Nanoseries 2/5 : How are carbon nanotubes made?

I told you the carbon nanotubes are not synthesized as a graphite sheet that rolls up so how are they made the mechanism is still not fully understood but in this video I will show you the setup for the main different techniques used by scientists to produce carbon nanotubes there are two main techniques the first one to be used was art discharge this is the chamber for the arc discharge which is filled with an unreactive gas inside two rods of graphite will be placed and we will apply a current one of the rods will be the anode and the other will be the cathode when the two rods are brought together and the count is applied a spark is produced between the rods which instantly vaporizes the tip of one of the rods and this carbon gas forms the nanotubes black soot is produced and starts to cover the whole chamber including the window so after a while we can't see anything anymore when we open the chamber we can see how the anode is being consumed and the black powder is deposited everywhere around on the cathode there is also black powder where we will find carbon nanotubes normally with twenty to thirty walls although if we also include a metal catalyst in the anode we can obtain single walled nanotubes the nanotubes made with this technique are quite perfect free of defects but the problem is that there are another bunch of carbon forms that are also produced so then it is very difficult to separate them it's also hard to make a lot this way the other main technique is chemical vapour deposition but it is most commonly known by its abbreviation CVD in this case the starting material is not graphite but some carbon-based gas a hydrocarbon we also need a metal catalyst to form tiny particles which will act like seeds in this CVD machine at Oxford University the metal is included in the starting molecules they use ferrocene which contains one iron atom per molecule the young scientist takes a clean tube and sets up next moment he introduces a clean base in the tube and closes all empty space with heat-resistant cotton to keep the heating a nonreactive gas is passed through the heated solution of the hydrocarbon the mixture passes through the furnace where the temperature can be from 300 up to 1150 degrees C he can run the experiment for as little as 5 minutes up to hours in order to get longer tubes once the experiment is finished he collects nanotubes from the short stuck on their tube site and also the bass previously clean which now has nanotubes all over it CVD is probably the most promising method to produce carbon nanotubes for industrial use it is easy to introduce other elements such as boron or nitrogen in the starting chemical the diameter of the tubes can be chosen by the size of the metal catalyst particles also we can grow the tubes on the surface which helps for future applications arc discharge and CVD are the most common techniques but there are others like laser ablation in this technique a laser is used to vaporize the carbon atoms from a graphite target laser ablation normally produces single walled nanotubes another less common technique is electrolysis this technique is in some ways similar to the arc discharge because it also uses two graphite electrodes but in this case the electrodes are immersed in molten ionic salts with this technique only multi-role nanotubes are produced they have very few walls 10 to15 and are normally bundled together as you can see there are different techniques to produce carbon nanotubes and each techniques produces nanotubes of different qualities

Channel: nano2hybrids

Views: 154,641

Rating: 4.8449111 out of 5

Keywords: nanotechnology, CVD, arc, discharge, electrolysis, laser, ablation, carbon, nanotube

Id: B4VTfgaKLAM

Length: 3min 29sec (209 seconds)

Published: Tue Nov 11 2008