Geology Reference
In-Depth Information
Added to vanadium, it becomes softer, something which improves its workability
(vanadium steel). As with other heavy REE, erbium is a good neutron absorber
and is used in control rods of nuclear power plants. Erbium is expect to constitute
0.4% of global REE supply by 2015. For more details see Sec. B.2.50.
B.2.20 Europium
Europium is one of the rarest (<1% in REO mixtures) and most expensive REE.
It is the most reactive of the group and is quite ductile. Its photo-luminescence
properties provide its commercial importance. It confers the reddish-orange and
blue colours in those phosphors used in LCD displays and in compact fluorescent
lights. In fact, europium is a phosphor activator of yttrium vanadate in TV screens.
It is also used in lasers and in mercury-vapour lamps. It finds important applications
in organic light-emitting diodes and memory devices. Its fluorescent property also
permits its use as a bio-tag material in live tissue scanning. In spite of its price,
its demand highly exceeds supply which makes this element a critical resource.
Europium is expected to enjoy 0.4% share of world REE supply by 2015. For more
details see Sec. B.2.50.
B.2.21 Fluorine
Fluorine is the lightest and most reactive element of the halogens. The three most
important minerals of fluorine are fluorite CaF
2
, cryolite Na
3
AlF
6
and flourapatite
Ca
5
(PO
4
)
3
F. Of these only fluorite is extensively used commercially. Cryolite is
a rare mineral, the only commercial deposit being in Greenland, and most of it is
used in the aluminium industry. By far the largest amount of fluorine contained
within the Earth's crust is in the form of fluorapatite. Minor occurrences of fluorine
are in the rare elements topaz or bastanesite.
Atomic and molecular fluorine are used for plasma etching in semiconductor
manufacturing, flat panel display production and microelectromechanical systems
fabrication. Sodium hexafluoroaluminate (cryolite), is used in the electrolysis of
aluminium. It is also indirectly used for the production of plastics such as teflon
and halons such as freon. Fluorides are added to toothpaste to prevent dental
cavities. Other compounds of fluorine are used in pharmaceuticals as antibiotics,
antidepressants and for the prevention of infections.
B.2.22 Gadolinium
Gadolinium is a very expensive REE. It is a ferromagnetic element that losses
this property at 292 K (Curie temperature). Alloys with gadolinium show im-
portant properties. As gadolinium presents the highest thermal neutron capture
cross-section of any element, alloys with nickel, chromium and molybdenum are
used in nuclear applications for absorbing neutrons and radiation shielding. The
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