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Superconductivity was first observed almost a century ago while Heike Kamerlingh Onnes was studying the properties of mercury at extremely low temperatures. At the time the production of liquid helium had just become possible and it enabled experiments to be conducted at cryogenic temperatures close to absolute zero or zero degrees Kelvin 0° K (-273.16° C). Onnes noted that when the temperature dropped below 4.2° K the electric resistance of the mercury dropped dramatically. Further investigation revealed that the resistance did not only drop dramatically but it dropped to exactly zero, meaning that it produced no resistance to the flow of electricity whatsoever.
Over the next few decades research revealed that there were several other substances that exhibited superconductivity at cryogenic temperatures. For example lead Pb becomes superconductive at 7° K. Prior to 1986 scientists believed that BSC theory (see links below for further reading) which attempted to explain superconductivity, would limit superconductivity to temperatures below around 30° K. However, the discovery of lanthanum-based cuprate which became superconductive at 35° K created new interest in the subject. A further breakthrough came quickly when it was discovered that if you replaced the lanthanum with yttrium forming YBCO the critical temperature could be raised to 92° K. This was a major breakthrough as it meant superconductivity could be achieved using liquid nitrogen at 77° K rather than the more problematic, dangerous and expensive liquid helium. To date the highest temperature that superconductivity has been demonstrated is 138° K in a ceramic that contains thallium, mercury, copper, barium, calcium, strontium and oxygen. There is evidence that InSnBa4Tm4Cu6O18 may exhibit superconductive at 150° K, but was unable to confirm this.
There have been several claims of so called room temperature superconductors, however, detailed investigation has shown that these claims have always been flawed at some fundamental level. As a result claims of the development of room temperature superconductors are treated with considerable scepticism. To date the highest temperature at which superconductivity has been demonstrated is 168° K or slightly less than -105° C.
There has been considerable hype about superconductors and how they will be a panacea to many of the problems we are currently facing with the generation, distribution and consumption of electrical energy. However, the low temperatures that are currently needed to produce superconductivity have severely limited the application of superconductors with any gain in efficiency being offset by the energy required to maintain the required temperature.
There have, however, been some demonstration applications of superconductor technology.
- Magnetic Levitation: There are several ways levitation can be generated using magnetic fields.
- Diamagnetic Materials: These are materials that act exactly the opposite way to ferromagnetic materials. Rather than being attracted to a magnet like ferromagnetic materials diamagnetic materials are repelled. Unfortunately the repulsive force created by such materials is extremely weak and requires extremely powerful magnetic fields. As a result the diamagnetic effect is usually limited to devices that only demonstrate the effect rather than apply it.
- Magnetic Repulsion: When two like magnetic poles are moved towards each other a repulsive force is created that is proportional to the inverse of the square of the distance separating them. In other words the closer they get to each other the more they try and push each other away. Electromagnets built for superconducting coils are easily capable of generating the sort of field strength that is required to lift items like trains.
- Meissner Effect: Without going into the theory, the Meissner Effect is the reflection of a magnetic field by a superconductor in a way that is analogous to light being reflected in a mirror. In the example below a small rare earth magnet is placed over a superconducting medium which is being chilled by liquid nitrogen. While the medium acts as a superconductor the magnetic field generated by the magnet is reflected. This reflected field then repels the magnet and provided the field strength is sufficient the force of gravity is overcome and the magnet rises above the superconductor..
- While there have been demonstrations of maglev technology including Yamanashi Maglev Test Line in Japan and the Pudong International Airport Link in China the first application in England was shut down in 1997 after operating for 11 years. Health concerns of long term exposure to high strength magnetic fields and the limitations of the technology have severely limited such applications.
- Magnetic Resonance Imaging: The principles of MRI have been known since the 1940s but it took till 1977 for the technology to develop to the point of generating a useful image. Even so the equipment required was huge and it took up to five hours to generate a single image. While the improvement in computer technology has speeded up the process considerably the use of superconductors has also been important as it has reduced the size and increased the resolution of MRI systems.
- Magneto-encephalography MEG: The development of Superconductive Quantum Interference Devices SQuID has enabled the detection and monitoring of the extremely weak magnetic fields generated by the human brain. The ability to detect and monitor these miniscule magnetic fields has allowed MEG to take place.
- Large Hadron Collider: Without superconducting electromagnets it would be extremely difficult and most likely impossible to construct such a powerful high energy collider.
- Electricity Generation: The use of high temperature superconductors instead of copper or other normal conducting materials can increase the efficiency of electricity to over 99% while reducing the size by around 50%. General Electric Power Systems are reported to have been working towards the commercial use of high temperature super conductor generators since 2002 and have received a US$12.3 million grant from the US Department of Energy to develop the technology. However, I have unfortunately been unable to find any details of what they are doing or what stage the development is currently at.
There are a myriad of places where the use of superconductors could greatly improve the efficiency of energy conversion, transmission and distribution. However, the technology is severely limited by the low temperatures that are required for superconductivity to occur and any improvement in efficiency can be easily offset and often swamped by the energy required to maintain the temperatures at which superconductivity occurs.
There also seems to be considerable flexibility in what people claim to be superconductors. In my research for this thread I came across several companies that claim to be manufacturing high temperature superconductive cables and devices. However, careful reading of their claims reveals that while the products they are claiming to be superconductors have considerably lower resistance than normal copper or aluminium conductors the resistance they have is NOT ZERO at any temperature let alone room or normal operating temperature. Put simply they ARE NOT SUPERCONDUCTORS just extremely good conductors.
The widespread use of true superconductors still has a considerable way to go before it becomes economic. Unless the temperature that superconductivity occurs at can be raised to something that is closer to normal atmospheric conditions the useful and economic use of superconductors is going to be severely limited to situations where there is no other option and the maintenance of a sub 150° K temperature is not problematic.
As usual you can read further on superconductors by following these links and I invite all to add their comments and opinions.
The New & Improved Blog
When I started the An engineer's Look at the Future of Energy blog, I asked CR4 participants to list any technology they believed may help reduce our dependence on fossil fuels. The result was the Possible Technologies for Future Energy & Power Production list, which we have been steadily working through. There is an axiom that states "all good things must come to an end" and unfortunately this thread marks the completion of the list.
However, I prefer the axioms "when you're on a good thing stick to it" and "you can't get too much of a good thing". After considerable thought (at least a couple of minutes) and discussion with other CR4 members (at least one or two) I have decided to continue the blog by expanding its scope. The result will be a new and improved blog that will cover a couple of my pet subjects which I believe most CR4 participants will not only find informative but entertaining as well. Not only that, but one of the additional themes is an area of scientific endeavor where the work of amateurs is not only accepted but is actively encouraged so any CR4 members who feel so inclined can easily participate directly. I also will not be shelving the original theme and as information on new technologies comes to hand I will be creating appropriate threads.
The An engineer's Look at the Future of Energy blog has been a great success and I thank all those who have participated for their effort and time. The blog is really your blog as all I did was to ask a few questions and do some collating. It was your responses that added the meat to the bones and made the blog work.
So I thank all those who have participated to date and ask you to stand by till next week when I launch The New & Improved Blog.
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Re: Future Energy Sources 7.0 Superconductors
