Principles for making continuous sheet graphene
Previously, we explored a speculative new idea for a continuous process that can make graphene in large-scale sheets. Chris Bentley of the Strategy Exchange, read my column and immediately recommended a book by Arthur C Clarke. I always pay attention to Chris’ advice and this time it led me to some startling connections, read on…
There are limits for elevator (lift) cables. For example the steel cables in a 400-metre-high lift weigh about 18,650kg. This weight is a concern for design engineers. Make the cables too long and they eventually tear apart under their own weight. This places limits on how high we can build skyscrapers. Make the cables stronger and lighter and we can build taller buildings. Continuous graphene sheet could be made as ribbons by the method we outlined – and layered for strength. This layered graphene ribbon would be ideal for making elevator cable. This could usher in a new age of ultra-tall buildings across the world where the occupants do not have to keep changing elevators to reach higher floors.
And we could stop there, dear InvestorIntel reader, except for the fact that I made time to read the book Chris mentioned. Those of you familiar with the fountains of paradise will be ahead of me by now…
Arthur C Clarke imagined a rather different type of elevator. In the novel he describes the construction of a space elevator linked to a satellite in a geostationary orbit some 36,000 km above the earth. Using an elevator like this, payloads can be lifted into orbit without the need for expensive rockets. The elevator cable he called hyperfilament and described it as being made from “a continuous pseudo-one-dimensional diamond crystal”
If this sounds like science fiction, well it is. Except for the fact that NASA thinks this idea is credible enough to become reality. The Europeans agree too and have their own European space elevator challenge.
NASA’s Institute for Advanced Concepts funded leading scientists to study whether this was achievable. Dr Bradley C Edwards and his team identified and addressed all the technical issues for the construction of a space elevator. They would locate the base station on a movable platform at the equator in the Pacific Ocean. Hurricanes do not cross the equator; few commercial aeroplanes fly there and the incidence of lighting and terrorist attack are small. The space elevator would have the orbital satellite tethered to the ground with a ribbon 1m wide and 100km long.
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The team concluded that all the necessary underlying technology exists, except the material for the ribbon tether that they thought should be made from carbon. So, at the turn of the century, the Office of the Chief Technologist at NASA added a competitive stimulus to its collection of Centennial Challenges called the Strong Tether Challenge.
A tether is the ribbon (or cable) that connects the satellite with the ground and the challenge is for any team that can fabricate this. As NASA says: “This challenge offers a prize purse of $2 million. Competitions have been held in 2006, 2007, 2009, 2010 and 2011. As yet no team has claimed the prize.”
I suspect the reason Chris contacted me was because he realised that the graphene sheet manufacturing process I proposed in the previous column could be applied to solve the technical challenge of making the tether ribbon.
Let’s run with the ideas we’ve started and speculate a little further…
The NASA scientists proposed making the ribbon on earth and sending in to orbit by rocket. The continuous graphene manufacturing process we outlined could make it possible to make the ribbon in space and lower it down to the base station from orbit.
The proposed process relies on creating a solution of carbon in metal melt and allowing graphene layer to form on the surface of a flotation tank. The layer can then be pulled from the surface using the freezewall. In the vacuum of space gases are not an ideal raw material to handle so rather than using methane the process can be adapted by dissolving solid carbon in the metal. We know this will work because a team at the University of California-Riverside proved that carbon will dissolve in molten metal.
Of course you will realise that flotation tanks cannot work without gravity. So a series of flotation tanks need to be placed on the inside of a rotating cylinder in orbit. This creates artificial gravity due to centripetal acceleration. Pulling the graphene sheet from the flotation tanks can form a ribbon of stacked graphene sheets. To make a stronger ribbon add more flotation tanks and therefore more layers to the ribbon. If you want more detail about how this orbital graphene foundry operates please message me.
There may be one further advantage of making graphene tether ribbon in a vacuum. Think about the edges of the graphene sheet. In our design for an atmospheric process methane will provide a source of hydrogen that will cap the edges of the graphene sheet. In a vacuum this will not happen and, if the sheet is kept flat, the carbon may not be capped until two graphene layers are placed in contact with one another. Then the edge carbon atoms could connect – bonding each layer and making the resulting ribbon so much stronger.
This process should be capable of making graphene ribbon that can then be lowered down to the base station. Now dear reader, I need to remind you that this is a proposed manufacturing method for graphene elevator cables. We will watch and see if organisations pick up on these principles and turn them into reality because this will be an investment opportunity that will literally be out of this world.
Adrian Nixon is a Senior Editor at InvestorIntel. He began his career as a scientist and is a Chartered Chemist and Member of the Royal ... <Read more about Adrian Nixon>