Zirconium is a very strong, malleable,
ductile, lustrous silver-gray metal with a melting point of 1852.0¡ãC. At
ordinary temperatures it has a hexagonal close-packed crystalline structure.
Its chemical and physical properties are similar to those of titanium, the
element above it in Group 4 of the periodic table. Zirconium is extremely
resistant to heat and corrosion. Low neutron-capture cross-section and good
resistance to corrosion under normal service conditions of Zr alloys make them
useful in nuclear energy applications. In powder form, zirconium is highly
flammable, but the solid form is far less prone to ignition. The inherent
toxicity of zirconium compounds is low. Hafnium is invariably found in
zirconium ores, and the separation is difficult. Commercial grade zirconium
contains 1 to 3% hafnium.
The purified metal is primarily used in
the nuclear industry to form outer layers of fuel rods in nuclear reactors.
Zirconium is also used in corrosion-resistant piping, heat exchangers, and lamp
filaments. Alloys of zirconium are used for medical implants and prosthetic
devices. Its alloy with niobium is superconductive at low temperatures. Also,
zirconium-aluminum alloys are used to make high-strength bicycle frames and lacrosse
sticks.
This metal also boasts many other
uses, such as in photographic flashbulbs and surgical instruments, in the
removal of residual gases from electronic vacuum tubes, and as a hardening
agent in alloys, especially in steel. This metal is mainly used in nuclear
reactors. It is employed in tubes for cladding uranium oxide fuel. The reason
why It is well suited for this purpose is because it is corrosion-resistant and
will not easily absorb thermal neutrons. It is specially purified without
hafnium, which absorbs neutrons much more readily. It is usually alloyed with
other metals to make it more corrosion-resistant for these uses.
Zirconium is very resistant to
corrosion by many common acids and alkalis and by sea water. It is therefore
used extensively in the chemical industry where corrosive agents are employed.
This metal is used as an alloying agent in steel and is employed for making
surgical appliances as well. Zirconium/niobium alloys are used to make super
conductor magnets. Alloys with zinc become magnetic at temperatures below 35 K.
Zirconium is used as a "getter" in vacuum tubes, in flash bulbs for
photography, in explosive primers, and in lamp filaments.
Zirconium alloys can be machined by
conventional methods, but they have a tendency to gall and work harden during
machining. Consequently, tools with clearance angles higher than normal are
needed to penetrate previously work-hardened surfaces. Zirconium has better
weldability than some of construction metals including some alloy steels and aluminum
alloys that are more common. Low distortion during welding stems from a low
coefficient of thermal expansion. Welding zirconium requires proper shielding
because of the metal¡¯s reactivity to gases at welding temperatures. Welding
without proper shielding (argon or helium) causes absorption of oxygen,
hydrogen, and nitrogen from the atmosphere, resulting in brittle welds.
As a result of its exceptional
corrosion resistance, zirconium is used extensively in corrosive environments in
the chemical industry where zirconium alloys can be found in pipes, fittings
and heat exchangers.
Zircon (zirconium silicate, ZrSiO4) is
a natural gemstone and synthetic cubic zirconia (zirconium dioxide, ZrO2) is
produced as a low-cost substitute for diamond.
Zirconium-based catalysts are used in
amination, hydrogenation, isomerization and oxidation reactions.
Lithium zirconate can be used to
absorb carbon dioxide. The reaction is reversible so the carbon dioxide can be
released in well-chosen location and the lithium zirconate can be used again.
This application may be useful in addressing environmental concerns about the
release of carbon dioxide into the atmosphere.
Zirconium resists corrosion, and
hence, it is used as an alloying agent in materials that often come in contact
with corrosive agents. Some of these materials are used as surgical appliances,
vacuum tube getters, and filaments or explosive primers. Being heat-resistant,
the alloys of zirconium are employed in space vehicles. Its biocompatibility,
appearance, and strength make oxidized zirconium useful for dentists to prepare
the crowning of the teeth.
Other important uses include its use
in the core structural material of a nuclear reactor. Here, this metal is used
because of its strength and thermal neutron absorption, which allows the
structural material to absorb the thermal neutrons. If you lower the thermal
neutron absorption, then the efficiency of the nuclear reactor increases.