Rare earth superconductor Materials
Rare earth superconductor Materials
一、Rare earth superconductor Materials
When a material is below a certain temperature, the phenomenon of zero resistance is superconducting phenomenon, which is the critical temperature (Tc). Superconductor is an anti magnet, which, when below the critical temperature, rejects any magnetic field that is trying to exert it, which is called the Meissner effect. The addition of rare earth in the superconducting material can greatly increase the critical temperature TC, generally reach the 70~90k, thus making the superconducting material used in the cheap and easy liquid nitrogen, which greatly promotes the development of the superconducting materials.
The superconducting phenomenon was first discovered by a Dutch physicist in 1911, and when Mercury temperature dropped to 43K, Mercury lost its resistance. The research and development of superconductors followed, and by 1973 scientists had made a niobium-germanium alloy with a critical temperature of 23.3K. Some new superconductors were discovered in the 1986, and a breakthrough was made in superconducting research, when a lanthanum barium-copper-oxygen ceramic was found with a critical temperature of 35K. February 1987 also found that the critical temperature of the yba2cu3o7-x high-temperature superconductors reached more than 90K, much more than the boiling point of nitrogen (77K). The new rare earth high temperature material can work at the temperature of liquid nitrogen.
二、Superconducting material main application fields
1.Basic science
Superconducting device can be used to correctly measure the magnetic field intensity, magnetic flux, current, voltage, electromagnetic energy and many other physical quantities, and the instrument very high resolving power, such as the hearts of the men of superconducting quantum interferometer can correctly measure the magnetic, magnetic and magnetic brain.Ordinary superconductor application market is the largest in the field of low temperature physics, first applied to the probe, welding equipment and particle accelerators.
2.The electronics industry
Electronic industry is likely to be the new superconductor first sales market, on the computer by using high temperature superconducting material has two advantages: one is that it reduces the needed for cooling J osephson device cooling;Second, it by memory signal transmission speed, improved with ordinary chip machine performance.Large scale high temperature superconducting thin film in computer can speed up the calculation.Its operation is 1000 times faster than silicon devices.
Time constant of the circuit depends on the resistance and capacitance of the circuit.If there is no resistance, reduce time constant to zero, will accelerate the signals in the circuit.In normal computer with a semiconductor chip, usable way to improve the running speed switching speed acceleration components.Circuit can spread on a chip, in order to keep them cool, but it reduces the speed.Because the distance of the signal to go long, and switching time of the J osephson contact only 10-12 seconds, almost no heat generated.If all the connections and zero resistance, can greatly reduce the heat and power consumption.
3.In the aspect of power generation and power transmission
In electric power engineering facilities, such as generators, motors, transformers, power transmission line and energy storage systems, due to the line resistance, so there will be a lot of electric loss and go into heat.As a result of the superconductor resistance is zero, YBa2Cu3O7 superconductor ceramic thermal conductivity is very low, so, their application potential in this respect is very big.Britain's ICI institute of advanced materials used YBa2Cu3O7 coil manufacture a generator, the coil RPM to 1500 RPM, the generator can produce 2.5 V voltage.At present the main problems of the application of superconductor in the electric power facilities is a current-carrying capacity small, before superconductors to industrial power generation, still need to do a lot of research and experimental work.
In superconducting magnetic energy storage system and the electromagnet used in high temperature superconducting coil, can produce a stronger magnetic field, thus reduces the volume and weight of the magnet, and without core.Superconducting magnetic energy storage system can store off-peak redundant power, so that the peak use.
A superconductor other potential applications in energy with MHD power generation, thermonuclear power generation and magnetic separator.Magnetic separator to remove sulfur in coal mine, to remove the impurity in the China clay or ore.
4.Superconducting maglev train
Beside the train wheels installed small superconducting magnet, when train travels forward, superconducting magnet is to have a powerful magnetic field, and installed in the aluminum ring on both sides of the orbital interaction, produce a kind of upward buoyancy, eliminate the friction of the wheels and rails, and accelerate the speed of the car.High temperature superconductor in suspension train applied research focused on Japan.
Superconductivity in carrying on other applications, there may be used as the power of superconducting motor electromagnetic space launch vehicles and aircraft suspended the runway.
5.Microwave technology
Microwave technology is a high temperature superconducting material may soon get important application areas.In recent years, our country has carried out the study of superconducting microwave devices, superconducting filter, made of superconducting antenna, delay line, oscillator, superconducting junction mixer device has the international advanced level.
Such as, in order to meet the need of space communication developed 4.5 GHz YBCO superconductor circular polarization microstrip antenna, the antenna under the temperature of 77 k of the reflection coefficient of 1.5 dB, matching is good, meet the requirements of superconducting magnetic window project from the ministry.Development of superconducting microwave bandpass filter, more than 10175 + 50 MHZ bandwidth, the insertion loss of 1.2 dB or less, stopband L p 40 dB, standing wave ratio of 1.5 or less.Superconducting quantum interference device is the device can measure the weak magnetic field.During the period of "five-year" key to the manufacture and application of the device in large geomagnetic measurement project.The twin knot, steps, step edge node devices developed results are close to the world's advanced level.In cooperation with Germany large geomagnetic measurement, achieved good effect.
6.other
Medical superconductor meson generator can be used to treat cancer, superconducting magnets can be used to treat cerebral tumors.In addition, the military use of superconductivity can destroy the missile.
三、The development situation of three superconducting materials, rare earth
Since 1911, since the superconductivity of mercury was observed for the first time, on the theor y of superconductivity, experiment and application have made great achievements.Until the mid - 1980 - s, however, the traditional superconductor must be run in a very low temperature, usually working substance is liquid helium (4.2 K).Superconducting material is metal and its compounds, such as Nb3Sn, the critical temperature of 18.0 K.
This makes the wide application of superconducting materials are greatly constrained.In 1986 in Zurich, Switzerland, IBM lab j. g. Bednorg and k. a. Muller found A new type of structure of rare earth oxide superconductor YBa2Cu3O7 - x, opened A new direction for improving the superconducting transition temperature.This groundbreaking work soon won the Nobel Prize in physics, and the high temperature superconducting hot international.
Our zhong-xian zhao academician also made many contributions in this aspect.Since high temperature superconducting materials, superconducting critical temperature quickly break through the liquid nitrogen temperature (77 k), or even to more than 130 k.Also engaged in the study of the institutions of our country from the full flowering transition state to set up the national superconducting research center, a unified management coordination, superconducting national laboratory is established.
Our country also organized many times. International conference on high temperature superconducting.In the aspect of application, our country also successfully developed into a high temperature superconducting wires, create conditions for application of high voltage, strong magnetic field, at the same time, the study of high temperature superconducting thin film devices have also made important progress, squids device resolution was magnetic measurement can be used in the brain, cardiovascular and magnetic measurement has made a number of clinical trials, and had practical such units in geomagnetic detection.