Aluminium has a split personality.
It may look dull, but it is one of the most reactive metals in th...
Aluminium has a split personality.
It may look dull, but it is one of the most reactive metals in the periodic table.
"Aluminium fires are quite terrifying," says Andrea Sella, chemistry professor at University College London.
"When you take aluminium and you burn it, you get a very, very intense fire."
From that point of view, it may not be ideal for aircraft construction - but this disadvantage is outweighed by its strength, flexibility and exceptional lightness.
The soft, malleable metal's alter ego is aluminium oxide, which forms a skin on the pure metal the moment it is exposed to air (and makes it unlikely that an aircraft will catch fire).
This oxide is so hard that it is used to make sandpaper and other abrasive materials.
Among gemstones, sapphires - crystals formed from the oxide - are second only to diamonds in their hardness.
Indeed, there is a growing industry for manufacturing industrial sapphires the size of a large bucket, suitable for use in bullet-proof glass, aeroplane windows and soon - unscratchable smartphone displays.
Although Aluminium is the third most abundant element in the earth's crust, it was not isolated until 1825, and remained so scarce that it was valued more highly than silver for decades.
The reason it remained hidden for so long, unlike gold or silver, is that it is too reactive to occur in its pure form.
Instead it is found as bauxite, a reddish-brown ore named after the French town Les Baux, where it was first discovered.
Bauxite is found across the globe, and mining it is the easy part. Far trickier is extracting the metal. It was not until 1886 that a Frenchman and an American both cracked it.
You have to melt the bauxite in another mineral called cryolite, and then pass an electric current through it, separating the oxygen atoms from the aluminium. It takes four tonnes of bauxite to produce one tonne of aluminium.
The process is highly energy-intensive and therefore expensive.
But recycling aluminium uses a fraction of the energy.
"Beverage cans get recycled within 60 days, so a can of soda is back on the shelves 60 days later," says Nick Madden, who is responsible for buying raw metal for Novelis, the world's biggest manufacturer of rolled aluminium sheets.
Once you have the metal, you can re-use it again and again, almost indefinitely.
"It is one of the few materials that is genuinely 100% recyclable," Madden says.
In theory, a day may come when we have mined all we need, and we can just keep re-using what we already have.
"If demand stops growing, and scrap comes back from older uses like buildings in the future, then that will start to reduce the required primary consumption," says Madden.
For now, though, demand is growing, and carmakers are one reason why. Lighter car bodies mean more fuel efficiency, better acceleration and braking, and lower carbon emissions.
Novelis has seen a 25% increase in demand from the motor industry in the last year, most of it coming from one of its biggest customers, Jaguar Land Rover, which has just begun manufacturing Range Rovers with aluminium.
The new car uses use 25% less fuel partly because its body is 39% lighter, helping to reduce the car's total weight by 420kg (925lb).
"That's the equivalent of five people," says Nick Rogers, the Range Rover vehicle line director.
"So, if you imagine driving around with all your family in the car - you feel the weight of the vehicle.
"When you get in the new Range Rover Sport, all of your family has gone."
Currently, Novelis obtains almost 50% of its aluminium used to make a new Range Rover from junk - empty cans, scrapped vehicles, demolition sites - and it aims to raise that to 80% by 2020.
One challenge is to ensure that more aluminium finds its way into the recycling loop.
"In the UK, I believe the recycle rate [of household aluminium waste] is about 75%," Madden says.
Whether bauxite mining is still needed in our grandchildren's day may depend on the proportion we succeed in recycling, and whether we keep coming up with new uses for aluminium - either the light, malleable metal, or the hard almost unscratchable sapphire.
BBC News | By Laurence Knight and Tim Bowler