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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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A superconductor is in a different league to a conductor, even a really good one. That's all this appears to be about, a really good conductor.
Isn't this more akin to seeding crystal growth? Using the word cloning might confuse the lay person.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
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
armchair physicists
;-)
Smalley was a chemist. He won the Nobel Prize in chemistry. Synthesizing nano-tubes is done by chemists. This ain't physics we're talking about.
Then again, what discussions have those armchair physicists not gotten themselves into.
I am defenseless. Use your button. Mod me down with all of your hatred.
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.
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.
> Adding superconductors to the power subsystem in
> a computer would do nothing to reduce the
> radiated heat.
Much of the heat generated in integrated circuits is due to the resistance of the aluminum traces used to connect the transistors on the chip. Replacing it with superconductor or with this "ultraconductor" would substantially reduce power dissipation.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
on average around 2% of energy is lost during transmission over power lines. It'll be different in different countries. It all depends how far you are from the station.
On the other hand, convertng fuel to heat in order to generate electricity is typically around 40% efficient with a 60% loss of energy. Combined cycle power stations are closer to 60% efficient with a 40% loss of energy. The laugh is that the single largest use of electricity is to produce heat, but we're only doing it at around 40% efficiency with a 60% loss.
What we should be doing is using that 60% waste heat from the power stations to heat our houses and offices directly and using the electricity to power stuff. It's called Combined Heat and Power (CHP) or District Heating (DH). We'd then be closer to 80% -> 90% efficient.
CHP and DH systems have already been in use in northern european countries (Denmark, Finland etc) for decades, they are nothing new. I guess the UK and USA literally have money to burn.
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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.
> I suspect that if the wire is in a magnetic
> field it will lose it's superconductivity
> - thus it wouldn't work in an electric motor.
1) Superconductors only lose their superconductivity when exposed to a field strength in excess of the threshold for the material they are made of. Superconductors are, in fact, used to produce extremely strong magnetic fields for things like MRI machines. Motors and generators (some very large) _have_ been made with them and they have real advantages: they are just not cost effective in most applications.
2) We are not talking about superconductors. I see no reason why ballistic ultraconductors should not work in high magnetic fields.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
> The electronics revolution has given us the
...it locks your muscles and thus causes you to
> means to step DC power almost as easily and as
> efficiently (more efficiently?) than an AC
> inductor.
Solid-state DC-DC converters are much more complicated than transformers: they include semiconductor power switching devices, integrated circuits, resistors, capacitors, _and_ inductors. Mechanical DC-DC converters include motors and generators. Transformers are just copper, iron, and insulation.
> A few volts DC is enough to kill you...
Not true. According to UL it takes more than 5 milliamperes to be dangerous and your skin resistance is too high to permit that much current to flow at a potential of "a few volts". Try grabbing both posts of a car battery.
>
> continue to hold on to the wire that you grabbed
> in the first place.
60Hz will do that as well if the current is sufficient, and 60Hz is actually slightly more likely to stop your heart than DC.
> Hence why all electric fences in the united
> states are required by law to be pulsed...
Pulsed or limited to less than 5ma of current. Current-limited fencers are sometimes sold as "pet fencers" but only fools and the ignorant will buy them. They are ineffective on large animals but will kill very small ones.
> Unable to let go, the would take many minutes
> to die from low-voltage current.
There are basically two ways to die from electrocution: heart failure and severe burns from very high current. The former can happen at 120V but the latter usually involves tangling with transmission lines.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.