High temperature superconductive material, with high criticaltransition temperature(Tc) canliquid nitrogenOperating at temperatureSuperconductive material。Because it is mainly oxide material, it is also called high temperature oxide superconductor material.
Superconducting technology is a technology with great development potential and strategic significance in the 21st century. Superconducting materials have high current carrying capacity and low energy consumption characteristics, and can be widely used in energy, national defense, transportation, medical and other fields.becauseHigh temperature superconductorHigh critical temperature, low price and convenient operation of liquid ammonia used for its cooling make it a new energy material with practical significance.Since the discovery in the 1980sOxide superconductorSince then, the world has set off an upsurge of research on high-temperature superconductivity.Since then, people have found various series of high temperature superconductors with increasingly high superconducting transition temperature. At present, the transition temperature of mercury superconductors has reached more than 130 K.At the same time of basic research, countries all over the world have also invested a lot of manpower and material resources in the industrial research of superconducting materials[1]。
history
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High temperature superconductors usually refer to superconductive materials above liquid nitrogen temperature (77 K).When superconductors were discovered (1911), people were attracted by their unique properties (namely, zero resistance, diamagnetism, and quantum tunneling effect).However, in the 75 years since then, all discovered superconductors have shown superconductivity only at extremely low temperatures (23 K), so their applications have been greatly limited.
High temperature superconductors generally refer to superconductors whose critical temperature is above 77K absolute temperature and whose resistance is close to zero. They can be used in cheap liquid nitrogen (77K) refrigeration environment. They are mainly divided into two types: yttrium barium copper oxide (YBCO) and bismuth strontium calcium copper oxide (BSCCO).Yttrium barium copper oxide is generally used for preparationSuperconducting film, applied in electronic, communication and other fields;Bismuth strontium calcium copper oxide is mainly used in the manufacture of wire rod.
In 1911,Leiden UniversityKamolin Onnis of the University of California unexpectedly found that when mercury was cooled to - 268.98 ° C, the resistance of mercury suddenly disappeared;Later, he found that many metals and alloys have the characteristics of losing resistance at low temperature similar to the mercury mentioned above. Because of its special conductivity, Kamoline Onnis called it superconducting state, and he also obtained the 1913Nobel Prize。
In 1933, Messner and Olsenfeld of the Netherlands jointly discovered another extremely important property of superconductorsMagnetic inductionIt is zero, but the magnetic field originally existing in the body is squeezed out.The experiment on single crystal tin ball shows that when the tin ball transits to the superconducting state, the magnetic field around the tin ball suddenly changes, and the magnetic line of force seems to be excluded from the superconductor all of a sudden. People call this phenomenon "Meissner effect".
Since Kamelin Onnis discovered the superconductivity of mercury near 4.2K, new superconductors have been found all over the worldperiodic table of ele mentsFrom light element boron and lithium to transitional heavy metal uranium series.The initial research of superconducting materials mainly focused on elements, alloys, transition metal carbides and nitrides.By 1973, a series of A15 type superconductors and ternary superconductors had been discovered. Superconducting materials can only be superconducting when liquid helium is used as refrigerant, so their applications are greatly limited.In 1986, Bernoz and Mueller discovered the 35K superconductive lanthanum barium copper oxygen system.This breakthrough discovery led to a series of rare earth barium with higher temperatureCopper oxide superconductorDiscovery of.Through element replacement, in early 1987, Wu Maokun (Zhu Jingwu) of the United States and Zhao Zhongxian of the Institute of Physics of China announced the discovery of 90K yttrium barium copper oxide superconductor, which achieved the first breakthrough in the temperature barrier of liquid nitrogen temperature (77 K).Bernoz and Mueller also won the 1987 annual award for their pioneering workThe nobel prize in physics。
This type of superconductor is usually calledHigh temperature superconductor。The discovery of yttrium barium copper oxide superconductors above liquid nitrogen temperature makes ordinary physics laboratories have the conditions to conduct superconducting experiments. Therefore, a global upsurge of exploring new high-temperature superconductors has been set off.At the end of 1987, Sheng Zhengzheng, a Chinese scholar studying in the United States, first discovered the first Tl Ba Cu O high-temperature superconductor without rare earth.In early 1988, Japan developed bismuth strontium calcium copper oxide superconductors with a critical temperature of 110K.In February 1988, Sheng Zhengzheng and others further discovered 125K Tl Ba Ca Cu O superconductor.A few years later (1993), French scientists discovered 135K mercury barium calcium copper oxide superconductor.
On July 12, 2023, Nature published the scientific achievement led by Professor Wang Meng of Sun Yat sen University: the first discovery of nickel oxide superconductor at liquid nitrogen temperature.This is a new high-temperature superconductor system first discovered by Chinese scientists in the world. It is the second unconventional superconductor material found in the liquid nitrogen temperature region and a breakthrough in the basic research field from 0 to 1.[2]
Preparation process
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In order to meet the requirements of various applications, high temperature superconducting materials mainly include film materials (thin film, thick film), bulk materials, wire and tape.
film
High temperature superconductor thin films are the basis of high temperature superconductor electronic devices.The preparation of high temperature superconducting thin films is almost always carried out on single crystal substrates by vapor deposition or epitaxial growth. After ten years of research, the preparation technology of high temperature superconducting thin films has become mature and reached the practical level. At present, the two most commonly used and effective coating technologies are: magnetron sputtering (MS) andpulsed laser deposition (PLD)。These two methods have their own unique features,Magnetron sputteringIt is one of the best growth methods suitable for large area deposition.The pulsed laser deposition method can easily make the chemical composition of the film consistent with the chemical composition of the target, and can control the thickness of the film.
thick film
High temperature superconductor thick film is mainly used for HTS magnetic shielding, microwave resonator, antenna, etc.Its difference from the film is not only the thickness of the film, but also the deposition method.The main differences are as follows: (1) Generally, single crystal substrate is required for film deposition;(2) The deposited film has a certain degree of orientation relative to the crystal orientation of the substrate;(3) Generally, vacuum technology is required for the fabrication of thin films.There are many methods to obtain thick films, such as thermal spraying and electrophoretic deposition. The most common technologies are screen printing and scraping, which are widely used in the electronic industry.
Wire and strip
The application of superconductors in strong electricity requires that high-temperature superconductors must be processed into composite multi wire wires or tapes containing superconductors and a common metal.However, ceramic high temperature superconductors themselves are very brittle, so they cannot be drawn into thin wires.In manySuperconducting ceramicsSilver tube rolling (Ag PIT) of bismuth ceramic powder is the most mature and ideal method of wire preparation.However, the critical current density of bismuth series strip produced by pressing is much higher than that of strip produced by rolling technology.
Block
initialOxide superconductorThe powder is obtained by solid phase method or chemical method, and then the block is obtained by conventional powder metallurgy processes such as mechanical briquetting and sintering. The preparation method is relatively simple.
application
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Based on the current development of superconducting technology, superconducting technology can be applied and expanded in the following industries:
power
The combination of superconducting technology and electric power technology will bring revolutionary changes to the power generation, transmission and distribution in the electric power industry. The electric power industry is the most important application place and market of superconducting industry.The application of superconducting technology in power mainly includes:
The expansion of existing cables has been puzzling the development of urban power.The traditional urban underground power transmission cable has many problems, such as small flux, large loss, thermal pollution and oil pollution to soil and groundwater, high cost of civil construction, etc. It is more and more difficult to expand urban power capacity.High temperature superconducting cable has the advantages of small size, low cost, high energy saving, pollution-free, etc. It has huge economic and environmental benefits and will eventually replace the traditional cable.
The large-scale application of high temperature superconducting cable can greatly improve the operation efficiency of power transmission system and reduce the operation cost.At present, the overall development trend of high-temperature superconducting cables in the world is to develop large capacity, low AC loss, and ultra long high-temperature superconducting cables.According to experts' estimation, the high-temperature superconducting cable is most likely to take the lead in realizing practicality and commercialization.
The motor is the most commonly used electrical equipment, but the traditional motor consumes a lot of power.American industry experts estimate that industrial motors with more than 1000 horsepower consume about 25% of American energy.Compared with conventional motors, superconducting motors have the advantages of good energy saving, small size, large single unit capacity, low cost and operation cost, good stability, and good economic and environmental benefits.With the same power supply, the size of superconducting motor is 1/3 of that of conventional motor, the manufacturing cost can be reduced by 40%, the current loss can be reduced by 50%, and the operating cost can be reduced by 50%.The US Department of Energy estimates that high temperaturesSuperconducting motorIts low loss can reduce operating costs by billions of dollars every year.
The application of high temperature superconducting motors in military warships makes the warships smaller in size and weight, more flexible in space layout, more reliable in propulsion system operation, higher in efficiency, more convenient in control, better in speed regulation performance, which can greatly improve the concealment and achieve high-speed and quiet operation, and has important military significance.
Conventional transformers have many disadvantages, such as high load loss, large weight and size, low overload capacity, no current limiting capacity, oil pollution and short life.In the United States, the total installed capacity of transformers is about 3-4 times of the total power generation, and the network loss of its power system is about 7.34% of the total power generation, of which 25% is transformer loss.In comparison, the superconducting transformer has the advantages of small size, light weight, high voltage conversion energy efficiency, low fire environmental accident probability, no oil pollution, etc., which can improve the reliability and operation performance of the power system, reduce costs, and save money
Energy and environmental protection are of great practical significance.
Current limiter (FCL) is a kind of power equipment to improve the stability of power grid.With the development of the society, the quality of the power grid is required to be higher and higher, and the traditional current limiter is difficult to limit the pulse current of the power grid in a short time.The high temperature superconducting current limiter just makes up for the shortcomings of the traditional current limiter. Its current limiting time can be less than hundreds of microseconds, which can quickly and effectively limit the current.Superconducting current limiter uses the physical characteristics of superconductor's superconducting normal transition to meet the current limiting requirements. It can simultaneously detect, trigger and limit current. It is considered to be the best and only effective short-circuit fault current limiting device at present.Since 1989, the United States, Germany, France, Switzerland and Japan have all carried out research on high-temperature superconducting current limiter.At present, the technical performance of high-temperature superconducting current limiter (HTS FCL) for power distribution system in the world has approached the level of application, but it is still in the demonstration test stage.
Superconducting energy storage device is a kind of power facility that uses superconducting coils to store electromagnetic energy directly, and then returns electromagnetic energy to the power grid or other loads when needed.Since the energy storage coil is wound by a superconductor and maintained in a superconducting state, the energy stored in the coil is stored almost permanently without loss until it needs to be released.Superconducting energy storage device can not only be used to adjust the peak and valley of power system or solve the impact of power grid instantaneous outage on electrical equipment, but also can be used to reduce or eliminate low-frequency power oscillation of power grid to improve the voltage and frequency characteristics of power grid, and can also be used to adjust reactive power and power factor to improve the stability of power system.
medical care
1) Magnetic resonance imaging of human body (MRI)
MRI is a kind of equipment to diagnose pathological changes by detecting different signals induced by various human organs under the magnetic field.Traditional MRI uses conventional magnets, which have a small magnetic field, so it is difficult to detect initial lesions. At the same time, its main magnetic field is in a closed magnetic cavity. When scanning, the subject needs to be placed in a narrow space isolated from the outside world, which is easy to cause people to produceClaustrophobia, which has greatly affected the extensive application of this equipment. Therefore, cryogenic superconducting magnets are widely used in MRI.Due to the temperature requirement of cryogenic superconductor liquid helium, its operation and maintenance costs are very high.Some countries have accelerated the research of high temperature superconducting MRI. In 1998, Oxford Magnet Technology Co., Ltd. and Siemens Co., Ltd. jointly developed a high temperature superconducting magnet for human MRI.
With the development of the national economy, the society has higher and higher requirements for transportation, and high-speed trains came into being.Compared with the existing four traditional transportation modes of railway, highway, waterway and aviation,Superconducting maglev trainWith the advantages of high speed, safety, low noise and small land occupation, it is an ideal vehicle in the future.
High speed computer requirementsIntegrated circuit chipThe components and connecting lines on the are densely arranged, but the densely arranged circuits will generate a lot of heat when working, and the heat dissipation isvlsiDifficulties faced.For the VLSI in the superconducting computer, the interconnects between its components are made of superconducting devices with near zero resistance and ultramicro heating, so there is no heat dissipation problem. At the same time, the computing speed of the computer is greatly improved.In addition, scientists are studying the use of semiconductors and superconductors to make transistors, or even the use of superconductors to make transistors entirely.
2) Superconducting switch:
Superconducting switches can be divided into resistive switches and inductive switches.The resistance switch uses the following properties of superconductor: if you change any of the three parameters of magnetic field, current and temperature, you can make it change from zero resistance state to resistive state.For example, using a cryotron as a switch is made by using the magnetic field generated by a completely superconducting control element to control the resistance of the gate element by making the gate element superconducting normal transition.The low resistance state of this switch is zero, and the high resistance state is typically of the order of milliohms, so the switch ratio is infinite.The principle of inductive switch is that the inductance of circuit elements other than coils and wires can be used to make the transition between normal state and superconducting state for superconductors close to it, or move the superconducting surface near circuit elements to make the same transition.
