Ultimate Strength of CNT Ribbon: Article by Pugno
There’s been some discussion recently (as well as emails sent directly to us) about the Nature letter which summarizes an article by N. Pugno predicting that the maximum strength possible in bulk CNTs will be roughly 30 GPa (as opposed to the 130 GPa predicted by Edwards 4+ years ago).
I posted about the paper mentioned in Nature to our forums back in January, and some (mostly non-LiftPort) people responded:
http://www.liftport.com/forums/showthread.php?t=356. Here is what I just wrote in an email about the issue:
I’ve discussed the article with a couple of CNT researchers, and they say that they’re not convinced by the paper. My attitude is that we have to wait and see what really happens, because there’s a lot about carbon nanotubes that we don’t know yet.
Despite anyone’s predictions, we won’t know what the material will be like until it’s made. There’s a LOT of other work that needs to be done on SE development regardless of what the material winds up being. And in the “worst” case, you can still build a space elevator on the moon with near-term materials.
One thing to remember is that, even if bulk CNT were limited to 30 GPa, we could still build the space elevator. It would just become limited by finances. That’s because, with a density of 1300kg/m^3 and a strength of 30GPa, the mass of a seed ribbon (using the same assumptions as in my November article – safety factor of 2, and 1,000kg capacity) would be roughly 3,440 tonnes (i.e., 3.44*10^6 kg), or roughly 170 rocket launches (using current medium-lift rockets) to loft it (i.e., ~80 times as massive as in the 2002 NIAC report). The expense and logistics of creating a seed ribbon at that point (assuming you’re launching from Earth) becomes much more daunting, but not impossible.
May 25th, 2006 at 8:39 pm
[...] Tom Nugent at LiftPort is not discouraged. [...]
May 27th, 2006 at 4:19 pm
The path to a difficult goal can be more valuable then to reach it at once.
Even if the costs would be incredibly high to achieve this.. Imagine a space station being build by just lifting the pieces up. Wouldn’t the cost lower drastically by not having to buy rockets ?
Human kind tries to resolve all problems they encounter on their quest in all industries.
I’m happy there are still people trying to achieve practically impossible missions.
May 27th, 2006 at 10:04 pm
Paul, that is often referred to as the elastic energy problem. And no, it has not been resolved one way or the other. It is, in my mind, the biggest outstanding potential show-stopper. I did some extremely rough calculations in February of this year, and I’ve been talking to a couple of people about doing more detailed analyses. But the simple truth is that no one really knows what kind of problem it would be.
June 15th, 2006 at 11:28 am
Tom, have you considered electron irradiation? There’s a paper in Science, vol 312, pg 1199, which claims that CNTs contract when irradiated. This process should cure defects in the nanotubes, and pack them tight enough to achieve 130 GPa without spinning them. This process might also repair cosmic ray damage when applied by a climber.
Tight packing might help the elastic energy problem as your paper suggests, but I still favor separated threads rather than a ribbon. Rockets would put up the first thread, climbers would put up hundreds more, then they would all be connected under equal tension with appropriate spacer bars.
June 15th, 2006 at 6:24 pm
There is an overlooked adjunct/alternative to carbon nanotubes – something that is exactly what Arthur C. Clarke envisioned in The Fountains of Paradise – diamond fiber.
The new polymer, poly(hydridocarbyne), PHC, thermolizes to hexagonal diamond in an inert atmosphere at low temperature (http://en.wikipedia.org/wiki/Poly%28hydridocarbyne%29).
Upon a moment’s reflection one can see that by using PHC infused into a carbon nanotube yarn, and then themolizing to diamond maxtrix surrounding the CNT yarn, that many of Pugno’s objections may well be obviated.
Of course, spinning a pure PHC fiber and then thermolizing to a pure diamond fiber would yield exactly what Clarke posited.
The Wiki reference above has citations for the polymer.
July 17th, 2006 at 3:32 pm
Is there a list of proposed methods to make CNTs?
I know of at least three that should be investigated, one of which should make single wall tubes–possible in mile lengths.
Keith Henson
July 25th, 2006 at 8:50 am
Here’s a spiral-shaped carbon nano-tube that’s just recently been discovered that’s dozens of times stronger than the conventional cylendrical tube.
http://www.pinktentacle.com/2006/05/polygonal-spiral-shaped-carbon-nanotubes-dis\
covered/
Whatever the usefulness of this particular one is, the pace of discovery is very promising I think.
April 13th, 2007 at 5:10 am
[...] Our response to Pugno’s paper was written by Tom Nugent – here. [...]
April 13th, 2007 at 11:51 am
I already knew that the hexagons in the CNTs could have 2 different orientations and one looks stronger than the other. What research are we doing on the stronger version? What research are we doing on poly(hydridocarbyne) PHC? If we can use PHC to make defect-free diamond nanofiber of any length then the problem is solved. We should put almost all of the $4 million prize money into PHC contests.
Poly(hydridocarbyne)
From Wikipedia, the free encyclopedia
Poly(hydridocarbyne)
Formula [HC]n
Molecular mass 200,000 to 100 million Daltons
Melting point decomposes @ 100°C
Boiling point N/A
Density ??.?? g/cm∏
CAS number ???-??-?
SMILES ???????
Poly(hydridocarbyne) (PHC) is one of a class of carbon-based random network polymers primarily composed of tetrahedrally hybridized carbon atoms, each having one hydride substituent, exhibiting the generic formula [HC]n. PHC is made from bromoform, a liquid halocarbon that is commercially manufactured from methane. At room temperature, poly(hydridocarbyne) is a dark brown powder. It can be easily dissolved in a number of solvents (tetrahydrofuran, ether, toluene etc.), forming a colloidal suspension that is clear and non-viscous, which may then be deposited as a film or coating on various substrates. Upon thermolysis in argon at atmospheric pressure and temperatures of 110° C to 1000° C, decomposition of poly(hydridocarbyne) results in hexagonal diamond (Lonsdaleite).
The novelty of PHC (and its related polymer poly(methylsilyne)) is that the polymer may be readily fabricated into various forms (e.g. films, fibers, plates) and then thermolized into a final hexagonal diamond ceramic.
References
* Bianconi, P. et al (2004), Diamond and Diamond-like Carbon from a Preceramic Polymer. J. Am. Chem. Soc. Vol. 126, No. 10, 3191-3202
* Bianconi, P. et al (2004) High molecular weight polymers, U.S. Patent 20040010108
Retrieved from “http://en.wikipedia.org/wiki/Poly%28hydridocarbyne%29″