What Is the Insula?
Substances that are not good at conducting current are called insulators, and insulators are also called dielectrics. Their resistivity is extremely high. Definition of insulator: An object that is not easily conductive is called an insulator. There is no absolute boundary between insulators and conductors. Insulators can be converted into conductors under certain conditions. Here we should pay attention to the reason for conducting electricity: whether there are electrons or ions that can move freely inside, whether it is solid or liquid, he can conduct electricity. There is no freely moving charge. Under certain conditions, conductive particles can be generated, so it can also become a conductor.
- Chinese name
- Insulator
- Foreign name
- Insulator
- Definition
- Substances that are not good at conducting current
- Classification
- Solid, liquid, gas
- Substances that are not good at conducting current are called insulators, and insulators are also called dielectrics. Their resistivity is extremely high. Definition of insulator: An object that is not easily conductive is called an insulator. There is no absolute boundary between insulators and conductors. Insulators can be converted into conductors under certain conditions. Here we should pay attention to the reason for conducting electricity: whether there are electrons or ions that can move freely inside, whether it is solid or liquid, he can conduct electricity. There is no freely moving charge, and under certain conditions, conductive particles can be generated, then it can also become a conductor.
Basic definition of insulator
- An insulator is a substance that does not conduct current under normal circumstances. Also called dielectric. The characteristics of insulators are that the positive and negative charges in the molecule are tightly bound, there are very few charged particles that can move freely, and the resistivity is very large, about 10 to 10 ohm · m, so in general, free charges under the action of an external electric field can be ignored. The macroscopic current formed by the movement is considered to be a non-conductive substance. Insulators can be divided into gaseous states (such as hydrogen, oxygen, nitrogen and all gases in a non-ionized state), liquid states (such as pure water, oil, lacquer and organic acids, etc.) and solid states (such as glass, ceramics, rubber, paper, quartz, etc.) Etc.) three categories. Solid insulators are divided into crystalline and amorphous. The actual insulator is not completely non-conductive. Under the action of a strong electric field, the positive and negative charges inside the insulator will break free from the restraint, and become free charges, and the insulation performance is damaged. This phenomenon is called dielectric breakdown. The maximum electric field strength that a dielectric material can withstand is called the breakdown field strength. In an insulator, there is a bound charge. Under the action of an external electric field, this charge will undergo a microscopic displacement, which will generate a polarized charge, which is the so-called dielectric polarization. Dielectrics can be divided into two types of isotropic dielectrics and anisotropic dielectrics according to their physical properties. The polarization mechanism can be divided into two types: polar molecules and polar molecules. Insulators are widely used in engineering as electrical insulation materials, capacitor dielectrics, and special dielectric devices such as piezoelectric crystals. [1]
- The conductivity of an insulator depends on the behavior of the electrons in the substance. The electron behavior in the crystal depends on the band structure. A substance with a completely empty conduction band and a full valence band is an insulator. The energy difference between the bottom of the conduction band and the top of the valence band (band When the gap is very large, it is not conductive under the usual electric field. For substances with smaller energy gaps, although they are insulators at lower temperatures, when the temperature increases, the valence band electrons are excited to the conduction band and will also conduct. In addition, electrons or holes at the impurity level in the band gap can also conduct electricity when excited to the conduction or valence band. The substances in these two cases are usually called semiconductors. When the insulator is irradiated with light with energy greater than the band gap, the valence band electrons are excited to the conduction band, leaving holes in the valence band, both of which can conduct electricity. This phenomenon It is called photoconductance. Most insulators have polarization properties, so insulators are sometimes called dielectrics. Insulators are insulated under general voltage. When the voltage increases to a certain limit, dielectric breakdown will occur and the insulation state will be destroyed. [2]
Insulator structure
- An insulator is a substance that prevents the flow of heat (thermal insulator) or charge (electric insulator). The opposite substance of an electrical insulator is a conductor and a semiconductor, which allow the charge to flow smoothly. (Note: In the strict sense, a semiconductor is also an insulator, because at low temperatures, it will prevent the flow of charge unless it is doped in the semiconductor. Atoms, which can release excess charge to carry current). The term electrical insulator has the same meaning as dielectric, but the two terms are used in different fields.
- A complete thermal insulator cannot exist according to the second law of thermodynamics. However, some materials (such as silica) are not
- Insulator
- Until a better synthetic (physical or chemical reaction) substance was invented, mica and asbestos could be good thermal and electrical insulators in nature's inherent substances.
Insulator principle
- Under certain external conditions, such as heating, high voltage, etc., the insulator will be "broken down" and transformed into a conductor. The insulator is not an absolutely non-conductive object until it is broken down. If a voltage is applied across the insulating material, a weak current will appear in the material.
- Insulating materials usually have only a small amount of free electrons. The charged particles that participated in the conduction before being broken down are mainly intrinsic ions and impurity particles dissociated by thermal movement. The electrical properties of the insulator are reflected in the conductance, polarization, loss, and breakdown processes.
Insulator conduction
- Insulators are substances that do not have electrical conductivity. Electron energy band theory states that electrons in solids are only allowed to exist in certain energy states, and these energy states form separate energy bands. Electrons tend to occupy the lowest energy band first. The highest energy band that can be filled at absolute zero is called the valence band. The band above the valence band is called the conduction band. The gap between the valence band and the conduction band is called energy. Gap. Above absolute zero, the valence band electrons are excited and transition to the conduction band, becoming conduction band electrons, and leaving holes in the valence band. According to the band theory, a band filled with electrons or an empty band does not contribute to the conductance. The conductance only comes from the half-full band. The conduction band electrons and valence band holes are collectively called carriers. The conduction band of the metal is partially filled and therefore has a good electrical conductivity. For semiconductors and insulators, the valence band is filled at absolute zero, while the conduction band has no electrons. At normal temperature, semiconductors have a certain electrical conductivity because they have a small energy gap and can form electron-hole pairs through thermal excitation. In contrast, most insulators usually have a very large band gap width, and valence band electrons are difficult to be excited to the conduction band. Therefore, the carrier concentration of the insulator is extremely low, and accordingly the conductance is extremely low, or the material is insulated.
For insulators, there is always a breakdown voltage that gives enough energy to the valence band electrons to excite them to the conduction band. Once the breakdown voltage is exceeded, the material is no longer insulated. However, breakdown is often accompanied by physical or chemical changes that disrupt the insulation of the material.
The discussion above has dealt only with electron conduction. In addition to the absence of electronic conduction, there must be no other electrical conductivity in the insulator. For example, if ions are present in a liquid or gas, the ions can be directed to form a current, so this material is a conductor. Electrolyte or plasma are both conductors, with or without the flow of electrons.
Insulator breakdown
- Insulators are affected by electrical breakdown. When the applied electric field exceeds a certain threshold (this threshold is proportional to the material's energy gap width), the insulator will suddenly turn into a conductor, which may bring disastrous consequences. In the process of electrical breakdown, free electrons are accelerated to a sufficiently high speed by a strong electric field. These high-speed electrons collide with the bound electrons, which can release the bound electrons from the atomic bond (ionization). The new free electrons can be accelerated and impact other atoms, generating more free electrons, forming a chain reaction. Soon the insulator will be filled with movable carriers, so its resistance will drop to a very low level. In air, corona discharges are normal currents near high-voltage conductors; arc discharges are abnormal and undesired currents. Similarly, breakdown can occur in any insulator, even a solid. Even vacuum has some form of breakdown, but this breakdown, or vacuum arc, is related to the emission of electrons from the electrode surface, not caused by the vacuum itself. [3]
Insulator type
- There are many types of insulators:
- Mica
- solid
- Such as plastic, rubber, glass, ceramics, etc .;
- liquid
- Such as various natural mineral oils, silicone oils, trichlorobiphenyls, etc .;
- gas
- Such as air, carbon dioxide, sulfur hexafluoride and so on.
- Relationship with conductor
- Insulators and conductors are not absolute, and there is no insurmountable gap between the two.
- product
Insulator preparation
- Used in high voltage transmission environment, it is usually ceramic insulator or synthetic insulator. Ceramic insulators are made of clay, quartz, aluminum, and feldspar. Aluminum insulators are used in applications requiring high mechanical strength.
- Terminology related to insulators: [4]
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Insulator use
- Insulator
- Insulators are often used as the outer covering of cables. In fact, air itself is an insulator and does not require other substances for insulation. High-voltage transmission lines are insulated by air because it is not practical to use a solid (such as plastic) coating. However, contact between the wires can cause short circuits and
- Insulators (5 photos)
In electronic systems, printed circuit boards are usually made of epoxy plastic and glass fiber, and a non-conductive substrate supports the copper wire layer. In electronic equipment, tiny and precise active parts are embedded in non-conductive epoxy, phenolic, glass or ceramic coatings.
In microelectronic components such as transistors and integrated circuits, the doped silicon material is usually a conductor. But by heating in an oxygen environment, silicon can also be easily converted into an insulator. Oxidation of silicon produces quartz, also called silicon dioxide.
In high-voltage systems with transformers and capacitors, liquid insulating motor oil is often used to prevent arcing. Where it is necessary to withstand relatively high voltages without being punctured by electricity, people use oil instead of air for insulation. Other insulation methods include the use of ceramic, glass, vacuum, etc., or air can be used when the wires are far apart. [5]