TITANIUM is fantastic stuff鈥攊t鈥檚 lighter than steel yet strong and
tough enough to survive the extremes of space or the corrosive salts and
pressures of the deep ocean with hardly a blemish. In fact, just about the only
drawback with the material is its price tag. Titanium is currently six times as
expensive as stainless steel. But this looks set to change, with the discovery
of a new way to extract titanium metal that requires little more than black sand
and electricity. It鈥檚 a far cry from the usual method, which is slow, expensive
and consumes tonnes of corrosive chemicals. Best of all, the process promises to
slash the price of the metal by up to three-quarters.
Put this new technology to work and titanium could infiltrate our lives in
all kinds of ways. Manufacturers could replace steel, aluminium and even some
plastics, creating a new generation of lightweight, high-speed ships and
fuel-efficient engines. With titanium beams, cables and tie rods, engineers
could stretch skyscrapers and bridges to new extremes. Cars built with titanium
parts and bodies would never rust.
The new process also promises exotic titanium alloys and shape-memory metals,
and we may even see entirely new materials that can鈥檛 be made by conventional
techniques. 鈥淭his is the century of titanium,鈥� says Rod Beddows, director of
British Titanium, a company set up to exploit this new technology.
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Like many of the best discoveries, this one was made entirely by accident.
Derek Fray, head of the department of materials science and metallurgy at
Cambridge, wasn鈥檛 even trying to extract titanium. Together with a couple of
colleagues, he was simply attempting to purify it.
Titanium usually contains a small amount of dissolved oxygen near its surface
which can weaken the material. So Fray, Tom Farthing and George Chen decided to
try to remove this impurity using electrolysis. They hoped that current flowing
through the titanium would drag the oxygen ions to the surface of the material
where they could be removed. But the researchers noticed an unexpected side
effect.
The titanium they were using had a thin layer of oxide on its
surface鈥攕omething which always forms when the metal is exposed to air.
They noticed that during the electrolysis this oxide coating was converted back
to the pure metal. The discovery seemed too good to be true, so they tried the
trick on particles of solid titanium dioxide鈥攖he same stuff used to whiten
paper and paint. Unbelievably, the electrolysis converted the oxide to titanium
metal.
The researchers realised they had stumbled across a completely new way to
extract titanium. The following year Fray sent a confidential report to
Britain鈥檚 Defence Evaluation and Research Agency, DERA, and visited DERA
metallurgist Malcolm Ward-Close to discuss the Cambridge results. 鈥淚 could
hardly believe it,鈥� Ward-Close says. 鈥淚 got very excited and offered to develop
the technology and scale it up.鈥�
Funding for such a speculative idea was hard to come by. The project remained
on hold until James Hamilton, the chairman of Bushveld Alloys, a South African
titanium exploration company, visited DERA. He offered to fund a pilot plant in
exchange for an exclusive licence, and the team set up British Titanium. Work on
the pilot plant began soon afterwards.
A few years later and the first production trials at DERA have finished. The
small plant has proved extremely successful. 鈥淚t worked like a dream,鈥� says
Ward-Close.
The process takes place in an electrolytic cell. The cathode is connected to
a pellet of titanium dioxide powder, while the anode is made of an inert
material such as carbon. The two electrodes are immersed in a bath of molten
calcium chloride, which acts as the electrolyte. When the power is switched on,
electrons at the cathode decompose the titanium dioxide into titanium metal and
oxygen ions. The ions flow through the electrolyte to the anode, where oxygen is
released as a gas.
Now British Titanium plans to build a much larger pilot plant and to move
towards full commercial exploitation of the technology鈥攏ow named the FFC
Cambridge process after its discoverers.
Light work
Compared to the Kroll process鈥攖he method used at the moment to extract
titanium from its ore鈥擣FC is revolutionary, says Hamilton. The Kroll
process converts titanium ore into titanium tetrachloride and then reacts it
with liquid magnesium to produce titanium metal and magnesium chloride. It is a
batch process that is expensive, labour intensive and relatively slow. 鈥淭he
process takes several days and produces only a few tonnes of titanium per
reactor vessel,鈥� says Harvey Flower, a metallurgist at Imperial College, London.
What鈥檚 more, mass production is difficult with the Kroll process. All in all it
has some pretty serious limitations.
On the other hand, Ward-Close estimates that the FFC process would take less
than 24 hours to produce the same amount of titanium a Kroll reactor vessel
produces in a week. Crucially for mass-production purposes, FFC could be a
continuous process, churning out slabs of titanium from one end while the oxide
is fed in at the other. It鈥檚 also far less polluting than the Kroll process and
incredibly reliable, says Hamilton. DERA is successfully producing kilogram
batches of titanium metal time and time again.
If the process scales up to an industrial level as expected, the price of
titanium should fall substantially鈥攑erhaps by as much as 75 per cent. 鈥淚t
will create a new demand for titanium metal,鈥� says Hamilton. In about a decade,
he predicts, we could have a full-scale titanium revolution.
British Titanium believes it could eventually increase titanium usage from
its current level of 60,000 tonnes up to 1 million tonnes per year. There鈥檚
certainly no shortage of raw materials. Titanium is the ninth commonest ore in
the Earth鈥檚 crust.
So where will we see the benefits of the revolution? Well, there are all its
current applications, of course鈥攖itanium is already used in the aircraft
industry and for prosthetic implants such as hip replacements. Cheaper titanium
would certainly expand the repertoire of materials used in these areas.
Architects, too, like the stuff. Pretty soon, shimmering titanium cladding like
that on the Guggenheim Museum in Bilbao could be springing up all over the
place. And why not use it structurally, says Simon Cardwell, a metallurgist at
London-based engineering consultants Arup. Titanium may not be as stiff as
steel, but with its strength and corrosion resistance, it could help engineers
design bigger and longer-lasting bridges and skyscrapers.
And then there鈥檚 the motor industry. Car manufacturers have long had their
eyes on titanium as a substitute for steel, but it has always been too
expensive. 鈥淭he car industry would like to use titanium as it is light, strong
and highly corrosion resistant,鈥� says Fray. An engine containing titanium parts,
for example, would be much lighter so you could expect significantly better fuel
consumption than today鈥檚 engines offer.
Unfortunately, it鈥檚 going to be quite some time before your car鈥檚 body panels
are cast from titanium. The price of the material would have to fall even
further if it is to replace the kinds of cheap steel currently used in car
bodies. Ward-Close has a solution, however, and he found it on the beach. 鈥淲e
are looking at using rutile sand, which is basically black sand,鈥� he says. 鈥淭he
better stuff is about 96 per cent titanium dioxide.鈥� He thinks that the FFC
process could turn rutile sand into a cheap and cheerful titanium alloy suitable
for car body panels.
But it鈥檚 in alloy production that FFC really seems to excel. It can produce
alloys directly, including the most widely used one, which contains 6 per cent
aluminium and 4 per cent vanadium. 鈥淭he Kroll process cannot do this,鈥� Flower
says.
This is a major breakthrough. Alloys are generally much more useful than pure
metals because the proportions can be adjusted to give the mixture much better
properties than the individual metals. And with the FFC process, alloy
production is simplicity itself. 鈥淚t鈥檚 just like making a cake,鈥� says
Ward-Close. You simply blend in the alloying additions as oxides, stick them
together and bake the mixture in a kiln. This high-tech cake then forms the
cathode in the FFC process, and the oxides are all converted into metal. Et
voila! The perfect alloy almost every time.
Better still, the process isn鈥檛 restricted to titanium. Fray has produced
zirconium, niobium, iron and chromium from their oxides, and turned out many of
their alloys too. He believes the process will enable them to make exotic alloys
and compounds that are usually difficult鈥攐r impossible鈥攖o make.
Things like shape-memory alloys, for example. These are alloys that change shape
when heated or cooled in the right way. Most can be bent into any shape you want
at low temperatures, but return to their original shape when heated.
Nickel-titanium is a common shape-memory alloy, but it is hard to produce
because nickel and titanium have different densities. With the FFC process, says
Fray, nickel-titanium would be far cheaper. They are also looking at making
superconducting alloys鈥攕uch as niobium-titanium鈥攁nd magnetic
materials, which should cost about one-tenth as much as the same materials made
using conventional techniques.
With this array of exotic alloys in the pipeline, we may even see a new
generation of cheap supersonic aircraft or lightweight, personal
mini-helicopters. And thanks to its corrosion resistance, titanium is a natural
for naval applications鈥擩apan already has a number of small craft and
racing yachts made using titanium.
In a decade or so, you may find yourself at the quayside, ready to set sail
in a gleaming, lightweight titanium cruise liner. Because the metal is so light,
the ship would sit high in the water as it whisks you across the ocean. If its
titanium-alloy engines are efficient enough, the ship may even be able to skim
over the water鈥檚 surface, cutting the journey time to a fraction of what
traditional steel liners can manage.
By the time all these grand designs for titanium come about, you鈥檒l probably
be used to it cluttering up your house as well. 鈥淚f titanium overlaps with
stainless steel in price, it could take a big slice of the market,鈥� says
Ward-Close. This high-tech metal could end up in lightweight saucepans, washing
machines and cookers鈥攅ven the kitchen sink. 鈥淗ow about a canteen of
titanium cutlery?鈥� Flower suggests.
Titanium may have proved itself in the aerospace industry and on missions to
the ends of the Solar System, but when it finally makes it into the home, it
will face its ultimate test. Could titanium toys ever be tough enough to survive
the temper tantrums of a three-year-old?