Education, Secondary education and schools
Dielectric - what is it? Properties of dielectrics
A dielectric is a material or substance that practically does not transmit electric current. Such conductivity is obtained due to a small number of electrons and ions. These particles are formed in a non-conductive material only when high temperature properties are reached. About what is a dielectric and will be discussed in this article.
Each electronic or radio engineering conductor, semiconductor or charged dielectric passes through itself an electric current, but the dielectric feature is that a current of small magnitude will flow in it even at a high voltage above 550 V. The electric current in the dielectric is the motion of charged particles in a certain direction (can be positive and negative).
Types of currents
The electrical conductivity of dielectrics is based on:
- Absorption currents are a current that flows in a dielectric at a constant current until it reaches an equilibrium state, changing the direction when the voltage is turned on and applied to it and when it is disconnected. With alternating current, the strength in the dielectric will be present in it all the time while it is in the action of the electric field.
- Electronic electrical conductivity - the movement of electrons under the action of a field.
- Ionic conductivity is the motion of ions. It is found in solutions of electrolytes - salts, acids, alkali, as well as in many dielectrics.
- Molyon electric conductivity is the motion of charged particles called the molyons. It is found in colloid systems, emulsions and suspensions. The phenomenon of motion of molyons in an electric field is called electrophoresis.
Electrical insulating materials are classified according to the aggregate state and chemical nature. The former are divided into solid, liquid, gaseous and solidifying. By chemical nature are divided into organic, inorganic and organoelemental materials.
Electrical conductivity of dielectrics according to the aggregate state:
- Electrical conductivity of gases. Gaseous substances have a sufficiently low current conductivity. It can occur in the presence of free charged particles, which appears due to the influence of external and internal, electronic and ionic factors: radiation of X-rays and radioactive species, collisions of molecules and charged particles, thermal factors.
- Electrical conductivity of a liquid dielectric. Dependence factors: the structure of the molecule, temperature, impurities, the presence of large charges of electrons and ions. The electrical conductivity of liquid dielectrics depends to a large extent on the presence of moisture and impurities. The conductivity of the electricity of polar substances is created by means of a liquid with dissociated ions. When comparing polar and nonpolar liquids, an obvious advantage in conductivity is the first. If the liquid is cleaned of impurities, this will help reduce its conductive properties. As the conductivity of the liquid substance and its temperature increase, a decrease in its viscosity occurs, leading to an increase in the mobility of the ions.
- Solid dielectrics. Their electrical conductivity is caused by the movement of charged particles of a dielectric and impurities. In strong fields of electric current, electrical conductivity is revealed.
Physical properties of dielectrics
With a resistivity of material equal to less than 10-5 Ohm * m, they can be attributed to conductors. If more than 108 Ohm * m - to dielectrics. There are cases when the resistivity will be many times greater than the conductor resistance. In the interval 10-5-108 Ω * m there is a semiconductor. Metal material is an excellent conductor of electric current.
Of the entire Mendeleyev table, only 25 elements refer to non-metals, and 12 of them, possibly, will be with the properties of a semiconductor. But, of course, besides the substances in the table, there are many more alloys, compositions or chemical compounds with the property of a conductor, semiconductor or dielectric. Proceeding from this, it is difficult to draw a definite face of the values of various substances with their resistances. For example, with a reduced temperature factor, the semiconductor will behave like a dielectric.
The use of non-conductive materials is very extensive, because it is one of the most popular classes of electrical components. It has become quite clear that they can be used thanks to the properties in the active and passive form.
In a passive form, the properties of dielectrics are used for use in electrical insulating material.
In active form they are used in ferroelectrics, as well as in materials for radiators of laser technology.
Common types include:
- Pure water.
What is dielectric liquid?
Polarization of this type occurs in the field of electric current. Fluid conductors are used in the technique for pouring or impregnating materials. There are 3 classes of liquid dielectrics:
Oil oils are weakly viscous and mostly non-polar. They are often used in high-voltage equipment: transformer oil, high-voltage water. Transformer oil is a nonpolar dielectric. Cable oil has found application in the impregnation of insulating and paper wires with voltage up to 40 kV, as well as coatings based on metal with a current of more than 120 kV. The transformer oil has a purer structure than the condenser oil. This type of dielectric has become widespread in production, despite the high cost of production in comparison with analog substances and materials.
What is a synthetic dielectric? Nowadays, it is banned almost everywhere due to high toxicity, since it is produced on the basis of chlorinated carbon. A liquid dielectric, based on silicon organic, is safe and environmentally friendly. This species does not cause metallic rust and has properties of low hygroscopicity. There is a dilute dielectric containing an organofluorine compound, which is especially popular because of its incombustibility, thermal properties and oxidative stability.
And the last kind is vegetable oils. They are weakly polar dielectrics, including linen, castor, tung, and hemp. Castor oil is highly heated and is used in paper condensers. The remaining oils are evaporable. Evaporation in them is caused not by natural evaporation, but by a chemical reaction called polymerization. It is actively used in enamels and paints.
The article was considered in detail what is a dielectric. Various species and their properties were mentioned. Of course, in order to understand all the subtlety of their characteristics, we will have to study in greater depth the physics section about them.