With a different manufacturing process, a graphene/aerogel composite can be created that weaves carbon nanotubes (a single-walled carbon nanotube is effectively a rolled sheet of graphene) into ultra-strong cables.
Carbon nanotubes have been created with a length-to-diameter ratio of 132,000,000:1 – significantly longer (and stronger) than any other known material (reference: Wang, X.; Li, Qunqing; Xie, Jing; Jin, Zhong; Wang, Jinyong; Li, Yan; Jiang, Kaili; Fan, Shoushan (2009). “Fabrication of Ultralong and Electrically Uniform Single-Walled Carbon Nanotubes on Clean Substrates”. Nano Letters). In other words, carbon nanotubes that are 0.000002mm thick x 300mm long have been created.
Along their lengths, carbon nanotubes are as strong as sheets of graphene – i.e. 100-300x stronger than steel – and they aren’t much thicker. Carbon nanotubes can also be cut along their lengths – forming graphene nano-ribbons. These graphene nano-ribbons can then be aligned using atomic-level forces called Van der Waals forces, in which a group of graphene nano-ribbons become aligned along the same positive/negative polarities. This process can be adjusted so that a long ribbon of aligned nano-ribbons (or a long, flat thread of carbon nanotubes) is formed.
By shifting the Van der Waals forces whilst building up successive layers of graphene and aerogel, a layered lattice structure can be formed – similarly to how a plywood sheet is formed. This process imparts a great of strength to the GCL graphene/aerogel composite.
The key to the strength ultra-strong cables is the length of the carbon nanotubes and/or graphene nano-ribbons. We expect that the aerogel layer will act a shock/vibration absorber, so that the forces that cause cables to break (shear forces) are quickly and effectively dispersed (see Figure below).
As with the GCL graphene/aerogel bulletproof armour, because the graphene/aerogel composite takes far fewer layers to reach a given thickness than a pure graphene ultra-cable would, we expect that production costs can be much lower.
The main customer groups for these ultra-strong cables are lift manufacturers, the construction industry, and large crane/pulley producers.
Lift manufacturers (such as Otis Elevators and Kone) have long faced a height constraint – steel lifting cables can only run up 500 meters before the weight of the steel in the cable itself begins to pull it apart. That is why one needs to change lifts in very tall buildings. Kone has recently developed a carbon-fibre based tape that can reach 800 meters – but that still isn’t long enough for some of the tallest buildings.
Given their much higher strength-to-weight ratios and their much greater shock absorption/vibration dampening abilities, GCL graphene/aerogel ultra-strong cables should be able to reach much greater heights – theoretically, heights of 50,000 meters – 50 km – could be achieved.
Space elevator cable
This could enable a revolutionary idea for space travel – the space elevator – to be created. First proposed in 1895 by Konstantin Tsiolkovsky and popularised by Arthur C Clarke in his 1979 book, The Fountains of Paradise, the idea of the space elevator was to attach a cable anchored on Earth’s equator to a counterweight beyond geostationary orbit (35,800 km above Earth). If the centre of mass for the system was above the geostationary orbit level, the centrifugal force along the cable would hold it tight – enabling an object to be lifted into space by travelling up the space elevator cable. This would require far less energy (over 99% less) than a rocket propulsion system.
In 2003, the NASA Institute for Advanced Concepts released a study that investigated the use of carbon nanotubes to create the cable, and their conclusion was that it was theoretically possible. The required strength of the cable material was 100 GPa (gigapascals), steel cable, in comparison, was rated at 3 GPa. NASA estimated that the theoretical strength of carbon nanotubes was 300 GPa – i.e. roughly treble the strength required to produce the space elevator cable. However, there were a number of technical challenges with the carbon nanotubes (e.g. variances in batch purity and strength) as well as the logistical production challenge of weaving together trillions of strands of carbon nanotubes.
Depending on the structure, the GCL graphene/aerogel composite could reduce the number of strands required by a factor of 1,000 – significantly lowering the production costs. The graphene/aerogel cable should also be better able to withstand shocks and vibrations versus a carbon nanotube-only cable.
In the 2003 study, NASA estimated the technical cost of developing the space elevator at $6.5bn, +/- $0.5bn, with the vast bulk of the expenditure being on manufacturing the cable. If this space elevator could be developed, we believe it could not only attract the $6.5bn in potential funding for the space elevator, it could eventually replace all commercial rocket launches.
Graphene Composites Ltd 