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Quantum Wires
Silverlancer writes "Room temperature superconductors have often been a hallmark of far-future science fiction. But fortunately for us, they're here today, according to MIT's Technology Review. Richard Smalley, winner of the 1996 Nobel Prize for the discovery of the buckyball, is currently heading a project to produce a prototype carbon nanotube superconductor. They've already produced some wires up to 100 meters long--the only thing left to do is figure out how to produce only a certain type of nanotube, the "5,5 armchair nanotube," that conducts so well that it can be considered a superconductor."
Interestingly,Dr. Smalley talked about armchair nanotube technology at the senate Oversight hearing on sustainable, low emission, electricity generation Full Committee Hearing almost one year ago. The full text is here.
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And just in case anyone wants to know what exactly, a 5,5 armchair nanotube looks like, there are some images of models here.
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At same voltage and current, the electromagnetic radiation should stay the same. The advantage of reduced resistance though come in two points:
1. Lower losses in cables, so less power needs to be transmitted
2. Lower resistance means we can pump more power into them. This becomes handy in electromagnetics (example: maglev trains). Less energy is wasted in heat, and less cooling is required.
The most essential thing about a superconductor isn't the zero resistance, but the meissner effect. So if they manage to create wires with near-zero resistance, they will not have created `near-superconductors'.
For energy transportation and storage it doesn't matter all that much, cause zero resistance (even without superconductivity) would make energy transportation and storage better
http://www.businessweek.com/magazine/content/05_16 /b3929120_mz018.htm
From the url:
"Even though such transistors are still in their infancy, says IBM's Avouris, "Carbon nanotubes can get around most of the problems that doom very small silicon devices." In the lab, he has backed this statement up. It took him four years to assemble his current, third-generation prototype of a carbon nanotube transistor, but in the end, the device can carry up to 1,000 times the current of the copper wires used in today's silicon chips, making it vastly more efficient."
I assume you're talking about the different effects of resistance on AC and DC currents: as electricity travels through a conventional conductor, the resistance of the conductor gives up some of the electrical power as heat (as Ohm's law describes). That's why we use high-voltage AC to distribute electric power, and even higher-voltage AC to transmit power over long distances--by transmitting at high AC voltages, you don't lose quite as much power as you otherwise would.
So if you could replace vast swaths of conventional copper electric transmission and distribution lines with superconductors, you could theoretically switch to DC power in these applications, which would have some interesting effects on the rest of the electrical distribution system.
Strict DC voltage on the power lines would virtually eliminate the EM radiation. You would still get some EM when you turned things on or off, or if the amount of power the line carries changed at all, but there would be a HELL of a lot less.
Lower voltages could be used, which would be safer (less chance of electrocuting people), and connectors (plugs, receptacles) designed with lowe voltages in mind would be cheaper to produce and certify.
Also, many devices in the home (especially computer equipment, or anything with circuit logic in it) need to convert the 110V AC current into much lower-voltage DC (2-5V DC, usually) to operate chip logic. This in generally an inefficient process, with a lot of power given up in the transformers and inverters to heat. Granted, you'd have to redesign all the home devices that currently use AC power directly (mostly lights and appliances) to run on DC, it could be done.
Really, the only problem would be the massive costs of switching over from one standard to another. All of those applicances and such would become useless on the new standard, which means everybody has to go out and buy new stuff. If you tried to switch the distribution over to DC in one go, I can see a lot of people having a lot of problems with it. And it wouldn't be practical to change the distribution bit-by-bit, either.
If you just wanted to change the transmission side, and leave the consumer out of it entirely, you'd have to replace a lot of power generation infrastructure. This could be done more slowly, I'd imagine, but it would still be expensive.
But then again, there's nothing that prevents you from continuing to run AC current on superconducting wires. That's probably what will happen, because it's the cheapest option.
I don't see anyone caring too much about interference from power lines in the 60Hz frequency band, anyway--not like we use those frequencies for anything.
Two years later Sheng et al demonstrated superconductivity in carbon nanotubes. The experiment was conducted below 20K and the data collected was consistent with the Bardeen-Cooper-Schreiffer (BCS) theory of superconductivity.
For practical applications one wants the superconducting phenomenon to occur at much higher temperature. A material becomes superconducting when its electrons pair up. Normally such negatively charged particles would repel each other, but in a positively charged crystal structure, vibrations called phonons help them get together. In carbon nanotubes, the frequency of these vibrations is very high, which, in theory at least, means superconductivity at higher temperatures.
Actually, it's called a ballistic conductor. There is a small resistance when electrons pass through the ends of the nanotube, and while it is traveling along the rest of the tube there is no resistance.
what sig?
Carbon nanotubes are not superconductors. In an ideal (the kind they are trying to build), they have a resistance that is independent of length, however it is not zero like in actual superconductors. The resistance of an individual nanotube is about 20 kOhms, but because they are so small an array of a large number of them in parallel can have a small resistance, and still not be very large. Because the restance does not increase for longer tubes, they are similar to a superconductor, and would be useful for transmitting power over long distances. However, the physics behind the conduction is different.
I'm at Rice University, and I can tell you what the real situation is. Smalley has DARPA and NASA money to try to do something he calls continued growth: to take an existing carbon nanotube, and increase its length in a gas-phase chemical vapor deposition process. They are having limited success. Don't go buying your space-elevator stock yet.
Separately, Smalley and collaborators have been working on spinning fibers from ropes of nanotubes (basically short (less than 1 micron) tubes bundled together by van der waals forces). Those are the fibers that can be meters long. These fibers do not consist of meter-long tubes!
Finally, metallic nanotubes are not room temperature superconductors. In fact, they are not even ballistic over length scales larger than a micron. Smalley's habit of implying otherwise is really annoying to any physicist who knows anything about these systems.
Now, a long fiber of only metallic nanotubes would still have conductivity better than copper at much less the weight, and would therefore be very important industrially if it could be made economically. There is a huge difference between that and having no electrical resistance, though.