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Tiny threads of carbon are revolutionising our lives. Because of them, planes fly faster, cars are safer, and tennis stars hit faster aces. Carbon fibre is costly compared with steel and aluminium, but it is stronger and lighter.
As a result, it is found in an ever-widening range of products, from space shuttles, Formula One cars and firearms to electric vehicles, fishing rods and loudspeakers. It can even be wrapped around the legs of ageing bridges to make them more earthquake-resistant.
Carbon fibre is up to five times as strong as steel, yet half the weight. Its remarkable qualities result from the way it is made. Carbon fibres form when certain organic polymers are carbonised – heated to temperatures as high as 3000 °C.
The atoms vibrate fiercely, driving off hydrogen and nitrogen. What is left behind is a 7-micrometre-thick fibre composed almost entirely of carbon atoms. Manufacturers twist tens of thousands of these fibres into threads which they then weave into fabric.
From here, the fabric can be used to make products of wildly different shapes by embedding it in resin to make a composite. This versatility is another of carbon fibre’s advantages. The shapes are stiff, light, corrosion-proof, tear-resistant and heat-resistant.
The use of carbon-fibre reinforced composites has expanded explosively since the 1970s. They are, for example, displacing aluminium as the most common material in commercial jets, which benefits both the environment and the passengers, says Anthony Kelly, emeritus professor at the University of Cambridge’s department of materials science.
“The lighter weight provides greatly reduced fuel burn and a side advantage is that high humidity in the passenger cabin is possible because composites do not corrode like aluminium,” he says. Carbon composites account for at least half the weight of the Boeing 787 Dreamliner and the Airbus A350.
The first commercial carbon fibre may have been created by American inventor Thomas Edison. He carbonised bamboo strands to make filaments for his early light bulbs. Yet the usually astute entrepreneur did not realise the structural significance of these threads, which were later replaced with tungsten wire.
The modern era of carbon fibre began in 1958 when Roger Bacon at the Union Carbide Corporation in Cleveland, Ohio, reported the first graphite ‘whisker’. His fibre had a tensile strength – a measure of the stretch a material can withstand without breaking – 20 times that of steel.
The fibre was also very stiff, with a Young’s modulus – a measure of its elasticity – more than three times that of steel. But, astonishing though the material was, it was too costly to roll out commercially.
In 1964, Bacon and two colleagues unveiled a far cheaper option, made by carbonising strands of rayon. Although strong, it was not as stiff as steel.
Meanwhile, scientists elsewhere had found a more effective solution. In 1961, Akio Shindo at the Government Industrial Research Institute in Osaka, Japan, created carbon fibres from polyacrylonitrile. The fibres’ tensile strength was three times that of rayon-based fibres.
In 1964, Willie Watt and two colleagues at the Royal Aircraft Establishment in Farnborough, UK, used polyacrylonitrile to produce an even stronger material. “He wasn’t the first person to make a carbon fibre, but he was the first to make a truly effective one,” says Kelly.
The secret to Watt’s success was his multiple-stage heating process. After warming the polyacrylonitrile to 300 °C, which causes it to form stable, ladder-shaped chains, he raised the temperature to 700 °C. This drove off the hydrogen atoms.
Finally, Watt hiked up the temperature to 1300 °C in the absence of oxygen, causing the chains to expel nitrogen and fuse into ribbons. On a fibre’s surface, these ribbons lie parallel to its axis. But inside the fibre, they fold into hairpins and interlock, strengthening it.
Today, 90 per cent of all carbon fibre is made from polyacrylonitrile. Watt died in 1985, but lived to put his discovery into practice – golf practice, that is. According to his obituary in the Biographical Memoirs of Fellows of the Royal Society, Watt’s carbon-fibre golf club added a good 20 metres to his tee shots.