Nanotubes: Applications today and tomorrow

1. Nanotubes: Applications today and tomorrow By: Rickard Nilsson, Anders Lundskog, Christian Ohm

2. Outline 1. Introduction: 1.1 What is a carbon nanotube (CNT)? 1.2 Key properties 2. Applications: 2.1 Electric field emission and flat-panels 2.2 Strong and conducting plastics 2.3 Solving heat-related problems in computer chips 2.4 Space elevator 3. Conclusion

3. 1. Introduction • Nanotubes are made of rolled-up sheets of graphite SWNT – Single-Walled Nanotube MWNT – Multi-Walled Nanotube Nanotubes is one of the hottest subjects in nanotechnology for both scientists and industry and enormous amounts of money are spent on research.

4. Key properties 1 Why are the tubes so exciting? - The tubes have amazing mechanical and electrical properties. - Nanotubes are incredibly strong - the tubes could be at least 100 times stronger than steel at one sixth of its weight. Scientists believe that nanotubes are one of the strongest materials that can be manufactured with to day’s knowledge of materials. - Example: A bundle of nanotubes as thick as a human hair is estimated to be able to lift a semi trailer without breaking.

5. Mechanical strain simulation Twisting of a SWNT Bending of a SWNT Compression of a MWNT

6. Key properties 2 The electrical properties of the CNT is depending on how the graphite layer is rolled up. • ”Armchair” – metal-like conductivity • ”Zig-zag” – semiconductor • Superconductivity is has been observed at very low temperatures. These tubes exhibit electrical conductivity as high as copper, thermal conductivity as high as diamond. • (The way of folding does not seem to affect the mechanical properties) A) B)

7. Electric Field Emission • Because of the very good electrical conductivity of the CNTs and the fact that they are extremely thin they make great emitters of electrical fields. • Enables a new generation of flat panels. Today’s CRT monitors: A single stream of electrons is bent to light up individual pixels on the screen Tomorrow’s CNT display: Each pixel can be controlled with it’s very own field emitter in the form of a CNT. Advantages: - Low energy consumption - Can be made incredibly thin

8. Strong and conducting plastics Plastics are known to be good electrical insulators and they have a lot weaker mechanical properties than metals. Both of these can be changed by loading carbon nanotubes in the plastic mixture. A filling of 5% nanotubes into the mixture will result in more than enough conductivity to dissipate static electricity. The good mechanical properties of the nanotubes also make the plastics a lot stronger and stiffer. This has been done before by including larger fibres into the plastic mixture but not without affecting the viscosity. The fact that the nanotubes are among the smallest structures ever created solves that problem as well. This means that with a loading of CNTs you can still expect to be able to mold your mixture into very small and thin shapes.

9. Example: Car mirror housing These properties are already made of use is in the plastic mirror housings on cars. Introducing a load of CNTs in the mixture → no need for an electro- static layer of paint. If this was achieved with another filler, with larger fibres, the surface would not be as smooth.

10. CNTs in electronics • One of the biggest problems with computer chips these days is overheating. Processors in normal PCs require large and noisy fans to stay cool. Heat – problems and possible solutions P: The electrons travelling through the wires inside the processors experience some friction which causes heat. S: By using superconducting metallic single-walled carbon nanotubes as wires this problem would be reduced remarkably. P: Today’s coolers have trouble leading the heat away from the chip. S: Let the nanotubes actually lead off the heat. Carbon nanotubes have great thermal conductivity which makes them ideal for this purpose.

11. Space elevator Space travel is expensive. Each take-off costs a lot of money and a lot of them are just for transport (1 kg costs about $22000 to transport out to space). Building a space elevator would reduce these costs greatly (around $1.48).

12. Space elevator The cable If the cable is made out of steel and have a thickness of about 1 mm at the earth’s surface it would have to have a diameter of 40 biljons kilometers at it’s thickest point just to hold it’s own weight… If it is made out of kevlar it would have to be 16 m at it’s thickest point to be able to hold its own weight (around 2 gigatonnes)… Unfortunately the cable has to be at least 10 cm at the earth’s surface. To be able to do this calculations show that a cable with a tensile strength of about 63 GPa is needed (about 17 times that of kevlar). Fortunately the CNTs have a tensile strength of at least 130 GPa and would theoretically give us a solution to the problem.

13. Conclusion • CNTs display extremely good mechanical properties • Their electrical properties depend on how the graphite layer is folded • These exciting facts make CNTs ideal for applications like - Flat-panels - Improving mechanical and electrical properties of plastics - Reducing heat problems in computer circuits - Light-weight construction…