2
0>
Magnetic transformation temperature. Single-crystal strain-free praseodymium does not order magnetically; most
polycrystalline samples order at various temperatures below 25 K.
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. 28.4% for λ= 645 nm from 931 to 1537 °C
Nuclear Properties
Thermal neutron cross section. 11 b
Chemical Properties
Corrosion behavior. Praseodymium oxidizes in air at room temperature, but at a lower rate than lanthanum or cerium.
Oxidation rates increase with temperature and humidity. Interstitial impurities in the metal increase the rate of corrosion
in air. Hydrogen will react with praseodymium at room temperature.
Resistance to specify corroding agents. Praseodymium reacts vigorously with dilute acids. It reacts slowly with
concentrated sulfuric acid. The presence of the fluoride ion retards acid attack due to the formation of PrF
3
on the surface
of the metal.
Mechanical Properties
Tensile properties. At 24 °C: tensile strength, 147 MPa; yield strength, 73 MPa; elongation, 15.4%; reduction in area,
67%
Hardness. 20 HV
Poisson's ratio. 0.281
Elastic modulus. At 27 °C: tension, 37.3 GPa; shear, 14.8 GPa; bulk, 28.8 GPa
Elastic constants along crystal axes. At 27 °C: c
11

= 49.35 GPa; c
12
= 22.95 GPa; c
13
= 14.3 GPa; c
33
= 57.40 GPa;
c
44
= 13.59 GPa
Kinematic liquid viscosity. 0.432 mm
2
/s at 935 °C
Liquid surface tension. 0.707 N/m at 935 °C
Promethium (Pm)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Promethium is used in luminous watch dials and as a lightly shielded radioisotope power source. It is also a highly
radioactive β emitter (
147
Pm).
Structure
Crystal structure. α phase, double close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.365 nm, c = 1.165 at 24 °C. β phase,
probably body-centered cubic, a = 0.410 nm (estimated) at 890 °C

Minimum interatomic distance. At 24 °C: r
a
= 0.1825 nm; r
c
= 0.1797 nm; radius CN
12
= 0.1811
Mass Characteristics
Atomic weight. 145
Density. α phase, 7.264 g/cm
3
at 24 °C; β phase, 6.99 g/cm
3
(estimated) at 890 °C; liquid, 6.9 g/cm
3
(estimated) at 1050
°C
Thermal Properties
Melting point. 1042 °C
Boiling point. 3000 °C (estimated)
Phase transformation temperature. 890 °C
Coefficient of thermal expansion. At 24 °C. Linear (estimated): 11 μm/m · K. Linear along crystal axes 9 μm/m · K
along a axis, 16 μm/m · K along c axis. Volumetric: 34 × 10
-6
per K
Specific heat. 0.188 kJ/kg · K at 25 °C (estimated)
Entropy. At 25 °C: 494 J/kg · K (estimated)
Latent heat of fusion. 53 kJ/kg (estimated)
Latent heat of transformation. 21 kJ/kg (estimated)
Latent heat of vaporization. 2.4 MJ/kg at 25 °C (estimated)

Thermal conductivity. 15 W/m · K at 27 °C (estimated)
Heat of combustion. For monoclinic Pm
2
O
3
at 25 °C:

c
H
∆
o
= -6.3 MJ/kg Pr;
f
G
∆
o
= -6.0 MJ/kg Pm (estimated)
Recrystallization temperature. 400 °C (estimated)
Electrical Properties
Electrical resistivity. 750 nΩ · m at 25 °C (estimated)
Ionization potential. Pm(I), 5.554 eV; Pm(II), 10.90 eV; Pm(III), 22.3 eV; Pm(IV), 41.1 eV
Magnetic Properties
Magnetic susceptibility. Probably strongly paramagnetic with a susceptibility somewhat greater than that of cerium at
24 °C
Magnetic transformation temperature. Probably exhibits two Néel temperatures that fall between those observed
in neodymium and samarium
Optical Properties
Color. Metallic silver
Chemical Properties
General corrosion behavior. About the same as that of neodymium

Resistance to specific corroding agents. About the same as that of neodymium
Mechanical Properties
Tensile properties. About the same as that of neodymium
Hardness. 63 HK
Poisson's ratio. 0.28 (estimated)
Elastic modulus. At 27 °C: tension, 46 GPa (estimated); shear, 18 GPa; bulk, 33 GPa
Liquid surface tension. 0.68 N/m (estimated) at 1045 °C
Samarium (Sm)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Alloyed with cobalt, samarium is used as a permanent magnet, Sm
2
Co
17
-SmCo
5
. Samarium is also used as a burnable
poison in nuclear reactors, as a phosphor, and in catalysts and ceramic capacitors.
Samarium oxidizes slowly in air at room temperature. Storage in an inert atmosphere or vacuum is recommended.
Turnings can be ignited easily. Finely divided samarium should not be handled in air.
Structure
Crystal structure. α phase, rhombohedral, R3m
3d
5
D
; a = 0.89834 nm, a = 23.311° (hexagonal parameters, a = 0.36290
nm, c = 2.6207 nm at 24 °C). α phase, close-packed hexagonal, P6
3
/mmc
6h

4
D
; a = 0.36630 nm; c = 0.58448 nm at 450
°C. γ phase, body-centered cubic, Im3m
9
h
O
; a = 0.410 nm (estimated) at 922 °C
Minimum interatomic distance. At 24 °C: r
a
= 0.18145 nm; r
c
= 0.17937 nm; radius CN
12
= 0.18041 nm
Mass Characteristics
Atomic weight. 150.4
Density. α phase, 7.520 g/cm
3
at 24 °C β phase, 7.353 g/cm
3
at 450 °C; γ phase, 7.25 g/cm
3
(estimated) at 922 °C liquid,
7.16 g/cm
3
at 1075 °C
Volume change on freezing. 3.6% contraction
Thermal Properties
Melting point. 1074 °C

Boiling point. 1794 °C
Phase transformation temperature. α to β phase, 734 °C; β to α phase, 727 °C; β to γ phase, 922 °C
Coefficient of thermal expansion. At 24 °C. Linear: 12.7 μm/m · K. Linear along crystal axes: 9.6 μm/m · K along
a axis; 19.0 μm/m · K along c axis. Volumetric, 38.1 × 10
-6
per K
Specific heat. 0.1962 kJ/kg · K at 25 °C
Entropy. At 25 °C: 462.2 J/kg · K
Latent heat of fusion. 57.3 KJ/kg
Latent heat of transformation. β to γ phase, 20.7 kJ/kg
Latent heat of vaporization. 1.375 MJ/kg at 25 °C
Heat of combustion. For monoclinic Sm
2
O
3
at 25 °C:
c
H
∆
o
= -6.06 MJ/kg Sm;
f
G
∆
o
= -5.77 MJ/kg Sm
Recrystallization temperature. About 440 °C
Thermal conductivity. 13.3 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 508 °C; 0.101 Pa at 642 °C; 10.1 Pa at 835 °C; 1013 Pa at 1150 °C
Electrical Properties

Electrical resistivity. 940 nΩ · m at 25 °C, 67 nΩ · m at 4 K. Liquid: 1820 nΩ · m at 1075 °C
Ionization potential. Sm(I), 5.631 eV; Sm(II), 11.07 eV; Sm(III), 23.4 eV; Sm(IV), 41.4 eV
Hall coefficient. -0.021 nV · m/A · T at 25 °C
Temperature of superconductivity. Bulk samarium is not superconducting down to 0.37 K at atmospheric pressure.
Magnetic Properties
Magnetic susceptibility. Volume: 8.03 × 10
-4
mks at 17 °C; does not obey Curie-Weiss law
Saturation magnetization. >35 T at 4 K along <0001> and >30 T at 4 K along <11
2
0>
Magnetic transformation temperature. Ordering temperatures at 14 K (cubic sites) and 106 K (hexagonal sites)
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. Solid, 43.7% for λ= 645 nm from 852 to 1074 °C; liquid, 43.7% for λ= 645 nm
at 1075 °C
Nuclear Properties
Thermal neutron cross section. 5600 b
Chemical Properties
General corrosion behavior. Samarium oxidizes slowly at room temperature in air. The rate of oxidation increases
with temperature. Hydrogen will react at about 250 °C with samarium metal.
Resistance to specific corroding agents. Samarium reacts vigorously with dilute acids but only slowly with
concentrated sulfuric acid. The presence of fluoride ion retards acid attack due to the formation of SmF
3
on the surface of
the metal.
Mechanical Properties
Tensile properties. Tensile strength, 156 MPa; yield strength, 68 MPa; elongation, 17%; reduction in area, 29.5%
Hardness. 39 HV
Poisson's ratio. 0.274

Strain-hardening exponent. 0.23
Elastic modulus. At 27 °C: tension, 49.7 GPa; shear, 19.5 GPa, bulk, 37.8 GPa
Liquid surface tension. 0.431 N/m at 1075 °C
Scandium (Sc)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Scandium is used as a neutron window or filter in reactors. It is also used in high-intensity lamps because of the
multilined spectrum of incandescent scandium vapor. Turning of scandium can be ignited and will burn white hot. Finely
divided scandium should not be handled in air. Ingots of pure scandium can be stored in air.
Structure
Crystal structure. α phase, close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.33088 nm ; c = 0.52680 nm at 24 °C. β
phase, body-centered cubic, Im3m; a = 0.373 nm (estimated) at 1337 °C
Minimum interatomic distance. At 24 °C: r
a
= 0.16544 nm; r
c
= 0.16269 nm; radius CN
12
= 0.16407 nm
Mass Characteristics
Atomic weight. 44.95591
Density. α phase, 2.989 g/cm
3
at 24 °C; β phase, 2.88 g/cm

3
at 1337 °C; liquid, 2.80 g/cm
3
at 1550 °C
Thermal Properties
Melting point. 1541 °C
Boiling point. 2836 °C
Phase transformation temperature. α to β phase, 1337 °C
Coefficient of thermal expansion. At 24 °C. Linear: 10.2 μm/m · K. Linear along crystal axis: 7.6 μm/m · K along a
axis; 15.3 μm/m · K along c axis. Volumetric: 30.5 × 10
-6
per K
Specific heat. 0.5674 kJ/kg · K at 25 °C
Entropy. 769.6 kJ/kg · K at 25 °C
Latent heat of fusion. 313.6 kJ/kg
Latent heat of transformation. 89.0 kJ/kg
Latent heat of vaporization. 8.404 MJ/kg at 25 °C
Heat of combustion. For cubic Sc
2
O
3
at 25 °C:
c
H
∆
o
= -21.23 MJ/kg Sc;
f
G
∆

o
= -20.23 MJ/kg Sc
Recrystallization temperature. About 550 °C
Thermal conductivity. 15.8 W/m · K at 25 °C
Vapor pressure. 0.0010 Pa at 1036 °C; 0.101 Pa at 1243 °C; 10.1 Pa at 1533 °C; 1013 Pa at 1999 °C
Electrical Properties
Electrical resistivity. 562 nΩ · m at 25 °C; 1.6 nΩ · m at 4 K. Along crystal axes at 25 °C: 709 nΩ · m along a axis;
269 nΩ · m along c axis
Ionization potential. Sc(I), 6.54 eV; Sc(II), 12.80 eV; Sc(III), 24.76 eV; Sc(IV), 73.47 eV; Sc(V), 91.66 eV; Sc(VI),
111.1 eV
Hall coefficient. -0.013 nV · m/A · T at 25 °C
Temperature of superconductivity. Bulk scandium is not superconducting down to 0.032 K at atmospheric
pressure; however, it is superconducting at 0.050 and 18.6 GPa.
Magnetic Properties
Magnetic susceptibility. Volume (mks units) at 24 °C: 2.466 × 10
-4
. Along crystal axes: 2.490 × 10
-4
along a axis;
2.419 × 10
-4
along c axis
Optical Properties
Color. Metallic silver
Nuclear Properties
Thermal neutron cross section. 24 b
Chemical Properties
General corrosion behavior. Scandium remains shiny in air at room temperature; discoloration starts at about 300
°C. Oxidation proceeds slowly to completion at 1000 °C.
Resistance to specific corroding agents. Scandium reacts readily with most acids. The presence of fluoride ions

causes the formation of ScF
3
, which retards attack by nitric, hydrochloric, and other acids.
Mechanical Properties
Tensile properties. Tensile strength, 255 MPa; yield strength, 173 MPa; elongation, 5%; reduction in area, 8%
Hardness. Anisotropic: 132 HV (0001) and 36 HV (10
1
0)
Poisson's ratio. 0.279
Elastic modulus. At 27 °C: Tension, 74.4 GPa; shear, 29.1 GPa; bulk, 56.6 GPa
Elastic constants along crystal axes. At 27 °C: c
11
= 98.1 GPa; c
12
= 45.7 GPa; c
13
= 29.4 GPa; c
33
= 105.1 GPa;
c
44
= 27.2 GPa
Liquid surface tension. 0.954 N/m at 1545 °C
Terbium (Tb)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Terbium is used as a phosphor and in magnetostrictive materials (Tb
0.3
Dy
0.7

Fe
2
) and catalysts. Amorphous Tb-Co alloys
are used as magnetooptic storage devices. Terbium will remain shiny in air at room temperature. Turnings can be ignited
and will burn white hot. Finely, divided terbium should not be handled in air.
Structure
Crystal structure. α' phase, orthorhombic, Cmcm
2h
27
D
; a = 0.3605 nm, b = 0.6244 nm, c = 0.5706 nm at -53 °C. α
phase, close-packed hexagonal, P6
3
/mmc
6h
4
D
; a = 0.36055 nm, c = 0.56966 nm at 24 °C. β phase, body-centered cubic,
Im3m
9
h
O
; a = 0.407 nm at 1289 °C
Minimum interatomic distance. r
a
= 0.18028; r
c
= 0.17639; radius CN
12
= 0.17833 nm

Mass Characteristics
Atomic weight. 158.92534
Density. α phase, 8.230 g/cm
3
at 24 °C; β phase, 7.82 g/cm
3
at 1289 °C; liquid, 765 g/cm
3
at 1360 °C
Volume change on freezing. 3.1% contraction
Thermal Properties
Melting point. 1356 °C
Boiling point. 3230 °C
Phase transformation temperature. α to α' phase, -53 °C; α to β phase, 1289 °C
Coefficient of thermal expansion. At 24 °C. Linear: 10.3 μm/m · K. Linear along crystal axes: 9.3 μm/m · K along
a axis, 12.4 μm/m · K along c axis. Volumetric: 31.0 × 10
-6
per K
Specific heat. 0.1818 kJ/kg · K at 25 °C
Entropy. 461.2 J/kg · K at 25 °C
Latent heat of fusion. 67.9 kJ/kg
Latent heat of transformation. 31.6 kJ/kg
Latent heat of vaporization. 2.446 MJ/kg at 25 °C
Heat of combustion. For cubic Tb
2
O
3
at 25 °C:
c
H

∆
o
= -5.87 MJ/kg Tb;
f
G
∆
o
= -5.59 MJ/kg Tb
Recrystallization temperature. 500 °C
Thermal conductivity. 11.1 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 1124 °C; 0.101 Pa at 1354 °C; 10.1 Pa at 1698 °C; 1013 Pa at 2237 °C
Electrical Properties
Electrical resistivity. 1150 nΩ · m at 25 °C; 35 nΩ · m at 4 K. Along crystal axes at 25 °C: 1235 nΩ · m along a axis,
1015 nΩ · m along c axis. Liquid: 1930 nΩ · m at 1358 °C
Ionization potentials. Tb(I), 5.842 eV; Tb(II), 11.52 eV; Tb(III), 21.91 eV; Tb(IV), 39.79 eV
Hall coefficient. Along crystal axes at 20 °C: -0.10 nV · m/A · T along b axis; -0.37 nV · m/A · T along c axis
Temperature of superconductivity. Bulk terbium is not superconducting down to 0.37 K at atmospheric pressure.
Magnetic Properties
Magnetic susceptibility. Volume (mks units): χ
a
= 0.129 and χ
c
= 0.0738 at 27 °C; obeys Curie-Weiss law above 240
K with an effective moment of 9.77 μ
B
, θ
a
= 239 K and θ
c
= 195 K

Saturation magnetization. 13 T at 4.2 K along <11
2
0>
Magnetic transformation temperatures. Curie temperature, 219.5 K; Néel temperature, 230 K
Optical Properties
Color. Metallic silver
Nuclear Properties
Thermal neutron cross section. 45 b
Chemical Properties
General corrosion behavior. Terbium stays shiny in air at room temperature. The rate of oxidation is slow even at
1000 °C due to the formation of a dark, tightly adhering oxide on the surface. Water vapor increases the rate of oxidation.
After heating to 550 °C in vacuum, hydrogen will react at 250 °C.
Resistance to specific corroding agents. Terbium does not react with cold or hot water, but it will react
vigorously with dilute acids. It is slowly attacked by concentrated sulfuric acid. The presence of the fluoride ion retards
acid attack due to the formation of TbF
3
.
Mechanical Properties
Tensile properties. About the same as those of gadolinium
Hardness. 38 HV for polycrystalline; 30 HV for {10
1
0} prismatic face; 80 HV for {0001} basal plane
Poisson's ratio. 0.261
Elastic modulus. At 27 °C: tension, 55.7 GPa; shear, 22.1 GPa; bulk, 38.7 GPa
Elastic constants along crystal axes. At 27 °C: c
11
= 69.24 GPa; c
12
= 24.98 GPa; c
13

= 21.79 GPa; c
33
= 74.39
GPa; c
44
= 21.75 GPa
Liquid surface tension. 0.669 N/m at 1360 °C
Thulium (Tm)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Thulium is used in phosphors, ferrite bubble devices, and catalysts. Irradiated thulium (
169
Tm) is used as a portable
radiographic source. Thulium will remain shiny in air at room temperature. Turnings can be ignited and will burn white
hot. Finely divided thulium should not be handled in air. Because of its high vapor pressure at its melting point, thulium
should not be arc melted.
Structure
Crystal structure. Close-packed hexagonal: P6
3
/mmc
6h
4
D
; a = 0.35375 nm, c = 0.55540 nm at 25 °C
Minimum interatomic distance. At 24 °C: r
a
= 0.17688 nm; r
c
= 0.17236 nm; radius CN
12

= 0.17462 nm
Mass Characteristics
Atomic weight. 168.93421
Density. 9.321 g/cm
3
at 24 °C; liquid, 9.0 g/cm
3
(estimated) at 1550 °C
Volume change on freezing. 6.9% contraction
Thermal Properties
Melting point. 1545 °C
Boiling Point. 1950 °C
Coefficient of thermal expansion. At 24 °C. Linear: 13.3 μm/m · K. Linear along crystal axes: 8.8 μm/m · K along
a axis, 22.2 μm/m · K along c axis. Volumetric: 39.8 × 10
-6
per K
Specific heat. 0.1598 kJ/kg · K at 25 °C
Entropy. At 25 °C: 438.0 J/kg · K
Latent heat of fusion. 99.4 kJ/kg
Latent heat of vaporization. 1.374 MJ/kg at 25 °C
Latent heat of combustion. For cubic Tm
2
O
3
at 25 °C:
c
H
∆
o
= -5.59 MJ/kg Tm;

f
G
∆
o
= -5.32 MJ/kg Tm
Recrystallization temperature. About 600 °C
Thermal conductivity. 16.9 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 599 °C; 0.101 Pa at 748 °C; 10.1 Pa at 964 °C; 1013 Pa at 1300 °C
Electrical Properties
Electrical resistivity. 676 nΩ · m at 25 °C; 56 nΩ · at 4 K. At 25 °C: 880 nΩ · m along c axis
Ionization potentials. Tm(I), 6.18436 eV; Tm(II), 12.05 eV; Tm(III), 23.68 eV; Tm(IV), 42.69 eV
Hall coefficient. -0.18 nV · m/A · T at 20 °C
Temperature of superconductivity. Bulk thulium is not superconducting down to 0.35 K at atmospheric pressure.
Magnetic Properties
Magnetic susceptibility. Volume (mks units): χ
a
= 0.0160 and χ
c
= 0.0195 at 25 °C; obeys Curie-Weiss law above 55
K with an effective moment of 7.61 μ
B
, θ
a
= -17 K and θ
c
= 41 K
Saturation magnetization. 2.79 T at 4.2 K along <0001>
Magnetic transformation temperatures. Curie temperature, 32 K; a spin rearrangement at 42 K, Néel temperature,
58 K
Optical Properties

Color. Metallic silver
Nuclear Properties
Thermal neutron cross section. 125 b
Chemical Properties
General corrosion behavior. Thulium stays shiny in air at room temperature. Even at 1000 °C, the rate of oxidation
is low due to the formation of a dark, tightly adhering oxide on the surface of the metal.
Resistance to specific corroding agents. Thulium doe not react with cold or hot water, but it reacts vigorously
with dilute acids. The attack by concentrated sulfuric acid is slow. The presence of the fluoride ion retards acid attack due
to the formation of TmF
3
on the surface of the metal.
Mechanical Properties
Tensile properties. About the same as those of erbium
Hardness. 48 HV
Poisson's ratio. 0.213
Elastic modulus. At 27 °C: tension, 74.0 GPa; shear, 30.5 GPa; bulk, 44.5 GPa
Ytterbium (Yb)
Compiled by K.A Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory, U.S. Department of Energy, Iowa State University

Ytterbium is used in phosphors, ceramic capacitors, ferrite devices, and catalysts. Ytterbium (
170
Yb), which has been
formed by neutron irradiation of thulium (
169
Tm), is used as a portable radiograph source; ytterbium foils are used to
measure pressure and as stress transducers. Ytterbium will tarnish slightly at room temperature in air. Massive ytterbium
can be handled in air, but should be stored in an inert atmosphere or vacuum. Finely divided ytterbium should not be
handled in air.
Structure
Crystal structure. α phase, close-packed hexagonal, P6

3
/mmc
h
4
D
; a = 0.38799 nm, c = 0.63859 nm at 24 °C. β phase,
face-centered cubic, Fm3m
5
h
O
; a = 0.54848 nm at 24 °C. γ phase, body-centered cubic, Im3m
9
h
O
; a = 0.444 nm at 763
°C
Minimum interatomic distance. 0.19392 nm at 24 °C
Mass Characteristics
Atomic weight. 173.04
Density. α phase, 6.903 g/cm
3
at 23 °C; β phase, 6.966 g/cm
3
at 24 °C; γ phase, 6.57 g/cm
3
at 763 °C; liquid, 6.21 g/cm
3

at 820 °C
Volume change on freezing. 5.1% contraction

Volume change on phase transformation. β to γ phase, 0.1% volume contraction on heating
Thermal Properties
Melting point. 819 °C
Boiling point. 1196 °C
Phase transformation temperature. α to βphase: A
s
= 280 K; β to α, M
s
260 K; β to γ, 795 °C
Coefficient of thermal expansion. At 24 °C. Linear: 26.3 μm/m · K. Linear along crystal axes: 26.3 μm/m · K along
a axis. Volumetric: 78.9 × 10
-6
per K
Specific heat. 0.1543 kJ/kg · K at 25 °C
Entropy. 345.6 J/kg · K at 25 °C
Latent heat of fusion. 44.3 kJ/kg
Latent heat of transformation. 10.1 J/kg
Latent heat of vaporization. 0.8790 kJ/kg at 25 °C
Heat of combustion. For cubic Yb
2
O
3
at 25 °C:

c
H
∆
o
= -5.24 MJ/kg Yb;
f

G
∆
o
= -5.00 MJ/kg Yb
Recrystallization temperature. About 300 °C
Thermal conductivity. 38.5 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 301 °C; 0.101 Pa at 400 °C; 10.1 Pa at 541 °C; 1013 Pa at 776 °C
Electrical Properties
Electrical resistivity. 250 nΩ · m at 25 °C; 10 nΩ · m at 4 K. Liquid, 1130 nΩ · m at 821 °C
Ionization potentials. Yb(I), 6.25394 eV; Yb(II), 12.184 eV; Yb(III), 25.03 eV; Yb(IV), 43.74 eV
Hall coefficient. +0.377 nV · m/A · T at 20 °C
Temperature of superconductivity. Bulk ytterbium is not superconducting down to 0.015 K at atmospheric
pressure.
Magnetic Properties
Magnetic susceptibility. Volume: 3.4 × 10
-6
mks at 17 °C
Optical Properties
Color. Metallic silver
Nuclear Properties
Thermal neutron cross section. 37 b
Chemical Properties
General corrosion behavior. Ytterbium tarnishes slightly in moist air. It oxidizes slowly at elevated temperatures
and reacts readily with hydrogen at 250 °C.
Resistance to specific corroding agents. Ytterbium does not react with cold water, but it will tarnish in hot water.
It reacts vigorously with dilute acids.
Mechanical Properties
Tensile properties. Tensile strength, 58 MPa; yield strength, 7 MPa; elongation, 43%; reduction in area, 92%
Hardness. 17 HV
Poisson's ratio. 0.207

Strain-hardening exponent. 0.62
Elastic modulus. At 27 °C: tension, 23.9 GPa; shear, 9.9 GPa; bulk, 30.5 GPa
Kinematic liquid viscosity. 0.430 mm
2
/s at 824 °C
Liquid surface tension. 0.320 N/m at 820 °C
Yttrium (Y)
Compiled by K.A. Gschneidner, Jr. and B.J. Beaudry, Ames Laboratory U.S. Department of Energy, Iowa State University

Yttrium is used in magnesium alloys and oxidation-resistant alloys; it is also used in garnets and ferrites for electronic
components. Yttrium is a host material for rare earth phosphors, including the red color (Eu) in color television screens.
Yttrium oxide is used to stabilize cubic zirconia for structural and electronic ceramics, and as an oxide dispersant in
superalloys; it is a major component in the high-temperature oxide superconductors (YBa
2
Cu
3
O
7-x
).
Yttrium tarnishes slowly in air at room temperature. Turnings can be ignited quite easily and burn with great evolution of
heat. Finely divided yttrium should be handled with great care and should be kept away from air and oxidizing agents.
Structure
Crystal structure. α phase, close-packed hexagonal, P6
3
/mmc; a = 0.36428 nm, c = 0.57318 nm at 25 °C. β phase,
body-centered cubic, Im3m; a = 0.410 nm above 1478 °C
Slip planes. [10
1
0]<[1
2

10]> from -196 to 224 °C; [0002]<[1
2
10]> from -196 to 224 °C
Twinning planes. [11
2
1]<
11
26> at 25 °C
Minimum interatomic distance. At 24 °C: r
a
= 1.824 nm; r
c
= 1.7783 nm; radius CN
12
= 1.8012 nm
Fracture behavior. Primarily ductile
Mass Characteristics
Atomic weight. 88.90585
Density. α phase, 4.469 g/cm
3
at 24 °C; β phase, 4.28 g/cm
3
at 1478 °C; liquid, 4.24 g/cm
3
at 1525 °C
Thermal Properties
Melting point. 1522 °C
Boiling point. 3345 °C
Phase transformation temperature. 1478 °C
Coefficient of thermal expansion. Linear: 10.6 μm/m · K. Linear along crystal axes: 6.0 μm/m · K along a axis;

19.7 μm/m · K along c axis. Volumetric 31.7 × 10
-6
per K
Specific heat. 0.2981 kJ/kg · K at 25 °C
Entropy. At 298.15 K: 499.4 J/kg · K
Latent heat of fusion. 128.2 kJ/kg
Latent heat of transformation. hcp
→
bcc, 56.1 kJ/kg
Latent heat of vaporization. 4.777 MJ/kg at 25 °C
Heat of combustion. For cubic Y
2
O
3
at 25 °C:
c
H
°
∆
= -10.72 MJ/kg Y;
f
G
∆
o
= -10.22 MJ/kg Y
Recrystallization temperature. 550 °C
Thermal conductivity. 17.2 W/m · K at 25 °C
Vapor pressure. 0.001 Pa at 1222 °C; 0.101 Pa at 1460 °C; 10.1 Pa at 1812 °C; 1013 Pa at 2360 °C
Electrical Properties
Electrical resistivity. 596 nΩ · m at 25 °C; 32 nΩ · m at 4 K. Along crystal axes at 25 °C: 725 nΩ · m along a axis;

355 nΩ · m along c axis
Ionization potentials. Y(I), 6.38 eV; Y(II), 12.24 eV; Y(III), 20.52 eV; Y(IV), 61.8 eV; Y(V), 77.0 eV
Hall coefficient. R
H,b
= -0.027 nV · m/A · T and R
H,c
= -0.16 nV · m/A · T at 25 °C
Temperature of superconductivity. Bulk yttrium is not superconducting down to 0.006 K at atmospheric pressure;
it becomes superconducting at 1.3 K and 11 GPa.
Magnetic Properties
Magnetic susceptibility. Volume at 25 °C (mks units): 1.186 × 10
-4
. Along crystal axes: 1.233 × 10
-4
along a axis;
1.109 × 10
-4
along c axis
Nuclear Properties
Thermal neutron cross section. 1.3 b
Optical Properties
Color. Metallic silver
Spectral hemispherical emittance. Solid: 36.8% for λ= 645 nm at 1200 to 1522 °C. Liquid: 36.8% for λ= 645 nm
at 1522 to 1647 °C
Chemical Properties
General corrosion behavior. Yttrium metal remains shiny in air at room temperature; discoloration starts at 350
°C.
Resistance to specific chemical agents. Yttrium metal reacts vigorously with hydrochloric and nitric acids. It does
not react with hydrofluoric acid or with HCl or HNO
3

in the presence of the fluoride ion.
Mechanical Properties
Tensile properties. At 25 °C, annealed rod: tensile strength, 129 MPa; yield strength, 42 MPa; elongation, 34% in 25
mm
Hardness. 40 HV; highly anisotropic
Poisson's ratio. 0.243
Strain-hardening exponent. n = 0.23
Elastic modulus. Tension, Young's, 63.5 GPa; shear, 25.6 GPa; bulk, 41.2 GPa
Elastic modulus along crystal axes. c
11
= 77.9 GPa; c
12
= 29.2 GPa; c
13
= 21.0 GPa; c
33
= 76.9 GPa; c
44
= 24.7 GPa
Liquid surface tension. 0.871 N/m at 1525 °C
Properties of the Actinide Metals (Ac-Pu)

Actinium (Ac)
Compiled by Lester R. Morss, Chemistry Division, Argonne National Laboratory
Structure
Crystal structure. Face-centered cubic (Fm3m) a
0
= 0.5315 ± 0.0005 nm
Mass Characteristics
Atomic weight. 227.0277

Density. 10.1 g/cm
3
(calculated from x-ray lattice parameter). Variation in density with temperature: unknown
Volume change on freezing Unknown
Thermal Properties
Melting point. 1430 °C (estimated)
Boiling point. 3200 ± 300 °C (estimated)
Phase transformation temperature. No known solid-solid phase transformation
Coefficient of thermal expansion. Unknown
Entropy. S°
298K
= 61.9 ± 0.8 kJ/mol (predicted)
Specific heat. Unknown
Enthalpy. Unknown
Latent heat (enthalpy) of fusion. 10.9 kJ/mol (estimated)
Latent heat (enthalpy) of sublimation. 418 ± 13 kJ/mol at 298 K
Enthalpy of oxide. Ac
2
O
3
formation: -1756 ± 80 kJ/mol (estimated)
Free energy of oxide formation. Unknown
Thermal conductivity of metal. Unknown
Thermal conductivity versus temperature. Unknown
Vapor pressure. 0.9 Pa (0.007 torr) at 1600 °C (estimated)
Diffusion coefficient. Unknown
Electrical Properties
Unknown
Magnetic Properties
Magnetic susceptibility. Unknown

Magnetic permeability. Unknown
Optical Properties
Color. Silvery white, sometimes with golden cast
Emissivity. Unknown
Nuclear Properties
Radioactive isotopes. All isotopes (
209
Ac through
232
Ac) are radioactive. The longest-lived isotope,
227
Ac, has a half-
life of 21.773 years and decays by β
-
emission (98.62%) and α emission (1.38%). It is the most abundant isotope, and has
been recovered in milligram quantities from uranium ores and produced in gram quantities by thermal neutron irradiation
of
226
Ra:
226
Ra (n, γ)
227
Ra (β
-
, 41.2 min)
227
Ac


This reaction can also be expressed as the end product of two separate equations:

226
Ra + n
→
227
Ra + γ


and
227
227.41,2
RaAc
β
−
→


Effect of neutron irradiation : Unknown
Thermal neutron cross sections. σ
c
= 900 ± 150 b; σ
f
= 3.5 × 10
-4
b
Chemical Properties
Oxidizes rapidly in moist air. Oxide coating somewhat inhibits further attack.
Fabrication Characteristics
Unknown
Mechanical Properties
Tensile properties. Unknown

Compressive properties. Unknown
Hardness. Unknown
Poisson's ratio. Unknown

Neptunium (Np)
Compiled by J.A. Fahey, Bronx Community College, City University of New York

Neptunium was the first artificial element to be discovered. It was produced by the bombardment of uranium with slow
neutrons. Many isotopes of neptunium are known, and all are radioactive.
237
Np is the most stable isotope, with an α
decay half-life of 2.14 × 10
6
years. The 59.6 keV γ ray associated with the α decay of
237
Np to an excited state of
233
Pa
makes it important in the investigation of the electronic, structural, and magnetic properties of the solid compounds and
metallic phases of neptunium by Mössbauer spectroscopy. The isotope
237
Np is used for most studies because of its long
half-life and its relative availability.
237
Np and
239
Np are produced, along with
239
Pu, in the operation of conventional
nuclear reactors.

237
Np is also important because it is the source material for the production of
238
Pu for use in atomic-
powered batteries. Most of the health concerns associated with neptunium are related to the possible presence of residual
amounts (0.5%) of
239
Pu, a strong carcinogen, due to incomplete separation in the purification process.
Structure
Crystal structure. α phase: orthorhombic (Pnma); a = 0.4723 nm, b = 0.4887 nm, c = 0.6663 nm at 25 °C. β phase:
tetragonal, P4/nmm; a = 0.4897 nm, c = 0.3388 nm at 313 °C. γ phase: bcc Im3m; a = 0.3518 nm at 600 °C
The unit cell of α neptunium contains eight atoms. Half the atoms are in a site with the seven nearest neighbors at an
average distance of 0.2968 nm (2.968
A
o
), and the other half are in a site with the five nearest neighbors at an average
distance of 0.2854 nm (2.854
A
o
).
The unit cell of β neptunium contains four atoms. Half the atoms are in a site with the four nearest neighbors at an
average distance of 0.3206 nm (3.206
A
o
), and the other half are in a site with the four nearest neighbors at an average
distance of 0.3232 nm (3.232
A
o
).
The unit cell of γ neptunium contains two atoms. Each atom has its eight nearest neighbors at a distance of 0.297 nm

(2.97
A
o
) when extrapolated to 20 °C
Mass Characteristics
Atomic weight.
237
Np, 237.0482
Density. α phase: 20.48 g/cm
3
at 25 °C (x-ray); 20.25 g/cm
3
at 25 °C (measured). β phase: 19.38 g/cm
3
at 313 °C (x-
ray); 19.31 g/cm
3
at 25 °C (measured). γ phase: 18.08 g/cm
3
at 600 °C (x-ray)
Thermal Properties
Melting point. 637 °C
Boiling point. ~3902 °C
Phase transformation temperatures. At 1 atm pressure: α to β, 280 °C; β to γ, 577 °C; γ to liquid, 637 °C
Coefficient of thermal expansion. Volumetric, as determined by x-ray diffraction. α neptunium between 20 and 275
°C: α
100
= 24 × 10
-6
per K; α

010
= 25 × 10
-6
per K; α
001
= 34 × 10
-6
per K. β neptunium between 278 and 530 °C: α
100
= α
010

= 64 × 10
-6
per K; α
001
0.0.
The thermal expansion of neptunium metal has been measured by dilatometry. A typical dilatometric run is shown in Fig.
140. The values of the coefficient of linear expansion were found to be 27.5 × 10
-6
per °C for the α phase (40 to 240 °C)
and 41 × 10
-6
°C for the β phase (300 to 540 °C). The dilatometric behavior also shows a discontinuous change of slope at
the phase transitions.

Fig. 140 Thermal expansion of neptunium metal. Source: Ref 571

Specific heat. The heat capacity of pure neptunium metal reaches the Dulong-Petit value of 3R (where R is the
universal gas constant) at 140 °C and 29.68 J · K

-1
at 300 K. Measuring the specific heat of neptunium metal between 7.4
and 300 K yields a γ(coefficient of the electronic term in the specific heat) of 14 mJ/mol · K
2
. The specific heat of
neptunium metal is a smooth function over this temperature range. The Debye temperature of neptunium metal is
calculated to be 240 ± 4 K.
Latent heat of phase transformation. α to β, 5607 J/mol; β to γ, 5272 J/mol
Latent heat of fusion. 5230 J/mol
Enthalpy of solution. Neptunium metal in 1.5 M HCl: -165.7 ± 0.2 kcal/mol at 25 °C
Enthalpy of oxide formation. NpO
2
, -1074 ± 3 kJ/mol
Free energy of oxide formation. NpO
2
, -1022 ± 3 kJ/mol
Vapor pressure. Liquid: log P = -(20,610 ± 1280)/T + (5.10 ± 0.70), where P is in atm and T is in K. See Fig. 141.