In 1911, Camourin-Onnes of Leiden University in the Netherlands unexpectedly discovered that when mercury was cooled to -268.98°C, the resistance of mercury suddenly disappeared; later he discovered that many metals and alloys have Similar to the above-mentioned mercury, it loses resistance at low temperatures. Due to its special conductive properties, Camourin-Onnes calls it a superconducting state. Kamaulin won the 1913 Nobel Prize for his discovery.
This discovery caused shock around the world. After him, people began to call conductors in a superconducting state "superconductors." The DC resistivity of superconductors suddenly disappears at a certain low temperature, which is called the zero resistance effect. There is no resistance in the conductor, and no heat loss occurs when current flows through the superconductor. The current can flow large currents in the wire without any resistance, thus generating a super strong magnetic field. In 1933, Meissner and Ossenfeld of the Netherlands jointly discovered another extremely important property of superconductors. When the metal is in a superconducting state, the magnetic induction intensity in the superconductor is zero, but the original existence The magnetic field in the body is pushed out. Experiments on single crystal tin balls found that when the tin ball transitions to a superconducting state, the magnetic field around the tin ball suddenly changes, and the magnetic field lines seem to be repelled out of the superconductor. This phenomenon is called "stepping". Snar effect".
Later, people also did such an experiment: in a shallow and flat tin plate, a small but very strong permanent magnet was placed, and then the temperature was lowered to make the tin plate appear superconducting. At this time, you can see that the small magnet actually leaves the surface of the tin plate, floats slowly, and hangs motionless in the air.
The Meissner effect is of great significance. It can be used to determine whether a material is superconducting.
In order to make superconducting materials practical, people began to explore high-temperature superconductivity. From 1911 to 1986, the superconducting temperature increased from 4.2K of mercury to 23.22K (absolute zero code-named K = -273.16 degrees Celsius). In January 1986, it was discovered that the superconducting temperature of barium lanthanum copper oxide was 30K. On December 30, this record was refreshed to 40.2K. In January 1987, it rose to 43K, and soon it rose to 46K and 53K. On February 15 The 98K superconductor was discovered in Japan, and signs of superconductivity at 14°C were soon discovered. A huge breakthrough was made in high-temperature superconductors, which led to the large-scale application of superconducting technology.
Superconducting materials and superconducting technology have broad application prospects. The Meissner effect in superconductivity allows people to use this principle to create superconducting trains and superconducting ships. Since these vehicles will operate in a frictionless state, this will greatly improve their speed and safety. Superconducting trains have successfully carried out manned feasibility tests in the 1970s. Starting in 1987, Japan began trial operations, but failures often occurred. This phenomenon may be caused by the bumps caused by high-speed driving. The superconducting ship was launched for sea trials on January 27, 1992, and has not yet entered the practical stage. There are still certain technical obstacles to using superconducting materials to manufacture transportation vehicles, but it is bound to trigger a wave of transportation revolution.
The zero-resistance properties of superconducting materials can be used to transmit electricity and create large magnets. Ultra-high voltage power transmission will cause great losses, and the use of superconductors can minimize the losses. However, superconductors with high critical temperatures have not yet entered the practical stage, which limits the use of superconducting power transmission. With the development of technology and the continuous emergence of new superconducting materials, the hope of superconducting power transmission can be realized in the near future.
Existing high-temperature superconductors are still in a state where they must be cooled with liquid nitrogen, but it is still considered one of the greatest discoveries of the 20th century. 1. Bill Lee
In 1911, Dutch scientist Onness used liquid helium to cool mercury. When the temperature dropped to 4.2K, he found that the resistance of mercury completely disappeared. This phenomenon is called superconductivity. In 1933, two scientists, Meissner and Oxenfeld, discovered this phenomenon, which they called diamagnetism.
Superconductivity and diamagnetism are two important properties of superconductors. The temperature at which the resistance of a superconductor becomes zero is called the superconducting critical temperature. After decades of efforts by scientists, the magnetoelectric barrier of superconducting materials has been overcome. The next difficulty is to break through the temperature barrier, which is to seek high-temperature superconducting materials.
2. Strange superconducting ceramics
In 1973, people discovered the superconducting alloy-niobium-germanium alloy. Its critical superconducting temperature is 23.2K. This record has been maintained for 13 years. Year. In 1986, the American IBM Research Center in Zurich, Switzerland, reported that an oxide (lanthanum-barium-copper-oxygen) had high-temperature superconductivity of 35K, breaking the traditional concept that "oxide ceramics are insulators." caused a sensation in the world's scientific community. Since then, scientists have been racing against time to tackle the problem, and new research results appear almost every few days.
At the end of 1986, the critical superconducting temperature of the oxide superconducting material studied by Bell Laboratories in the United States reached 40K, and the "temperature barrier" (40K) of liquid hydrogen was crossed. In February 1987, Chinese-American scientist Zhu Jingwu and Chinese scientist Zhao Zhongxian successively raised the critical superconducting temperature to more than 90K on yttrium-barium-copper-oxygen series materials, and the restricted area of ??liquid nitrogen (77K) was miraculously broken through. At the end of 1987, thallium-barium-calcium-copper-oxygen series materials raised the record of critical superconducting temperature to 125K. In just over a year from 1986 to 1987, the critical superconducting temperature increased by more than 100K. This is a miracle in the history of material development and even the history of technological development! The continuous emergence of high-temperature superconducting materials paves the way for superconducting materials to move from laboratories to applications.