Cambridge Team Spins Nanotube Yarn

FridayBob writes "They say it's bound to happen soon, although nobody knows exactly how and when. Well, perhaps the answer has arrived. It now seems as though some bright folks at the Cambridge-MIT Institute have figured out a way to continuously spin carbon nanotubes into a fiber. Will it be strong enough for a space elevator?" They're getting closer to commercialization (see older story) but not there yet...

Comments

"Electrical current", eh?

[lfm_the_couch]

...then could we put out satellites with massive solar cells and harvest the electricity directly through the tether, rather than inventing "beamed power"? Probably not, if my dim understanding of electrical physics is any use...

Re:"Electrical current", eh?

[breadbot]

Unfortunately, the cable is too long to send power through efficiently, since it has to reach up at least to geosynchronous orbit. Estimates of conductivity for a composite fiber are in the range of copper or other good metallic conductors. You'd get a heck of a lot of resistance through 25,000 miles of cable. Gotta beam it down or something.

According to this calculator, 25,000 miles of copper with 1 cm^2 cross section (probably an over-estimate), would have a resistance of about 6700 Ohm.

Re:"Electrical current", eh?

[another_henry]

Actually, the beamed power is not tricky at all. It is easy to do using microwaves, which can be produced efficiently with magnetrons (evidence is in your microwave oven) and converted back into electricity using rectennas.

A rectenna is basically an array of tiny antennas and diodes which rectify the microwaves back to DC. They have been around since the '60s and can operate at up to 80% efficiency (record is 84% efficiency for 30kW of power).

In 1964 William C. Brown succeeded in demonstrating a microwave-powered helicopter! (Sorry, I was unable to find any pictures). You can find more interesting info on this google search.

Re:"Electrical current", eh?

[Orne]

The longest land based transmission line is in the Congo at 1700 km, running at 500 KV DC. For the rest of us, that's 1,056 miles. So basically, we'd need 25x the longest transmission line ever built to date... so we could carry less energy than building one medium size fossil fuel plant on the ground.

Now there are several tricks to power transmission. One, raise the voltage and lower the current, and you'll have less heating of the line, as temperature is proportional to current and resistance. Needless to say, this would incredibly complicate your anchoring system on earth. Next, current flows on the surface of a wire, so transmission lines are actually bundles of smaller "threads" wound together in parallel. This evenly distributes the energy, reducing the net resistance of the "wire".

For a wire that long, you have to work with the old RCLG formulase for losses across the line... reactive charging losses and resistive heat losses. The line would be so long that the voltage would decay long before you'd reach the other end, and no power could be transferred.

Chain Mail

[justanyone]

Can no one see the fault in this scenario?

If you want a super-strong (tensile strength) fabric, you don't make it by crochet or other weaving methods. You make chain mail with it.

The crucial facts (IMHO) are these:

• Nanotubes have very high tensile strength (100 GPa?)
• They have very low surface friction
• they are difficult to make in long lengths
• Snags are inevitable in any real-world situation

The key here is that making a fabric like chain mail, by having nanotubes that are of a specified uniform length like 1/2 cm, formed into a continuous loop (torroid or donut shape), and interlocking these loops in a redundant chain-mail fashion (no pun intended), will lead to exceedingly strong fabric.

However, making a weave, with a long, continuous string, will lead to a fabric that can collapse by the cutting of the string at any point along it's course - this will lead to fraying and the fabric will pull apart.

Solid state physisists, please enlighten us if I'm way off base here, but it certainly seems the better way to go for high-strength tethers and fabrics.

Humbly but convincedly,

--Kevin J. Rice

Re:Chain Mail

[jgardn]

It can't happen like that. You are talking about a level of organization that only crystals exhibit.

Exactly how do you propose to make toroidal nanotubes? Exactly how are you going to interlock them into a pattern? This is the difficult part, and if you figure that out, I see a Nobel prize in your future.

Right now, the current thought in nanotube technology is that you aren't going to make a single, continuous tube. Even if you could, the maximum length is not going to be practically infinite.

Instead, what needs to happen is that you must "spin a thread", like we spin thread today. You take fibers and organize them so that they are randomly interlocking.

The difficult part is getting the nanotubes to stick together with a strength equal to the strength of the nanotubes. This is no problem with cotton, polyester, or sheep's wool, because each individual fiber is hairy and they stick together like velcro. The strength of the connection can be stronger than the strength of the individual fibers.

It is known that nanotubes are "sticky" to each other. There is a mutual attraction caused by various forces. This laboratory used that to their advantage by continuously spinning thread at the rate of several cm per second (!). However, the thread isn't sticking very well to each other or the stickiness isn't strong enough. The end result are threads that aren't much better than sewing threads.

Perhaps they can add a step where they put the nanotubes into a bath of chemicals and stretch the nanotubes or compress them to cause them to stick more strongly together. Perhaps if those threads are weaved together, the weave itself will cause the nanotubes to stick together better. Perhaps a thread can be developed that when put under tension compresses and thus increases the friction. These are all possible scenarios, and are the next steps.

Or perhaps this is just a really good way to make and store millions of nanotubes a second, to be dissolved and organized later.

Or maybe you can take these nanotubes and assemble them with some kind of process to line them up end to end. Maybe they will weld themselves chemically if they are lined up and brought near to each other's ends.

More experimentation is needed. Wouldn't you like to be in that lab at this time, playing with these threads?

Re:Chain Mail

[Goldsmith]

As a solid state physicist, working with nanotubes, who is also a member of the SCA, I found your post quite interesting.

The first problem is that nanotubes don't grow into toroids. They can form spirals that look like toroids under any but the most powerfull microscopes, but these spirals will unravel very quickly. That point is a weak rebuttal, because we could probably close those rings with an electron or ion beam if we really wanted to.

Also, keep in mind that there are very, very few molecules which are "stiff" all by themselves. Carbon nanotubes are definitely not one of them. It would be like making chainmail out of very strong cooked noodles. Really what you want is more than the 4 links provided by chainmail. By tangling these up, we can link up to many times more other nanotubes than by controllable copying of a two dimensional nearest-neighbor lattice. For example, if we have a three dimensional cubic lattice of interlocking rings, we have 6 links in a nearest neighbor (chainmail) case, and 14 in a nearest and next-nearest neighbor case, increasing redundancy and bonding energy. We could keep going by weaving these things together. In a really tight weave (or a huge tangle like what these nanotube fibers really are), you may have one fiber connected to hundreds of others.

Except for one more issue, all the weaving done right now might still theoretically be made stronger by closing the ends of the nantubes to avoid unravelling (so your general idea is good). If stress is put on a bend in a nanotube, it will lead to a "5-7" defect where two hexagonal rings become one ring of 5, and one of 7, inducing a 15 degree permanant bend in the tube. These defects lead to nanotubes which have at best 50% the tensile strength of a non-defective tube, but often more like 15%. That's why so much work is being put into aligned nanotube fibers. These fibers have been measured to be stronger than any other known material. If these aligned fibers are then woven, they are lighter and stronger than Kevlar. Coincidentally, the molecularly woven (tangled) nanotube fibers made by these guys at MIT are not much stronger than generic clothing fiber. The key is to weave the fibers macroscopically and allow the nanotubes to bend less than 15 degrees on a molecular scale.

Hope this was helpful.

new MIT course this fall...

[Glog]

Nanotube Knitting 101

Re:New at Sears!

[MoonBuggy]

I see Darwin Awards soon after the release of these:

Hey look Bob, I can shoot myself and this shirt protects me.
*bang*
Ouch. This isn't my nanotube shirt.

Toxicity of Carbon Nanotubes

[EigenHombre]

I noticed noone here has commented on the toxicity of carbon nanotubes. From the NIH website:

"These results show that, for the test conditions described here and on an equal-weight basis, if carbon nanotubes reach the lungs, they are much more toxic than carbon black and can be more toxic than quartz, which is considered a serious occupational health hazard in chronic inhalation exposures."

Not sure I'd wear a shirt or even chain mail made of these things....