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Published on May 1, 2008

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Superconductivity and Classroom Applications:  Superconductivity and Classroom Applications By: Ken Bowles (Apopka High School) Brian McClain (Godby High School) Slide2:  Peering into the body without cutting it open Traveling hundreds of miles per hour in a levitated train Steering antimatter moving at the speed of light Why Is All This Important?:  Why Is All This Important? “Superconductivity” generates over 200,000 hits on any given web search Addresses major societal issues such as energy. Attracts thousands of scientists from all over the world to conferences. Government and Private Investments are in Billions of Dollars What Defines a Superconductor?:  What Defines a Superconductor? There are TWO distinct properties. They have ZERO resistance They exhibit DIAMAGNETISM Diamagnetism: repelled by a magnet Condition: The superconductor must be cooled by liquid nitrogen. How This All Began?:  How This All Began? H.K. Onnes first discovered the idea of zero resistance in 1911 while doing experiments on mercury cooled with liquid helium. Three different hypotheses existed on how resistance would respond as temperature approaches 0 K:  Resistance would increase (Kelvin) Resistance would plateau (Matthiessen) Resistance would continue to drop gradually to 0  and 0 K (Dewar). Unpredicted Results :  Unpredicted Results The idea that a superconductor can pin a magnet in free space was first characterized by Meissner and Ochsenfeld in 1933. This phenomenom is now known as the “Meissner effect.” None of the three hypotheses predicted the real data – the resistance of mercury SUDDENLY drops to ZERO near 4.2 K. Superconductivity is discovered. Superconductor Fabrication Techniques:  Superconductor Fabrication Techniques There are a number of methods of preparing yttrium-barium-copper-oxide superconductors. Most techniques involve a four step process. 1. Mixing the chemicals 2. CALCINATION (the initial firing) 3. THE INTERMEDIATE FIRING(S) 4. The final oxygen annealing Mixing The Chemicals:  Mixing The Chemicals The chemicals must be mixed in the proper proportions so that the atomic ratios of yttrium, barium, and copper are 1:2:3. The proper weight ratios for a small pellet are: Yttrium oxide, Y2O3 1.13 grams Barium carbonate, BaCO3 3.95 grams Cupric oxide, CuO 2.39 grams The recommended procedure for modestly equipped laboratories is to first use a mortar and pestle to grind down any lumps or large particles in the chemical powders. Acetone can also be used to make a paste. The slurry will reform into a powder as the acetone dissolves. Heating,Cooling, and Pressing the Superconductors:  Heating,Cooling, and Pressing the Superconductors Heat the sample at 900 degrees Celsius for 1 day to drive off unwanted carbon dioxide. After the first heating, allow the sample to cool, re-grind, and re-heat for 1 day at 950 degrees. After the second heating, re-grind, place in metal die and press into a pellet using a lab press at 3 metric tons. After the pressing, allow the pellet to heat in the presence of flowing oxygen. The flowing oxygen is vital to the crystal structure. Other Fabrication Techniques: Wires and Tapes:  Other Fabrication Techniques: Wires and Tapes The powder is packed into a cylinder made of silver or silver alloy, drawn into long strands and packed together as a group of fine filaments. Then the silver-sheathed superconductor precursor is heated, causing the powder to react chemically and form superconducting material inside the silver sheath. Making the superconducting ceramic filaments thin and bundling them together allows the wires to tolerate a certain amount of bending. Tape can be made by a process called Deposition, where the superconductor is deposited by a laser on a special buffer substrate. Uses of Superconductors: MRI:  Uses of Superconductors: MRI MRI is a technique that allows doctors to see what is happening inside the body without directly performing surgery. The development of superconductors has improved the field of MRI as the superconducting magnet can be smaller and more efficient than an equivalent conventional magnet. Radiofrequency receivers that are currently made of copper coils can be replaced by superconducting receiver coils, increasing signal-to-noise ratio by a factor of two in some cases. This change is especially important in low-strength MRI fields (based on lower cost magnets), where weak fields mean weak signals. Superconducting coils could boost the performance of these machines by improving image quality and reducing measurement time. Uses of Superconductors: Magnetic field sensing :  Uses of Superconductors: Magnetic field sensing Compared with the rest of the body’s low current operations, the heart is a highly electric organ. Its faint magnetic field (about 100 picoteslas) can be measured with superconducting quantum interference devices (SQUIDs), the most sensitive magnetic sensors known. When arranged in arrays, SQUIDs can provide an image of the heart ’s magnetic field and yield clues to abnormal conduction patterns that are the basis of some heart arrhythmias (abnormal rhythms). About 3 million persons are treated for arrhythmias each year in the United States. Uses of Superconductors: Levitation:  Uses of Superconductors: Levitation 'MagLev' trains have been under development in Japan for the past two decades Superconducting magnets are used create a strong magnetic force to propel the vehicle. But they offer more than just propulsion—they also levitate the vehicles and guide them within the bounds of the guideway. The system takes advantage of the naturally stabilizing effect provided by electromagnet induction. No controlling devices whatsoever are needed to keep the train on its guideway, and there is no risk of the train ‘derailing.’ The magnetic levitation force is ideal for supporting a train at very high speeds. Applied Uses of Superconductors:  Applied Uses of Superconductors Electric generators made with superconducting wire are far more efficient than conventional generators wound with copper wire. Their efficiency is above 99% and their size about half that of conventional generators. They make lucrative ventures for power utilities. Recently, power utilities have begun to use superconductor-based transformers and "fault limiters". Superconducting fault limiters can respond within a few milli-seconds to limit thousands of amperes of current – such as after a lightning strike. An idealized application for superconductors is to employ them in the transmission of commercial power to cities. BUT, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short "test runs". Superconducting material takes up less space. In one instance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper cable, making it over 7000% more space-efficient. Applied uses of superconductors:  Applied uses of superconductors Faster (petaflop) computers. A petaflop is a measure of a computer's processing speed and can be expressed as: A thousand trillion floating point operations per second (FLOPS) Today's fastest computing operations have only reached "teraflop" speeds - trillions of operations per second. Currently the fastest are NEC's Earth Simulator, which operates at a top-end of 40 teraflops Cellular(wireless) technology Since super-conducting wire has near zero resistance, even at high frequencies, many more filter stages can be employed to achieve a desired frequency response. This translates into an ability to pass desired frequencies and block undesirable frequencies in applications such as cellular telephone systems. Applied Uses of Superconductors:  Applied Uses of Superconductors Among emerging technologies are a stabilizing momentum wheel (gyroscope) for earth-orbiting satellites that employs the "flux-pinning“ properties of imperfect superconductors to reduce friction to near zero. Ultra-sensitive, ultra-fast, superconducting light detectors are being adapted to telescopes due to their ability to detect a single photon of light. Superconductors may play a role in Internet communications soon. In late February, 2000, Irvine Sensors Corporation received a $1 million contract to research and develop a superconducting digital router for high-speed data communications. Since Internet data traffic is doubling every 100 days, superconductor technology is being called upon to meet this super need. Classroom Applications: Earth/Space Science:  Classroom Applications: Earth/Space Science Students should understand: Some superconductors are considered to be a bulk ceramic. The composition of perovskites could be discussed. Properties of matter Environmental Health How we use the light detectors to determine the composition of stars Classroom Applications: Biology:  Classroom Applications: Biology Students should understand: Biochemistry and biophysics, atomic and molecular structures Improve medicine with more precise and non-invasive techniques   Interdisciplinary nature of modern biology How advances in technology can: improve the human impact on the environment Classroom Applications: Chemistry:  Classroom Applications: Chemistry Students should understand: Laboratory procedures and safety applications Difference between elements and compounds Stoichiometric analysis Factors that play a role on reaction kinetics, such as HEAT. Molecular geometries Scientific method Fundamental Properties of the Periodic Table Classroom Applications: Physics:  Classroom Applications: Physics Students should understand: Laboratory procedures and safety applications Basics of diffraction in order to use the XRD Electricity and magnetism principles in order to measure critical current and field. Basic circuitry. Temperature’s role on a superconductor’s resistance. Scientific method Sunshine State Standards ( Just a Few):  Sunshine State Standards ( Just a Few) Sc.A.1.4 #4 - experiments and determines that the rates of reaction among atoms and molecules depend on the concentration, pressure, and temperature of the reactants and the presence or absence of catalysts. Sc.A.2.4 #2 - knows the difference between an element, a molecule,and a compound. Sc.C.2.4 #6 - explains that all forces come in pairs commonly called action and reaction. Sc.H.1.4 #4 - knows that investigations are conducted to explore new phenomena, to check on previous results, to test how well a theory predicts, and to compare different theories. Special Thanks To::  Special Thanks To: Dr. Justin Schwartz and Dr. Sastry Pamidi   Dr. Pat Dixon, Ms. Gina LaFrazza-Hickey and the CIRL staff of the NHMFL

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