21
  Sc  
44.955910
Scandium

Name: Scandium
Symbol: Sc
Atomic Number: 21
Atomic Weight: 44.955910
Family: Transition Metals
CAS RN: 7440-20-2
Description: Soft silvery white metal that tarnishes in air and burns easily once ignited.
State (25 C): Solid
Oxidation states: +3

Molar Volume: 15.04 cm3/mole
Valence Electrons: 3d14s2

Boiling Point:  3104K, 2831C, 5128F
Melting Point:
1812K, 1539C, 2802F
Electrons Energy Level: 2, 8, 9, 2
Isotopes: 17 + 1 Stable
Heat of Vaporization: 314.2 kJ/mol
Heat of Fusion: 14.1 kJ/mol
Density: 2.99 g/cm3 @ 300K
Specific Heat: 0.6 J/gK
Atomic Radius: 2.09
Ionic Radius: 0.745
Electronegativity: 1.36 (Pauling); 1.2 (Allrod Rochow)
Vapor Pressure: 22.1 Pa @ 1539C

1s2 2s2p6 3s2p6d1 4s2

History

Dmitri Mendeleev used his periodic law, in 1869, to predict the existence of, and some properties of, three unknown elements, including one he called ekaboron.

Lars Fredrick Nilson and his team, apparently unaware of that prediction in the spring of 1879, were looking for rare earth metals.  By using spectral analysis, they found a new element within the minerals Euxenite and Gadolinite.  They named it scandium, from the Latin Scandia meaning "Scandinavia", and in the process of isolating the scandium, they processed 10 kilograms of euxenite, producing about 2.0 grams of a very pure Scandium Oxide, Sc2O3.

Per Teodor Cleve of Sweden concluded that scandium corresponded well to the hoped-for ekaboron, and he notified Mendeleev of this in August.

Fischer, Brunger, and Grienelaus prepared metallic scandium for the first time in 19337, by electrolysis of a eutectic melt of potassium, lithium, and scandium chlorides at a temperature of 700 to 800C.  Tungsten wires in a pool of liquid zinc were the electrodes in a graphite crucible.  The first pound of 99% pure scandium metal was not produced until 1960.

Characteristics

Scandium is a rare, soft, silvery, very light metallic element that develops a slightly yellowish or pinkish cast when exposed to air.  It is sometimes considered along with yttrium, and the lanthanides and actinides, to be a rare earth.  This metal is not attacked by a 1:1 mixture of Nitric Acid, HNO3,  and Hydrofluoric Acid, HF.  The rarity of scandium is not an arbitrary fact. In this area of atomic numbers, the thermonuclear reactions that produced the elements, very much more commonly produces elements with an even atomic number.  This is because these elements were usually produced by the fusion of lighter elements with Helium-4 nuclei, starting with Carbon-12 (element six).  Thus, the common elements in the range of scandium are number 18 Argon, number 20 Calcium, number 22 Titanium, number 24 Chromium; with the odd-numbered elements 19 Potassium, 21 Scandium, and 23 Vanadium being rarely produced, and much less common.  The production of the odd-numbered elements in this range results from much-less common thermonuclear reactions, as is explained elsewhere.

Occurrence

Scandium is distributed sparsely on earth, occurring only as trace quantities in many minerals.  Rare minerals from Scandinavia and Madagascar, such as Thortveitite, Euxenite, and Gadolinite are the only known concentrated sources of this element (which is never found as a free metal).  It is also found in residues that remain after Tungsten is extracted from Wolframite, and from ores after Uranium and Thorium have been extracted.

Scandium is more common in the sun and certain stars than on Earth.  Scandium is only the 50th most common element on earth (35th most abundant in the Earth's crust), but it is the 23rd most common element in the sun.

The blue color of the aquamarine variety of beryl is thought to be caused by scandium impurities in it.

Isolation

Thortveitite and kolbeckite are the primary mineral sources of scandium.   Uranium-mill tailings by-products also are an important source.  Pure scandium is commercially produced by reducing scandium fluoride with metallic calcium.

Applications

Since it is a very rare metal, scandium doesn't have many applications. If it were more common, it might be useful in the making of aircraft and spacecraft structures, probably alloyed with other metals.

It is also used in various lacrosse sticks; the light yet strong metal is needed for precise accuracy and speed. At least one U.S. gun manufacturer is producing pistol frames and cylinders made of an aluminum-scandium alloy.

Approximately 20 kg (as Sc2O3) of scandium is used annually in the United States to make high-intensity lights.  Scandium iodide added to mercury-vapor lamps produces an efficient artificial light source that resembles sunlight, and which allows good color-reproduction with TV cameras.  About 80 kg of scandium is used in light bulbs globally per year.  The radiioactive isotope Sc-46 is used in oil refineries as a tracing agent.

The main application of scandium by weight is in aluminum-scandium alloys for minor aerospace industry components, and for unusual designs sports equipment (bikes, baseball bats, firearms, etc.) which rely on high performance materials. However, titanium, being much more common, and similar in lightness and strength, is much more widely used, with tons found in some aircraft, especially military ones.

When added to aluminum, scandium substantially lowers the rate of recrystallization and associated grain-growth in weld heat-affected zones. Aluminum, being a face-centred-cubic metal, is not particularly subject to the strengthening effects of the decrease in grain diameter. However, the presence of fine dispersions of Al3Sc does increase strength by a small measure, much as any other precipitate system in aluminum alloys. It is added to aluminum alloys primarily to control that otherwise excessive grain growth in the heat-affected zone of weldable structural aluminum alloys, which gives two knock-on effects; greater strengthening via finer precipitation of other alloying elements and by reducing the precipitate-free zones that normally exist at the grain boundaries of age-hardening aluminum alloys.

The original use of scandium-aluminum alloys was in the nose cones of some USSR submarine-launched ballistic missiles (SLBMs). The strength of the resulting nose cone was enough to enable it to pierce the ice-cap without damage, and so, enabling a missile launch while still submerged under the Arctic ice cap.

Market

The metal is lightweight and fairly corrosion-resistant.  It also has a high melting point and therefore finds applications in the aerospace industry.   Scandium is widely distributed on the earth and has an abundance similar to cobalt and lithium.  Most commercial scandium is obtained from the uranium refining process.

World production of scandium is in the order of 2,000kg per year, generally as a byproduct of uranium and nickel-cobalt-copper or PGE mining. Consumption is in the order of 5,000kg, and typically is consumed in bicycle frames in Sc-Al alloys at the rate of 2-5% Sc.

The present main source of scandium metal to meet this shortfall is from the military stockpiles of the former Soviet Union (mainly in the country of Ukraine), which were extracted from uranium tailings. There is no primary production in the Americas, Europe, or Australia, although gigantic scandium deposits are associated with uranium, nickel-copper-cobalt laterite deposits and associated with ultramafic rocks worldwide.

Scandium can also be extracted from tantalum residues, tungsten processing wastes, tin slags and a variety of other such industrial waste streams, and it is sometimes recovered from rare earth ores, particularly the rare earth oxide deposits of Bayan Obo, China.

The strength and commerciality of the scandium market is yet to be demonstrated as it is a specialty metal and a single producer could corner the supply with minimal tonnage production. The current price of refined scandium is in the order of $600 per kilogram.

Compounds

The most common oxidation state of scandium in compounds is +3.  Scandium chemically resembles yttrium and the rare earth metals more than it resembles aluminum or titanium.   Thus scandium is sometimes seen as the scandium oxide, Sc2O3, and as scandium chloride, ScCl3.

Scandium Ores
Euxenite, (Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)2O6
Thortveitite, (Sc, Y)2Si2O7
Bazzite, Be3(Sc, Al)2Si6O18

Isotopes

Naturally occurring scandium is composed of 1 stable isotope  45Sc.   17 radioisotopes have been characterized with the most stable being 46Sc with a half-life of 83.8 days, 47Sc with a half-life of 3.35 days, and 48Sc with a half-life of 43.7 hours. All of the remaining radioactive isotopes have half-lifes that are less than 4 hours, and the majority of these have half-lifes that are less than 2 minutes. This element also has 5 meta states with the most stable being 44mSc (t 58.6 h).

The isotopes of scandium range in atomic weight from 40 amu (40Sc) to 54 amu (54Sc).  The primary decay mode at masses lower than the only stable isotope, 45Sc, is electron capture, and the primary mode at masses above it is beta emission.  The primary decay products at atomic weights below 45Sc are calcium isotopes and the primary products from higher atomic weights are titanium isotopes.

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
Sc36 36.015  
Sc37 37.003  
Sc38 37.995 < 300 ns
Sc39 38.9848  
Sc40 39.978 182.3 ms
Sc41 40.9693 596.3 ms
Sc42 41.9655 681.3 ms
Sc43 42.9612 3.891 hours
Sc44 43.9594 3.927hours
Sc45 44.9559 Stable
Sc46 45.9552 83.79 days
Sc47 46.9524 3.3492 days
Sc48 47.9522 43.67 hours
Sc49 48.95 57.2 minutes
Sc50 49.9522 102.5 seconds
Sc51 50.9536 12.4 seconds
Sc52 51.957 8.2 seconds
Sc53 52.959 > 3 seconds
Sc54 53.963 0.22 seconds
Sc55 54.97 0.12 seconds
Sc56 55.973 80 ms
Sc57 56.977  
Sc58 57.983  
Sc59 58.988  

atom.gif (700 bytes)

Scandium Data

 

Atomic Structure

  • Atomic Radius: 2.09
  • Atomic Volume: 15cm3/mol
  • Covalent Radius: 1.44
  • Cross Section (Thermal Neutron Capture) Barns: 27.2
  • Crystal Structure: Hexagonal
  • Electron Configuration:
    1s2 2s2p6 3s2p6d1 4s2
  • Electrons per Energy Level: 2, 8, 9, 2
  • Ionic Radius: 0.745
  • Filling Orbital: 3d1
  • Number of Electrons (with no charge): 21
  • Number of Neutrons (most common/stable nuclide): 24
  • Number of Protons: 21
  • Oxidation States: 3
  • Valence Electrons: 3d1 4s2

Chemical Properties

  • Electrochemical Equivalent: 0.55914 g/amp-hr
  • Electron Work Function: 3.5eV
  • Electronegativity: 1.36 (Pauling); 1.2 (Allrod Rochow)
  • Heat of Fusion: 14.1kJ/mol
  • Incompatibilities:
  • Ionization Potential
    • First: 6.54
    • Second: 12.8
    • Third: 24.76
  • Valence Electron Potential (-eV): 58

Physical Properties

  • Atomic Mass Average: 44.95591
  • Boiling Point: 3104K, 2831C, 5128F
  • Coefficient of Lineal Thermal Expansion/K-1: 10E-6
  • Conductivity
    Electrical: 0.0177 106/cm
    Thermal: 0.158 W/cmK
  • Density: 2.99 g/cm3 @ 300K
  • Description:
    Soft silvery white metal that tarnishes in air and burns easily once ignited.
  • Elastic Modulus:
    • Bulk: 56.6/GPa
    • Rigidity: 29.1/GPa
    • Youngs: 74.4/GPa
  • Enthalpy of Atomization: 343 kJ/mole @ 25C
  • Enthalpy of Fusion: 14.1 kJ/mole
  • Enthalpy of Vaporization: 314.2 kJ/mole
  • Flammablity Class:
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 750 MN m-2
  • Heat of Vaporization: 314.2kJ/mol
  • Melting Point: 1812K, 1539C, 2802F
  • Molar Volume: 15.04 cm3/mole
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.6 J/gK
  • Vapor Pressure: 22.1 Pa @ 1539C

Regulatory / Health

  • CAS Number
    • 7440-20-2
  • OSHA Permissible Exposure Limit (PEL)
    • No limits set by OSHA
  • OSHA PEL Vacated 1989
    • No limits set by OSHA
  • NIOSH Recommended Exposure Limit (REL)
    • No limits set by NIOSH
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: 0.008
    • Bone/p.p.m: 0.001
    • Liver/p.p.m: 0.0004-0.0014
    • Muscle/p.p.m: n/a
    • Daily Dietary Intake: 0.00005 mg
    • Total Mass In Avg. 70kg human: 0.2 mg
  • Discovery Year: 1879
  • Name Origin:
    From Latin Scandia for Scandinavia.
  • Abundance:
    • Earth's Crust/p.p.m.: 16
    • Seawater/p.p.m.:
      • Atlantic Suface: 6.1E-07
      • Atlantic Deep: 8.8E-07
      • Pacific Surface: 3.5E-07
      • Pacific Deep: 7.9E-07
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 1100

Ionization Energy (eV): 6.561 eV
Estimated Crustal Abundance: 2.2101 milligrams per kilogram
Estimated Oceanic Abundance:
2.410-4 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0

(L. Scandia, Scandinavia) On the basis of the Periodic System, Mendeleev predicted the existence of ekaboron, which would have an atomic weight between 40 of calcium and 48 of titanium. The element was discovered by Nilson in 1878 in the minerals euxenite and gadolinite, which had not yet been found anywhere except in Scandinavia. By processing 10 kg of euxenite and other residues of rare-earth minerals, Nilson was able to prepare about 2 g of scandium oxide of high purity. It was later pointed out that Nilson's scandium was identical with Mendeleev's ekaboron. Scandium is apparently a much more abundant element in the sun and certain stars than here on earth. It is about the 23rd most abundant element in the sun, compared to the 50th most abundant on earth. It is widely distributed on earth, occurring in very minute quantities in over 800 mineral species. The blue color of beryl (aquamarine variety) is said to be due to scandium. It occurs as a principal component in the rare mineral thortveitite, found in Scandinavia and Malagasy. It is also found in the residues remaining after the extraction of tungsten from Zinnwald wolframite, and in wiikite and bazzite. Most scandium is presently being recovered from thortveitite or is extracted as a by-product from uranium mill tailings. Metallic scandium was first prepared in 1937 by Fischer, Brunger, and Grienelaus who electrolyzed a eutectic melt of potassium, lithium, and scandium chlorides at 700 to 800oC. Tungsten wire and a pool of molten zinc served as the electrodes in a graphite crucible. Pure scandium is now produced by reducing scandium fluoride with calcium metal. The production of the first pound of 99% pure scandium metal was announced in 1960. Scandium is a silver-white metal which develops a slightly yellowish or pinkish cast upon exposure to air. It is relatively soft, and resembles yttrium and the rare-earth metals more than it resembles aluminum or titanium. It is a very light metal and has a much higher melting point than aluminum, making it of interest to designers of spacecraft. Scandium is not attacked by a 1:1 mixture of HNO3 and 48% HF. Scandium oxide costs about $75/g. About 20 kg of scandium (as Sc2O3) are now being used yearly in the U.S. to produce high-intensity lights, and the radioactive isotope 46Sc is used as a tracing agent in refinery crackers for crude oil, etc. Scandium iodide added to mercury vapor lamps produces a highly efficient light source resembling sunlight, which is important for indoor or night-time color TV. Little is yet known about the toxicity of scandium; therefore it should be handled with care.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond