Marvellous materials

Low density solids 

Aerogels are remarkable materials that have the lowest density of any known solid. The materials have structures similar to honeycombs and are typically made of carbon or silicon. They are excellent thermal insulators and can withstand high temperatures so are being considered for use in a number of applications in spaceflight, including as thermal insulation in Mars rovers.

Three times the strength of a diamond 

One contender for the strongest material, at least when tested at a temperature of 77K, is an arrangement of carbon atoms known as carbyne, which is reported to have a strength of at least 251 GPa. Carbyne consists of a chain of carbon atoms linked by double or alternating single and triple bonds and has twice the tensile strength of carbon nanotubes and three times the strength of diamond. Researchers at the University of Vienna have recently found a method to produce the material in bulk quantities.

Strong spider silk 

Physics students at the University of Leicester have calculated that spider silk might be capable of some of the feats shown in the Spiderman films. For example, in Spiderman 2, the hero stops a runaway train using his spider silk, an effect that is estimated to require the exertion of a force of around 105 N. The maximum stress on the strands of silk is estimated to be 1.3 GPa, which is within the typical range for the yield stress of spider’s silk of 1.1-1.5 GPa.

Spider silk has the unusual property of being partially elastic and partially plastic. Even small applied forces cause spider silk to deform slightly, meaning some energy dissipation occurs for any load. Researchers have found that whilst many wires made from materials, such as Kevlar and metal, oscillate around their starting point when twisted, spider silk does not. The silk’s ability to yield under small displacements dampens the amplitude of rotational oscillations and stops a spider from spinning for long periods of time when descending on a piece of silk.

Though spider silk is often cited as the strongest naturally occurring material, researchers at the University of Portsmouth have discovered that limpets’ teeth might be stronger. The tensile strength of the teeth was found to be in the range of 3-6.5 GPa. Their impressive strength is explained by the presence of reinforcing nanofibres.