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Texas Scientists Spin Carbon Nanotube Fiber
RedCard writes "According to this article at news24.com, University of Texas scientists have managed to spin a fiber made of 60% carbon nanotubes that is five times stronger than steel and is "tougher than any natural or synthetic fibre described so far" - including spider silk! Previous attempts at making fibers like this have only produced relatively short lengths, but these guys have produced lengths of 100 metres at the rate of 70cm per minute!"
One can estimate theoretically the ultimate strength of a nanotube be examining the microscopic failure modes, i.e. the ways in which atoms rearrange in response to an external stress (i.e. stretching). In the case of perfect, defect-free nanotubes, there are two modes that seem to be important. First, the rotation of a single carbon-carbon bond by 90 degrees, which converts a patch of 4 hexagons (remember that carbon atoms are arranged in a chicken-wire or honeycomb pattern on the tube wall) into two pentagons and two heptagons (relevant references are Zhang & Crespi from Penn State in Physical Review Letters and work by Bernholc at NC State and Yacobson at Rice I think, but the exact journal escapes me at the moment). This mode is a plastic distortion of the tube; the tube with the bonds rearranged is a bit longer than it was before. The second failure mode is for one of the hexagonal rings of carbon atoms to break open, i.e. for a carbon-carbon bond to break. This is a more catastrophic event, in that the tube then quickly breaks near the point of failure. Which way a tube fails may actually depend on how the honeycomb pattern is rolled into a tube shape. Now that's just the microscopic theory on the ideal, defect-free system. In a real tube, one expects there to be pre-existing defects in the structure. The failure under tension will then be at the defective points But, since nanotubes are so small, it's plausible that a single tube or bunch of tubes might grow entirely defect-free, in which case one can access the ultimate theoretical failure strength. Experiments on trying to stretch and break single bundles of nanotubes (Lieber's group at Harvard) show that one can extend a nanotube by about 6% of it's length before it breaks. This is in good agreement with the theoretical predictions mentioned above (and it's a legit prediction- the theory came first!). So it appears that in small enough systems, one can attain the theoretical mechanical strength.
Kudos to you, my good man.
I seem to recall that a bright source of light can make carbon nanotubes burn up like ignited magnesium.
Yea, I'd be the first to wear or use this fabric.. "Smile for the camera!"
"No, wait!" *clic-FLASH* "AAAARGH THE HUMANITY!"
"Could this stuff, if produced cheaply enough in the next 20 years, be the end-all of condoms?"
Yeah because Slashdotters are all in immediate danger of unwanted pregnancies.
The effect only works with single walled carbon nanotubes, and even then only when in air. The effect actually happens because the tubes are very black and very porus, absorbing a large amount of light and rapidly converting it to a violent expansion of the surrounding Oxygen in the air igniting the nanotube. This will never occur if the tubes are incorporated into an epoxy string.
- "Hear that?! The percolations are imminent! Cease your ingress!"
The elevator becomes feasible at around 130GPa, so there is a little ways to go yet. It is only a matter of time now.
Actually, myself and another poster re-derived the minimum tensile strength for a space elevator the last time the subject came up. The figure for a minimal self-supporting space elevator that barely supports its own weight is about 63 GPa, and everything past that is gravy, so we're even closer than your numbers suggest.
Range Voting: preference intensity matters
The highlift people are using that figure (130GPa) in their calculations. Since the previous record on strength was achieved fairly recently at 3.6 GPa, anything over 20 GPa means a tremendous jump in the state of the art. Not only is it stronger but it's made faster.
We're not at elevator strength yet but we're getting there.
Highlift did not go down the toilet. They existed to be an entity to receive money from NASA for the NIAC Phase 1 and Phase 2 grants. Those phases are over, and therefore Highlift has no reason to exist (it wasn't really a 'company' per se).
Contrary to what Slashdot has said, LiftPort (www.liftport.com/www.liftport.org) is not a competitor to Highlift - it was simply the natural next step (in Michael Laine's opinion - Brad Edwards thought that the time wasn't right for a public push yet) of moving from a government-funded research lab to a privately-funded company.
Incidentally, if you haven't been to www.liftport.com recently, they overhauled their website (it looks very good now) and are in an investment phase - they've already received over $1M in funding (not bad!). The "public" end, akin to Highlift, is going to be at www.liftport.org.
"Requires" is a slippery word, because to some extent you can make up for a weaker material by tapering the cable so it's thicker in the middle where it's holding the "weight" of both ends, and thinner at the ends so there's less load.
The amount of taper gets absurd in no time for materials weaker than unobtainium. High Lift Systems quotes a taper ratio of 1.7E33 for steel and 2.6E8 for Kevlar, and that's apparently for a cable stressed to the breaking point.
10 or 20 times stronger than steel would be usable, in other words.
whoa...