Titanium
Last updated: November 8, 2007.
Concorde, they called it, but it
could just as easily have been named Titan.
Whizzing through the sky at twice the speed of sound (up to 2200 km/h
or 1350 mph), the world's
favourite supersonic plane
was protected from air friction by a heatproof titanium
skin
that could grow as much as 25 cm (10 in.) during flight!
It's not surprising titanium is the metal of choice in
airplanes like this: it's as strong as steel but only about half as
heavy and it doesn't go rusty. Let's take a closer look at how this
amazing material works.
Photo: Concorde: a titanium tube comes in to
land?
Photo by Jose Lopez courtesy of US
Defense Visual Information Center.
What's it like?
Think "strong, light, and rustproof" and you have the essence of
what makes titanium so important. It's a brilliant all-round
material—similar to aluminum but very much
stronger and quite a bit
heavier.
Like aluminum, titanium is a silvery-weight metal that resists
corrosion (rusting): that's because it reacts readily with oxygen and
forms a
protective layer of titanium oxide that keeps out air and water.
Titanium also resists attack by strong acids and alkalis. It's
relatively hard and brittle when it's cold and you have to heat it up
to work it into shape or draw it into wires. In chemical reactions, it
forms lots of interesting compounds
(when atoms
of titanium bond to
atoms of other elements); it also forms some extremely useful
alloys
(when titanium metal is "mixed" with other metals to combine their
useful properties).
Photo: Using sunlight and titanium dioxide to
purify water.
Photo of research at Sandia National Laboratories by courtesy of US
Department of Energy.
What's it used for?
Titanium compounds and alloys have a huge range of
applications, from the manufacture of toothpaste and false teeth to the
development of artificial hip joints and deep-diving submarines.
Perhaps the best-known use of titanium is in the compound titanium
dioxide (TiO2 also known as
titanium
white), which is one of the whitest substances known. Over 95 percent
of the titanium we consume is used in titanium dioxide, which puts the
whiteness in everything from paints, toothpastes, and
paper to porcelain ceramics, floor
coverings, and textiles.
Photo: These eyeglass frames made from a
nickel-titanium alloy were
developed for aircraft crew
at Brooks Air Force Base, Texas. They're called "shape memory" frames
because you can bend them and they'll
spring straight back to shape.
Photo by courtesy of US Defense Visual Information Center.
Arguably titanium's use as a whitener is a trivial—if economically
very important—use for
such a versatile material, because it doesn't really matter what color
our toothpaste and paint is: we could live without such things, if we
really had to.
But could we live without the titanium
alloys that are used to make airplane parts? In some modern planes,
titanium has been used in everything from the outer "skin" and the
landing gear to the
hydraulic pipes and the innermost parts
of the jet engines
(because it's light and good at withstanding high-temperatures and the
stresses
and strains caused by friction when air moves through at supersonic
speeds). Since titanium is so useful in airplanes, it's not surprising
it's used in spacecraft too.
And what about medical items made from titanium—could we live
without those? Many people have strong but flexible eyeglasses made
from titanium alloys. Thanks to its protective oxide coating, titanium
is a
perfect metal for making things like replacement hip joints because it
won't rust or react adversely with tissue or bone. The same quality
makes it ideal for lining food manufacturing equipment. You can
probably
see that strength, lightness, and an ability to resist rusting in
seawater for years on end also makes titanium a perfect construction
material for submarines.
Photo: These titanium-coated windows reflect
heat back into the building
and save energy.
Photo courtesy of US
National Renewable Energy Laboratory.
Titanium and its compounds are also important in the manufacture of
other chemicals. Titanium chlorides are used as catalysts (accelerators
that speed up chemical reactions) in the manufacture of plastic
polypropylene and many other organic (carbon-based) chemicals.
If all that sounds a bit mundane, how about jewelry made from
titanium?
There's a gem called titania that's made from titanium oxide. It's even
more brilliant than diamond, though it's much softer, so less
useful. Wedding rings made from titanium are also increasingly popular.
Where does titanium come from?
Although similar in many ways to aluminum, titanium is somewhat less
common. While aluminium is the third most abundant element in Earth's
crust, titanium ranks only ninth. Even so, it's still found in
virtually all rocks, sands, soils, and clays, as well as in
plants, animals, and water. Like aluminum, titanium's readiness to
react with oxygen means it is never found on Earth as a pure metal.
Instead, it has to be made from mineral ores called ilmenite (a complex
compound of iron, titanium, and oxygen with chemical formula FeTiO3)
and rutile (mostly titanium
dioxide, a compound of titanium and oxygen with
chemical formula TiO2) using a series of
chemical reactions that can be
difficult and costly.
Photo: There's even titanium on the Moon.
This false-color photo is a composite of 15 images taken by the Galileo spacecraft.
Areas colored blue are richer in titanium than those colored orange or red.
The deep blue, titanium-rich patch on the right is Mare Tranquillitatis (Sea of Tranquility)
where Apollo 11 landed in 1969.
Photo courtesy of
NASA Jet Propulsion Laboratory (NASA-JPL).
Most titanium is now made by the Kroll process,
in which titanium dioxide is reacted with chlorine to form titanium
tetrachloride, which is then reacted with magnesium to strip away the
chlorine and leave behind the pure metal (known as titanium "sponge").
The sponge is then cast into large bars called ingots. Japan leads
world titanium sponge metal production, followed by Kazakhstan,
China, and the Ukraine.
A brief history of titanium
- 1791: British clergyman William
Gregor (1761–1817) discovers a
mysterious substance in the mineral menachanite and names it menachite.
- 1795: A German chemist named Martin
H. Klaproth (1732–1817) finds the same substance in the mineral
rutile and gives it its modern name, titanium, after the
powerful Greek rulers named the Titans.
- 1910: American chemist Matthew
A. Hunter made the first 99.9 percent pure
sample of titanium metal from titanium tetrachloride.
- 1930s: William Justin Kroll
(1889–1973), a metallurgist from Luxembourg, invents
the modern Kroll
process, making possible large-scale production of titanium.
- 1950s–: Thanks to the Kroll process, titanium becomes less
expensive and is soon prized for its strength, light weight, and
all-round versatility.
Further reading
