Geology Reference
In-Depth Information
It is extensively used in phosphors for compact fluorescent lamps and LED
bulbs. Yttrium compounds are doped with Eu(III) to create the red colours in
CRT displays or with Eu(III) and Tb(III) to produce the green luminescence.
The production of synthetic garnets is another important application. Yttrium
oxide forms garnets with iron and aluminium oxides, (Y
3
Fe
5
O
12
) and (Y
3
Al
5
O
12
),
known as Y IG and Y AG. Y IG is widely used as microwave communication devices,
resonators, tunable transistors, as well as magnetic bubble domain-type memories
due to its ferromagnetism. Y AG is also used in jewellery, mimicking diamond gem-
stones. Y AG doped ('1%) with neodymium, erbium or ytterbium is used for high
power solid state lasers in the near-infrared region, or with chromium (Cr : Y AG)
as a red solid state laser. Additionally, Y AG doped with cerium (Ce : Y AG) is
used as a white phosphor in LEDs. Garnets with gadolinium, Y GG, are used in
phase shifters, tuners and filters in military applications. Yttrium compounds are
extensive and work in catalysts for ethylene polymerisation and special electrodes.
Yttrium oxide -yttria- stabilises the zirconium oxide used as an excess oxygen sensor
in exhaust combustion gases or, in the hot sections of jet-engines. Yttria, mean-
while, increases the strength and avoids high temperature oxidation of magnesium
and aluminium alloys and is thereby used in crucibles. Yttrium oxide is also used
in jewellery together with cubic zirconia, in high performance ceramics, and in op-
tical lenses to increase shock resistance whilst lowering the possibility of thermal
expansion. Furthermore, the yttrium barium copper oxide is found to be a high
temperature superconductor at 93 K. Finally, -radioactive yttrium-90 is used in
cancer treatments.
Yttrium is expected to have a 5% share of REE world supply in 2015. Yttrium,
like lanthanum is invariably associated with the lanthanide elements in minerals
such as xenotime, monazite, fergusonite or gadolinite.
B.2.76 Zinc
Zinc is a bluish-white transition metal. It is the fourth most consumed metal in the
world. The main use of zinc is for the galvanising of iron sheets or wires. Zinc is
also used in the formation of alloys such as brass or bronze. Zinc oxide is used as a
white pigment in plastics, cosmetics, paper, printing inks, etc and as an activator
in the rubber industry.
The major ores of zinc are sphalerite ZnS and smithsonite ZnCO
3
. Its
less important ores are franklinite Zn
0:6
Mn
2
0:3
Fe
2
0:1
Mn
3
0:5
O
4
, hemimorphite
Zn
4
Si
2
O
7
(OH)
2
and wurtzite Zn
0:9
Fe
2
0:1
S.
B.2.77 Zirconium
Zirconium is a silver-grey metal with chemical and physical properties similar to
those of titanium. It is not a particularly rare element and occurs in Nature mainly
as a silicate mineral zircon ZrSiO
4
. Baddeleyite ZrO
2
is also an important ore for
Zr.
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