Superconductivity refers to the phenomenon that the resistance of some objects suddenly approaches zero when the temperature drops to a certain temperature. Materials with this property are called superconducting materials.
The temperature at which a superconductor changes from a normal state to a superconducting state is called the transition temperature (or critical temperature) of this substance. Because this temperature is very low, close to absolute zero. So far, it has not been widely used. But scientists are studying high temperature superconductivity. If the research is successful, this material will not consume electricity and heat when conducting electricity. This can save energy!
19 1 1 year, Dutch physicist Anis found that the resistance of mercury suddenly dropped to zero around 4.2k He called this phenomenon zero-resistance superconductivity. Figure 5- 13 shows the relationship between mercury resistance and temperature.
The temperature at which mercury resistance suddenly disappears is called transition temperature or critical temperature, which is often expressed by Tc.
An object with superconductivity at a certain temperature is called a superconductor. Metallic mercury is a superconductor. Further research shows that 26 metals in the periodic table have superconductivity, and their transition temperatures Tc are listed in Table 5-6. As can be seen from the table, the superconducting transition temperature of a single metal is very low and has no application value. Therefore, people gradually turn to study the superconductivity of metal alloys. Table 5-7 lists the transition temperatures of some superconducting alloys, among which Nb3Ge has a transition temperature of 23.2K, which was considered as the superconductor with the highest transition temperature in 1970s. When superconducting display conductive materials can only enter superconducting state at extremely low temperature, superconductivity cannot be discovered and superconducting materials are unimaginable without the development of low-temperature technology as the backing. Once again, we can see the relationship between material development and science and technology.
Low-temperature superconducting materials can only be superconducting by using liquid helium as refrigerant, so their application is greatly limited. People are eager to find high temperature superconductors. After decades of wandering, they finally made a breakthrough in 1986. Bednorz and Müller of Switzerland found that their La-Ba-CuO mixed metal oxides were superconducting, with a transition temperature of 35K. This is a major breakthrough in the research of superconducting materials and opens up the research direction of mixed metal oxide superconductors. Subsequently, Chinese and American scientists found that the mixed metal oxide of Y-Ba-CuO has superconductivity at 90K, and the transition temperature of this superconducting oxide is already higher than that of liquid nitrogen (77K), so the research on high-temperature superconducting materials has made great progress. A series of exciting discoveries have set off "super heat conduction" around the world. At present, a new series of superconducting oxides are constantly emerging, such as Bi-Ca-CuO, Tl-Ba-Ca-CuO, etc., whose superconducting transition temperature exceeds 120K K, and the research on high-temperature superconductors is in the ascendant. People are eagerly looking forward to the appearance of room-temperature superconducting materials.
It is found that C60 reacts with alkali metals to form AxC60(A stands for potassium, rubidium, cesium, etc. ), are superconductors. The superconducting transition temperatures are listed in Table 5-8. It can be seen from the data in the table that the transition temperature of most AxC60 superconductors is higher than that of metal alloy superconductors. Metal oxide superconductors are inorganic superconductors, all of which are layered structures and belong to two-dimensional superconductors. AxC60 is an organic superconductor with spherical structure and belongs to three-dimensional superconductivity. Therefore, superconductors like AxC60 are promising superconducting materials.
Superconducting research has attracted the attention of all countries. Once the room temperature superconductor is put into practical use and industrialized, it will have a far-reaching impact on the science and technology of modern civilized society. Some applications of superconductors are briefly introduced below.
(1) Power stations using superconducting materials transmit electricity to users through long transmission lines. Due to the resistance of the wire, when the current passes through the transmission line, a part of electric energy is consumed. If a superconducting cable made of superconducting material is used for transmission, the loss on the transmission line will be reduced to zero.
(2) Superconducting Generator The key components for manufacturing large-capacity generators are coils and magnets. Due to the resistance of the wire, the coil is seriously heated, and how to cool the coil becomes a difficult problem. If the superconducting generator is made of superconducting material and the coil is made of non-resistive superconducting material, it will not generate heat at all, so the cooling problem will be solved and the power loss can be reduced by 50%.
(3) Should the maglev train reach a speed of 500km/h? H- 1, ordinary trains are absolutely not acceptable. If superconducting magnets are installed in the train and aluminum rings are laid on the ground track, the relative movement between them will generate induced current in the aluminum rings, thus generating magnetic repulsion, which will lift the train off the ground about 10cm and make the train float on the ground at high speed.
A large amount of energy will be released in the process of controlled thermonuclear fusion. In order to continue the nuclear fusion reaction, the plasma must be confined to 108℃, which requires a strong magnetic field, and superconducting magnets can generate the magnetic field needed to confine the plasma. Only by mastering superconducting technology can human beings turn controllable thermonuclear fusion into reality and provide endless energy for human beings.