A superconducting material is one that manifests the ability to conduct electrical energy without resistance or energy loss under certain conditions. This quality is called Superconductivity, and was discovered in 1911 by Heike Kamerlingh Onnes .
It has been concluded that, as the temperature is reduced, the electrical resistivity of a metallic conductive material gradually becomes impoverished ; however, in the drivers usually employed, such as Copper Cu and Ag Silver, defects such as impurities generate a limit value in the substance . In the case of copper, even in the vicinity of absolute zero, a non-zero resistance is shown.
The resistance of a superconductor drops sharply to zero when the material cools below its critical temperature. An electric current flowing in a superconducting cable can persist indefinitely without a power source. Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon of quantum mechanics.
Magnetic Character of Superconductors
Although the most outstanding property of superconductors is the absence of resistance, it can not be said that it is a material with infinite conductivity. In fact, a type I superconducting material is perfectly diamagnetic . Diamagnetism is the quality of a material that allows you to chase away magnetic fields. Unlike Paramagnetism, which consists in reacting to the attraction of magnetic fields . This means that it does not allow the field to penetrate, which is known as the Meissner effect.
The magnetic fields differentiate two types of superconductors: those of type I, which do not allow an external magnetic field to penetrate(which entails a high energy effort, and implies the sudden rupture of the superconducting state if the critical temperature is exceeded ), and the Type II, which are imperfect superconductors , in the sense that the field actually penetrates through small channels called Abrikósov vortices, or fluxons . These two types of superconductors are in fact two different phases that were predicted by Lev Davidovich Landau and Aleksey Alekséyecih Abrikósov.
When a weak magnetic field is applied to a type II superconductor, it repels perfectly. If it is increased, the system becomes unstable and begins to introduce vortices to decrease its energy . These vortices are increasing in number, placing themselves in networks of vortices that can be observed by means of appropriate techniques. When the field is large enough, the number of defects is so high that the material ceases to be a superconductor. This is the critical field that makes a material stop being superconducting, and that depends on the temperature.
Electricity Character of Superconductors
The emergence of superdiamagnetism is due to the ability of the material to create supercurrents. The supercurrents are streams of electrons in which energy is not dissipated, so that they can be maintained eternally without obeying the Joule effect of energy loss by heat generation. The currents create the intense magnetic field necessary to sustain the Meissner effect. These same currents allow energy to be transmitted without energy expenditure, which represents the most outstanding effect of this type of material.
Because the amount of superconducting electrons is finite, the amount of current the material can withstand is limited. Therefore, there is a critical current from which the material ceases to be superconducting and begins to dissipate energy.
In type II superconductors, the appearance of fluxons causes that, even for currents less than critical, energy dissipation is detected due to the impact of the vortices with the atoms of the network.
High Temperature Superconductors
Due to the low temperatures that are needed to achieve superconductivity, the most common materials are usually cooled with liquid helium (liquid nitrogen is only useful when handling high temperature superconductors). The assembly required is complex and expensive, being used in a few applications, such as the construction of powerful electromagnets for nuclear magnetic resonance (NMR).
In the 80s, high temperature superconductorswere discovered , which present the phase transition at temperatures higher than the liquid-vapor transition of liquid nitrogen . This has reduced costs in the study of such materials, and opened the door to the existence of superconducting materials at room temperature, which would mean a revolution in the industry of the contemporary world.
The greatest disadvantage of high temperature superconductors is their ceramic composition, which makes them unsuitable for making cables by plastic deformation. However, new techniques have been developed for the production of tapes such as IBAD (Assisted Deposition by Ion Beam). Through this technique, cables of lengths greater than 1 Kilometer have been achieved.
Examples of Superconductor Applications
A superconductor behaves very differently from normal drivers. It is not a conductor whose resistance is close to zero, but the resistance is exactly zero. This can not be explained by the conventional models used for common drivers, such as the Drude model.
Superconducting magnets are some of the most powerful electromagnets known. They are used in maglev (magnetic levitation) trains, in machines for nuclear magnetic resonance (NMR) in hospitals and in the orientation of the beam of a particle accelerator. They can also be used for magnetic separation, where weak magnetic particles are extracted from a bottom of less or non-magnetic particles, as in the pigment industries.
Superconductors have also been used to manufacture digital circuits and radiofrequency and microwave filters for mobile telephone base stations.
Superconductors are used to construct Josephson junctions, which are the building blocks of SQUIDs (Quantum Interference Superconducting Devices), the most sensitive known magnetometers.
Depending on the operating mode, a Josephson junction can be used as a photon detector or as a mixer . The great change in resistance to the transition from the normal state to the superconducting state is used to construct thermometers in cryogenic photon detectors.
Innovative and future-proof applications include high-performance transformers, energy storage devices, electric power transmission, electric motors and magnetic levitation devices.
However, superconductivity is sensitive to moving magnetic fields so applications that use alternating current, such as transformers, will be more difficult to process than those that are powered by direct current.
Examples of Superconducting Materials
They can be metals, such as:
They can be non-Metals or Metalloids, such as: